Commentary: BTK inhibition in CLL and MCL, August 2023

The treatment landscape of chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL) has been transformed over the past decade with the advent of targeted therapies, including Bruton tyrosine kinase (BTK) inhibitors. Covalent BTK inhibitors, which are available in both the frontline and relapsed/refractory settings, include ibrutinib, acalabrutinib, and zanubrutinib.^1-3

BTK inhibitors have also demonstrated activity in higher-risk subgroups, including patients harboring TP53 aberrations. Clinical trials have shown encouraging outcomes of BTK inhibitors in these patients, and real-world studies have demonstrated similar findings.^4-6 Recently, a real-world Italian registry study similarly showed favorable outcomes in 747 patients with CLL carrying 17p- or TP53 or both mutations treated with first-line ibrutinib. in what appears to be the largest real-world analysis of this patient population (Rigolin et al). At 24 months, the median overall survival was not reached; the estimated treatment persistence and survival rates were 63.4% (95% CI 60.0%-67.0%) and 82.6% (95% CI 79.9%-85.4%), respectively. The median time to treatment discontinuation was 37.4 months (95% CI 34.8-42.2 months). Disease progression or death was the reason for discontinuation in 45.8% of patients. Although ibrutinib is not generally the favored BTK inhibitor given an improved safety profile with next-generation options, these data provide real-world estimates for outcomes with BTK inhibitors in this large dataset of high-risk patients.

Although outcomes have improved for patients with CLL or SLL, it is common for resistance to targeted therapy to eventually occur. Noncovalent BTK inhibitors, such as pirtobrutinib, offer a promising approach for this population. The BRUIN trial was a phase 1/2 trial of pirtobrutinib in patients with relapsed/refractory CLL or SLL (Mato et al). A total of 317 patients were treated, including 247 who had previously received a BTK inhibitor. Patients had been treated with a median of three prior lines of therapy and over 40% had been treated with a BCL-2 inhibitor. The overall response rate was 73.3% (95% CI 67.3%-78.7%) and increased to 82.2% (95% CI 76.8%-86.7%) when partial response with lymphocytosis was included. At a 19.4-month median follow-up, the median progression-free survival was 19.6 (95% CI 16.9-22.1) months. The drug was also well-tolerated, with 2.8% of patients discontinuing therapy owing to treatment-related adverse events. Adverse events that can be seen with BTK inhibition, including hypertension, atrial fibrillation or flutter, and bleeding, were rare. This trial demonstrates that CLL/SLL cells can maintain dependency on the B-cell receptor pathway following treatment with a covalent inhibitor and that ongoing BTK inhibition using a novel mechanism is a feasible strategy. The optimal sequencing of pirtobrutinib with other available therapies, including BCL-2 inhibitors, remains unknown.

BTK inhibitors are also active in mantle cell lymphoma (MCL). They are approved for relapsed/refractory disease and are being studied in earlier lines of therapy. Whereas early progression of disease (POD) has been shown to be an important prognostic marker in MCL, the impact of early relapse on outcome specifically after BTK inhibitor initiation is less clear.⁷ A recent multicente retrospective observational study aimed to determine the impact on time-to-POD between rituximab-containing front-line therapy and second-line BTK inhibitor and overall outcomes (Villa et al). This study included 360 adult patients with relapsed or refractory MCL treated with second-line BTK inhibitor. Not surprisingly, the authors found that patients with POD within 24 months of first-line therapy had significantly shorter median progression-free survival (0.45 year vs 2.3 years; P < .001) and overall survival (0.9 year vs 5.5 years P < .001) compared with patients with relapse beyond 24 months. Furthermore, they found that Ki-67 ≥ 30% and Mantle Cell Lymphoma International Prognostic Index (MIPI) were also associated with progression‐free survival and overall survival from the start of a second-line BTK inhibitor, though to a lesser extent than time-to-POD. These variables were subsequently used to determine a second-line BTK MIPI, which can help inform which patients are most likely to benefit from a BTK inhibitor compared with other available options, such as chimeric antigen receptor (CAR) T-cell therapy or a clinical trial strategy.

BTK inhibitors are an important drug class for the treatment of lymphoid cancers and have changed the treatment paradigms in CLL/SLL and MCL. Additional studies evaluating combination strategies, sequencing approaches, time-limited options, and predictors of response are likely to further refine optimization of use in these diseases.

Additional References

1.         Barr PM, Owen C, Robak T, et al. Up to 8-year follow-up from RESONATE-2: first-line ibrutinib treatment for patients with chronic lymphocytic leukemia. Blood Adv. 2022;6:3440-3450. doi:10.1182/bloodadvances.2021006434

2.         Sharman JP, Egyed M, Jurczak W, et al. Efficacy and safety in a 4-year follow-up of the ELEVATE-TN study comparing acalabrutinib with or without obinutuzumab versus obinutuzumab plus chlorambucil in treatment-naive chronic lymphocytic leukemia. Leukemia. 2022;36:1171-1175. doi:10.1038/s41375-021-01485-x

3.         Tam CS, Brown JR, Kahl BS, et al. Zanubrutinib versus bendamustine and rituximab in untreated chronic lymphocytic leukaemia and small lymphocytic lymphoma (SEQUOIA): a randomised, controlled, phase 3 trial. Lancet Oncol. 2022;23:1031-1043. doi:10.1016/S1470-2045(22)00293-5

4.         Ahn IE, Tian X, Wiestner A. Ibrutinib for chronic lymphocytic leukemia with TP53 alterations. N Engl J Med. 2020;383:498-500. doi:10.1056/NEJMc2005943

5.         Allan JN, Shanafelt T, Wiestner A, et al. Long-term efficacy of first-line ibrutinib treatment for chronic lymphocytic leukaemia in patients with TP53 aberrations: a pooled analysis from four clinical trials. Br J Haematol. 2022;196:947-953. doi:10.1111/bjh.17984

6.         Mato AR, Tang B, Azmi S, et al. A clinical practice comparison of patients with chronic lymphocytic leukemia with and without deletion 17p receiving first-line treatment with ibrutinib. Haematologica. 2022;107:2630-2640. doi:10.3324/haematol.2021.280376

7.         Bond DA, Switchenko JM, Villa D, et al. Early relapse identifies MCL patients with inferior survival after intensive or less intensive frontline therapy. Blood Adv. 2021;5:5179-5189. doi:10.1182/bloodadvances.2021004765

The treatment landscape of chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL) has been transformed over the past decade with the advent of targeted therapies, including Bruton tyrosine kinase (BTK) inhibitors. Covalent BTK inhibitors, which are available in both the frontline and relapsed/refractory settings, include ibrutinib, acalabrutinib, and zanubrutinib.^1-3

BTK inhibitors have also demonstrated activity in higher-risk subgroups, including patients harboring TP53 aberrations. Clinical trials have shown encouraging outcomes of BTK inhibitors in these patients, and real-world studies have demonstrated similar findings.^4-6 Recently, a real-world Italian registry study similarly showed favorable outcomes in 747 patients with CLL carrying 17p- or TP53 or both mutations treated with first-line ibrutinib. in what appears to be the largest real-world analysis of this patient population (Rigolin et al). At 24 months, the median overall survival was not reached; the estimated treatment persistence and survival rates were 63.4% (95% CI 60.0%-67.0%) and 82.6% (95% CI 79.9%-85.4%), respectively. The median time to treatment discontinuation was 37.4 months (95% CI 34.8-42.2 months). Disease progression or death was the reason for discontinuation in 45.8% of patients. Although ibrutinib is not generally the favored BTK inhibitor given an improved safety profile with next-generation options, these data provide real-world estimates for outcomes with BTK inhibitors in this large dataset of high-risk patients.

Although outcomes have improved for patients with CLL or SLL, it is common for resistance to targeted therapy to eventually occur. Noncovalent BTK inhibitors, such as pirtobrutinib, offer a promising approach for this population. The BRUIN trial was a phase 1/2 trial of pirtobrutinib in patients with relapsed/refractory CLL or SLL (Mato et al). A total of 317 patients were treated, including 247 who had previously received a BTK inhibitor. Patients had been treated with a median of three prior lines of therapy and over 40% had been treated with a BCL-2 inhibitor. The overall response rate was 73.3% (95% CI 67.3%-78.7%) and increased to 82.2% (95% CI 76.8%-86.7%) when partial response with lymphocytosis was included. At a 19.4-month median follow-up, the median progression-free survival was 19.6 (95% CI 16.9-22.1) months. The drug was also well-tolerated, with 2.8% of patients discontinuing therapy owing to treatment-related adverse events. Adverse events that can be seen with BTK inhibition, including hypertension, atrial fibrillation or flutter, and bleeding, were rare. This trial demonstrates that CLL/SLL cells can maintain dependency on the B-cell receptor pathway following treatment with a covalent inhibitor and that ongoing BTK inhibition using a novel mechanism is a feasible strategy. The optimal sequencing of pirtobrutinib with other available therapies, including BCL-2 inhibitors, remains unknown.

BTK inhibitors are also active in mantle cell lymphoma (MCL). They are approved for relapsed/refractory disease and are being studied in earlier lines of therapy. Whereas early progression of disease (POD) has been shown to be an important prognostic marker in MCL, the impact of early relapse on outcome specifically after BTK inhibitor initiation is less clear.⁷ A recent multicente retrospective observational study aimed to determine the impact on time-to-POD between rituximab-containing front-line therapy and second-line BTK inhibitor and overall outcomes (Villa et al). This study included 360 adult patients with relapsed or refractory MCL treated with second-line BTK inhibitor. Not surprisingly, the authors found that patients with POD within 24 months of first-line therapy had significantly shorter median progression-free survival (0.45 year vs 2.3 years; P < .001) and overall survival (0.9 year vs 5.5 years P < .001) compared with patients with relapse beyond 24 months. Furthermore, they found that Ki-67 ≥ 30% and Mantle Cell Lymphoma International Prognostic Index (MIPI) were also associated with progression‐free survival and overall survival from the start of a second-line BTK inhibitor, though to a lesser extent than time-to-POD. These variables were subsequently used to determine a second-line BTK MIPI, which can help inform which patients are most likely to benefit from a BTK inhibitor compared with other available options, such as chimeric antigen receptor (CAR) T-cell therapy or a clinical trial strategy.

BTK inhibitors are an important drug class for the treatment of lymphoid cancers and have changed the treatment paradigms in CLL/SLL and MCL. Additional studies evaluating combination strategies, sequencing approaches, time-limited options, and predictors of response are likely to further refine optimization of use in these diseases.

Additional References

1.         Barr PM, Owen C, Robak T, et al. Up to 8-year follow-up from RESONATE-2: first-line ibrutinib treatment for patients with chronic lymphocytic leukemia. Blood Adv. 2022;6:3440-3450. doi:10.1182/bloodadvances.2021006434

2.         Sharman JP, Egyed M, Jurczak W, et al. Efficacy and safety in a 4-year follow-up of the ELEVATE-TN study comparing acalabrutinib with or without obinutuzumab versus obinutuzumab plus chlorambucil in treatment-naive chronic lymphocytic leukemia. Leukemia. 2022;36:1171-1175. doi:10.1038/s41375-021-01485-x

3.         Tam CS, Brown JR, Kahl BS, et al. Zanubrutinib versus bendamustine and rituximab in untreated chronic lymphocytic leukaemia and small lymphocytic lymphoma (SEQUOIA): a randomised, controlled, phase 3 trial. Lancet Oncol. 2022;23:1031-1043. doi:10.1016/S1470-2045(22)00293-5

4.         Ahn IE, Tian X, Wiestner A. Ibrutinib for chronic lymphocytic leukemia with TP53 alterations. N Engl J Med. 2020;383:498-500. doi:10.1056/NEJMc2005943

5.         Allan JN, Shanafelt T, Wiestner A, et al. Long-term efficacy of first-line ibrutinib treatment for chronic lymphocytic leukaemia in patients with TP53 aberrations: a pooled analysis from four clinical trials. Br J Haematol. 2022;196:947-953. doi:10.1111/bjh.17984

6.         Mato AR, Tang B, Azmi S, et al. A clinical practice comparison of patients with chronic lymphocytic leukemia with and without deletion 17p receiving first-line treatment with ibrutinib. Haematologica. 2022;107:2630-2640. doi:10.3324/haematol.2021.280376

7.         Bond DA, Switchenko JM, Villa D, et al. Early relapse identifies MCL patients with inferior survival after intensive or less intensive frontline therapy. Blood Adv. 2021;5:5179-5189. doi:10.1182/bloodadvances.2021004765

The treatment landscape of chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL) has been transformed over the past decade with the advent of targeted therapies, including Bruton tyrosine kinase (BTK) inhibitors. Covalent BTK inhibitors, which are available in both the frontline and relapsed/refractory settings, include ibrutinib, acalabrutinib, and zanubrutinib.^1-3

BTK inhibitors have also demonstrated activity in higher-risk subgroups, including patients harboring TP53 aberrations. Clinical trials have shown encouraging outcomes of BTK inhibitors in these patients, and real-world studies have demonstrated similar findings.^4-6 Recently, a real-world Italian registry study similarly showed favorable outcomes in 747 patients with CLL carrying 17p- or TP53 or both mutations treated with first-line ibrutinib. in what appears to be the largest real-world analysis of this patient population (Rigolin et al). At 24 months, the median overall survival was not reached; the estimated treatment persistence and survival rates were 63.4% (95% CI 60.0%-67.0%) and 82.6% (95% CI 79.9%-85.4%), respectively. The median time to treatment discontinuation was 37.4 months (95% CI 34.8-42.2 months). Disease progression or death was the reason for discontinuation in 45.8% of patients. Although ibrutinib is not generally the favored BTK inhibitor given an improved safety profile with next-generation options, these data provide real-world estimates for outcomes with BTK inhibitors in this large dataset of high-risk patients.

Although outcomes have improved for patients with CLL or SLL, it is common for resistance to targeted therapy to eventually occur. Noncovalent BTK inhibitors, such as pirtobrutinib, offer a promising approach for this population. The BRUIN trial was a phase 1/2 trial of pirtobrutinib in patients with relapsed/refractory CLL or SLL (Mato et al). A total of 317 patients were treated, including 247 who had previously received a BTK inhibitor. Patients had been treated with a median of three prior lines of therapy and over 40% had been treated with a BCL-2 inhibitor. The overall response rate was 73.3% (95% CI 67.3%-78.7%) and increased to 82.2% (95% CI 76.8%-86.7%) when partial response with lymphocytosis was included. At a 19.4-month median follow-up, the median progression-free survival was 19.6 (95% CI 16.9-22.1) months. The drug was also well-tolerated, with 2.8% of patients discontinuing therapy owing to treatment-related adverse events. Adverse events that can be seen with BTK inhibition, including hypertension, atrial fibrillation or flutter, and bleeding, were rare. This trial demonstrates that CLL/SLL cells can maintain dependency on the B-cell receptor pathway following treatment with a covalent inhibitor and that ongoing BTK inhibition using a novel mechanism is a feasible strategy. The optimal sequencing of pirtobrutinib with other available therapies, including BCL-2 inhibitors, remains unknown.

BTK inhibitors are also active in mantle cell lymphoma (MCL). They are approved for relapsed/refractory disease and are being studied in earlier lines of therapy. Whereas early progression of disease (POD) has been shown to be an important prognostic marker in MCL, the impact of early relapse on outcome specifically after BTK inhibitor initiation is less clear.⁷ A recent multicente retrospective observational study aimed to determine the impact on time-to-POD between rituximab-containing front-line therapy and second-line BTK inhibitor and overall outcomes (Villa et al). This study included 360 adult patients with relapsed or refractory MCL treated with second-line BTK inhibitor. Not surprisingly, the authors found that patients with POD within 24 months of first-line therapy had significantly shorter median progression-free survival (0.45 year vs 2.3 years; P < .001) and overall survival (0.9 year vs 5.5 years P < .001) compared with patients with relapse beyond 24 months. Furthermore, they found that Ki-67 ≥ 30% and Mantle Cell Lymphoma International Prognostic Index (MIPI) were also associated with progression‐free survival and overall survival from the start of a second-line BTK inhibitor, though to a lesser extent than time-to-POD. These variables were subsequently used to determine a second-line BTK MIPI, which can help inform which patients are most likely to benefit from a BTK inhibitor compared with other available options, such as chimeric antigen receptor (CAR) T-cell therapy or a clinical trial strategy.

BTK inhibitors are an important drug class for the treatment of lymphoid cancers and have changed the treatment paradigms in CLL/SLL and MCL. Additional studies evaluating combination strategies, sequencing approaches, time-limited options, and predictors of response are likely to further refine optimization of use in these diseases.

Additional References

1.         Barr PM, Owen C, Robak T, et al. Up to 8-year follow-up from RESONATE-2: first-line ibrutinib treatment for patients with chronic lymphocytic leukemia. Blood Adv. 2022;6:3440-3450. doi:10.1182/bloodadvances.2021006434

2.         Sharman JP, Egyed M, Jurczak W, et al. Efficacy and safety in a 4-year follow-up of the ELEVATE-TN study comparing acalabrutinib with or without obinutuzumab versus obinutuzumab plus chlorambucil in treatment-naive chronic lymphocytic leukemia. Leukemia. 2022;36:1171-1175. doi:10.1038/s41375-021-01485-x

3.         Tam CS, Brown JR, Kahl BS, et al. Zanubrutinib versus bendamustine and rituximab in untreated chronic lymphocytic leukaemia and small lymphocytic lymphoma (SEQUOIA): a randomised, controlled, phase 3 trial. Lancet Oncol. 2022;23:1031-1043. doi:10.1016/S1470-2045(22)00293-5

4.         Ahn IE, Tian X, Wiestner A. Ibrutinib for chronic lymphocytic leukemia with TP53 alterations. N Engl J Med. 2020;383:498-500. doi:10.1056/NEJMc2005943

5.         Allan JN, Shanafelt T, Wiestner A, et al. Long-term efficacy of first-line ibrutinib treatment for chronic lymphocytic leukaemia in patients with TP53 aberrations: a pooled analysis from four clinical trials. Br J Haematol. 2022;196:947-953. doi:10.1111/bjh.17984

6.         Mato AR, Tang B, Azmi S, et al. A clinical practice comparison of patients with chronic lymphocytic leukemia with and without deletion 17p receiving first-line treatment with ibrutinib. Haematologica. 2022;107:2630-2640. doi:10.3324/haematol.2021.280376

7.         Bond DA, Switchenko JM, Villa D, et al. Early relapse identifies MCL patients with inferior survival after intensive or less intensive frontline therapy. Blood Adv. 2021;5:5179-5189. doi:10.1182/bloodadvances.2021004765