Leukemia, Myelodysplasia, Transplantation

Children’s Cancer Institute

Researchers say they have developed a more accurate risk scoring system for children with B-cell precursor acute lymphoblastic leukemia (BCP-ALL) who are typically thought to have standard- or medium-risk disease.

The scoring system includes 3 factors associated with higher-risk BCP-ALL—the presence of high-risk ALL gene microdeletions, having minimal residual disease (MRD) greater than 5 x 10^-5 at day 33, and being high-risk according to National Cancer Institute (NCI) classification.

The researchers found that children with 2 or more of these characteristics were most likely to relapse or die within 7 years of treatment initiation.

On the other hand, children without any of the 3 characteristics had high rates of relapse-free survival (RFS) and overall survival (OS).

Rosemary Sutton, PhD, of Children’s Cancer Institute in Sydney, New South Wales, Australia, and her colleagues devised this risk scoring system and described it in the British Journal of Haematology.

The researchers created their system with the help of data from 475 patients (ages 1 to 18) who had BCP-ALL and were considered non-high-risk. The patients were enrolled on the ANZCHOG ALL8 trial.

Dr Sutton and her colleagues noted that children with standard- or medium-risk BCP-ALL typically receive less intensive treatment than children with high-risk BCP-ALL. However, some of the standard- and medium-risk patients do relapse.

“For the standard- to medium-risk group, we needed more information to get a better handle on the biology of the child’s cancer to better determine their risk,” Dr Sutton said. “So we supplemented MRD results with 2 other pieces of patient information—the presence or absence of specific gene microdeletions and a score called the NCI risk, based on age and white blood cell count.”

“We tested for microdeletions in 9 genes involved in leukemia and found that 2 of the genes—IKZF1 and P2RY8-CRLF2—were important predictors of relapse.”

The researchers combined patients with IKZF1 intragenic deletions, P2RY8-CRLF2 gene fusion, or both into a “high-risk deletion group.”

And the team based the scoring system on 3 factors—the high-risk deletion group, MRD >5 x 10^-5 at day 33, and high risk according to NCI risk classification. Patients received 1 point for each of these factors.

The RFS rate was 93% for patients with a score of 0, 78% for those with a score of 1, and 49% for patients with a score of 2 or 3. The OS rate was 99%, 91%, and 71%, respectively.

The researchers said their scoring system provided greater discrimination than MRD-based risk stratification into a standard-risk group—which had an RFS of 89% and an OS of 96%—and a medium-risk group—which had an RFS of 79% and an OS of 91%.

Study author Toby Trahair, MBBS, PhD, of Sydney Children’s Hospital in Randwick, New South Wales, said this scoring system could make a big difference to the success of BCP-ALL treatment.

“We are always trying to improve how we diagnose and treat children with this most common childhood cancer,” Dr Trahair said. “This risk score will mean doctors can fine tune a child’s risk category and so fine tune their treatment. It will mean more kids can conquer this horrible disease, which, only 50 years ago, had survival rates of close to 0.”

Children’s Cancer Institute

Researchers say they have developed a more accurate risk scoring system for children with B-cell precursor acute lymphoblastic leukemia (BCP-ALL) who are typically thought to have standard- or medium-risk disease.

The scoring system includes 3 factors associated with higher-risk BCP-ALL—the presence of high-risk ALL gene microdeletions, having minimal residual disease (MRD) greater than 5 x 10^-5 at day 33, and being high-risk according to National Cancer Institute (NCI) classification.

The researchers found that children with 2 or more of these characteristics were most likely to relapse or die within 7 years of treatment initiation.

On the other hand, children without any of the 3 characteristics had high rates of relapse-free survival (RFS) and overall survival (OS).

Rosemary Sutton, PhD, of Children’s Cancer Institute in Sydney, New South Wales, Australia, and her colleagues devised this risk scoring system and described it in the British Journal of Haematology.

The researchers created their system with the help of data from 475 patients (ages 1 to 18) who had BCP-ALL and were considered non-high-risk. The patients were enrolled on the ANZCHOG ALL8 trial.

Dr Sutton and her colleagues noted that children with standard- or medium-risk BCP-ALL typically receive less intensive treatment than children with high-risk BCP-ALL. However, some of the standard- and medium-risk patients do relapse.

“For the standard- to medium-risk group, we needed more information to get a better handle on the biology of the child’s cancer to better determine their risk,” Dr Sutton said. “So we supplemented MRD results with 2 other pieces of patient information—the presence or absence of specific gene microdeletions and a score called the NCI risk, based on age and white blood cell count.”

“We tested for microdeletions in 9 genes involved in leukemia and found that 2 of the genes—IKZF1 and P2RY8-CRLF2—were important predictors of relapse.”

The researchers combined patients with IKZF1 intragenic deletions, P2RY8-CRLF2 gene fusion, or both into a “high-risk deletion group.”

And the team based the scoring system on 3 factors—the high-risk deletion group, MRD >5 x 10^-5 at day 33, and high risk according to NCI risk classification. Patients received 1 point for each of these factors.

The RFS rate was 93% for patients with a score of 0, 78% for those with a score of 1, and 49% for patients with a score of 2 or 3. The OS rate was 99%, 91%, and 71%, respectively.

The researchers said their scoring system provided greater discrimination than MRD-based risk stratification into a standard-risk group—which had an RFS of 89% and an OS of 96%—and a medium-risk group—which had an RFS of 79% and an OS of 91%.

Study author Toby Trahair, MBBS, PhD, of Sydney Children’s Hospital in Randwick, New South Wales, said this scoring system could make a big difference to the success of BCP-ALL treatment.

“We are always trying to improve how we diagnose and treat children with this most common childhood cancer,” Dr Trahair said. “This risk score will mean doctors can fine tune a child’s risk category and so fine tune their treatment. It will mean more kids can conquer this horrible disease, which, only 50 years ago, had survival rates of close to 0.”

Children’s Cancer Institute

Researchers say they have developed a more accurate risk scoring system for children with B-cell precursor acute lymphoblastic leukemia (BCP-ALL) who are typically thought to have standard- or medium-risk disease.

The scoring system includes 3 factors associated with higher-risk BCP-ALL—the presence of high-risk ALL gene microdeletions, having minimal residual disease (MRD) greater than 5 x 10^-5 at day 33, and being high-risk according to National Cancer Institute (NCI) classification.

The researchers found that children with 2 or more of these characteristics were most likely to relapse or die within 7 years of treatment initiation.

On the other hand, children without any of the 3 characteristics had high rates of relapse-free survival (RFS) and overall survival (OS).

Rosemary Sutton, PhD, of Children’s Cancer Institute in Sydney, New South Wales, Australia, and her colleagues devised this risk scoring system and described it in the British Journal of Haematology.

The researchers created their system with the help of data from 475 patients (ages 1 to 18) who had BCP-ALL and were considered non-high-risk. The patients were enrolled on the ANZCHOG ALL8 trial.

Dr Sutton and her colleagues noted that children with standard- or medium-risk BCP-ALL typically receive less intensive treatment than children with high-risk BCP-ALL. However, some of the standard- and medium-risk patients do relapse.

“For the standard- to medium-risk group, we needed more information to get a better handle on the biology of the child’s cancer to better determine their risk,” Dr Sutton said. “So we supplemented MRD results with 2 other pieces of patient information—the presence or absence of specific gene microdeletions and a score called the NCI risk, based on age and white blood cell count.”

“We tested for microdeletions in 9 genes involved in leukemia and found that 2 of the genes—IKZF1 and P2RY8-CRLF2—were important predictors of relapse.”

The researchers combined patients with IKZF1 intragenic deletions, P2RY8-CRLF2 gene fusion, or both into a “high-risk deletion group.”

And the team based the scoring system on 3 factors—the high-risk deletion group, MRD >5 x 10^-5 at day 33, and high risk according to NCI risk classification. Patients received 1 point for each of these factors.

The RFS rate was 93% for patients with a score of 0, 78% for those with a score of 1, and 49% for patients with a score of 2 or 3. The OS rate was 99%, 91%, and 71%, respectively.

The researchers said their scoring system provided greater discrimination than MRD-based risk stratification into a standard-risk group—which had an RFS of 89% and an OS of 96%—and a medium-risk group—which had an RFS of 79% and an OS of 91%.

Study author Toby Trahair, MBBS, PhD, of Sydney Children’s Hospital in Randwick, New South Wales, said this scoring system could make a big difference to the success of BCP-ALL treatment.

“We are always trying to improve how we diagnose and treat children with this most common childhood cancer,” Dr Trahair said. “This risk score will mean doctors can fine tune a child’s risk category and so fine tune their treatment. It will mean more kids can conquer this horrible disease, which, only 50 years ago, had survival rates of close to 0.”

A lot has happened in oncology since the American Society of Clinical Oncology (ASCO) first issued its guidelines on platelet transfusion for patients with cancer in 2001, noted the authors of the updated recommendations.

“The expense of platelet transfusions, coupled with potential adverse effects such as febrile and allergic reactions, transfusion-related acute lung injury, and bacterial contamination point to the importance of evidence-based transfusion practice,” wrote Charles A Schiffer, MD, of Wayne State Michigan, Detroit, and his colleagues in the updated guidelines.

Many of the original recommendations remain unchanged, but there are updated evidence-based recommendations in five key areas.

For example, regarding platelet transfusion thresholds in the setting of hematologic stem-cell transplantation in adults, the guidelines incorporate evidence from randomized clinical trials showing that among adults who have received autologous hematologic stem-cell transplantation, bleeding rates with decreased use of platelets are similar whether patients are treated prophylactically or at the first sign of bleeding, “and this approach may be used in experienced centers,” wrote Dr. Schiffer and his colleagues (J Clin Oncol. 2017 Nov 28. doi: 10.1200/JCO.2017.76.1734).

The authors caution, however, that the recommendation applies to adults only.

Other updated recommendations include:

• Rhesus D alloimmunization from platelet transfusions to RhD-negative patients can be prevented through either exclusive use of platelet products from RhD-negative donors or immunoprophylaxis. The guidelines note that there is a low rate of RhD alloimmunization in cancer patients in general, but state that prevention may be used in girls and in women of child-bearing age who are being treated with curative intent.

• For patients with acute myeloid leukemia, receiving induction chemotherapy, the use of leukoreduced platelet and red blood cell products can reduce the likelihood that patients will develop alloantibody-mediated refractory reactions to plate transfusions.

“It is therefore appropriate to provide leukoreduced blood products to patients with [acute myeloid leukemia] from the time of diagnosis to ameliorate this important clinical problem,” the investigators wrote.

They noted that leukoreduction to prevent alloimmunization might benefit patients with other leukemia histologies and with other types of cancer who are undergoing chemotherapy, but added that there is a lack of evidence to support this as a recommendation outside of acute myeloid leukemia.

To reduce the risk of bleeding due to thrombocytopenia in patients with solid tumors who are undergoing chemotherapy, the panelists recommend transfusing patients when their platelet levels fall below 10 x 109 per liter. It is appropriate to give platelet transfusions to patients with higher levels when there is active localized bleeding, they stated.

The guideline authors also recommend that when refractoriness to platelet infusions is suspected, clinicians should perform platelet counts from 10 to 60 minutes after the transfusion is completed. A refractoriness determination should be made only after two or more infusions of ABO-compatible units that have been stored for less than 72 hours result in poor increments, they advised.

The guideline development process is supported by ASCO. Dr. Schiffer and six other guideline authors disclosed consulting or advisory roles, research funding, honoraria and/or fees with various pharmaceutical companies or other corporate entities.
 

A lot has happened in oncology since the American Society of Clinical Oncology (ASCO) first issued its guidelines on platelet transfusion for patients with cancer in 2001, noted the authors of the updated recommendations.

“The expense of platelet transfusions, coupled with potential adverse effects such as febrile and allergic reactions, transfusion-related acute lung injury, and bacterial contamination point to the importance of evidence-based transfusion practice,” wrote Charles A Schiffer, MD, of Wayne State Michigan, Detroit, and his colleagues in the updated guidelines.

Many of the original recommendations remain unchanged, but there are updated evidence-based recommendations in five key areas.

For example, regarding platelet transfusion thresholds in the setting of hematologic stem-cell transplantation in adults, the guidelines incorporate evidence from randomized clinical trials showing that among adults who have received autologous hematologic stem-cell transplantation, bleeding rates with decreased use of platelets are similar whether patients are treated prophylactically or at the first sign of bleeding, “and this approach may be used in experienced centers,” wrote Dr. Schiffer and his colleagues (J Clin Oncol. 2017 Nov 28. doi: 10.1200/JCO.2017.76.1734).

The authors caution, however, that the recommendation applies to adults only.

Other updated recommendations include:

• Rhesus D alloimmunization from platelet transfusions to RhD-negative patients can be prevented through either exclusive use of platelet products from RhD-negative donors or immunoprophylaxis. The guidelines note that there is a low rate of RhD alloimmunization in cancer patients in general, but state that prevention may be used in girls and in women of child-bearing age who are being treated with curative intent.

• For patients with acute myeloid leukemia, receiving induction chemotherapy, the use of leukoreduced platelet and red blood cell products can reduce the likelihood that patients will develop alloantibody-mediated refractory reactions to plate transfusions.

“It is therefore appropriate to provide leukoreduced blood products to patients with [acute myeloid leukemia] from the time of diagnosis to ameliorate this important clinical problem,” the investigators wrote.

They noted that leukoreduction to prevent alloimmunization might benefit patients with other leukemia histologies and with other types of cancer who are undergoing chemotherapy, but added that there is a lack of evidence to support this as a recommendation outside of acute myeloid leukemia.

To reduce the risk of bleeding due to thrombocytopenia in patients with solid tumors who are undergoing chemotherapy, the panelists recommend transfusing patients when their platelet levels fall below 10 x 109 per liter. It is appropriate to give platelet transfusions to patients with higher levels when there is active localized bleeding, they stated.

The guideline authors also recommend that when refractoriness to platelet infusions is suspected, clinicians should perform platelet counts from 10 to 60 minutes after the transfusion is completed. A refractoriness determination should be made only after two or more infusions of ABO-compatible units that have been stored for less than 72 hours result in poor increments, they advised.

The guideline development process is supported by ASCO. Dr. Schiffer and six other guideline authors disclosed consulting or advisory roles, research funding, honoraria and/or fees with various pharmaceutical companies or other corporate entities.
 

A lot has happened in oncology since the American Society of Clinical Oncology (ASCO) first issued its guidelines on platelet transfusion for patients with cancer in 2001, noted the authors of the updated recommendations.

“The expense of platelet transfusions, coupled with potential adverse effects such as febrile and allergic reactions, transfusion-related acute lung injury, and bacterial contamination point to the importance of evidence-based transfusion practice,” wrote Charles A Schiffer, MD, of Wayne State Michigan, Detroit, and his colleagues in the updated guidelines.

Many of the original recommendations remain unchanged, but there are updated evidence-based recommendations in five key areas.

For example, regarding platelet transfusion thresholds in the setting of hematologic stem-cell transplantation in adults, the guidelines incorporate evidence from randomized clinical trials showing that among adults who have received autologous hematologic stem-cell transplantation, bleeding rates with decreased use of platelets are similar whether patients are treated prophylactically or at the first sign of bleeding, “and this approach may be used in experienced centers,” wrote Dr. Schiffer and his colleagues (J Clin Oncol. 2017 Nov 28. doi: 10.1200/JCO.2017.76.1734).

The authors caution, however, that the recommendation applies to adults only.

Other updated recommendations include:

• Rhesus D alloimmunization from platelet transfusions to RhD-negative patients can be prevented through either exclusive use of platelet products from RhD-negative donors or immunoprophylaxis. The guidelines note that there is a low rate of RhD alloimmunization in cancer patients in general, but state that prevention may be used in girls and in women of child-bearing age who are being treated with curative intent.

• For patients with acute myeloid leukemia, receiving induction chemotherapy, the use of leukoreduced platelet and red blood cell products can reduce the likelihood that patients will develop alloantibody-mediated refractory reactions to plate transfusions.

“It is therefore appropriate to provide leukoreduced blood products to patients with [acute myeloid leukemia] from the time of diagnosis to ameliorate this important clinical problem,” the investigators wrote.

They noted that leukoreduction to prevent alloimmunization might benefit patients with other leukemia histologies and with other types of cancer who are undergoing chemotherapy, but added that there is a lack of evidence to support this as a recommendation outside of acute myeloid leukemia.

To reduce the risk of bleeding due to thrombocytopenia in patients with solid tumors who are undergoing chemotherapy, the panelists recommend transfusing patients when their platelet levels fall below 10 x 109 per liter. It is appropriate to give platelet transfusions to patients with higher levels when there is active localized bleeding, they stated.

The guideline authors also recommend that when refractoriness to platelet infusions is suspected, clinicians should perform platelet counts from 10 to 60 minutes after the transfusion is completed. A refractoriness determination should be made only after two or more infusions of ABO-compatible units that have been stored for less than 72 hours result in poor increments, they advised.

The guideline development process is supported by ASCO. Dr. Schiffer and six other guideline authors disclosed consulting or advisory roles, research funding, honoraria and/or fees with various pharmaceutical companies or other corporate entities.
 

Research Hospital

An antimalarial drug and a BH3 mimetic have demonstrated promise for treating BCR-ABL-positive acute lymphoblastic leukemia (ALL), according to work published in Clinical Cancer Research.

Investigators found the widely used antimalarial dihydroartemisinin (DHA) sensitized BCR-ABL+ ALL to the BH3 mimetic navitoclax (formerly ABT-263).

The combination therapy had a synergistic effect on mouse and human BCR-ABL+ leukemic cell death and extended the lives of mice with BCR-ABL+ ALL.

“Survival rates for children and adults with this leukemia still lag, highlighting the urgent need for new therapies,” said study author Joseph Opferman, PhD, of St. Jude Children’s Research Hospital in Memphis, Tennessee.

“Our findings suggest that combining DHA with ABT-263 can significantly improve treatment response.”

As opposed to mice that received navitoclax alone, there was no evidence of navitoclax resistance in mice treated with navitoclax and DHA.

The investigators determined that DHA worked by repressing production of MCL-1, a protein that is elevated in many cancers and helps malignant cells resist BH3 mimetics.

“MCL-1 is widely recognized as an important survival molecule in many normal cell types as well as cancer,” Dr Opferman said. “MCL-1 inhibitors are in development, but none are currently available for treating patients.”

“And because MCL-1 is essential for proper functioning of many normal cell types, there is concern about potential toxicity. We sought to identify drugs that are available now to augment treatment of BCR-ABL+ ALL.”

The search for a drug to sensitize BCR-ABL+ ALL to navitoclax and related compounds led Dr Opferman and his colleagues to DHA. A drug screen showed that DHA killed BCR-ABL+ ALL cells from mice.

The investigators showed how DHA induced expression of the protein CHOP, which is a key regulator of the endoplasmic reticulum stress pathway in cells. CHOP expression triggered the stress pathway in BCR-ABL+ ALL cells from mice and led to the suppression of MCL-1.

“MCL-1 has a short half-life, so the cell’s MCL-1 stores are rapidly depleted if the protein’s translation is repressed,” said study author Amit Budhraja, PhD, a postdoctoral fellow in Dr Opferman’s lab.

Now, the investigators are studying the mechanism in human BCR-ABL+ leukemic cells as well as in other cancers.

“Identifying the mechanism will allow us to study the pathway in detail for other points to target for anticancer drug development,” Dr Opferman said.

Research Hospital

An antimalarial drug and a BH3 mimetic have demonstrated promise for treating BCR-ABL-positive acute lymphoblastic leukemia (ALL), according to work published in Clinical Cancer Research.

Investigators found the widely used antimalarial dihydroartemisinin (DHA) sensitized BCR-ABL+ ALL to the BH3 mimetic navitoclax (formerly ABT-263).

The combination therapy had a synergistic effect on mouse and human BCR-ABL+ leukemic cell death and extended the lives of mice with BCR-ABL+ ALL.

“Survival rates for children and adults with this leukemia still lag, highlighting the urgent need for new therapies,” said study author Joseph Opferman, PhD, of St. Jude Children’s Research Hospital in Memphis, Tennessee.

“Our findings suggest that combining DHA with ABT-263 can significantly improve treatment response.”

As opposed to mice that received navitoclax alone, there was no evidence of navitoclax resistance in mice treated with navitoclax and DHA.

The investigators determined that DHA worked by repressing production of MCL-1, a protein that is elevated in many cancers and helps malignant cells resist BH3 mimetics.

“MCL-1 is widely recognized as an important survival molecule in many normal cell types as well as cancer,” Dr Opferman said. “MCL-1 inhibitors are in development, but none are currently available for treating patients.”

“And because MCL-1 is essential for proper functioning of many normal cell types, there is concern about potential toxicity. We sought to identify drugs that are available now to augment treatment of BCR-ABL+ ALL.”

The search for a drug to sensitize BCR-ABL+ ALL to navitoclax and related compounds led Dr Opferman and his colleagues to DHA. A drug screen showed that DHA killed BCR-ABL+ ALL cells from mice.

The investigators showed how DHA induced expression of the protein CHOP, which is a key regulator of the endoplasmic reticulum stress pathway in cells. CHOP expression triggered the stress pathway in BCR-ABL+ ALL cells from mice and led to the suppression of MCL-1.

“MCL-1 has a short half-life, so the cell’s MCL-1 stores are rapidly depleted if the protein’s translation is repressed,” said study author Amit Budhraja, PhD, a postdoctoral fellow in Dr Opferman’s lab.

Now, the investigators are studying the mechanism in human BCR-ABL+ leukemic cells as well as in other cancers.

“Identifying the mechanism will allow us to study the pathway in detail for other points to target for anticancer drug development,” Dr Opferman said.

Research Hospital

An antimalarial drug and a BH3 mimetic have demonstrated promise for treating BCR-ABL-positive acute lymphoblastic leukemia (ALL), according to work published in Clinical Cancer Research.

Investigators found the widely used antimalarial dihydroartemisinin (DHA) sensitized BCR-ABL+ ALL to the BH3 mimetic navitoclax (formerly ABT-263).

The combination therapy had a synergistic effect on mouse and human BCR-ABL+ leukemic cell death and extended the lives of mice with BCR-ABL+ ALL.

“Survival rates for children and adults with this leukemia still lag, highlighting the urgent need for new therapies,” said study author Joseph Opferman, PhD, of St. Jude Children’s Research Hospital in Memphis, Tennessee.

“Our findings suggest that combining DHA with ABT-263 can significantly improve treatment response.”

As opposed to mice that received navitoclax alone, there was no evidence of navitoclax resistance in mice treated with navitoclax and DHA.

The investigators determined that DHA worked by repressing production of MCL-1, a protein that is elevated in many cancers and helps malignant cells resist BH3 mimetics.

“MCL-1 is widely recognized as an important survival molecule in many normal cell types as well as cancer,” Dr Opferman said. “MCL-1 inhibitors are in development, but none are currently available for treating patients.”

“And because MCL-1 is essential for proper functioning of many normal cell types, there is concern about potential toxicity. We sought to identify drugs that are available now to augment treatment of BCR-ABL+ ALL.”

The search for a drug to sensitize BCR-ABL+ ALL to navitoclax and related compounds led Dr Opferman and his colleagues to DHA. A drug screen showed that DHA killed BCR-ABL+ ALL cells from mice.

The investigators showed how DHA induced expression of the protein CHOP, which is a key regulator of the endoplasmic reticulum stress pathway in cells. CHOP expression triggered the stress pathway in BCR-ABL+ ALL cells from mice and led to the suppression of MCL-1.

“MCL-1 has a short half-life, so the cell’s MCL-1 stores are rapidly depleted if the protein’s translation is repressed,” said study author Amit Budhraja, PhD, a postdoctoral fellow in Dr Opferman’s lab.

Now, the investigators are studying the mechanism in human BCR-ABL+ leukemic cells as well as in other cancers.

“Identifying the mechanism will allow us to study the pathway in detail for other points to target for anticancer drug development,” Dr Opferman said.

Henrique Orlandi Mourao

The US Food and Drug Administration (FDA) has granted fast track designation to crenolanib for the treatment of patients with FLT3 mutation-positive relapsed or refractory acute myeloid leukemia (AML).

Crenolanib is a benzimidazole type I tyrosine kinase inhibitor (TKI) that selectively inhibits signaling of wild-type and mutant isoforms of FLT3 and PDGFRα/β.

Crenolanib is being developed by Arog Pharmaceuticals, Inc.

The company is preparing for a phase 3, randomized, double-blind trial of crenolanib versus placebo in combination with best supportive care in patients with FLT3+ relapsed or refractory AML.

Results from a phase 2 trial of crenolanib in relapsed/refractory FLT3+ AML were presented at the 2016 ASCO Annual Meeting (abstract 7008).

The trial enrolled 69 patients who had a median age of 60 (range, 21-87). Twenty-nine patients had FLT3 ITD, 29 had ITD and D835, and 11 had D835.

Nineteen patients were TKI-naïve, 39 had received a prior TKI, and 11 had secondary AML.

Patients received crenolanib at 100 mg three times a day (n=43) or 66 mg/m² three times a day (n=26).

In the TKI-naïve patients, the overall response rate (ORR) was 47% (n=9), and 37% of patients had a complete response (CR) or CR with incomplete count recovery (CRi). The median overall survival (OS) was 238 days (range, 25-547).

In patients who previously received a TKI, the ORR was 28% (n=11), and the CR/CRi rate was 15% (n=6). The median OS was 94 days (range, 8-338).

In patients with secondary AML, the ORR was 9% (n=1, partial response). The median OS in this group was 64 days (range, 27-221).

Treatment-emergent adverse events (all grades and grade 3/4, respectively) included nausea (70%, 9%), vomiting (58%, 9%), diarrhea (56%, 2%), fatigue (36%, 11%), febrile neutropenia (35%, 35%), pneumonia (32%, 23%), peripheral edema (30%, 2%), pleural effusion (21%, 8%), dyspnea (20%, 5%), and epistaxis (20%, 8%).

Two patients discontinued crenolanib due to adverse events. One patient discontinued due to grade 3 fatigue, abdominal pain, and headache. The other discontinued due to grade 3 pneumonia.

There were 2 neutropenic septic deaths, which occurred 2 days and 21 days after the discontinuation of crenolanib.

About fast track designation

The FDA’s fast track program is designed to facilitate the development and expedite the review of products intended to treat or prevent serious or life-threatening conditions and address unmet medical need.

Through the fast track program, a product may be eligible for priority review. In addition, the company developing the product may be allowed to submit sections of the new drug application or biologics license application on a rolling basis as data become available.

Fast track designation also provides the company with opportunities for more frequent meetings and written communications with the FDA.

Henrique Orlandi Mourao

The US Food and Drug Administration (FDA) has granted fast track designation to crenolanib for the treatment of patients with FLT3 mutation-positive relapsed or refractory acute myeloid leukemia (AML).

Crenolanib is a benzimidazole type I tyrosine kinase inhibitor (TKI) that selectively inhibits signaling of wild-type and mutant isoforms of FLT3 and PDGFRα/β.

Crenolanib is being developed by Arog Pharmaceuticals, Inc.

The company is preparing for a phase 3, randomized, double-blind trial of crenolanib versus placebo in combination with best supportive care in patients with FLT3+ relapsed or refractory AML.

Results from a phase 2 trial of crenolanib in relapsed/refractory FLT3+ AML were presented at the 2016 ASCO Annual Meeting (abstract 7008).

The trial enrolled 69 patients who had a median age of 60 (range, 21-87). Twenty-nine patients had FLT3 ITD, 29 had ITD and D835, and 11 had D835.

Nineteen patients were TKI-naïve, 39 had received a prior TKI, and 11 had secondary AML.

Patients received crenolanib at 100 mg three times a day (n=43) or 66 mg/m² three times a day (n=26).

In the TKI-naïve patients, the overall response rate (ORR) was 47% (n=9), and 37% of patients had a complete response (CR) or CR with incomplete count recovery (CRi). The median overall survival (OS) was 238 days (range, 25-547).

In patients who previously received a TKI, the ORR was 28% (n=11), and the CR/CRi rate was 15% (n=6). The median OS was 94 days (range, 8-338).

In patients with secondary AML, the ORR was 9% (n=1, partial response). The median OS in this group was 64 days (range, 27-221).

Treatment-emergent adverse events (all grades and grade 3/4, respectively) included nausea (70%, 9%), vomiting (58%, 9%), diarrhea (56%, 2%), fatigue (36%, 11%), febrile neutropenia (35%, 35%), pneumonia (32%, 23%), peripheral edema (30%, 2%), pleural effusion (21%, 8%), dyspnea (20%, 5%), and epistaxis (20%, 8%).

Two patients discontinued crenolanib due to adverse events. One patient discontinued due to grade 3 fatigue, abdominal pain, and headache. The other discontinued due to grade 3 pneumonia.

There were 2 neutropenic septic deaths, which occurred 2 days and 21 days after the discontinuation of crenolanib.

About fast track designation

The FDA’s fast track program is designed to facilitate the development and expedite the review of products intended to treat or prevent serious or life-threatening conditions and address unmet medical need.

Through the fast track program, a product may be eligible for priority review. In addition, the company developing the product may be allowed to submit sections of the new drug application or biologics license application on a rolling basis as data become available.

Fast track designation also provides the company with opportunities for more frequent meetings and written communications with the FDA.

Henrique Orlandi Mourao

The US Food and Drug Administration (FDA) has granted fast track designation to crenolanib for the treatment of patients with FLT3 mutation-positive relapsed or refractory acute myeloid leukemia (AML).

Crenolanib is a benzimidazole type I tyrosine kinase inhibitor (TKI) that selectively inhibits signaling of wild-type and mutant isoforms of FLT3 and PDGFRα/β.

Crenolanib is being developed by Arog Pharmaceuticals, Inc.

The company is preparing for a phase 3, randomized, double-blind trial of crenolanib versus placebo in combination with best supportive care in patients with FLT3+ relapsed or refractory AML.

Results from a phase 2 trial of crenolanib in relapsed/refractory FLT3+ AML were presented at the 2016 ASCO Annual Meeting (abstract 7008).

The trial enrolled 69 patients who had a median age of 60 (range, 21-87). Twenty-nine patients had FLT3 ITD, 29 had ITD and D835, and 11 had D835.

Nineteen patients were TKI-naïve, 39 had received a prior TKI, and 11 had secondary AML.

Patients received crenolanib at 100 mg three times a day (n=43) or 66 mg/m² three times a day (n=26).

In the TKI-naïve patients, the overall response rate (ORR) was 47% (n=9), and 37% of patients had a complete response (CR) or CR with incomplete count recovery (CRi). The median overall survival (OS) was 238 days (range, 25-547).

In patients who previously received a TKI, the ORR was 28% (n=11), and the CR/CRi rate was 15% (n=6). The median OS was 94 days (range, 8-338).

In patients with secondary AML, the ORR was 9% (n=1, partial response). The median OS in this group was 64 days (range, 27-221).

Treatment-emergent adverse events (all grades and grade 3/4, respectively) included nausea (70%, 9%), vomiting (58%, 9%), diarrhea (56%, 2%), fatigue (36%, 11%), febrile neutropenia (35%, 35%), pneumonia (32%, 23%), peripheral edema (30%, 2%), pleural effusion (21%, 8%), dyspnea (20%, 5%), and epistaxis (20%, 8%).

Two patients discontinued crenolanib due to adverse events. One patient discontinued due to grade 3 fatigue, abdominal pain, and headache. The other discontinued due to grade 3 pneumonia.

There were 2 neutropenic septic deaths, which occurred 2 days and 21 days after the discontinuation of crenolanib.

About fast track designation

The FDA’s fast track program is designed to facilitate the development and expedite the review of products intended to treat or prevent serious or life-threatening conditions and address unmet medical need.

Through the fast track program, a product may be eligible for priority review. In addition, the company developing the product may be allowed to submit sections of the new drug application or biologics license application on a rolling basis as data become available.

Fast track designation also provides the company with opportunities for more frequent meetings and written communications with the FDA.

Three myeloproliferative neoplasms (MPN), polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF), are associated with an abnormal somatic mutation of the JAK2 gene. Essential thrombocythemia is considered when there is a persistent increase in the peripheral blood platelet count, associated with a proliferation of atypical megakaryocytes in the bone marrow. The manifestations of PV, ET, and PMF all typically occur within the sixth or seventh decade of life. A patient may present with an abnormal blood count but be asymptomatic at the time. Over the course and progression of the disease, increases in hematocrit or platelet counts along with symptoms such as headaches, blurred vision, and plethora may occur.¹ The JAK2 V617F mutation is responsible for the production of the JAK2 protein, which is continuously activated, promoting the growth and division of cells such as erythrocytes, granulocytes, and platelets. It has been reported that there is a nearly 100% incidence of the JAK2 mutation in patients with polycythemia vera, and a 50% incidence in patients with essential thrombocythemia and primary myelofibrosis.²

The discovery of the JAK2 mutation in PV, ET, and PMF was an important advancement in helping distinguish these disorders from other MPNs, including chronic myelogenous leukemia, but its presence does not explain why some individuals develop ET and others, PV or PMF.³ Although there have been familial cases proven of ET, the somatic JAK2 mutation is acquired and not inherited. In this report, we describe the unusual circumstance of JAK2 V617F mutation in a brother and a sister who were both diagnosed with essential thrombocythemia.

Case presentations and summaries

RS, a 69-year-old white man, was referred to our service in 2006 for continued care of previously diagnosed essential thrombocythemia. At the time of his initial visit to our clinic, his complete blood count was normal, the platelet count being adequately controlled by anagrelide at a daily dose of 4.0 mg. He complained of palpitations and peripheral neuropathy. A bone marrow biopsy was performed, revealing moderate hypercellularity, atypical megakaryocytosis, and a negative BCR-ABL mutation but a positive JAK2 V617F mutation. The patient is now treated with hydroxyurea 1,000 mg daily in divided doses, which better controls his counts and does not have the side effects of anagrelide.

SW, a 73-year-old woman, and brother of RS (they share the same biological mother and father), was noted to have a mild thrombocytosis in 2008. In 2013, her platelet count rose to 865,000 cells/uL (normal, 150,000-450,000 cells/uL, age and sex adjusted) and she was referred to our clinic. A bone marrow biopsy was performed, revealing borderline hypercellularity with atypical megakaryocytosis and the presence of a JAK2 V617F mutation. As with her brother, the BCR-ABL mutation was not present. She has also responded to treatment with hydroxyurea, but at a reduced dosage of 500 mg daily.

A third sibling, AS, again of the same biological mother and father, had died of multiple veno-occlusive cerebral vascular events long before the diagnoses on his younger siblings had been made. The suggestion of any underling hematologic pathology would be interesting, but speculative. Nothing is known about the parents’ medical history. None of the three siblings had children.

Discussion

Much research has been done to understand the pathogenesis of and find a cure for myeloproliferative disorders, but despite some progress, a cure remains elusive. However, there have been some advances that have contributed to partial cures for MPNs. One of the major breakthroughs in MPN research, about 50 years ago, was related to the “sporadic vs familial debate” around the Philadelphia chromosome.4 It led to the discovery of the reciprocal translocation between chromosomes 9 and 22, known as the BCR-ABL mutation, which is found in many CML patients. This discovery allowed researchers to focus their attention on other tyrosine kinase domains, such as the JAK2 V617F mutation, which is presented in the three other MPNs; PV, ET, and PMF. Both the JAK2 V617F and BCR-ABL mutations are active in signaling transcription, more commonly growth of cells.⁴

Since the discovery of the JAK2 V617F mutation in early 2005, it has become a leading diagnostic criteria for myeloproliferative diseases. The presence of the JAK2 V617F mutation and the measurement of its allele burden can be assessed by examination of either peripheral blood or bone marrow samples.⁵

The JAK2 V617F mutation is a result of a single change in the DNA nucleotide base pair that causes a substitution of a valine amino acid for a phenylalanine amino acid at the 617 position on exon 14 within the JAK2 kinase regulatory domain. This point mutation disrupts the regular control of the JAK2 by removing its ability to turn off, leading to uncontrolled blood cell growth.⁶ When the JAK2 V617F mutation cannot be demonstrated in a patient with the hallmarks of an MPN, the detection of other JAK2 and MPL proto-oncogene, thrombopoietin receptor mutations may be used as a diagnostic procedure for other MPNs.⁷

Other mutations incorporated in JAK2 domain can be detected in the coding portions of the DNA known as exons. One such mutation is the JAK2 exon 12, which is involved in JAK2 V617F-negative PV patients. This mutation is not detected in patients with ET or PMF and is 2%-5% present in patients with PV. There are other somatic mutations in the thrombopoietin receptors that work in accordance with thrombopoietin: MPL W515L and MPL W515K, which are found at chromosome 1p34, are identified in about 5% of PMF and 1% of ET patients, but are not present in PV patients.^8.9

Pikman and colleagues reported in 2009 that the JAK2 V617F mutation is not acquired randomly.⁹ Their findings showed that, only in white populations, does the JAK2 V617F mutation arise preferentially on a specific constitutional JAK2 46/1 haplotype. According to the authors, the preconceived notion a of randomly acquired JAK2 V617F mutation does not account for familial MPN’s. Familial MPNs are thought to be produced by sporadic and extremely penetrant substitutions in genes that still are not identified and the 46/1 haplotype does not explain for the phenotypic diversity correlated with the JAK2 V617F gene. The 46/1 haplotype, however, correlates more frequently with different MPN subtypes. There are two hypotheses that try to explain how an acquired mutation as prevailing as the JAK2 V617F mutation can be associated with certain inherited backgrounds. The first hypothesis asserts the V617F accumulates at a faster rate than other genes because of the fundamentally unstable genetics of the 46/1 haplotype. The second theory is that all the mutated genes, including the V617F, arise at equal rates, but 46/1 may grant a selective advantage to the V617F-positive clone or interacts in some way to increase the likelihood of abnormal blood counts. A study that examined both these hypotheses concluded that the 46/1 haplotype was present more frequently in patients with myeloproliferative disorders than in their control groups and even more so in cases that were proven to be V617F-positive.10

There are very few cases that have reported familial MPN’s, especially as the pedigrees of the familial MPN’s illustrate that inheritance patterns are notably heterogeneous, indicating that there may be a range of different germline mutations driving the susceptibility. With recent data, the JAK2 V617F mutation in tandem with MPL W515L/K and inactivating TET2 mutations still continue to be the most frequently acquired mutations involved in both familial and sporadic MPN. As far as we know, there have been no cases to prove that JAK2 V617F and MPL W515L/K mutations are inherited through the germline, but there are other alleles that may pass through the germline that can be associated with hereditary thrombocytosis.¹¹ Further cytogenetic studies will clarify the pathogenesis of these disorders and possibly lead to effective targeted therapies.

Three myeloproliferative neoplasms (MPN), polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF), are associated with an abnormal somatic mutation of the JAK2 gene. Essential thrombocythemia is considered when there is a persistent increase in the peripheral blood platelet count, associated with a proliferation of atypical megakaryocytes in the bone marrow. The manifestations of PV, ET, and PMF all typically occur within the sixth or seventh decade of life. A patient may present with an abnormal blood count but be asymptomatic at the time. Over the course and progression of the disease, increases in hematocrit or platelet counts along with symptoms such as headaches, blurred vision, and plethora may occur.¹ The JAK2 V617F mutation is responsible for the production of the JAK2 protein, which is continuously activated, promoting the growth and division of cells such as erythrocytes, granulocytes, and platelets. It has been reported that there is a nearly 100% incidence of the JAK2 mutation in patients with polycythemia vera, and a 50% incidence in patients with essential thrombocythemia and primary myelofibrosis.²

The discovery of the JAK2 mutation in PV, ET, and PMF was an important advancement in helping distinguish these disorders from other MPNs, including chronic myelogenous leukemia, but its presence does not explain why some individuals develop ET and others, PV or PMF.³ Although there have been familial cases proven of ET, the somatic JAK2 mutation is acquired and not inherited. In this report, we describe the unusual circumstance of JAK2 V617F mutation in a brother and a sister who were both diagnosed with essential thrombocythemia.

Case presentations and summaries

RS, a 69-year-old white man, was referred to our service in 2006 for continued care of previously diagnosed essential thrombocythemia. At the time of his initial visit to our clinic, his complete blood count was normal, the platelet count being adequately controlled by anagrelide at a daily dose of 4.0 mg. He complained of palpitations and peripheral neuropathy. A bone marrow biopsy was performed, revealing moderate hypercellularity, atypical megakaryocytosis, and a negative BCR-ABL mutation but a positive JAK2 V617F mutation. The patient is now treated with hydroxyurea 1,000 mg daily in divided doses, which better controls his counts and does not have the side effects of anagrelide.

SW, a 73-year-old woman, and brother of RS (they share the same biological mother and father), was noted to have a mild thrombocytosis in 2008. In 2013, her platelet count rose to 865,000 cells/uL (normal, 150,000-450,000 cells/uL, age and sex adjusted) and she was referred to our clinic. A bone marrow biopsy was performed, revealing borderline hypercellularity with atypical megakaryocytosis and the presence of a JAK2 V617F mutation. As with her brother, the BCR-ABL mutation was not present. She has also responded to treatment with hydroxyurea, but at a reduced dosage of 500 mg daily.

A third sibling, AS, again of the same biological mother and father, had died of multiple veno-occlusive cerebral vascular events long before the diagnoses on his younger siblings had been made. The suggestion of any underling hematologic pathology would be interesting, but speculative. Nothing is known about the parents’ medical history. None of the three siblings had children.

Discussion

Much research has been done to understand the pathogenesis of and find a cure for myeloproliferative disorders, but despite some progress, a cure remains elusive. However, there have been some advances that have contributed to partial cures for MPNs. One of the major breakthroughs in MPN research, about 50 years ago, was related to the “sporadic vs familial debate” around the Philadelphia chromosome.4 It led to the discovery of the reciprocal translocation between chromosomes 9 and 22, known as the BCR-ABL mutation, which is found in many CML patients. This discovery allowed researchers to focus their attention on other tyrosine kinase domains, such as the JAK2 V617F mutation, which is presented in the three other MPNs; PV, ET, and PMF. Both the JAK2 V617F and BCR-ABL mutations are active in signaling transcription, more commonly growth of cells.⁴

Since the discovery of the JAK2 V617F mutation in early 2005, it has become a leading diagnostic criteria for myeloproliferative diseases. The presence of the JAK2 V617F mutation and the measurement of its allele burden can be assessed by examination of either peripheral blood or bone marrow samples.⁵

The JAK2 V617F mutation is a result of a single change in the DNA nucleotide base pair that causes a substitution of a valine amino acid for a phenylalanine amino acid at the 617 position on exon 14 within the JAK2 kinase regulatory domain. This point mutation disrupts the regular control of the JAK2 by removing its ability to turn off, leading to uncontrolled blood cell growth.⁶ When the JAK2 V617F mutation cannot be demonstrated in a patient with the hallmarks of an MPN, the detection of other JAK2 and MPL proto-oncogene, thrombopoietin receptor mutations may be used as a diagnostic procedure for other MPNs.⁷

Other mutations incorporated in JAK2 domain can be detected in the coding portions of the DNA known as exons. One such mutation is the JAK2 exon 12, which is involved in JAK2 V617F-negative PV patients. This mutation is not detected in patients with ET or PMF and is 2%-5% present in patients with PV. There are other somatic mutations in the thrombopoietin receptors that work in accordance with thrombopoietin: MPL W515L and MPL W515K, which are found at chromosome 1p34, are identified in about 5% of PMF and 1% of ET patients, but are not present in PV patients.^8.9

Pikman and colleagues reported in 2009 that the JAK2 V617F mutation is not acquired randomly.⁹ Their findings showed that, only in white populations, does the JAK2 V617F mutation arise preferentially on a specific constitutional JAK2 46/1 haplotype. According to the authors, the preconceived notion a of randomly acquired JAK2 V617F mutation does not account for familial MPN’s. Familial MPNs are thought to be produced by sporadic and extremely penetrant substitutions in genes that still are not identified and the 46/1 haplotype does not explain for the phenotypic diversity correlated with the JAK2 V617F gene. The 46/1 haplotype, however, correlates more frequently with different MPN subtypes. There are two hypotheses that try to explain how an acquired mutation as prevailing as the JAK2 V617F mutation can be associated with certain inherited backgrounds. The first hypothesis asserts the V617F accumulates at a faster rate than other genes because of the fundamentally unstable genetics of the 46/1 haplotype. The second theory is that all the mutated genes, including the V617F, arise at equal rates, but 46/1 may grant a selective advantage to the V617F-positive clone or interacts in some way to increase the likelihood of abnormal blood counts. A study that examined both these hypotheses concluded that the 46/1 haplotype was present more frequently in patients with myeloproliferative disorders than in their control groups and even more so in cases that were proven to be V617F-positive.10

There are very few cases that have reported familial MPN’s, especially as the pedigrees of the familial MPN’s illustrate that inheritance patterns are notably heterogeneous, indicating that there may be a range of different germline mutations driving the susceptibility. With recent data, the JAK2 V617F mutation in tandem with MPL W515L/K and inactivating TET2 mutations still continue to be the most frequently acquired mutations involved in both familial and sporadic MPN. As far as we know, there have been no cases to prove that JAK2 V617F and MPL W515L/K mutations are inherited through the germline, but there are other alleles that may pass through the germline that can be associated with hereditary thrombocytosis.¹¹ Further cytogenetic studies will clarify the pathogenesis of these disorders and possibly lead to effective targeted therapies.

Three myeloproliferative neoplasms (MPN), polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF), are associated with an abnormal somatic mutation of the JAK2 gene. Essential thrombocythemia is considered when there is a persistent increase in the peripheral blood platelet count, associated with a proliferation of atypical megakaryocytes in the bone marrow. The manifestations of PV, ET, and PMF all typically occur within the sixth or seventh decade of life. A patient may present with an abnormal blood count but be asymptomatic at the time. Over the course and progression of the disease, increases in hematocrit or platelet counts along with symptoms such as headaches, blurred vision, and plethora may occur.¹ The JAK2 V617F mutation is responsible for the production of the JAK2 protein, which is continuously activated, promoting the growth and division of cells such as erythrocytes, granulocytes, and platelets. It has been reported that there is a nearly 100% incidence of the JAK2 mutation in patients with polycythemia vera, and a 50% incidence in patients with essential thrombocythemia and primary myelofibrosis.²

The discovery of the JAK2 mutation in PV, ET, and PMF was an important advancement in helping distinguish these disorders from other MPNs, including chronic myelogenous leukemia, but its presence does not explain why some individuals develop ET and others, PV or PMF.³ Although there have been familial cases proven of ET, the somatic JAK2 mutation is acquired and not inherited. In this report, we describe the unusual circumstance of JAK2 V617F mutation in a brother and a sister who were both diagnosed with essential thrombocythemia.

Case presentations and summaries

RS, a 69-year-old white man, was referred to our service in 2006 for continued care of previously diagnosed essential thrombocythemia. At the time of his initial visit to our clinic, his complete blood count was normal, the platelet count being adequately controlled by anagrelide at a daily dose of 4.0 mg. He complained of palpitations and peripheral neuropathy. A bone marrow biopsy was performed, revealing moderate hypercellularity, atypical megakaryocytosis, and a negative BCR-ABL mutation but a positive JAK2 V617F mutation. The patient is now treated with hydroxyurea 1,000 mg daily in divided doses, which better controls his counts and does not have the side effects of anagrelide.

SW, a 73-year-old woman, and brother of RS (they share the same biological mother and father), was noted to have a mild thrombocytosis in 2008. In 2013, her platelet count rose to 865,000 cells/uL (normal, 150,000-450,000 cells/uL, age and sex adjusted) and she was referred to our clinic. A bone marrow biopsy was performed, revealing borderline hypercellularity with atypical megakaryocytosis and the presence of a JAK2 V617F mutation. As with her brother, the BCR-ABL mutation was not present. She has also responded to treatment with hydroxyurea, but at a reduced dosage of 500 mg daily.

A third sibling, AS, again of the same biological mother and father, had died of multiple veno-occlusive cerebral vascular events long before the diagnoses on his younger siblings had been made. The suggestion of any underling hematologic pathology would be interesting, but speculative. Nothing is known about the parents’ medical history. None of the three siblings had children.

Discussion

Much research has been done to understand the pathogenesis of and find a cure for myeloproliferative disorders, but despite some progress, a cure remains elusive. However, there have been some advances that have contributed to partial cures for MPNs. One of the major breakthroughs in MPN research, about 50 years ago, was related to the “sporadic vs familial debate” around the Philadelphia chromosome.4 It led to the discovery of the reciprocal translocation between chromosomes 9 and 22, known as the BCR-ABL mutation, which is found in many CML patients. This discovery allowed researchers to focus their attention on other tyrosine kinase domains, such as the JAK2 V617F mutation, which is presented in the three other MPNs; PV, ET, and PMF. Both the JAK2 V617F and BCR-ABL mutations are active in signaling transcription, more commonly growth of cells.⁴

Since the discovery of the JAK2 V617F mutation in early 2005, it has become a leading diagnostic criteria for myeloproliferative diseases. The presence of the JAK2 V617F mutation and the measurement of its allele burden can be assessed by examination of either peripheral blood or bone marrow samples.⁵

The JAK2 V617F mutation is a result of a single change in the DNA nucleotide base pair that causes a substitution of a valine amino acid for a phenylalanine amino acid at the 617 position on exon 14 within the JAK2 kinase regulatory domain. This point mutation disrupts the regular control of the JAK2 by removing its ability to turn off, leading to uncontrolled blood cell growth.⁶ When the JAK2 V617F mutation cannot be demonstrated in a patient with the hallmarks of an MPN, the detection of other JAK2 and MPL proto-oncogene, thrombopoietin receptor mutations may be used as a diagnostic procedure for other MPNs.⁷

Other mutations incorporated in JAK2 domain can be detected in the coding portions of the DNA known as exons. One such mutation is the JAK2 exon 12, which is involved in JAK2 V617F-negative PV patients. This mutation is not detected in patients with ET or PMF and is 2%-5% present in patients with PV. There are other somatic mutations in the thrombopoietin receptors that work in accordance with thrombopoietin: MPL W515L and MPL W515K, which are found at chromosome 1p34, are identified in about 5% of PMF and 1% of ET patients, but are not present in PV patients.^8.9

Pikman and colleagues reported in 2009 that the JAK2 V617F mutation is not acquired randomly.⁹ Their findings showed that, only in white populations, does the JAK2 V617F mutation arise preferentially on a specific constitutional JAK2 46/1 haplotype. According to the authors, the preconceived notion a of randomly acquired JAK2 V617F mutation does not account for familial MPN’s. Familial MPNs are thought to be produced by sporadic and extremely penetrant substitutions in genes that still are not identified and the 46/1 haplotype does not explain for the phenotypic diversity correlated with the JAK2 V617F gene. The 46/1 haplotype, however, correlates more frequently with different MPN subtypes. There are two hypotheses that try to explain how an acquired mutation as prevailing as the JAK2 V617F mutation can be associated with certain inherited backgrounds. The first hypothesis asserts the V617F accumulates at a faster rate than other genes because of the fundamentally unstable genetics of the 46/1 haplotype. The second theory is that all the mutated genes, including the V617F, arise at equal rates, but 46/1 may grant a selective advantage to the V617F-positive clone or interacts in some way to increase the likelihood of abnormal blood counts. A study that examined both these hypotheses concluded that the 46/1 haplotype was present more frequently in patients with myeloproliferative disorders than in their control groups and even more so in cases that were proven to be V617F-positive.10

There are very few cases that have reported familial MPN’s, especially as the pedigrees of the familial MPN’s illustrate that inheritance patterns are notably heterogeneous, indicating that there may be a range of different germline mutations driving the susceptibility. With recent data, the JAK2 V617F mutation in tandem with MPL W515L/K and inactivating TET2 mutations still continue to be the most frequently acquired mutations involved in both familial and sporadic MPN. As far as we know, there have been no cases to prove that JAK2 V617F and MPL W515L/K mutations are inherited through the germline, but there are other alleles that may pass through the germline that can be associated with hereditary thrombocytosis.¹¹ Further cytogenetic studies will clarify the pathogenesis of these disorders and possibly lead to effective targeted therapies.

Image by Lance Liotta

New research has revealed a potential therapeutic target for acute myeloid leukemia (AML)—the methyl transferase enzyme METTL3.

Researchers found that inhibiting METTL3 destroys human and mouse AML cells without harming non-leukemic blood cells.

The team also discovered why METTL3 is required for AML cell survival by deciphering the mechanism it uses to regulate several other leukemia genes.

The researchers described this work in Nature.

“New treatments for AML are desperately needed, and we have been looking for genes that would be good drug targets,” said study author Tony Kouzarides, PhD, of University of Cambridge in the UK.

“We identified the methyl transferase enzyme METTL3 as a highly viable target against AML. Our study will inspire pharmaceutical efforts to find drugs that specifically inhibit METTL3 to treat AML.”

In their attempt to find therapeutic targets for AML, Dr Kouzarides and his colleagues used CRISPR-Cas9 to screen AML cells for vulnerable points.

The researchers created mouse leukemia cells with mutations in genes that may be targeted in human AML cells and systematically tested each gene, finding which were essential for AML survival.

The team ended up with 46 likely candidate genes, many of which produce proteins that could modify RNA. Among these, METTL3 was one of the genes with the strongest effect.

Experiments revealed that METTL3 was essential for the survival of AML cells, but it was not required for healthy blood cells.

Having found a potential target in METTL3, the researchers investigated how it worked.

They discovered that the protein produced by METTL3 bound to the beginning of 126 different genes, including several required for AML cell survival.

As RNAs were produced, the METTL3 protein added methyl groups to their middle section, something which had not been previously observed. These middle methyl groups increased the ability of the RNAs to be translated into proteins.

The researchers then found that when METTL3 was inhibited, no methyl groups were added to the RNA. This prevented the production of their essential proteins, so the AML cells started dying.

“This study uncovered an entirely new mechanism of gene regulation in AML that operates through modifications of RNA,” said study author Konstantinos Tzelepis, PhD, of Wellcome Trust Sanger Institute in Cambridge, UK.

“We discovered that inhibiting the methyl transferase activity of METTL3 would stop the translation of a whole set of proteins that the leukemia needs. This mechanism shows that a drug to inhibit methylation could be effective against AML without affecting normal cells.”

Image by Lance Liotta

New research has revealed a potential therapeutic target for acute myeloid leukemia (AML)—the methyl transferase enzyme METTL3.

Researchers found that inhibiting METTL3 destroys human and mouse AML cells without harming non-leukemic blood cells.

The team also discovered why METTL3 is required for AML cell survival by deciphering the mechanism it uses to regulate several other leukemia genes.

The researchers described this work in Nature.

“New treatments for AML are desperately needed, and we have been looking for genes that would be good drug targets,” said study author Tony Kouzarides, PhD, of University of Cambridge in the UK.

“We identified the methyl transferase enzyme METTL3 as a highly viable target against AML. Our study will inspire pharmaceutical efforts to find drugs that specifically inhibit METTL3 to treat AML.”

In their attempt to find therapeutic targets for AML, Dr Kouzarides and his colleagues used CRISPR-Cas9 to screen AML cells for vulnerable points.

The researchers created mouse leukemia cells with mutations in genes that may be targeted in human AML cells and systematically tested each gene, finding which were essential for AML survival.

The team ended up with 46 likely candidate genes, many of which produce proteins that could modify RNA. Among these, METTL3 was one of the genes with the strongest effect.

Experiments revealed that METTL3 was essential for the survival of AML cells, but it was not required for healthy blood cells.

Having found a potential target in METTL3, the researchers investigated how it worked.

They discovered that the protein produced by METTL3 bound to the beginning of 126 different genes, including several required for AML cell survival.

As RNAs were produced, the METTL3 protein added methyl groups to their middle section, something which had not been previously observed. These middle methyl groups increased the ability of the RNAs to be translated into proteins.

The researchers then found that when METTL3 was inhibited, no methyl groups were added to the RNA. This prevented the production of their essential proteins, so the AML cells started dying.

“This study uncovered an entirely new mechanism of gene regulation in AML that operates through modifications of RNA,” said study author Konstantinos Tzelepis, PhD, of Wellcome Trust Sanger Institute in Cambridge, UK.

“We discovered that inhibiting the methyl transferase activity of METTL3 would stop the translation of a whole set of proteins that the leukemia needs. This mechanism shows that a drug to inhibit methylation could be effective against AML without affecting normal cells.”

Image by Lance Liotta

New research has revealed a potential therapeutic target for acute myeloid leukemia (AML)—the methyl transferase enzyme METTL3.

Researchers found that inhibiting METTL3 destroys human and mouse AML cells without harming non-leukemic blood cells.

The team also discovered why METTL3 is required for AML cell survival by deciphering the mechanism it uses to regulate several other leukemia genes.

The researchers described this work in Nature.

“New treatments for AML are desperately needed, and we have been looking for genes that would be good drug targets,” said study author Tony Kouzarides, PhD, of University of Cambridge in the UK.

“We identified the methyl transferase enzyme METTL3 as a highly viable target against AML. Our study will inspire pharmaceutical efforts to find drugs that specifically inhibit METTL3 to treat AML.”

In their attempt to find therapeutic targets for AML, Dr Kouzarides and his colleagues used CRISPR-Cas9 to screen AML cells for vulnerable points.

The researchers created mouse leukemia cells with mutations in genes that may be targeted in human AML cells and systematically tested each gene, finding which were essential for AML survival.

The team ended up with 46 likely candidate genes, many of which produce proteins that could modify RNA. Among these, METTL3 was one of the genes with the strongest effect.

Experiments revealed that METTL3 was essential for the survival of AML cells, but it was not required for healthy blood cells.

Having found a potential target in METTL3, the researchers investigated how it worked.

They discovered that the protein produced by METTL3 bound to the beginning of 126 different genes, including several required for AML cell survival.

As RNAs were produced, the METTL3 protein added methyl groups to their middle section, something which had not been previously observed. These middle methyl groups increased the ability of the RNAs to be translated into proteins.

The researchers then found that when METTL3 was inhibited, no methyl groups were added to the RNA. This prevented the production of their essential proteins, so the AML cells started dying.

“This study uncovered an entirely new mechanism of gene regulation in AML that operates through modifications of RNA,” said study author Konstantinos Tzelepis, PhD, of Wellcome Trust Sanger Institute in Cambridge, UK.

“We discovered that inhibiting the methyl transferase activity of METTL3 would stop the translation of a whole set of proteins that the leukemia needs. This mechanism shows that a drug to inhibit methylation could be effective against AML without affecting normal cells.”

Micrograph showing MDS

The US Food and Drug Administration (FDA) has granted orphan drug designation to AMV564, a CD33/CD3 bispecific antibody, for the treatment of acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS).

AMV564 is a T-cell engager, derived from human protein sequences, that binds both CD33 and CD3 to mediate T-cell directed lysis of CD33-positive cancer cells.

Amphivena Therapeutics Inc., is currently conducting a phase 1 trial of AMV564 in relapsed or refractory AML. The company plans to launch a phase 1 trial in patients with MDS in early 2018.

According to Amphivena, AMV564 has demonstrated “potent activity” in AML patient samples, and that activity was independent of CD33 expression level, disease stage, and cytogenetic risk.

AMV564 also eliminated nearly all blasts from the bone marrow and spleen in a stringent AML patient-derived xenograft murine model.

In addition, Amphivena established a therapeutic window for AMV564 in cynomolgus monkeys, with rapid and sustained elimination of CD33-expressing cells during AMV564 dosing and rapid hematopoietic recovery following dosing.

About orphan designation

The FDA grants orphan designation to products intended to treat, diagnose, or prevent diseases/disorders that affect fewer than 200,000 people in the US.

The designation provides incentives for sponsors to develop products for rare diseases. This may include tax credits toward the cost of clinical trials, prescription drug user fee waivers, and 7 years of market exclusivity if the product is approved.

Micrograph showing MDS

The US Food and Drug Administration (FDA) has granted orphan drug designation to AMV564, a CD33/CD3 bispecific antibody, for the treatment of acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS).

AMV564 is a T-cell engager, derived from human protein sequences, that binds both CD33 and CD3 to mediate T-cell directed lysis of CD33-positive cancer cells.

Amphivena Therapeutics Inc., is currently conducting a phase 1 trial of AMV564 in relapsed or refractory AML. The company plans to launch a phase 1 trial in patients with MDS in early 2018.

According to Amphivena, AMV564 has demonstrated “potent activity” in AML patient samples, and that activity was independent of CD33 expression level, disease stage, and cytogenetic risk.

AMV564 also eliminated nearly all blasts from the bone marrow and spleen in a stringent AML patient-derived xenograft murine model.

In addition, Amphivena established a therapeutic window for AMV564 in cynomolgus monkeys, with rapid and sustained elimination of CD33-expressing cells during AMV564 dosing and rapid hematopoietic recovery following dosing.

About orphan designation

The FDA grants orphan designation to products intended to treat, diagnose, or prevent diseases/disorders that affect fewer than 200,000 people in the US.

The designation provides incentives for sponsors to develop products for rare diseases. This may include tax credits toward the cost of clinical trials, prescription drug user fee waivers, and 7 years of market exclusivity if the product is approved.

Micrograph showing MDS

The US Food and Drug Administration (FDA) has granted orphan drug designation to AMV564, a CD33/CD3 bispecific antibody, for the treatment of acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS).

AMV564 is a T-cell engager, derived from human protein sequences, that binds both CD33 and CD3 to mediate T-cell directed lysis of CD33-positive cancer cells.

Amphivena Therapeutics Inc., is currently conducting a phase 1 trial of AMV564 in relapsed or refractory AML. The company plans to launch a phase 1 trial in patients with MDS in early 2018.

According to Amphivena, AMV564 has demonstrated “potent activity” in AML patient samples, and that activity was independent of CD33 expression level, disease stage, and cytogenetic risk.

AMV564 also eliminated nearly all blasts from the bone marrow and spleen in a stringent AML patient-derived xenograft murine model.

In addition, Amphivena established a therapeutic window for AMV564 in cynomolgus monkeys, with rapid and sustained elimination of CD33-expressing cells during AMV564 dosing and rapid hematopoietic recovery following dosing.

About orphan designation

The FDA grants orphan designation to products intended to treat, diagnose, or prevent diseases/disorders that affect fewer than 200,000 people in the US.

The designation provides incentives for sponsors to develop products for rare diseases. This may include tax credits toward the cost of clinical trials, prescription drug user fee waivers, and 7 years of market exclusivity if the product is approved.

Introduction

Hairy cell leukemia (HCL) is a rare chronic lymphoproliferative disorder, with only approximately 2000 new cases diagnosed in the United States each year.¹ It is now recognized that there are 2 distinct categories of HCL, classic HCL (cHCL) and variant HCL (vHCL), with vHCL now classified as a separate entity under the World Health Organization Classification of Hematopoietic Tumors.² For this reason, the 2 diseases will be discussed separately. However, they do bear many clinical and microscopic similarities and because of this were originally indistinguishable using diagnostic techniques previously available. Even in the modern era using immunophenotypic, molecular, and genetic testing, differentiating between the classic and variant disease subtypes is sometimes difficult.

For cHCL the median age of diagnosis is 55 years, with vHCL occurring in patients who are somewhat older; HCL has been described only in the adult population, with 1 exception.^3,4 There is a 4:1 male predominance, and Caucasians are more frequently affected than other ethnic groups. While the cause of the disease remains largely unknown, it has been observed to occur more frequently in farmers and in persons exposed to pesticides and/or herbicides, petroleum products, and ionizing radiation.⁴ The Institute of Medicine recently updated their position regarding veterans and Agent Orange, stating that there is sufficient evidence of an association between herbicides and chronic lymphoid leukemias (including HCL) to consider these diseases linked to exposure.⁵ Familial forms have also been described that are associated with specific HLA haplotypes, indicating a possible hereditary component.⁶ Most likely, a combination of environmental and genetic factors ultimately contributes to the development of HCL.

In recent years enormous progress has been made with respect to new insights into the biology of cHCL and vHCL, with significant refinement of diagnostic criteria. In addition, tremendous advances have occurred in both treatment and supportive care regimens, which have resulted in a dramatically increased overall life expectancy as well as decreased disease-related morbidity. This has meant that more patients are affected by HCL over time and are more likely to require care for relapsed HCL or associated comorbidities. Although no curative treatment options exist outside of allogeneic transplantation, therapeutic improvements have resulted in patients with cHCL having a life expectancy similar to that of unaffected patients, increasing the need for vigilance to prevent foreseeable complications.

Biology and Patheogenisis

The family of HCLs are chronic B-cell malignancies that account for approximately 2% of all diagnosed leukemias.⁷ The first detailed characterization of HCL as a distinct clinical entity was performed by Dr. Bouroncle and colleagues at the Ohio State University in 1958.⁸ Originally called leukemic reticuloendotheliosis, it was renamed HCL following more detailed description of the unique morphology of these malignant cells.⁹ Significant advances have recently been made in identifying distinctive genetic, immunophenotypic, and morphologic features that distinguish HCL from other B-cell malignancies.

HCL B cells tend to accumulate in the bone marrow, splenic red pulp, and (in some cases) peripheral blood. Unlike other lymphoproliferative disorders, HCL only rarely results in lymphadenopathy. HCL derives its name from the distinct appearance of the malignant hairy cells (Figure). Morphologically, HCL cells are mature, small lymphoid B-cells with a round or oval nucleus and abundant pale blue cytoplasm. Irregular projections of cytoplasm and microvilli give the cells a serrated, “hairy” appearance.¹⁰ The biological significance of these fine hair-like projections remains unknown and is an area of ongoing investigation. Gene expression profiling has revealed that HCL B cells are most similar to splenic marginal zone B cells and memory B cells.^11–13 A recent analysis of common genetic alterations in HCL suggests that the cell of origin is in fact the hematopoietic stem cell.¹⁴

Compared to other hematologic malignancies, the genomic profile of HCL is relatively stable, with few chromosomal defects or translocations observed. A seminal study by Tiacci and colleagues revealed that the BRAF V600E mutation was present in 47 out of 47 cHCL cases examined, results that have since been replicated by other groups, confirming that BRAF V600E is a hallmark mutation in cHCL.¹⁵ The BRAF V600E gain-of-function mutation results in constitutive activation of the serine-threonine protein kinase B-Raf, which regulates the mitogen-activated protein kinase (MAPK)/RAF-MEK-ERK pathway. Indeed, cHCL B cells have elevated MAPK signaling, leading to enhancement of growth and survival.¹⁶ This specific mutation in the BRAF gene is also seen in a number of solid tumor malignancies including melanoma and thyroid cancer, and represents a therapeutic target using BRAF inhibitors already developed to treat these malignancies.¹⁷ Testing for BRAF V600E by polymerase chain reaction or immunohistochemical staining is now routinely performed when HCL is suspected.

While BRAF V600E is identified in nearly all cases of cHCL, it is rare in vHCL.¹⁸ The variant type of HCL was classified as a distinct clinical entity in 2008 and can now often be distinguished from cHCL on the basis of BRAF mutational status, among other differences. Interestingly, in the rare cases of BRAF V600E–negative cHCL, other mutations in BRAF or downstream targets as well as aberrant activation of the RAF-MEK-ERK signaling cascade are observed, indicating that this pathway is critical in HCL and may still represent a viable therapeutic target. Expression of the IGHV4-34 immunoglobulin rearrangement, while more common in vHCL, has also been identified in 10% of cHCL cases and appears to confer poor prognosis.¹⁹ Other mutated genes that have been identified in HCL include CDKN1B, TP53, U2AF1, ARID1A, EZH2, and KDM6A.²⁰

Classic HCL is characterized by the immunophenotypic expression of CD11c, CD25, CD103, and CD123, with kappa or lambda light chain restriction indicating clonality; HCL B cells are generally negative for CD5, CD10, CD23, CD27, and CD79b. In contrast, vHCL often lacks expression of CD25 and CD123.¹⁸ The B-cell receptor (BCR) is expressed on hairy cells and its activation promotes proliferation and survival in vitro.²¹ The role of BCR signaling in B-cell malignancies is increasingly recognized, and therapies that target the BCR and associated signaling molecules offer an attractive treatment strategy.²² HCL B cells also typically express CD19, CD20, CD22, CD79a, CD200, CD1d, and annexin A1. Tartrate-resistant acid phosphatase (TRAP) positivity by immunohistochemistry is a hallmark of cHCL. Interestingly, changes to the patient’s original immunophenotype have been observed following treatment and upon disease recurrence, highlighting the importance of tracking immunophenotype throughout the course of disease.

Diagnosis

Prior to the advent of annual screening evaluations with routine examination of complete blood counts (CBC), patients were most often diagnosed with HCL when they presented with symptoms of the disease such as splenomegaly, infections, or complications of anemia or thrombocytopenia.²³ In the current era, patients are more likely to be incidentally diagnosed when they are found to have an abnormal value on a CBC. Any blood lineage may be affected and patients may have pancytopenia or isolated cytopenias. Of note, monocytopenia is a common finding in cHCL that is not entirely understood. The cells typical of cHCL do not usually circulate in the peripheral blood, but if present would appear as mature lymphocytes with villous cytoplasmic projections, pale blue cytoplasm, and reniform nuclei with open chromatin (Figure).⁹ Even if the morphologic examination is highly suggestive of HCL, additional testing is required to differentiate between cHCL, vHCL, and other hematologic malignancies which may also have cytoplasmic projections. A complete assessment of the immunophenotype, molecular profile, and cytogenetic features is required to arrive at this diagnosis.

The international Hairy Cell Leukemia Foundation recently published consensus guidelines for the diagnosis and treatment of HCL.²⁴ These guidelines recommend that patients undergo examination of the peripheral blood for morphology and immunophenotyping and further recommend obtaining bone marrow core and aspirate biopsy samples for immunophenotyping via immunohistochemical staining and flow cytometry. The characteristic immunophenotype of cHCL is a population of monoclonal B lymphocytes which co-express CD19, CD20, CD11c, CD25, CD103, and CD123. Variant HCL is characterized by a very similar immunophenotype but is usually negative for CD25 and CD123. It is notable that CD25 positivity may be lost following treatment, and the absence of this marker should not be used as the sole basis of a cHCL versus vHCL diagnosis. Because marrow fibrosis in HCL may prevent a marrow aspirate from being obtained, many of the key diagnostic studies are performed on the core biopsy, including morphological evaluation and immunohistochemical stains such as CD20 (a pan-B cell antigen), annexin-1 (an anti-inflammatory protein expressed only in cHCL), and VE1 (a BRAF V600E stain).

As noted above, recurrent cytogenetic abnormalities have now been identified that may inform the diagnosis or prognosis of HCL. Next-generation sequencing and other testing of the genetic landscape are taking on a larger role in subtype differentiation, and it is likely that future guidelines will recommend evaluation for significant mutations. Given that BRAF V600E mutation status is a key feature of cHCL and is absent in vHCL, it is important to perform this testing at the time of diagnosis whenever possible. The mutation may be detected via VE1 immunohistochemical staining, allele-specific polymerase chain reaction, or next-generation sequencing. Other less sensitive tests exist but are utilized less frequently.

Minimal Residual Disease

There is currently no accepted standard for minimal residual disease (MRD) monitoring in HCL. While detection of MRD has been clearly associated with increased risk of disease progression, cHCL cells typically do not circulate in the peripheral blood, limiting the use of peripheral blood immunophenotyping for quantitative MRD assessment. For quantitative monitoring of marrow involvement by HCL, immunohistochemical staining of the bone marrow core biopsy is usually required. Staining may be performed for CD20, or, in patients who have received anti-CD20 therapy, DBA.44, VE-1, or CD79a. There is currently not a consensus regarding what level of disease involvement constitutes MRD. One group studied this issue and found that relapse could be predicted by evaluating MRD by percentage of positive cells in the marrow by immunohistochemical staining, with less than 1% involvement having the lowest risk for disease relapse and greater than 5% having the highest risk for disease relapse.²⁵ A recent study evaluated MRD patterns in the peripheral blood of 32 cHCL patients who had completed frontline therapy. This group performed flow cytometry on the peripheral blood of patients at 1, 3, 6, and 12 months following therapy. All patients had achieved a complete response with initial therapy and peripheral blood MRD negativity at the completion of therapy. At a median follow-up of 100 months post therapy, 5 patients converted from peripheral blood–MRD negative to peripheral blood–MRD positive, and 6 patients developed overt disease progression. In all patients who progressed, progression was preceded by an increase in detectable peripheral blood MRD cells.²⁶ Although larger studies are needed, peripheral blood flow cytometric monitoring for MRD may be a useful adjunct to predict ongoing response or impending relapse. In addition, newer, more sensitive methods of disease monitoring may ultimately supplant flow cytometry.

Risk Stratification

Although much progress has been made in the risk stratification profiling of hematologic malignancies in general, HCL has unfortunately lagged behind in this effort. The most recent risk stratification analysis was performed in 1982 by Jansen and colleagues.²⁷ This group of researchers performed a retrospective analysis of 391 HCL patients treated at 22 centers. One of the central questions in their analysis was survival time from diagnosis in patients who had not yet undergone splenectomy (a standard treatment at the time). This group consisted of a total of 154 patients. As this study predated modern pathological and molecular testing, clinical and laboratory features were examined, and these mostly consisted of physical exam findings and analysis of the peripheral blood. This group found that several factors influenced the survival of these patients, including duration of symptoms prior to diagnosis, the degree of splenomegaly, hemoglobin level, and number of hairy cells in the peripheral blood. However, because of interobserver variation for the majority of these variables, only hemoglobin and spleen size were included in the proportional hazard model. Using only these 2 variables, the authors were able to determine 3 clinical stages for HCL (Table 1). The stages were found to correlate with median survival: patients with stage 1 disease had a median survival not reached at 72 months, but patients with stage 2 disease had a median survival of 18 months, which decreased to only 12 months in patients with stage 3 disease.

Because the majority of patients with HCL in the modern era will be diagnosed prior to reaching stage 3, a risk stratification system incorporating clinical features, laboratory parameters, and molecular and genetic testing is of considerable interest and is a subject of ongoing research. Ultimately, the goal will be to identify patients at higher risk of early relapse so that more intensive therapies can be applied to initial treatment that will result in longer treatment-free intervals.

Treatment

Because there is no curative treatment for either cHCL or vHCL outside allogeneic transplantation, and it is not clear that early treatment leads to better outcomes in HCL, patients do not always receive treatment at the time of diagnosis or relapse. The general consensus is that patients should be treated if there is a declining trend in hematologic parameters or they experience symptoms from the disease.²⁴ Current consensus guidelines recommend treatment when any of the following hematologic parameters are met: hemoglobin less than 11 g/dL, platelet count less than 100 × 10³/µL, or absolute neutrophil count less than 1000/µL.²⁴ These parameters are surrogate markers that indicate compromised bone marrow function. Cytopenias may also be caused by splenomegaly, and symptomatic splenomegaly with or without cytopenias is an indication for treatment. A small number of patients with HCL (approximately 10%) do not require immediate therapy after diagnosis and are monitored by their provider until treatment is indicated.

First-Line Therapy

Despite advances in targeted therapies for HCL, because no treatment has been shown to extend the treatment-free interval longer than chemotherapy, treatment with a purine nucleoside analog is usually the recommended first-line therapy. This includes either cladribine or pentostatin. Both agents appear to be equally effective, and the choice of therapy is determined by the treating physician based on his or her experience. Cladribine administration has been studied using a number of different schedules and routes: intravenous continuous infusion (0.1 mg/kg) for 7 days, intravenous infusion (0.14 mg/kg/day) over 2 hours on a 5-day regimen, or alternatively subcutaneously (0.1–0.14 mg/kg/day) on a once-per-day or once-per-week regimen (Table 2).^28,29

Unlike cHCL, vHCL remains difficult to treat and early disease progression is common. The best outcomes have been seen in patients who have received combination chemo-immunotherapy such as purine nucleoside analog therapy plus rituximab or bendamustine plus rituximab.³¹ One pilot study of bendamustine plus rituximab in 12 patients found an overall response rate of 100%, with the majority of patients achieving a complete response.³¹ For patients who achieved a complete response, the median duration of response had not been reached, but patients achieving only a partial response had a median duration of response of only 20 months, indicating there is a subgroup of patients who will require a different treatment approach.³² A randomized phase 2 trial of rituximab with either pentostatin or bendamustine is ongoing.³³

Assessment of Response

Response assessment involves physical examination for estimation of spleen size, assessment of hematologic parameters, and a bone marrow biopsy for evaluation of marrow response. It is recommended that the bone marrow biopsy be performed 4 to 6 months following cladribine administration, or after completion of 12 doses of pentostatin. Detailed response assessment criteria are shown in Table 3.

Second-Line Therapy

Although the majority of patients treated with purine analogs will achieve durable remissions, approximately 40% of patients will eventually require second-line therapy. Criteria for treatment at relapse are the same as the criteria for initial therapy, including symptomatic disease or progressive anemia, thrombocytopenia, or neutropenia. The choice of treatment is based on clinical parameters and the duration of the previous remission. If the initial remission was longer than 65 months and the patient is eligible to receive chemotherapy, re-treatment with initial therapy is recommended. For a remission between 24 and 65 months, re-treatment with a purine analog combined with an anti-CD20 monoclonal antibody may be considered.³⁴ If the first remission is shorter than 24 months, confirmation of the original diagnosis as well as consideration for testing for additional mutations with therapeutic targets (BRAF V600E, MAP2K1) should be considered before a treatment decision is made. For these patients, alternative therapies, including investigational agents, should be considered.²⁴

Monoclonal antibody therapy has been studied in both the up-front setting and in relapsed or refractory HCL.³⁵ An initial study of 15 patients with relapsed HCL found an overall response rate of 80%, with 8 patients achieving a complete response. A subsequent study of 26 patients who relapsed after cladribine therapy found an overall response rate of 80%, with a complete response rate of 32%. Median relapse-free survival was 27 months.³⁶ Ravandi and others studied rituximab in the up-front setting in combination with cladribine, and found an overall response rate of 100%, including in patients with vHCL. At the time of publication of the study results, the median survival had not been reached.³⁷ As has been seen with other lymphoid malignancies, concurrent therapy with rituximab appears to enhance the activity of the agent with which it is combined. While its use in the up-front setting remains an area of active investigation, there is a clear role for chemo-immunotherapy in the relapsed setting.

In patients with cHCL, excellent results including complete remissions have been reported with the use of BRAF inhibitors, both as a single agent and when combined with anti-CD20 therapy. The 2 commercially available BRAF inhibitors are vemurafenib and dabrafenib, and both have been tested in relapsed cHCL.^38,39 The first study of vemurafenib was reported by Tiacci and colleagues, who found an overall response rate of 96% after a median of 8 weeks and a 100% response rate after a median of 12 weeks, with complete response rates up to 42%.³⁸ The median relapse-free survival was 23 months (decreasing to only 6 months in patients who achieved only a partial remission), indicating that these agents will likely need to be administered in combination with other effective therapies with non-overlapping toxicities. Vemurafenib has been administered concurrently with rituximab, and preliminary results of this combination therapy showed early rates of complete responses.⁴⁰ Dabrafenib has been reported for use as a single agent in cHCL and clinical trials are underway evaluating its efficacy when administered with trametinib, a MEK inhibitor.^39,41 Of note, patients receiving BRAF inhibitors frequently develop cutaneous complications of RAF inhibition including cutaneous squamous cell carcinomas and keratoacanthomas, and close dermatologic surveillance is required.

Variant HCL does not harbor the BRAF V600E mutation, but up to half of patients have been found to have mutations of MAP2K1, which upregulates MEK1 expression.⁴² Trametinib is approved by the US Food and Drug Administration for the treatment of patients with melanoma at a dose of 2 mg orally daily, and has been successfully used to treat 1 patient with vHCL.⁴³ Further evaluation of this targeted therapy is underway.

Ibrutinib, a Bruton tyrosine kinase inhibitor, and moxetumomab pasudotox, an immunotoxin conjugate, are currently being studied in National Institutes of Health–sponsored multi-institutional trials for patients with HCL. Ibrutinib is administered orally at 420 mg per day until relapse.⁴⁴ Moxetumomab pasudotox was tested at different doses between 5 and 50 μg/kg intravenously every other day for 3 doses for up to 16 cycles unless they experienced disease progression or developed neutralizing antibodies.⁴⁵ Both agents have been shown to have significant activity in cHCL and vHCL and will likely be included in the treatment armamentarium once trials are completed. Second-line therapy options are summarized in Table 4.

Complications and Supportive Care

The complications of HCL may be separated into the pre-, intra-, and post-treatment periods. At the time of diagnosis and prior to the initiation of therapy, marrow infiltration by HCL frequently leads to cytopenias which cause symptomatic anemia, infection, and/or bleeding complications. Many patients develop splenomegaly, which may further lower the blood counts and which is experienced as abdominal fullness or distention, with early satiety leading to weight loss. Patients may also experience constitutional symptoms with fatigue, fevers in the absence of infection, and unintentional weight loss even without splenomegaly.

For patients who initiate therapy with purine nucleoside analogs, the early part of treatment is associated with the greatest risk of morbidity and mortality. Chemotherapy leads to both immunosuppression (altered cellular immunity) as well as myelosuppression. Thus, patients who are already in need of treatment because of disease-related cytopenias will experience an abrupt and sometimes significant decline in the peripheral blood counts. The treatment period prior to recovery of neutrophils requires the greatest vigilance. Because patients are profoundly immunocompromised, febrile neutropenia is a common complication leading to hospital admission and the cause is often difficult to identify. Treatment with broad-spectrum antibiotics, investigation for opportunistic and viral infections, and considerations for antifungal prophylaxis or therapy are required in this setting. It is recommended that all patients treated with purine nucleoside analogs receive prophylactic antimicrobials for herpes simplex virus and varicella zoster virus, as well as prophylaxis against Pneumocystis jirovecii. Unfortunately, growth factor support has not proven successful in this patient population but is not contraindicated.⁴⁶

Following successful completion of therapy, patients may remain functionally immunocompromised for a significant period of time even with a normal neutrophil count. Monitoring of the CD4 count may help to determine when prophylactic antimicrobials may be discontinued. A CD4 count greater than 200 cells/µL is generally considered to be adequate for prevention of opportunistic infections. Although immunizations have not been well studied in HCL, it is recommended that patients receive annual influenza immunizations as well as age-appropriate immunizations against Streptococcus pneumoniae and other infectious illnesses as indicated. Live viral vaccines such as the currently available herpes zoster vaccine can lead to infections in this patient population and are not recommended.

Like many hematologic malignancies, HCL may be associated with comorbid conditions related to immune dysfunction. There is a known association with an increased risk of second primary malignancies, which may predate the diagnosis of HCL.⁴⁷ Therefore, it is recommended that patients continue annual cancer screenings as well as undergo prompt evaluation for potential symptoms of second malignancies. In addition, it is thought that there may be an increased risk for autoimmune disorders such as inflammatory arthritis or immune-mediated cytopenias. One case-control study found a possible association between autoimmune diseases and HCL, noting that at times these diseases are diagnosed concurrently.⁴⁸ However, because of the rarity of the disease it has been difficult to quantify these associated conditions in a systematic way. There is currently an international patient data registry under development for the systematic study of HCL and its complications which may answer many of these questions.

Survivorship and quality of life are important considerations in chronic diseases. It is not uncommon for patients to develop anxiety related to the trauma of diagnosis and treatment, especially when intensive care has been required. Patients may have lingering fears regarding concerns of developing infections due to exposure to ill persons or fears regarding risk of relapse and need for re-treatment. A proactive approach with partnership with psychosocial oncology may be of benefit, especially when symptoms of post-traumatic stress disorder are evident.

Conclusion

HCL is a rare, chronic lymphoid malignancy that is now subclassified into classic and variant HCL. Further investigations into the disease subtypes will allow more precise disease definitions, and these studies are underway. Renewed efforts toward updated risk stratification and clinical staging systems will be important aspects of these investigations. Refinements in treatment and supportive care have resulted in greatly improved overall survival, which has translated into larger numbers of people living with HCL. However, new treatment paradigms for vHCL are needed as the progression-free survival in this disease remains significantly lower than that of cHCL. Future efforts toward understanding survivorship issues and management of long-term treatment and disease-related complications will be critical for ensuring good quality of life for patients living with HCL.

Introduction

Hairy cell leukemia (HCL) is a rare chronic lymphoproliferative disorder, with only approximately 2000 new cases diagnosed in the United States each year.¹ It is now recognized that there are 2 distinct categories of HCL, classic HCL (cHCL) and variant HCL (vHCL), with vHCL now classified as a separate entity under the World Health Organization Classification of Hematopoietic Tumors.² For this reason, the 2 diseases will be discussed separately. However, they do bear many clinical and microscopic similarities and because of this were originally indistinguishable using diagnostic techniques previously available. Even in the modern era using immunophenotypic, molecular, and genetic testing, differentiating between the classic and variant disease subtypes is sometimes difficult.

For cHCL the median age of diagnosis is 55 years, with vHCL occurring in patients who are somewhat older; HCL has been described only in the adult population, with 1 exception.^3,4 There is a 4:1 male predominance, and Caucasians are more frequently affected than other ethnic groups. While the cause of the disease remains largely unknown, it has been observed to occur more frequently in farmers and in persons exposed to pesticides and/or herbicides, petroleum products, and ionizing radiation.⁴ The Institute of Medicine recently updated their position regarding veterans and Agent Orange, stating that there is sufficient evidence of an association between herbicides and chronic lymphoid leukemias (including HCL) to consider these diseases linked to exposure.⁵ Familial forms have also been described that are associated with specific HLA haplotypes, indicating a possible hereditary component.⁶ Most likely, a combination of environmental and genetic factors ultimately contributes to the development of HCL.

In recent years enormous progress has been made with respect to new insights into the biology of cHCL and vHCL, with significant refinement of diagnostic criteria. In addition, tremendous advances have occurred in both treatment and supportive care regimens, which have resulted in a dramatically increased overall life expectancy as well as decreased disease-related morbidity. This has meant that more patients are affected by HCL over time and are more likely to require care for relapsed HCL or associated comorbidities. Although no curative treatment options exist outside of allogeneic transplantation, therapeutic improvements have resulted in patients with cHCL having a life expectancy similar to that of unaffected patients, increasing the need for vigilance to prevent foreseeable complications.

Biology and Patheogenisis

The family of HCLs are chronic B-cell malignancies that account for approximately 2% of all diagnosed leukemias.⁷ The first detailed characterization of HCL as a distinct clinical entity was performed by Dr. Bouroncle and colleagues at the Ohio State University in 1958.⁸ Originally called leukemic reticuloendotheliosis, it was renamed HCL following more detailed description of the unique morphology of these malignant cells.⁹ Significant advances have recently been made in identifying distinctive genetic, immunophenotypic, and morphologic features that distinguish HCL from other B-cell malignancies.

HCL B cells tend to accumulate in the bone marrow, splenic red pulp, and (in some cases) peripheral blood. Unlike other lymphoproliferative disorders, HCL only rarely results in lymphadenopathy. HCL derives its name from the distinct appearance of the malignant hairy cells (Figure). Morphologically, HCL cells are mature, small lymphoid B-cells with a round or oval nucleus and abundant pale blue cytoplasm. Irregular projections of cytoplasm and microvilli give the cells a serrated, “hairy” appearance.¹⁰ The biological significance of these fine hair-like projections remains unknown and is an area of ongoing investigation. Gene expression profiling has revealed that HCL B cells are most similar to splenic marginal zone B cells and memory B cells.^11–13 A recent analysis of common genetic alterations in HCL suggests that the cell of origin is in fact the hematopoietic stem cell.¹⁴

Compared to other hematologic malignancies, the genomic profile of HCL is relatively stable, with few chromosomal defects or translocations observed. A seminal study by Tiacci and colleagues revealed that the BRAF V600E mutation was present in 47 out of 47 cHCL cases examined, results that have since been replicated by other groups, confirming that BRAF V600E is a hallmark mutation in cHCL.¹⁵ The BRAF V600E gain-of-function mutation results in constitutive activation of the serine-threonine protein kinase B-Raf, which regulates the mitogen-activated protein kinase (MAPK)/RAF-MEK-ERK pathway. Indeed, cHCL B cells have elevated MAPK signaling, leading to enhancement of growth and survival.¹⁶ This specific mutation in the BRAF gene is also seen in a number of solid tumor malignancies including melanoma and thyroid cancer, and represents a therapeutic target using BRAF inhibitors already developed to treat these malignancies.¹⁷ Testing for BRAF V600E by polymerase chain reaction or immunohistochemical staining is now routinely performed when HCL is suspected.

While BRAF V600E is identified in nearly all cases of cHCL, it is rare in vHCL.¹⁸ The variant type of HCL was classified as a distinct clinical entity in 2008 and can now often be distinguished from cHCL on the basis of BRAF mutational status, among other differences. Interestingly, in the rare cases of BRAF V600E–negative cHCL, other mutations in BRAF or downstream targets as well as aberrant activation of the RAF-MEK-ERK signaling cascade are observed, indicating that this pathway is critical in HCL and may still represent a viable therapeutic target. Expression of the IGHV4-34 immunoglobulin rearrangement, while more common in vHCL, has also been identified in 10% of cHCL cases and appears to confer poor prognosis.¹⁹ Other mutated genes that have been identified in HCL include CDKN1B, TP53, U2AF1, ARID1A, EZH2, and KDM6A.²⁰

Classic HCL is characterized by the immunophenotypic expression of CD11c, CD25, CD103, and CD123, with kappa or lambda light chain restriction indicating clonality; HCL B cells are generally negative for CD5, CD10, CD23, CD27, and CD79b. In contrast, vHCL often lacks expression of CD25 and CD123.¹⁸ The B-cell receptor (BCR) is expressed on hairy cells and its activation promotes proliferation and survival in vitro.²¹ The role of BCR signaling in B-cell malignancies is increasingly recognized, and therapies that target the BCR and associated signaling molecules offer an attractive treatment strategy.²² HCL B cells also typically express CD19, CD20, CD22, CD79a, CD200, CD1d, and annexin A1. Tartrate-resistant acid phosphatase (TRAP) positivity by immunohistochemistry is a hallmark of cHCL. Interestingly, changes to the patient’s original immunophenotype have been observed following treatment and upon disease recurrence, highlighting the importance of tracking immunophenotype throughout the course of disease.

Diagnosis

Prior to the advent of annual screening evaluations with routine examination of complete blood counts (CBC), patients were most often diagnosed with HCL when they presented with symptoms of the disease such as splenomegaly, infections, or complications of anemia or thrombocytopenia.²³ In the current era, patients are more likely to be incidentally diagnosed when they are found to have an abnormal value on a CBC. Any blood lineage may be affected and patients may have pancytopenia or isolated cytopenias. Of note, monocytopenia is a common finding in cHCL that is not entirely understood. The cells typical of cHCL do not usually circulate in the peripheral blood, but if present would appear as mature lymphocytes with villous cytoplasmic projections, pale blue cytoplasm, and reniform nuclei with open chromatin (Figure).⁹ Even if the morphologic examination is highly suggestive of HCL, additional testing is required to differentiate between cHCL, vHCL, and other hematologic malignancies which may also have cytoplasmic projections. A complete assessment of the immunophenotype, molecular profile, and cytogenetic features is required to arrive at this diagnosis.

The international Hairy Cell Leukemia Foundation recently published consensus guidelines for the diagnosis and treatment of HCL.²⁴ These guidelines recommend that patients undergo examination of the peripheral blood for morphology and immunophenotyping and further recommend obtaining bone marrow core and aspirate biopsy samples for immunophenotyping via immunohistochemical staining and flow cytometry. The characteristic immunophenotype of cHCL is a population of monoclonal B lymphocytes which co-express CD19, CD20, CD11c, CD25, CD103, and CD123. Variant HCL is characterized by a very similar immunophenotype but is usually negative for CD25 and CD123. It is notable that CD25 positivity may be lost following treatment, and the absence of this marker should not be used as the sole basis of a cHCL versus vHCL diagnosis. Because marrow fibrosis in HCL may prevent a marrow aspirate from being obtained, many of the key diagnostic studies are performed on the core biopsy, including morphological evaluation and immunohistochemical stains such as CD20 (a pan-B cell antigen), annexin-1 (an anti-inflammatory protein expressed only in cHCL), and VE1 (a BRAF V600E stain).

As noted above, recurrent cytogenetic abnormalities have now been identified that may inform the diagnosis or prognosis of HCL. Next-generation sequencing and other testing of the genetic landscape are taking on a larger role in subtype differentiation, and it is likely that future guidelines will recommend evaluation for significant mutations. Given that BRAF V600E mutation status is a key feature of cHCL and is absent in vHCL, it is important to perform this testing at the time of diagnosis whenever possible. The mutation may be detected via VE1 immunohistochemical staining, allele-specific polymerase chain reaction, or next-generation sequencing. Other less sensitive tests exist but are utilized less frequently.

Minimal Residual Disease

There is currently no accepted standard for minimal residual disease (MRD) monitoring in HCL. While detection of MRD has been clearly associated with increased risk of disease progression, cHCL cells typically do not circulate in the peripheral blood, limiting the use of peripheral blood immunophenotyping for quantitative MRD assessment. For quantitative monitoring of marrow involvement by HCL, immunohistochemical staining of the bone marrow core biopsy is usually required. Staining may be performed for CD20, or, in patients who have received anti-CD20 therapy, DBA.44, VE-1, or CD79a. There is currently not a consensus regarding what level of disease involvement constitutes MRD. One group studied this issue and found that relapse could be predicted by evaluating MRD by percentage of positive cells in the marrow by immunohistochemical staining, with less than 1% involvement having the lowest risk for disease relapse and greater than 5% having the highest risk for disease relapse.²⁵ A recent study evaluated MRD patterns in the peripheral blood of 32 cHCL patients who had completed frontline therapy. This group performed flow cytometry on the peripheral blood of patients at 1, 3, 6, and 12 months following therapy. All patients had achieved a complete response with initial therapy and peripheral blood MRD negativity at the completion of therapy. At a median follow-up of 100 months post therapy, 5 patients converted from peripheral blood–MRD negative to peripheral blood–MRD positive, and 6 patients developed overt disease progression. In all patients who progressed, progression was preceded by an increase in detectable peripheral blood MRD cells.²⁶ Although larger studies are needed, peripheral blood flow cytometric monitoring for MRD may be a useful adjunct to predict ongoing response or impending relapse. In addition, newer, more sensitive methods of disease monitoring may ultimately supplant flow cytometry.

Risk Stratification

Although much progress has been made in the risk stratification profiling of hematologic malignancies in general, HCL has unfortunately lagged behind in this effort. The most recent risk stratification analysis was performed in 1982 by Jansen and colleagues.²⁷ This group of researchers performed a retrospective analysis of 391 HCL patients treated at 22 centers. One of the central questions in their analysis was survival time from diagnosis in patients who had not yet undergone splenectomy (a standard treatment at the time). This group consisted of a total of 154 patients. As this study predated modern pathological and molecular testing, clinical and laboratory features were examined, and these mostly consisted of physical exam findings and analysis of the peripheral blood. This group found that several factors influenced the survival of these patients, including duration of symptoms prior to diagnosis, the degree of splenomegaly, hemoglobin level, and number of hairy cells in the peripheral blood. However, because of interobserver variation for the majority of these variables, only hemoglobin and spleen size were included in the proportional hazard model. Using only these 2 variables, the authors were able to determine 3 clinical stages for HCL (Table 1). The stages were found to correlate with median survival: patients with stage 1 disease had a median survival not reached at 72 months, but patients with stage 2 disease had a median survival of 18 months, which decreased to only 12 months in patients with stage 3 disease.

Because the majority of patients with HCL in the modern era will be diagnosed prior to reaching stage 3, a risk stratification system incorporating clinical features, laboratory parameters, and molecular and genetic testing is of considerable interest and is a subject of ongoing research. Ultimately, the goal will be to identify patients at higher risk of early relapse so that more intensive therapies can be applied to initial treatment that will result in longer treatment-free intervals.

Treatment

Because there is no curative treatment for either cHCL or vHCL outside allogeneic transplantation, and it is not clear that early treatment leads to better outcomes in HCL, patients do not always receive treatment at the time of diagnosis or relapse. The general consensus is that patients should be treated if there is a declining trend in hematologic parameters or they experience symptoms from the disease.²⁴ Current consensus guidelines recommend treatment when any of the following hematologic parameters are met: hemoglobin less than 11 g/dL, platelet count less than 100 × 10³/µL, or absolute neutrophil count less than 1000/µL.²⁴ These parameters are surrogate markers that indicate compromised bone marrow function. Cytopenias may also be caused by splenomegaly, and symptomatic splenomegaly with or without cytopenias is an indication for treatment. A small number of patients with HCL (approximately 10%) do not require immediate therapy after diagnosis and are monitored by their provider until treatment is indicated.

First-Line Therapy

Despite advances in targeted therapies for HCL, because no treatment has been shown to extend the treatment-free interval longer than chemotherapy, treatment with a purine nucleoside analog is usually the recommended first-line therapy. This includes either cladribine or pentostatin. Both agents appear to be equally effective, and the choice of therapy is determined by the treating physician based on his or her experience. Cladribine administration has been studied using a number of different schedules and routes: intravenous continuous infusion (0.1 mg/kg) for 7 days, intravenous infusion (0.14 mg/kg/day) over 2 hours on a 5-day regimen, or alternatively subcutaneously (0.1–0.14 mg/kg/day) on a once-per-day or once-per-week regimen (Table 2).^28,29

Unlike cHCL, vHCL remains difficult to treat and early disease progression is common. The best outcomes have been seen in patients who have received combination chemo-immunotherapy such as purine nucleoside analog therapy plus rituximab or bendamustine plus rituximab.³¹ One pilot study of bendamustine plus rituximab in 12 patients found an overall response rate of 100%, with the majority of patients achieving a complete response.³¹ For patients who achieved a complete response, the median duration of response had not been reached, but patients achieving only a partial response had a median duration of response of only 20 months, indicating there is a subgroup of patients who will require a different treatment approach.³² A randomized phase 2 trial of rituximab with either pentostatin or bendamustine is ongoing.³³

Assessment of Response

Response assessment involves physical examination for estimation of spleen size, assessment of hematologic parameters, and a bone marrow biopsy for evaluation of marrow response. It is recommended that the bone marrow biopsy be performed 4 to 6 months following cladribine administration, or after completion of 12 doses of pentostatin. Detailed response assessment criteria are shown in Table 3.

Second-Line Therapy

Although the majority of patients treated with purine analogs will achieve durable remissions, approximately 40% of patients will eventually require second-line therapy. Criteria for treatment at relapse are the same as the criteria for initial therapy, including symptomatic disease or progressive anemia, thrombocytopenia, or neutropenia. The choice of treatment is based on clinical parameters and the duration of the previous remission. If the initial remission was longer than 65 months and the patient is eligible to receive chemotherapy, re-treatment with initial therapy is recommended. For a remission between 24 and 65 months, re-treatment with a purine analog combined with an anti-CD20 monoclonal antibody may be considered.³⁴ If the first remission is shorter than 24 months, confirmation of the original diagnosis as well as consideration for testing for additional mutations with therapeutic targets (BRAF V600E, MAP2K1) should be considered before a treatment decision is made. For these patients, alternative therapies, including investigational agents, should be considered.²⁴

Monoclonal antibody therapy has been studied in both the up-front setting and in relapsed or refractory HCL.³⁵ An initial study of 15 patients with relapsed HCL found an overall response rate of 80%, with 8 patients achieving a complete response. A subsequent study of 26 patients who relapsed after cladribine therapy found an overall response rate of 80%, with a complete response rate of 32%. Median relapse-free survival was 27 months.³⁶ Ravandi and others studied rituximab in the up-front setting in combination with cladribine, and found an overall response rate of 100%, including in patients with vHCL. At the time of publication of the study results, the median survival had not been reached.³⁷ As has been seen with other lymphoid malignancies, concurrent therapy with rituximab appears to enhance the activity of the agent with which it is combined. While its use in the up-front setting remains an area of active investigation, there is a clear role for chemo-immunotherapy in the relapsed setting.

In patients with cHCL, excellent results including complete remissions have been reported with the use of BRAF inhibitors, both as a single agent and when combined with anti-CD20 therapy. The 2 commercially available BRAF inhibitors are vemurafenib and dabrafenib, and both have been tested in relapsed cHCL.^38,39 The first study of vemurafenib was reported by Tiacci and colleagues, who found an overall response rate of 96% after a median of 8 weeks and a 100% response rate after a median of 12 weeks, with complete response rates up to 42%.³⁸ The median relapse-free survival was 23 months (decreasing to only 6 months in patients who achieved only a partial remission), indicating that these agents will likely need to be administered in combination with other effective therapies with non-overlapping toxicities. Vemurafenib has been administered concurrently with rituximab, and preliminary results of this combination therapy showed early rates of complete responses.⁴⁰ Dabrafenib has been reported for use as a single agent in cHCL and clinical trials are underway evaluating its efficacy when administered with trametinib, a MEK inhibitor.^39,41 Of note, patients receiving BRAF inhibitors frequently develop cutaneous complications of RAF inhibition including cutaneous squamous cell carcinomas and keratoacanthomas, and close dermatologic surveillance is required.

Variant HCL does not harbor the BRAF V600E mutation, but up to half of patients have been found to have mutations of MAP2K1, which upregulates MEK1 expression.⁴² Trametinib is approved by the US Food and Drug Administration for the treatment of patients with melanoma at a dose of 2 mg orally daily, and has been successfully used to treat 1 patient with vHCL.⁴³ Further evaluation of this targeted therapy is underway.

Ibrutinib, a Bruton tyrosine kinase inhibitor, and moxetumomab pasudotox, an immunotoxin conjugate, are currently being studied in National Institutes of Health–sponsored multi-institutional trials for patients with HCL. Ibrutinib is administered orally at 420 mg per day until relapse.⁴⁴ Moxetumomab pasudotox was tested at different doses between 5 and 50 μg/kg intravenously every other day for 3 doses for up to 16 cycles unless they experienced disease progression or developed neutralizing antibodies.⁴⁵ Both agents have been shown to have significant activity in cHCL and vHCL and will likely be included in the treatment armamentarium once trials are completed. Second-line therapy options are summarized in Table 4.

Complications and Supportive Care

The complications of HCL may be separated into the pre-, intra-, and post-treatment periods. At the time of diagnosis and prior to the initiation of therapy, marrow infiltration by HCL frequently leads to cytopenias which cause symptomatic anemia, infection, and/or bleeding complications. Many patients develop splenomegaly, which may further lower the blood counts and which is experienced as abdominal fullness or distention, with early satiety leading to weight loss. Patients may also experience constitutional symptoms with fatigue, fevers in the absence of infection, and unintentional weight loss even without splenomegaly.

For patients who initiate therapy with purine nucleoside analogs, the early part of treatment is associated with the greatest risk of morbidity and mortality. Chemotherapy leads to both immunosuppression (altered cellular immunity) as well as myelosuppression. Thus, patients who are already in need of treatment because of disease-related cytopenias will experience an abrupt and sometimes significant decline in the peripheral blood counts. The treatment period prior to recovery of neutrophils requires the greatest vigilance. Because patients are profoundly immunocompromised, febrile neutropenia is a common complication leading to hospital admission and the cause is often difficult to identify. Treatment with broad-spectrum antibiotics, investigation for opportunistic and viral infections, and considerations for antifungal prophylaxis or therapy are required in this setting. It is recommended that all patients treated with purine nucleoside analogs receive prophylactic antimicrobials for herpes simplex virus and varicella zoster virus, as well as prophylaxis against Pneumocystis jirovecii. Unfortunately, growth factor support has not proven successful in this patient population but is not contraindicated.⁴⁶

Following successful completion of therapy, patients may remain functionally immunocompromised for a significant period of time even with a normal neutrophil count. Monitoring of the CD4 count may help to determine when prophylactic antimicrobials may be discontinued. A CD4 count greater than 200 cells/µL is generally considered to be adequate for prevention of opportunistic infections. Although immunizations have not been well studied in HCL, it is recommended that patients receive annual influenza immunizations as well as age-appropriate immunizations against Streptococcus pneumoniae and other infectious illnesses as indicated. Live viral vaccines such as the currently available herpes zoster vaccine can lead to infections in this patient population and are not recommended.

Like many hematologic malignancies, HCL may be associated with comorbid conditions related to immune dysfunction. There is a known association with an increased risk of second primary malignancies, which may predate the diagnosis of HCL.⁴⁷ Therefore, it is recommended that patients continue annual cancer screenings as well as undergo prompt evaluation for potential symptoms of second malignancies. In addition, it is thought that there may be an increased risk for autoimmune disorders such as inflammatory arthritis or immune-mediated cytopenias. One case-control study found a possible association between autoimmune diseases and HCL, noting that at times these diseases are diagnosed concurrently.⁴⁸ However, because of the rarity of the disease it has been difficult to quantify these associated conditions in a systematic way. There is currently an international patient data registry under development for the systematic study of HCL and its complications which may answer many of these questions.

Survivorship and quality of life are important considerations in chronic diseases. It is not uncommon for patients to develop anxiety related to the trauma of diagnosis and treatment, especially when intensive care has been required. Patients may have lingering fears regarding concerns of developing infections due to exposure to ill persons or fears regarding risk of relapse and need for re-treatment. A proactive approach with partnership with psychosocial oncology may be of benefit, especially when symptoms of post-traumatic stress disorder are evident.

Conclusion

HCL is a rare, chronic lymphoid malignancy that is now subclassified into classic and variant HCL. Further investigations into the disease subtypes will allow more precise disease definitions, and these studies are underway. Renewed efforts toward updated risk stratification and clinical staging systems will be important aspects of these investigations. Refinements in treatment and supportive care have resulted in greatly improved overall survival, which has translated into larger numbers of people living with HCL. However, new treatment paradigms for vHCL are needed as the progression-free survival in this disease remains significantly lower than that of cHCL. Future efforts toward understanding survivorship issues and management of long-term treatment and disease-related complications will be critical for ensuring good quality of life for patients living with HCL.

Introduction

Hairy cell leukemia (HCL) is a rare chronic lymphoproliferative disorder, with only approximately 2000 new cases diagnosed in the United States each year.¹ It is now recognized that there are 2 distinct categories of HCL, classic HCL (cHCL) and variant HCL (vHCL), with vHCL now classified as a separate entity under the World Health Organization Classification of Hematopoietic Tumors.² For this reason, the 2 diseases will be discussed separately. However, they do bear many clinical and microscopic similarities and because of this were originally indistinguishable using diagnostic techniques previously available. Even in the modern era using immunophenotypic, molecular, and genetic testing, differentiating between the classic and variant disease subtypes is sometimes difficult.

For cHCL the median age of diagnosis is 55 years, with vHCL occurring in patients who are somewhat older; HCL has been described only in the adult population, with 1 exception.^3,4 There is a 4:1 male predominance, and Caucasians are more frequently affected than other ethnic groups. While the cause of the disease remains largely unknown, it has been observed to occur more frequently in farmers and in persons exposed to pesticides and/or herbicides, petroleum products, and ionizing radiation.⁴ The Institute of Medicine recently updated their position regarding veterans and Agent Orange, stating that there is sufficient evidence of an association between herbicides and chronic lymphoid leukemias (including HCL) to consider these diseases linked to exposure.⁵ Familial forms have also been described that are associated with specific HLA haplotypes, indicating a possible hereditary component.⁶ Most likely, a combination of environmental and genetic factors ultimately contributes to the development of HCL.

In recent years enormous progress has been made with respect to new insights into the biology of cHCL and vHCL, with significant refinement of diagnostic criteria. In addition, tremendous advances have occurred in both treatment and supportive care regimens, which have resulted in a dramatically increased overall life expectancy as well as decreased disease-related morbidity. This has meant that more patients are affected by HCL over time and are more likely to require care for relapsed HCL or associated comorbidities. Although no curative treatment options exist outside of allogeneic transplantation, therapeutic improvements have resulted in patients with cHCL having a life expectancy similar to that of unaffected patients, increasing the need for vigilance to prevent foreseeable complications.

Biology and Patheogenisis

The family of HCLs are chronic B-cell malignancies that account for approximately 2% of all diagnosed leukemias.⁷ The first detailed characterization of HCL as a distinct clinical entity was performed by Dr. Bouroncle and colleagues at the Ohio State University in 1958.⁸ Originally called leukemic reticuloendotheliosis, it was renamed HCL following more detailed description of the unique morphology of these malignant cells.⁹ Significant advances have recently been made in identifying distinctive genetic, immunophenotypic, and morphologic features that distinguish HCL from other B-cell malignancies.

HCL B cells tend to accumulate in the bone marrow, splenic red pulp, and (in some cases) peripheral blood. Unlike other lymphoproliferative disorders, HCL only rarely results in lymphadenopathy. HCL derives its name from the distinct appearance of the malignant hairy cells (Figure). Morphologically, HCL cells are mature, small lymphoid B-cells with a round or oval nucleus and abundant pale blue cytoplasm. Irregular projections of cytoplasm and microvilli give the cells a serrated, “hairy” appearance.¹⁰ The biological significance of these fine hair-like projections remains unknown and is an area of ongoing investigation. Gene expression profiling has revealed that HCL B cells are most similar to splenic marginal zone B cells and memory B cells.^11–13 A recent analysis of common genetic alterations in HCL suggests that the cell of origin is in fact the hematopoietic stem cell.¹⁴

Compared to other hematologic malignancies, the genomic profile of HCL is relatively stable, with few chromosomal defects or translocations observed. A seminal study by Tiacci and colleagues revealed that the BRAF V600E mutation was present in 47 out of 47 cHCL cases examined, results that have since been replicated by other groups, confirming that BRAF V600E is a hallmark mutation in cHCL.¹⁵ The BRAF V600E gain-of-function mutation results in constitutive activation of the serine-threonine protein kinase B-Raf, which regulates the mitogen-activated protein kinase (MAPK)/RAF-MEK-ERK pathway. Indeed, cHCL B cells have elevated MAPK signaling, leading to enhancement of growth and survival.¹⁶ This specific mutation in the BRAF gene is also seen in a number of solid tumor malignancies including melanoma and thyroid cancer, and represents a therapeutic target using BRAF inhibitors already developed to treat these malignancies.¹⁷ Testing for BRAF V600E by polymerase chain reaction or immunohistochemical staining is now routinely performed when HCL is suspected.

While BRAF V600E is identified in nearly all cases of cHCL, it is rare in vHCL.¹⁸ The variant type of HCL was classified as a distinct clinical entity in 2008 and can now often be distinguished from cHCL on the basis of BRAF mutational status, among other differences. Interestingly, in the rare cases of BRAF V600E–negative cHCL, other mutations in BRAF or downstream targets as well as aberrant activation of the RAF-MEK-ERK signaling cascade are observed, indicating that this pathway is critical in HCL and may still represent a viable therapeutic target. Expression of the IGHV4-34 immunoglobulin rearrangement, while more common in vHCL, has also been identified in 10% of cHCL cases and appears to confer poor prognosis.¹⁹ Other mutated genes that have been identified in HCL include CDKN1B, TP53, U2AF1, ARID1A, EZH2, and KDM6A.²⁰

Classic HCL is characterized by the immunophenotypic expression of CD11c, CD25, CD103, and CD123, with kappa or lambda light chain restriction indicating clonality; HCL B cells are generally negative for CD5, CD10, CD23, CD27, and CD79b. In contrast, vHCL often lacks expression of CD25 and CD123.¹⁸ The B-cell receptor (BCR) is expressed on hairy cells and its activation promotes proliferation and survival in vitro.²¹ The role of BCR signaling in B-cell malignancies is increasingly recognized, and therapies that target the BCR and associated signaling molecules offer an attractive treatment strategy.²² HCL B cells also typically express CD19, CD20, CD22, CD79a, CD200, CD1d, and annexin A1. Tartrate-resistant acid phosphatase (TRAP) positivity by immunohistochemistry is a hallmark of cHCL. Interestingly, changes to the patient’s original immunophenotype have been observed following treatment and upon disease recurrence, highlighting the importance of tracking immunophenotype throughout the course of disease.

Diagnosis

Prior to the advent of annual screening evaluations with routine examination of complete blood counts (CBC), patients were most often diagnosed with HCL when they presented with symptoms of the disease such as splenomegaly, infections, or complications of anemia or thrombocytopenia.²³ In the current era, patients are more likely to be incidentally diagnosed when they are found to have an abnormal value on a CBC. Any blood lineage may be affected and patients may have pancytopenia or isolated cytopenias. Of note, monocytopenia is a common finding in cHCL that is not entirely understood. The cells typical of cHCL do not usually circulate in the peripheral blood, but if present would appear as mature lymphocytes with villous cytoplasmic projections, pale blue cytoplasm, and reniform nuclei with open chromatin (Figure).⁹ Even if the morphologic examination is highly suggestive of HCL, additional testing is required to differentiate between cHCL, vHCL, and other hematologic malignancies which may also have cytoplasmic projections. A complete assessment of the immunophenotype, molecular profile, and cytogenetic features is required to arrive at this diagnosis.

The international Hairy Cell Leukemia Foundation recently published consensus guidelines for the diagnosis and treatment of HCL.²⁴ These guidelines recommend that patients undergo examination of the peripheral blood for morphology and immunophenotyping and further recommend obtaining bone marrow core and aspirate biopsy samples for immunophenotyping via immunohistochemical staining and flow cytometry. The characteristic immunophenotype of cHCL is a population of monoclonal B lymphocytes which co-express CD19, CD20, CD11c, CD25, CD103, and CD123. Variant HCL is characterized by a very similar immunophenotype but is usually negative for CD25 and CD123. It is notable that CD25 positivity may be lost following treatment, and the absence of this marker should not be used as the sole basis of a cHCL versus vHCL diagnosis. Because marrow fibrosis in HCL may prevent a marrow aspirate from being obtained, many of the key diagnostic studies are performed on the core biopsy, including morphological evaluation and immunohistochemical stains such as CD20 (a pan-B cell antigen), annexin-1 (an anti-inflammatory protein expressed only in cHCL), and VE1 (a BRAF V600E stain).

As noted above, recurrent cytogenetic abnormalities have now been identified that may inform the diagnosis or prognosis of HCL. Next-generation sequencing and other testing of the genetic landscape are taking on a larger role in subtype differentiation, and it is likely that future guidelines will recommend evaluation for significant mutations. Given that BRAF V600E mutation status is a key feature of cHCL and is absent in vHCL, it is important to perform this testing at the time of diagnosis whenever possible. The mutation may be detected via VE1 immunohistochemical staining, allele-specific polymerase chain reaction, or next-generation sequencing. Other less sensitive tests exist but are utilized less frequently.

Minimal Residual Disease

There is currently no accepted standard for minimal residual disease (MRD) monitoring in HCL. While detection of MRD has been clearly associated with increased risk of disease progression, cHCL cells typically do not circulate in the peripheral blood, limiting the use of peripheral blood immunophenotyping for quantitative MRD assessment. For quantitative monitoring of marrow involvement by HCL, immunohistochemical staining of the bone marrow core biopsy is usually required. Staining may be performed for CD20, or, in patients who have received anti-CD20 therapy, DBA.44, VE-1, or CD79a. There is currently not a consensus regarding what level of disease involvement constitutes MRD. One group studied this issue and found that relapse could be predicted by evaluating MRD by percentage of positive cells in the marrow by immunohistochemical staining, with less than 1% involvement having the lowest risk for disease relapse and greater than 5% having the highest risk for disease relapse.²⁵ A recent study evaluated MRD patterns in the peripheral blood of 32 cHCL patients who had completed frontline therapy. This group performed flow cytometry on the peripheral blood of patients at 1, 3, 6, and 12 months following therapy. All patients had achieved a complete response with initial therapy and peripheral blood MRD negativity at the completion of therapy. At a median follow-up of 100 months post therapy, 5 patients converted from peripheral blood–MRD negative to peripheral blood–MRD positive, and 6 patients developed overt disease progression. In all patients who progressed, progression was preceded by an increase in detectable peripheral blood MRD cells.²⁶ Although larger studies are needed, peripheral blood flow cytometric monitoring for MRD may be a useful adjunct to predict ongoing response or impending relapse. In addition, newer, more sensitive methods of disease monitoring may ultimately supplant flow cytometry.

Risk Stratification

Although much progress has been made in the risk stratification profiling of hematologic malignancies in general, HCL has unfortunately lagged behind in this effort. The most recent risk stratification analysis was performed in 1982 by Jansen and colleagues.²⁷ This group of researchers performed a retrospective analysis of 391 HCL patients treated at 22 centers. One of the central questions in their analysis was survival time from diagnosis in patients who had not yet undergone splenectomy (a standard treatment at the time). This group consisted of a total of 154 patients. As this study predated modern pathological and molecular testing, clinical and laboratory features were examined, and these mostly consisted of physical exam findings and analysis of the peripheral blood. This group found that several factors influenced the survival of these patients, including duration of symptoms prior to diagnosis, the degree of splenomegaly, hemoglobin level, and number of hairy cells in the peripheral blood. However, because of interobserver variation for the majority of these variables, only hemoglobin and spleen size were included in the proportional hazard model. Using only these 2 variables, the authors were able to determine 3 clinical stages for HCL (Table 1). The stages were found to correlate with median survival: patients with stage 1 disease had a median survival not reached at 72 months, but patients with stage 2 disease had a median survival of 18 months, which decreased to only 12 months in patients with stage 3 disease.

Because the majority of patients with HCL in the modern era will be diagnosed prior to reaching stage 3, a risk stratification system incorporating clinical features, laboratory parameters, and molecular and genetic testing is of considerable interest and is a subject of ongoing research. Ultimately, the goal will be to identify patients at higher risk of early relapse so that more intensive therapies can be applied to initial treatment that will result in longer treatment-free intervals.

Treatment

Because there is no curative treatment for either cHCL or vHCL outside allogeneic transplantation, and it is not clear that early treatment leads to better outcomes in HCL, patients do not always receive treatment at the time of diagnosis or relapse. The general consensus is that patients should be treated if there is a declining trend in hematologic parameters or they experience symptoms from the disease.²⁴ Current consensus guidelines recommend treatment when any of the following hematologic parameters are met: hemoglobin less than 11 g/dL, platelet count less than 100 × 10³/µL, or absolute neutrophil count less than 1000/µL.²⁴ These parameters are surrogate markers that indicate compromised bone marrow function. Cytopenias may also be caused by splenomegaly, and symptomatic splenomegaly with or without cytopenias is an indication for treatment. A small number of patients with HCL (approximately 10%) do not require immediate therapy after diagnosis and are monitored by their provider until treatment is indicated.

First-Line Therapy

Despite advances in targeted therapies for HCL, because no treatment has been shown to extend the treatment-free interval longer than chemotherapy, treatment with a purine nucleoside analog is usually the recommended first-line therapy. This includes either cladribine or pentostatin. Both agents appear to be equally effective, and the choice of therapy is determined by the treating physician based on his or her experience. Cladribine administration has been studied using a number of different schedules and routes: intravenous continuous infusion (0.1 mg/kg) for 7 days, intravenous infusion (0.14 mg/kg/day) over 2 hours on a 5-day regimen, or alternatively subcutaneously (0.1–0.14 mg/kg/day) on a once-per-day or once-per-week regimen (Table 2).^28,29

Unlike cHCL, vHCL remains difficult to treat and early disease progression is common. The best outcomes have been seen in patients who have received combination chemo-immunotherapy such as purine nucleoside analog therapy plus rituximab or bendamustine plus rituximab.³¹ One pilot study of bendamustine plus rituximab in 12 patients found an overall response rate of 100%, with the majority of patients achieving a complete response.³¹ For patients who achieved a complete response, the median duration of response had not been reached, but patients achieving only a partial response had a median duration of response of only 20 months, indicating there is a subgroup of patients who will require a different treatment approach.³² A randomized phase 2 trial of rituximab with either pentostatin or bendamustine is ongoing.³³

Assessment of Response

Response assessment involves physical examination for estimation of spleen size, assessment of hematologic parameters, and a bone marrow biopsy for evaluation of marrow response. It is recommended that the bone marrow biopsy be performed 4 to 6 months following cladribine administration, or after completion of 12 doses of pentostatin. Detailed response assessment criteria are shown in Table 3.

Second-Line Therapy

Although the majority of patients treated with purine analogs will achieve durable remissions, approximately 40% of patients will eventually require second-line therapy. Criteria for treatment at relapse are the same as the criteria for initial therapy, including symptomatic disease or progressive anemia, thrombocytopenia, or neutropenia. The choice of treatment is based on clinical parameters and the duration of the previous remission. If the initial remission was longer than 65 months and the patient is eligible to receive chemotherapy, re-treatment with initial therapy is recommended. For a remission between 24 and 65 months, re-treatment with a purine analog combined with an anti-CD20 monoclonal antibody may be considered.³⁴ If the first remission is shorter than 24 months, confirmation of the original diagnosis as well as consideration for testing for additional mutations with therapeutic targets (BRAF V600E, MAP2K1) should be considered before a treatment decision is made. For these patients, alternative therapies, including investigational agents, should be considered.²⁴

Monoclonal antibody therapy has been studied in both the up-front setting and in relapsed or refractory HCL.³⁵ An initial study of 15 patients with relapsed HCL found an overall response rate of 80%, with 8 patients achieving a complete response. A subsequent study of 26 patients who relapsed after cladribine therapy found an overall response rate of 80%, with a complete response rate of 32%. Median relapse-free survival was 27 months.³⁶ Ravandi and others studied rituximab in the up-front setting in combination with cladribine, and found an overall response rate of 100%, including in patients with vHCL. At the time of publication of the study results, the median survival had not been reached.³⁷ As has been seen with other lymphoid malignancies, concurrent therapy with rituximab appears to enhance the activity of the agent with which it is combined. While its use in the up-front setting remains an area of active investigation, there is a clear role for chemo-immunotherapy in the relapsed setting.

In patients with cHCL, excellent results including complete remissions have been reported with the use of BRAF inhibitors, both as a single agent and when combined with anti-CD20 therapy. The 2 commercially available BRAF inhibitors are vemurafenib and dabrafenib, and both have been tested in relapsed cHCL.^38,39 The first study of vemurafenib was reported by Tiacci and colleagues, who found an overall response rate of 96% after a median of 8 weeks and a 100% response rate after a median of 12 weeks, with complete response rates up to 42%.³⁸ The median relapse-free survival was 23 months (decreasing to only 6 months in patients who achieved only a partial remission), indicating that these agents will likely need to be administered in combination with other effective therapies with non-overlapping toxicities. Vemurafenib has been administered concurrently with rituximab, and preliminary results of this combination therapy showed early rates of complete responses.⁴⁰ Dabrafenib has been reported for use as a single agent in cHCL and clinical trials are underway evaluating its efficacy when administered with trametinib, a MEK inhibitor.^39,41 Of note, patients receiving BRAF inhibitors frequently develop cutaneous complications of RAF inhibition including cutaneous squamous cell carcinomas and keratoacanthomas, and close dermatologic surveillance is required.

Variant HCL does not harbor the BRAF V600E mutation, but up to half of patients have been found to have mutations of MAP2K1, which upregulates MEK1 expression.⁴² Trametinib is approved by the US Food and Drug Administration for the treatment of patients with melanoma at a dose of 2 mg orally daily, and has been successfully used to treat 1 patient with vHCL.⁴³ Further evaluation of this targeted therapy is underway.

Ibrutinib, a Bruton tyrosine kinase inhibitor, and moxetumomab pasudotox, an immunotoxin conjugate, are currently being studied in National Institutes of Health–sponsored multi-institutional trials for patients with HCL. Ibrutinib is administered orally at 420 mg per day until relapse.⁴⁴ Moxetumomab pasudotox was tested at different doses between 5 and 50 μg/kg intravenously every other day for 3 doses for up to 16 cycles unless they experienced disease progression or developed neutralizing antibodies.⁴⁵ Both agents have been shown to have significant activity in cHCL and vHCL and will likely be included in the treatment armamentarium once trials are completed. Second-line therapy options are summarized in Table 4.

Complications and Supportive Care

The complications of HCL may be separated into the pre-, intra-, and post-treatment periods. At the time of diagnosis and prior to the initiation of therapy, marrow infiltration by HCL frequently leads to cytopenias which cause symptomatic anemia, infection, and/or bleeding complications. Many patients develop splenomegaly, which may further lower the blood counts and which is experienced as abdominal fullness or distention, with early satiety leading to weight loss. Patients may also experience constitutional symptoms with fatigue, fevers in the absence of infection, and unintentional weight loss even without splenomegaly.

For patients who initiate therapy with purine nucleoside analogs, the early part of treatment is associated with the greatest risk of morbidity and mortality. Chemotherapy leads to both immunosuppression (altered cellular immunity) as well as myelosuppression. Thus, patients who are already in need of treatment because of disease-related cytopenias will experience an abrupt and sometimes significant decline in the peripheral blood counts. The treatment period prior to recovery of neutrophils requires the greatest vigilance. Because patients are profoundly immunocompromised, febrile neutropenia is a common complication leading to hospital admission and the cause is often difficult to identify. Treatment with broad-spectrum antibiotics, investigation for opportunistic and viral infections, and considerations for antifungal prophylaxis or therapy are required in this setting. It is recommended that all patients treated with purine nucleoside analogs receive prophylactic antimicrobials for herpes simplex virus and varicella zoster virus, as well as prophylaxis against Pneumocystis jirovecii. Unfortunately, growth factor support has not proven successful in this patient population but is not contraindicated.⁴⁶

Following successful completion of therapy, patients may remain functionally immunocompromised for a significant period of time even with a normal neutrophil count. Monitoring of the CD4 count may help to determine when prophylactic antimicrobials may be discontinued. A CD4 count greater than 200 cells/µL is generally considered to be adequate for prevention of opportunistic infections. Although immunizations have not been well studied in HCL, it is recommended that patients receive annual influenza immunizations as well as age-appropriate immunizations against Streptococcus pneumoniae and other infectious illnesses as indicated. Live viral vaccines such as the currently available herpes zoster vaccine can lead to infections in this patient population and are not recommended.

Like many hematologic malignancies, HCL may be associated with comorbid conditions related to immune dysfunction. There is a known association with an increased risk of second primary malignancies, which may predate the diagnosis of HCL.⁴⁷ Therefore, it is recommended that patients continue annual cancer screenings as well as undergo prompt evaluation for potential symptoms of second malignancies. In addition, it is thought that there may be an increased risk for autoimmune disorders such as inflammatory arthritis or immune-mediated cytopenias. One case-control study found a possible association between autoimmune diseases and HCL, noting that at times these diseases are diagnosed concurrently.⁴⁸ However, because of the rarity of the disease it has been difficult to quantify these associated conditions in a systematic way. There is currently an international patient data registry under development for the systematic study of HCL and its complications which may answer many of these questions.

Survivorship and quality of life are important considerations in chronic diseases. It is not uncommon for patients to develop anxiety related to the trauma of diagnosis and treatment, especially when intensive care has been required. Patients may have lingering fears regarding concerns of developing infections due to exposure to ill persons or fears regarding risk of relapse and need for re-treatment. A proactive approach with partnership with psychosocial oncology may be of benefit, especially when symptoms of post-traumatic stress disorder are evident.

Conclusion

HCL is a rare, chronic lymphoid malignancy that is now subclassified into classic and variant HCL. Further investigations into the disease subtypes will allow more precise disease definitions, and these studies are underway. Renewed efforts toward updated risk stratification and clinical staging systems will be important aspects of these investigations. Refinements in treatment and supportive care have resulted in greatly improved overall survival, which has translated into larger numbers of people living with HCL. However, new treatment paradigms for vHCL are needed as the progression-free survival in this disease remains significantly lower than that of cHCL. Future efforts toward understanding survivorship issues and management of long-term treatment and disease-related complications will be critical for ensuring good quality of life for patients living with HCL.

Researchers in the United States and the United Kingdom believe they have found a new gene target that could aid in the development of more effective treatments for acute myeloid leukemia (AML).

Inhibition of the METTL3 gene allowed for the destruction of AML in human and mouse cells without damaging healthy blood cells, the researchers reported in a research letter published Nov. 27 in the journal Nature.

National Institutes of Health/Wikimedia Commons/Public Domain

[email protected]

On Twitter @maryellenny

Researchers in the United States and the United Kingdom believe they have found a new gene target that could aid in the development of more effective treatments for acute myeloid leukemia (AML).

Inhibition of the METTL3 gene allowed for the destruction of AML in human and mouse cells without damaging healthy blood cells, the researchers reported in a research letter published Nov. 27 in the journal Nature.

National Institutes of Health/Wikimedia Commons/Public Domain

[email protected]

On Twitter @maryellenny

Researchers in the United States and the United Kingdom believe they have found a new gene target that could aid in the development of more effective treatments for acute myeloid leukemia (AML).

Inhibition of the METTL3 gene allowed for the destruction of AML in human and mouse cells without damaging healthy blood cells, the researchers reported in a research letter published Nov. 27 in the journal Nature.

National Institutes of Health/Wikimedia Commons/Public Domain

[email protected]

On Twitter @maryellenny

Augusta University

New research has shown an increased risk of early death in patients with acute myeloid leukemia (AML) who have high levels of indoleamine 2,3 dioxygenase-1 (IDO-1), an enzyme known to suppress the immune system.

Researchers quantified IDO-1 expression in diagnostic samples from patients with AML and discovered that high levels of IDO-1 were significantly associated with induction failure and poor overall survival (OS).

Ravindra Kolhe, MD, PhD, of the Medical College of Georgia at Augusta University, and his colleagues recounted these findings in Scientific Reports.

The researchers reviewed data from 40 AML patients. They had a median age at diagnosis of 60 (range, 27–89), 60% were female, and 55% were self-reported as Caucasian.

Most patients (72.5%) received standard anthracycline and cytarabine as induction, 10% received hypomethylating agents, and 17.5% were untreated or had unknown treatment status.

Fifteen percent of patients underwent allogeneic hematopoietic stem cell transplant (allo-HSCT) at the time of first complete remission.

Half of all patients achieved remission, and half of those patients (n=10, 25%) had a subsequent relapse. The median OS was 283 days (range, 32–1941). Twenty percent of patients (n=8) were still alive at the time of data analysis.

IDO-1 analysis

“We wanted to look at what makes this leukemia so aggressive that initial induction chemotherapy is not working,” Dr Kolhe said. “Early relapse tends to predict early mortality in these patients, and one of the things we looked at was IDO.”

The researchers extracted IDO-1 mRNA from diagnostic bone marrow samples from 29 of the patients but assessed IDO-1 protein expression in all 40 patients via immunohistochemistry.

The team quantified IDO-1 expression using a “composite IDO-1 score.” They used a cut-off point of 0.45 and divided patients’ samples into 2 groups: high (≥0.45) and low (<0.45) IDO-1 score.

The researchers compared IDO-1 results across 4 survival groups, which included patients surviving:

• Less than 6 months
• More than 6 months to 1 year
• More than 1 year to less than 5 years
• Beyond 5 years.

The team found a direct correlation between poor OS and higher composite IDO-1 score (P=0.0005).

“The patients who died at 6 months had a high expression of IDO, while the blasts produced relatively little IDO in the patients who lived 5 years or more,” Dr Kolhe said.

Independent predictor

The researchers conducted a univariate analysis and identified several factors that were significantly associated with poor OS, including:

• Higher IDO-1 mRNA (P=0.005)
• Higher composite IDO-1 score (P<0.0001)
• Higher age (P=0.0018)
• Male gender (P=0.019)
• High-risk cytogenetics (P=0.002)
• Not undergoing allo-HSCT (P=0.0005).

In a multivariate analysis including the above variables, the researchers found that a higher composite IDO-1 score (P=0.007) and not undergoing allo-HSCT (P=0.007) were significantly associated with poor OS.

The team also found that patients who failed induction had a higher composite IDO-1 score (P=0.01).

“Most of the time, we don’t know why patients are not responding to chemotherapy,” Dr Kolhe noted. “But when the researchers adjusted for other risk factors for AML, like increased age and severe anemia, IDO levels were a standout. Right now, we know it’s high in patients who die at 6 months, and we show that it’s an independent indicator if you adjust for other known variables.”

Dr Kolhe said these results suggest IDO-1 expression should be measured when the diagnostic bone marrow biopsy is performed. This may help identify AML patients who could benefit from receiving an IDO inhibitor along with standard therapy.

Researchers are currently conducting a phase 1/2 trial of the IDO inhibitor indoximod in combination with idarubicin and cytarabine in patients with newly diagnosed AML (NCT02835729).

Augusta University

New research has shown an increased risk of early death in patients with acute myeloid leukemia (AML) who have high levels of indoleamine 2,3 dioxygenase-1 (IDO-1), an enzyme known to suppress the immune system.

Researchers quantified IDO-1 expression in diagnostic samples from patients with AML and discovered that high levels of IDO-1 were significantly associated with induction failure and poor overall survival (OS).

Ravindra Kolhe, MD, PhD, of the Medical College of Georgia at Augusta University, and his colleagues recounted these findings in Scientific Reports.

The researchers reviewed data from 40 AML patients. They had a median age at diagnosis of 60 (range, 27–89), 60% were female, and 55% were self-reported as Caucasian.

Most patients (72.5%) received standard anthracycline and cytarabine as induction, 10% received hypomethylating agents, and 17.5% were untreated or had unknown treatment status.

Fifteen percent of patients underwent allogeneic hematopoietic stem cell transplant (allo-HSCT) at the time of first complete remission.

Half of all patients achieved remission, and half of those patients (n=10, 25%) had a subsequent relapse. The median OS was 283 days (range, 32–1941). Twenty percent of patients (n=8) were still alive at the time of data analysis.

IDO-1 analysis

“We wanted to look at what makes this leukemia so aggressive that initial induction chemotherapy is not working,” Dr Kolhe said. “Early relapse tends to predict early mortality in these patients, and one of the things we looked at was IDO.”

The researchers extracted IDO-1 mRNA from diagnostic bone marrow samples from 29 of the patients but assessed IDO-1 protein expression in all 40 patients via immunohistochemistry.

The team quantified IDO-1 expression using a “composite IDO-1 score.” They used a cut-off point of 0.45 and divided patients’ samples into 2 groups: high (≥0.45) and low (<0.45) IDO-1 score.

The researchers compared IDO-1 results across 4 survival groups, which included patients surviving:

• Less than 6 months
• More than 6 months to 1 year
• More than 1 year to less than 5 years
• Beyond 5 years.

The team found a direct correlation between poor OS and higher composite IDO-1 score (P=0.0005).

“The patients who died at 6 months had a high expression of IDO, while the blasts produced relatively little IDO in the patients who lived 5 years or more,” Dr Kolhe said.

Independent predictor

The researchers conducted a univariate analysis and identified several factors that were significantly associated with poor OS, including:

• Higher IDO-1 mRNA (P=0.005)
• Higher composite IDO-1 score (P<0.0001)
• Higher age (P=0.0018)
• Male gender (P=0.019)
• High-risk cytogenetics (P=0.002)
• Not undergoing allo-HSCT (P=0.0005).

In a multivariate analysis including the above variables, the researchers found that a higher composite IDO-1 score (P=0.007) and not undergoing allo-HSCT (P=0.007) were significantly associated with poor OS.

The team also found that patients who failed induction had a higher composite IDO-1 score (P=0.01).

“Most of the time, we don’t know why patients are not responding to chemotherapy,” Dr Kolhe noted. “But when the researchers adjusted for other risk factors for AML, like increased age and severe anemia, IDO levels were a standout. Right now, we know it’s high in patients who die at 6 months, and we show that it’s an independent indicator if you adjust for other known variables.”

Dr Kolhe said these results suggest IDO-1 expression should be measured when the diagnostic bone marrow biopsy is performed. This may help identify AML patients who could benefit from receiving an IDO inhibitor along with standard therapy.

Researchers are currently conducting a phase 1/2 trial of the IDO inhibitor indoximod in combination with idarubicin and cytarabine in patients with newly diagnosed AML (NCT02835729).

Augusta University

New research has shown an increased risk of early death in patients with acute myeloid leukemia (AML) who have high levels of indoleamine 2,3 dioxygenase-1 (IDO-1), an enzyme known to suppress the immune system.

Researchers quantified IDO-1 expression in diagnostic samples from patients with AML and discovered that high levels of IDO-1 were significantly associated with induction failure and poor overall survival (OS).

Ravindra Kolhe, MD, PhD, of the Medical College of Georgia at Augusta University, and his colleagues recounted these findings in Scientific Reports.

The researchers reviewed data from 40 AML patients. They had a median age at diagnosis of 60 (range, 27–89), 60% were female, and 55% were self-reported as Caucasian.

Most patients (72.5%) received standard anthracycline and cytarabine as induction, 10% received hypomethylating agents, and 17.5% were untreated or had unknown treatment status.

Fifteen percent of patients underwent allogeneic hematopoietic stem cell transplant (allo-HSCT) at the time of first complete remission.

Half of all patients achieved remission, and half of those patients (n=10, 25%) had a subsequent relapse. The median OS was 283 days (range, 32–1941). Twenty percent of patients (n=8) were still alive at the time of data analysis.

IDO-1 analysis

“We wanted to look at what makes this leukemia so aggressive that initial induction chemotherapy is not working,” Dr Kolhe said. “Early relapse tends to predict early mortality in these patients, and one of the things we looked at was IDO.”

The researchers extracted IDO-1 mRNA from diagnostic bone marrow samples from 29 of the patients but assessed IDO-1 protein expression in all 40 patients via immunohistochemistry.

The team quantified IDO-1 expression using a “composite IDO-1 score.” They used a cut-off point of 0.45 and divided patients’ samples into 2 groups: high (≥0.45) and low (<0.45) IDO-1 score.

The researchers compared IDO-1 results across 4 survival groups, which included patients surviving:

• Less than 6 months
• More than 6 months to 1 year
• More than 1 year to less than 5 years
• Beyond 5 years.

The team found a direct correlation between poor OS and higher composite IDO-1 score (P=0.0005).

“The patients who died at 6 months had a high expression of IDO, while the blasts produced relatively little IDO in the patients who lived 5 years or more,” Dr Kolhe said.

Independent predictor

The researchers conducted a univariate analysis and identified several factors that were significantly associated with poor OS, including:

• Higher IDO-1 mRNA (P=0.005)
• Higher composite IDO-1 score (P<0.0001)
• Higher age (P=0.0018)
• Male gender (P=0.019)
• High-risk cytogenetics (P=0.002)
• Not undergoing allo-HSCT (P=0.0005).

In a multivariate analysis including the above variables, the researchers found that a higher composite IDO-1 score (P=0.007) and not undergoing allo-HSCT (P=0.007) were significantly associated with poor OS.

The team also found that patients who failed induction had a higher composite IDO-1 score (P=0.01).

“Most of the time, we don’t know why patients are not responding to chemotherapy,” Dr Kolhe noted. “But when the researchers adjusted for other risk factors for AML, like increased age and severe anemia, IDO levels were a standout. Right now, we know it’s high in patients who die at 6 months, and we show that it’s an independent indicator if you adjust for other known variables.”

Dr Kolhe said these results suggest IDO-1 expression should be measured when the diagnostic bone marrow biopsy is performed. This may help identify AML patients who could benefit from receiving an IDO inhibitor along with standard therapy.

Researchers are currently conducting a phase 1/2 trial of the IDO inhibitor indoximod in combination with idarubicin and cytarabine in patients with newly diagnosed AML (NCT02835729).