Dermpath Diagnosis

The Diagnosis: Endocrine Mucin-Producing Sweat Gland Carcinoma

Endocrine mucin-producing sweat gland carcinoma (EMPSGC) is a rare cutaneous adnexal tumor that characteristically presents as slowgrowing, flesh-colored papules, nodules, or cystic lesions around the periorbital skin in elderly female patients.¹ Histopathology of EMPSGCs reveals well-circumscribed multinodular dermal lesions that can be either cystic or solid and often are arranged in papillary and cribriform patterns (quiz image). Nests of uniform tumor cells are composed of small- to medium-sized epithelial cells with monomorphic nuclei showing fine to stippled chromatin.² Histologically, EMPSGC resembles a solid papillary carcinoma of the breast, which is attributed to their common embryologic origin.³ Intracytoplasmic and extracellular mucin often are seen on hematoxylin and eosin staining.² Variable immunohistochemical stain expression has been reported, including positive staining with synaptophysin and chromogranin. Other markers include cytokeratin CAM 5.2, epithelial membrane antigen, estrogen or progesterone receptors, and cytokeratin 7.⁴ Endocrine mucin-producing sweat gland carcinoma is thought to be a precursor to invasive neuroendocrine-type primary cutaneous mucinous carcinoma. Primary cutaneous mucinous carcinoma has been associated with EMPSGC in approximately 35.7% of cases. Histologically, primary cutaneous mucinous carcinoma that has transformed from EMPSGC would show an infiltration of tumor nests with desmoplastic stroma or mucin pools with clusters of tumor cells.²

Primary cutaneous adenoid cystic carcinoma is a rare malignant tumor that often presents on the head and neck. It usually appears as a single, slowly growing subcutaneous nodule or multinodular plaque.^5,6 Histologic features include basaloid cells in alternating tubular and cribriform patterns. The cribriform areas are composed of pseudoglandular adenoid spaces that contain mucin, basement membrane zone material, and cellular debris from necrotic neoplastic cells (Figure 1).⁷ Primary cutaneous adenoid cystic carcinoma predominantly is dermal with extension to the subcutaneous tissue. True ductal structures that demonstrate decapitation secretion also may be present.⁷

Basal cell carcinoma (adenoid type) presents as a pigmented or nonpigmented nodule or ulcer on sunexposed areas of the head and neck. Histopathology reveals basaloid cells surrounding islands of connective tissue resulting in a lacelike pattern (Figure 2). The lumina may contain a colloidal substance or amorphous granular material.⁸ The characteristic features of basal cell carcinomas, such as nests of basaloid cells with peripheral palisading cells, retraction of adjacent stroma, increased apoptosis and mitotic figures, and connection to the epidermis, can be helpful to distinguish basal cell carcinoma histologically from EMPSGC.²

Apocrine hidrocystomas clinically present as round, flesh-colored, shiny or translucent, dome-shaped papules or nodules near the eyelid margin or lateral canthus.⁹ Histologically, they are composed of proliferating apocrine secretory coils with an epithelial side of cuboidal or columnar cells and a luminal side exhibiting decapitation secretion (Figure 3).² An epidermal connection is absent.⁹ Apocrine hidrocystomas may exhibit complex architecture and papillary ductal hyperplasia that are difficult to distinguish from EMPSGC, especially if EMPSGC presents with cystic morphology. Apocrine cytomorphology and the lack of neuroendocrine marker expression and mucin production distinguish apocrine hidrocystomas. Furthermore, hidrocystomas infrequently demonstrate the nodular, solid, cribriform areas appreciated in EMPSGC.²

Microcystic adnexal carcinoma is a rare, slowly growing, locally aggressive sweat gland tumor that commonly presents as a flesh-colored to yellow papule, nodule, or plaque on the central face.¹⁰ Histopathologic examination reveals both eccrine and follicular differentiation. Keratin cysts, bland keratinocyte cords, and epithelium with ductal differentiation is observed in the superficial layers (Figure 4). Deep invasion into the subcutis and perineural invasion frequently is observed.

The Diagnosis: Endocrine Mucin-Producing Sweat Gland Carcinoma

Endocrine mucin-producing sweat gland carcinoma (EMPSGC) is a rare cutaneous adnexal tumor that characteristically presents as slowgrowing, flesh-colored papules, nodules, or cystic lesions around the periorbital skin in elderly female patients.¹ Histopathology of EMPSGCs reveals well-circumscribed multinodular dermal lesions that can be either cystic or solid and often are arranged in papillary and cribriform patterns (quiz image). Nests of uniform tumor cells are composed of small- to medium-sized epithelial cells with monomorphic nuclei showing fine to stippled chromatin.² Histologically, EMPSGC resembles a solid papillary carcinoma of the breast, which is attributed to their common embryologic origin.³ Intracytoplasmic and extracellular mucin often are seen on hematoxylin and eosin staining.² Variable immunohistochemical stain expression has been reported, including positive staining with synaptophysin and chromogranin. Other markers include cytokeratin CAM 5.2, epithelial membrane antigen, estrogen or progesterone receptors, and cytokeratin 7.⁴ Endocrine mucin-producing sweat gland carcinoma is thought to be a precursor to invasive neuroendocrine-type primary cutaneous mucinous carcinoma. Primary cutaneous mucinous carcinoma has been associated with EMPSGC in approximately 35.7% of cases. Histologically, primary cutaneous mucinous carcinoma that has transformed from EMPSGC would show an infiltration of tumor nests with desmoplastic stroma or mucin pools with clusters of tumor cells.²

Primary cutaneous adenoid cystic carcinoma is a rare malignant tumor that often presents on the head and neck. It usually appears as a single, slowly growing subcutaneous nodule or multinodular plaque.^5,6 Histologic features include basaloid cells in alternating tubular and cribriform patterns. The cribriform areas are composed of pseudoglandular adenoid spaces that contain mucin, basement membrane zone material, and cellular debris from necrotic neoplastic cells (Figure 1).⁷ Primary cutaneous adenoid cystic carcinoma predominantly is dermal with extension to the subcutaneous tissue. True ductal structures that demonstrate decapitation secretion also may be present.⁷

Basal cell carcinoma (adenoid type) presents as a pigmented or nonpigmented nodule or ulcer on sunexposed areas of the head and neck. Histopathology reveals basaloid cells surrounding islands of connective tissue resulting in a lacelike pattern (Figure 2). The lumina may contain a colloidal substance or amorphous granular material.⁸ The characteristic features of basal cell carcinomas, such as nests of basaloid cells with peripheral palisading cells, retraction of adjacent stroma, increased apoptosis and mitotic figures, and connection to the epidermis, can be helpful to distinguish basal cell carcinoma histologically from EMPSGC.²

Apocrine hidrocystomas clinically present as round, flesh-colored, shiny or translucent, dome-shaped papules or nodules near the eyelid margin or lateral canthus.⁹ Histologically, they are composed of proliferating apocrine secretory coils with an epithelial side of cuboidal or columnar cells and a luminal side exhibiting decapitation secretion (Figure 3).² An epidermal connection is absent.⁹ Apocrine hidrocystomas may exhibit complex architecture and papillary ductal hyperplasia that are difficult to distinguish from EMPSGC, especially if EMPSGC presents with cystic morphology. Apocrine cytomorphology and the lack of neuroendocrine marker expression and mucin production distinguish apocrine hidrocystomas. Furthermore, hidrocystomas infrequently demonstrate the nodular, solid, cribriform areas appreciated in EMPSGC.²

Microcystic adnexal carcinoma is a rare, slowly growing, locally aggressive sweat gland tumor that commonly presents as a flesh-colored to yellow papule, nodule, or plaque on the central face.¹⁰ Histopathologic examination reveals both eccrine and follicular differentiation. Keratin cysts, bland keratinocyte cords, and epithelium with ductal differentiation is observed in the superficial layers (Figure 4). Deep invasion into the subcutis and perineural invasion frequently is observed.

The Diagnosis: Endocrine Mucin-Producing Sweat Gland Carcinoma

Endocrine mucin-producing sweat gland carcinoma (EMPSGC) is a rare cutaneous adnexal tumor that characteristically presents as slowgrowing, flesh-colored papules, nodules, or cystic lesions around the periorbital skin in elderly female patients.¹ Histopathology of EMPSGCs reveals well-circumscribed multinodular dermal lesions that can be either cystic or solid and often are arranged in papillary and cribriform patterns (quiz image). Nests of uniform tumor cells are composed of small- to medium-sized epithelial cells with monomorphic nuclei showing fine to stippled chromatin.² Histologically, EMPSGC resembles a solid papillary carcinoma of the breast, which is attributed to their common embryologic origin.³ Intracytoplasmic and extracellular mucin often are seen on hematoxylin and eosin staining.² Variable immunohistochemical stain expression has been reported, including positive staining with synaptophysin and chromogranin. Other markers include cytokeratin CAM 5.2, epithelial membrane antigen, estrogen or progesterone receptors, and cytokeratin 7.⁴ Endocrine mucin-producing sweat gland carcinoma is thought to be a precursor to invasive neuroendocrine-type primary cutaneous mucinous carcinoma. Primary cutaneous mucinous carcinoma has been associated with EMPSGC in approximately 35.7% of cases. Histologically, primary cutaneous mucinous carcinoma that has transformed from EMPSGC would show an infiltration of tumor nests with desmoplastic stroma or mucin pools with clusters of tumor cells.²

Primary cutaneous adenoid cystic carcinoma is a rare malignant tumor that often presents on the head and neck. It usually appears as a single, slowly growing subcutaneous nodule or multinodular plaque.^5,6 Histologic features include basaloid cells in alternating tubular and cribriform patterns. The cribriform areas are composed of pseudoglandular adenoid spaces that contain mucin, basement membrane zone material, and cellular debris from necrotic neoplastic cells (Figure 1).⁷ Primary cutaneous adenoid cystic carcinoma predominantly is dermal with extension to the subcutaneous tissue. True ductal structures that demonstrate decapitation secretion also may be present.⁷

Basal cell carcinoma (adenoid type) presents as a pigmented or nonpigmented nodule or ulcer on sunexposed areas of the head and neck. Histopathology reveals basaloid cells surrounding islands of connective tissue resulting in a lacelike pattern (Figure 2). The lumina may contain a colloidal substance or amorphous granular material.⁸ The characteristic features of basal cell carcinomas, such as nests of basaloid cells with peripheral palisading cells, retraction of adjacent stroma, increased apoptosis and mitotic figures, and connection to the epidermis, can be helpful to distinguish basal cell carcinoma histologically from EMPSGC.²

Apocrine hidrocystomas clinically present as round, flesh-colored, shiny or translucent, dome-shaped papules or nodules near the eyelid margin or lateral canthus.⁹ Histologically, they are composed of proliferating apocrine secretory coils with an epithelial side of cuboidal or columnar cells and a luminal side exhibiting decapitation secretion (Figure 3).² An epidermal connection is absent.⁹ Apocrine hidrocystomas may exhibit complex architecture and papillary ductal hyperplasia that are difficult to distinguish from EMPSGC, especially if EMPSGC presents with cystic morphology. Apocrine cytomorphology and the lack of neuroendocrine marker expression and mucin production distinguish apocrine hidrocystomas. Furthermore, hidrocystomas infrequently demonstrate the nodular, solid, cribriform areas appreciated in EMPSGC.²

Microcystic adnexal carcinoma is a rare, slowly growing, locally aggressive sweat gland tumor that commonly presents as a flesh-colored to yellow papule, nodule, or plaque on the central face.¹⁰ Histopathologic examination reveals both eccrine and follicular differentiation. Keratin cysts, bland keratinocyte cords, and epithelium with ductal differentiation is observed in the superficial layers (Figure 4). Deep invasion into the subcutis and perineural invasion frequently is observed.

The Diagnosis: Pseudoangiomatous Squamous Cell Carcinoma

Pseudoangiomatous squamous cell carcinoma (PSCC), a variant of acantholytic squamous cell carcinoma (SCC), is a rare epithelial neoplasm that can mimic angiosarcoma.¹ Clinically, PSCC presents as a white-gray ulcer or nodular pink tumor on sun-exposed areas, typically on the head and neck. Due to its increased potential for metastasis, this variant of SCC is considered particularly aggressive. Histologically, PSCC shows nests of acantholytic atypical keratinocytes arranged in anastomosing arrays that form pseudovascular or pseudoglandular structures.² Acantholytic spaces frequently are filled with erythrocytes. Immunohistochemically, PSCC tumor cells express classic squamous markers such as cytokeratin (CK) 5 and p63 but not vascular markers such as CD31, CD34, and von Willebrand factor.³ In our patient, histopathology of the lesion revealed invasive nests, lobules, and interconnected columns of well-differentiated squamous tumor cells that emanated from the base of the epidermis. The tumor exhibited acantholysis forming ectatic and slitlike spaces, some of which contained erythrocytes. The neoplastic cells, including those lining pseudovascular spaces, positively stained for CK5 (Figure 1A) and nuclear p63 but lacked reactivity to CD31 (Figure 1B) and CD34, corroborating squamous and not vascular differentiation. Current treatment guidelines include Mohs micrographic surgery, excisional surgery, or radiation.⁴ Our patient’s lesion was completely removed by Mohs micrographic surgery. Three months later, there was no evidence of recurrence.

Angiosarcoma is an aggressive neoplasm associated with a poor prognosis and 5-year survival rate of 30% to 40%. The etiology of angiosarcoma still is unclear, but identified risk factors include prior radiation therapy, lymphedema (Stewart-Treves syndrome), and genetic predisposition.⁵ In the skin, angiosarcoma often occurs in the head and neck region, accounting for 60% of cutaneous cases.^5,6 Early in the disease, most patients present with a bruiselike lesion on the scalp or forehead, often delaying the diagnosis.⁶ As the cancer progresses, tissue infiltration, edema, and hemorrhage contribute to the formation of violaceous nodules, which eventually prompt for biopsy. Angiosarcoma spans a broad histologic spectrum depending on the cytology of malignant cells (eg, spindle, small round, epithelioid) and their capacity for vasoformation. Welldifferentiated angiosarcoma shows retiform slitlike spaces in between collagen bundles that are lined by hyperchromatic hobnailing endothelial cells (Figure 2).⁷ Epithelioid angiosarcoma can be mistaken for SCC.⁸ Immunohistochemically, angiosarcoma stains positively for CD31, CD34, ETS-related gene 1, D2-40, and factor VIII.9 In our patient, the neoplasm was negative for vascular markers CD31 and CD34.

Bacillary angiomatosis (BA), caused by Bartonella henselae, is a rare disease that first was identified in HIV patients with diminished CD4+ T-cell counts. In the skin, BA often manifests as centrally ulcerated, single or clustered, reddish-purple nodules.¹⁰ Histologically, it is characterized by highly vascularized, histiocyterich infiltrates with admixed neutrophils and plasma cells (Figure 3). Capillaries often proliferate in a lobular fashion.¹¹ Atypical cytology with areas of necrosis may mimic angiosarcoma.¹² The pathognomonic feature of BA is the presence of enlarged histiocytes with pink-purplish cytoplasm corresponding to intracytoplasmic aggregates of bacteria, which can be revealed by Warthin-Starry or Grocott-Gomori methenamine-silver staining. Immunohistochemically, proliferative benign capillaries are highlighted by CD34 and CD31, and histiocytes are decorated by CD68.¹² This diagnosis was excluded based on the patient’s history, clinical presentation, and positive staining for CK5 and p63.

Squamoid eccrine ductal carcinoma is an exceedingly rare subtype of eccrine carcinoma that mimics SCC both clinically and histologically.¹³ It most often occurs on the head and neck of elderly patients. This neoplasm can look similar to SCC and its variants, including PSCC. Histologically, squamoid eccrine ductal carcinoma exhibits a biphasic growth pattern.¹⁴ Well-differentiated squamous dysplasia transitions to carcinoma with eccrine duct formation as the tumor percolates deep into the dermis (Figure 4). As a result, superficial skin biopsies often lead to an incorrect diagnosis.¹⁵ Unlike SCC, the risk for locoregional and widespread metastasis is elevated. Identifying ducts in the deep aspect of the tumor is critical, thus immunohistochemical staining for carcinoembryonic antigen and epithelial membrane antigen is paramount for the diagnosis.¹⁵ Pseudoangiomatous SCC will stain negative for carcinoembryonic antigen, as was the case in our patient.

Pseudoepitheliomatous hyperplasia is a benign histologic reaction that can result from trauma, chronic inflammation (ie, pyoderma gangrenosum), tattoo placement, underlying neoplasia or fungal infection, or a spider bite reaction.^14,15 It most commonly is seen as a well-demarcated nodule or plaque associated with scaling or crusting. Papules vary in size from less than 1 cm to several centimeters. Histologically, it is defined by an acanthotic proliferation of the adnexal epithelium and epidermis (Figure 5).^16,17 Irregular strands, cords, and nests of squamoid cells can extend into the dermis.¹⁸ It can closely mimic SCC, but there are a few key differences. Pseudoepitheliomatous hyperplasia will not display atypical mitotic figures or atypical nuclei and will never invade lymphatics or vascular systems.¹⁹ Pseudoepitheliomatous hyperplasia shows identical histology to well-differentiated SCC, and thus clinicopathologic correlation and mindful histologic evaluation are crucial. The presence of an increased influx of neutrophils and histiocytes should prompt for microbial stains or deeper sectioning. A superficial biopsy should be followed by a deep biopsy. In our patient, microorganismal stains were negative.

The Diagnosis: Pseudoangiomatous Squamous Cell Carcinoma

Pseudoangiomatous squamous cell carcinoma (PSCC), a variant of acantholytic squamous cell carcinoma (SCC), is a rare epithelial neoplasm that can mimic angiosarcoma.¹ Clinically, PSCC presents as a white-gray ulcer or nodular pink tumor on sun-exposed areas, typically on the head and neck. Due to its increased potential for metastasis, this variant of SCC is considered particularly aggressive. Histologically, PSCC shows nests of acantholytic atypical keratinocytes arranged in anastomosing arrays that form pseudovascular or pseudoglandular structures.² Acantholytic spaces frequently are filled with erythrocytes. Immunohistochemically, PSCC tumor cells express classic squamous markers such as cytokeratin (CK) 5 and p63 but not vascular markers such as CD31, CD34, and von Willebrand factor.³ In our patient, histopathology of the lesion revealed invasive nests, lobules, and interconnected columns of well-differentiated squamous tumor cells that emanated from the base of the epidermis. The tumor exhibited acantholysis forming ectatic and slitlike spaces, some of which contained erythrocytes. The neoplastic cells, including those lining pseudovascular spaces, positively stained for CK5 (Figure 1A) and nuclear p63 but lacked reactivity to CD31 (Figure 1B) and CD34, corroborating squamous and not vascular differentiation. Current treatment guidelines include Mohs micrographic surgery, excisional surgery, or radiation.⁴ Our patient’s lesion was completely removed by Mohs micrographic surgery. Three months later, there was no evidence of recurrence.

Angiosarcoma is an aggressive neoplasm associated with a poor prognosis and 5-year survival rate of 30% to 40%. The etiology of angiosarcoma still is unclear, but identified risk factors include prior radiation therapy, lymphedema (Stewart-Treves syndrome), and genetic predisposition.⁵ In the skin, angiosarcoma often occurs in the head and neck region, accounting for 60% of cutaneous cases.^5,6 Early in the disease, most patients present with a bruiselike lesion on the scalp or forehead, often delaying the diagnosis.⁶ As the cancer progresses, tissue infiltration, edema, and hemorrhage contribute to the formation of violaceous nodules, which eventually prompt for biopsy. Angiosarcoma spans a broad histologic spectrum depending on the cytology of malignant cells (eg, spindle, small round, epithelioid) and their capacity for vasoformation. Welldifferentiated angiosarcoma shows retiform slitlike spaces in between collagen bundles that are lined by hyperchromatic hobnailing endothelial cells (Figure 2).⁷ Epithelioid angiosarcoma can be mistaken for SCC.⁸ Immunohistochemically, angiosarcoma stains positively for CD31, CD34, ETS-related gene 1, D2-40, and factor VIII.9 In our patient, the neoplasm was negative for vascular markers CD31 and CD34.

Bacillary angiomatosis (BA), caused by Bartonella henselae, is a rare disease that first was identified in HIV patients with diminished CD4+ T-cell counts. In the skin, BA often manifests as centrally ulcerated, single or clustered, reddish-purple nodules.¹⁰ Histologically, it is characterized by highly vascularized, histiocyterich infiltrates with admixed neutrophils and plasma cells (Figure 3). Capillaries often proliferate in a lobular fashion.¹¹ Atypical cytology with areas of necrosis may mimic angiosarcoma.¹² The pathognomonic feature of BA is the presence of enlarged histiocytes with pink-purplish cytoplasm corresponding to intracytoplasmic aggregates of bacteria, which can be revealed by Warthin-Starry or Grocott-Gomori methenamine-silver staining. Immunohistochemically, proliferative benign capillaries are highlighted by CD34 and CD31, and histiocytes are decorated by CD68.¹² This diagnosis was excluded based on the patient’s history, clinical presentation, and positive staining for CK5 and p63.

Squamoid eccrine ductal carcinoma is an exceedingly rare subtype of eccrine carcinoma that mimics SCC both clinically and histologically.¹³ It most often occurs on the head and neck of elderly patients. This neoplasm can look similar to SCC and its variants, including PSCC. Histologically, squamoid eccrine ductal carcinoma exhibits a biphasic growth pattern.¹⁴ Well-differentiated squamous dysplasia transitions to carcinoma with eccrine duct formation as the tumor percolates deep into the dermis (Figure 4). As a result, superficial skin biopsies often lead to an incorrect diagnosis.¹⁵ Unlike SCC, the risk for locoregional and widespread metastasis is elevated. Identifying ducts in the deep aspect of the tumor is critical, thus immunohistochemical staining for carcinoembryonic antigen and epithelial membrane antigen is paramount for the diagnosis.¹⁵ Pseudoangiomatous SCC will stain negative for carcinoembryonic antigen, as was the case in our patient.

Pseudoepitheliomatous hyperplasia is a benign histologic reaction that can result from trauma, chronic inflammation (ie, pyoderma gangrenosum), tattoo placement, underlying neoplasia or fungal infection, or a spider bite reaction.^14,15 It most commonly is seen as a well-demarcated nodule or plaque associated with scaling or crusting. Papules vary in size from less than 1 cm to several centimeters. Histologically, it is defined by an acanthotic proliferation of the adnexal epithelium and epidermis (Figure 5).^16,17 Irregular strands, cords, and nests of squamoid cells can extend into the dermis.¹⁸ It can closely mimic SCC, but there are a few key differences. Pseudoepitheliomatous hyperplasia will not display atypical mitotic figures or atypical nuclei and will never invade lymphatics or vascular systems.¹⁹ Pseudoepitheliomatous hyperplasia shows identical histology to well-differentiated SCC, and thus clinicopathologic correlation and mindful histologic evaluation are crucial. The presence of an increased influx of neutrophils and histiocytes should prompt for microbial stains or deeper sectioning. A superficial biopsy should be followed by a deep biopsy. In our patient, microorganismal stains were negative.

The Diagnosis: Pseudoangiomatous Squamous Cell Carcinoma

Pseudoangiomatous squamous cell carcinoma (PSCC), a variant of acantholytic squamous cell carcinoma (SCC), is a rare epithelial neoplasm that can mimic angiosarcoma.¹ Clinically, PSCC presents as a white-gray ulcer or nodular pink tumor on sun-exposed areas, typically on the head and neck. Due to its increased potential for metastasis, this variant of SCC is considered particularly aggressive. Histologically, PSCC shows nests of acantholytic atypical keratinocytes arranged in anastomosing arrays that form pseudovascular or pseudoglandular structures.² Acantholytic spaces frequently are filled with erythrocytes. Immunohistochemically, PSCC tumor cells express classic squamous markers such as cytokeratin (CK) 5 and p63 but not vascular markers such as CD31, CD34, and von Willebrand factor.³ In our patient, histopathology of the lesion revealed invasive nests, lobules, and interconnected columns of well-differentiated squamous tumor cells that emanated from the base of the epidermis. The tumor exhibited acantholysis forming ectatic and slitlike spaces, some of which contained erythrocytes. The neoplastic cells, including those lining pseudovascular spaces, positively stained for CK5 (Figure 1A) and nuclear p63 but lacked reactivity to CD31 (Figure 1B) and CD34, corroborating squamous and not vascular differentiation. Current treatment guidelines include Mohs micrographic surgery, excisional surgery, or radiation.⁴ Our patient’s lesion was completely removed by Mohs micrographic surgery. Three months later, there was no evidence of recurrence.

Angiosarcoma is an aggressive neoplasm associated with a poor prognosis and 5-year survival rate of 30% to 40%. The etiology of angiosarcoma still is unclear, but identified risk factors include prior radiation therapy, lymphedema (Stewart-Treves syndrome), and genetic predisposition.⁵ In the skin, angiosarcoma often occurs in the head and neck region, accounting for 60% of cutaneous cases.^5,6 Early in the disease, most patients present with a bruiselike lesion on the scalp or forehead, often delaying the diagnosis.⁶ As the cancer progresses, tissue infiltration, edema, and hemorrhage contribute to the formation of violaceous nodules, which eventually prompt for biopsy. Angiosarcoma spans a broad histologic spectrum depending on the cytology of malignant cells (eg, spindle, small round, epithelioid) and their capacity for vasoformation. Welldifferentiated angiosarcoma shows retiform slitlike spaces in between collagen bundles that are lined by hyperchromatic hobnailing endothelial cells (Figure 2).⁷ Epithelioid angiosarcoma can be mistaken for SCC.⁸ Immunohistochemically, angiosarcoma stains positively for CD31, CD34, ETS-related gene 1, D2-40, and factor VIII.9 In our patient, the neoplasm was negative for vascular markers CD31 and CD34.

Bacillary angiomatosis (BA), caused by Bartonella henselae, is a rare disease that first was identified in HIV patients with diminished CD4+ T-cell counts. In the skin, BA often manifests as centrally ulcerated, single or clustered, reddish-purple nodules.¹⁰ Histologically, it is characterized by highly vascularized, histiocyterich infiltrates with admixed neutrophils and plasma cells (Figure 3). Capillaries often proliferate in a lobular fashion.¹¹ Atypical cytology with areas of necrosis may mimic angiosarcoma.¹² The pathognomonic feature of BA is the presence of enlarged histiocytes with pink-purplish cytoplasm corresponding to intracytoplasmic aggregates of bacteria, which can be revealed by Warthin-Starry or Grocott-Gomori methenamine-silver staining. Immunohistochemically, proliferative benign capillaries are highlighted by CD34 and CD31, and histiocytes are decorated by CD68.¹² This diagnosis was excluded based on the patient’s history, clinical presentation, and positive staining for CK5 and p63.

Squamoid eccrine ductal carcinoma is an exceedingly rare subtype of eccrine carcinoma that mimics SCC both clinically and histologically.¹³ It most often occurs on the head and neck of elderly patients. This neoplasm can look similar to SCC and its variants, including PSCC. Histologically, squamoid eccrine ductal carcinoma exhibits a biphasic growth pattern.¹⁴ Well-differentiated squamous dysplasia transitions to carcinoma with eccrine duct formation as the tumor percolates deep into the dermis (Figure 4). As a result, superficial skin biopsies often lead to an incorrect diagnosis.¹⁵ Unlike SCC, the risk for locoregional and widespread metastasis is elevated. Identifying ducts in the deep aspect of the tumor is critical, thus immunohistochemical staining for carcinoembryonic antigen and epithelial membrane antigen is paramount for the diagnosis.¹⁵ Pseudoangiomatous SCC will stain negative for carcinoembryonic antigen, as was the case in our patient.

Pseudoepitheliomatous hyperplasia is a benign histologic reaction that can result from trauma, chronic inflammation (ie, pyoderma gangrenosum), tattoo placement, underlying neoplasia or fungal infection, or a spider bite reaction.^14,15 It most commonly is seen as a well-demarcated nodule or plaque associated with scaling or crusting. Papules vary in size from less than 1 cm to several centimeters. Histologically, it is defined by an acanthotic proliferation of the adnexal epithelium and epidermis (Figure 5).^16,17 Irregular strands, cords, and nests of squamoid cells can extend into the dermis.¹⁸ It can closely mimic SCC, but there are a few key differences. Pseudoepitheliomatous hyperplasia will not display atypical mitotic figures or atypical nuclei and will never invade lymphatics or vascular systems.¹⁹ Pseudoepitheliomatous hyperplasia shows identical histology to well-differentiated SCC, and thus clinicopathologic correlation and mindful histologic evaluation are crucial. The presence of an increased influx of neutrophils and histiocytes should prompt for microbial stains or deeper sectioning. A superficial biopsy should be followed by a deep biopsy. In our patient, microorganismal stains were negative.

The Diagnosis: Hybrid Schwannoma-Perineurioma

Hybrid nerve sheath tumors are rare entities that display features of more than one nerve sheath tumor such as neurofibromas, schwannomas, and perineuriomas.¹ These tumors often are found in the dermis or subcutaneous tissue of the extremities and abdomen²; however, cases of hybrid peripheral nerve sheath tumors have been reported in many anatomical locations without a gender predilection.³ The most common type of hybrid nerve sheath tumor is a schwannoma-perineurioma.^3,4 Histologically, they are well-circumscribed lesions composed of both spindled Schwann cells with plump nuclei and spindled perineural cells with more elongated thin nuclei.⁵ Although the Schwann cell component tends to predominate, the 2 cell populations interdigitate, making it challenging to definitively distinguish them by hematoxylin and eosin staining alone.4 However, immunohistochemical (IHC) staining can be used to help distinguish the 2 separate cell populations. Staining for S-100 and SRY-box transcription factor 10 (SOX-10) will be positive in the Schwann cell component, and staining for epithelial membrane antigen, Claudin-1, or glucose transporter-1 (Figure 1) will be positive in the perineural component. Other hybrid forms of benign nerve sheath tumors include neurofibroma-schwannoma and neurofibromaperineurioma.⁴ Neurofibroma-schwannomas usually have a schwannoma component containing Antoni A areas with palisading Verocay bodies. The neurofibroma cells typically have wavy elongated nuclei, fibroblasts, and mucinous myxoid material.³ Neurofibroma-perineurioma is the least common hybrid tumor. These hybrid tumors have a plexiform neurofibroma appearance with areas of perineural differentiation, which can be difficult to identify on routine histology and typically will require IHC staining to appreciate. The neurofibroma component will stain positive for S-100 and negative for markers of perineural differentiation, including epithelial membrane antigen, glucose transporter-1, and Claudin-1.³ Although schwannoma-perineuriomas are benign sporadic tumors not associated with neurofibromatosis, neurofibromaschwannomas are associated with neurofibromatosis types 1 and 2 (NF1 and NF2). Neurofibroma-perineurioma tumors usually are associated with only NF1.^3,6

Schwannomas typically present in middle-aged patients as tumors located on flexor surfaces.⁷ Although perineural cells can be seen at the periphery of a schwannoma forming a capsule, they do not interdigitate between the Schwann cells. Schwannomas are composed almost entirely of well-differentiated Schwann cells.^1,4,8 Schwannomas classically are well-circumscribed, encapsulated, biphasic lesions with alternating compact areas (Antoni A) and loosely arranged areas (Antoni B). The spindled cells occasionally may display nuclear palisading within the Antoni A areas, known as Verocay bodies (Figure 2). Antoni B areas are more disorganized and hypocellular with variable macrophage infiltrate.^1,4,8 The Schwann cells predominantly will have bland cytologic features, but scattered areas of degenerative nuclear atypia (also known as ancient change) may be present.⁴ Multiple schwannomas are associated with NF2 gene mutations and loss of merlin protein.8 There are different subtypes of schwannomas, including cellular and plexiform schwannomas.⁴ Because schwannomas are benign nerve sheath lesions, treatment typically consists of excision with careful dissection around the involved nerve.⁹

Neurofibromas are the most common peripheral nerve sheath tumors of the skin with no notable anatomic prediction, though one study found them to be more prevalent in the upper extremities.¹⁰ They typically present as sporadic solitary lesions, but multiple lesions may appear as superficial pedunculated growths that present in those aged 20 to 30 years.¹¹ Microscopically, neurofibromas typically are not well circumscribed and have an infiltrative growth pattern. Neurofibromas are composed of cytologically bland spindled Schwann cells with thin wavy nuclei in a variable myxoid stroma (Figure 3). In addition to Schwann cells, neurofibromas contain other cell components, including fibroblasts, mast cells, perineurial-like cells, and residual axons.⁴ Neurofibromas typically are located in the dermis but may extend into the subcutaneous tissue. Clinically, the overlying skin may show hyperpigmentation.8 Neurofibromas can be localized, diffuse, or plexiform, with the majority being localized. Diffuse neurofibromas clinically have a raised plaque appearance. Treatment is unnecessary because these lesions are benign.⁷

Desmoplastic melanoma (DM) is another diagnosis in the differential for this case. Patients with DM are older compared to non-DM melanoma patients, with a male predilection.¹² Desmoplastic melanomas are more likely to be located on the head and neck. In approximately one-third of cases, no in situ component will be identified, leading to confusion of the dermal lesion as a neural lesion or an area of scar formation. Microscopically, DM presents as a variable cellular infiltrative tumor composed of spindle cells with varying degrees of nuclear atypia. The spindled melanocytes are within a collagenous (desmoplastic) stroma (Figure 4).¹³ Desmoplastic melanoma has been described with a low mitotic index, leading to misdiagnosis with benign spindle cell neoplasms.¹⁴ The spindle cells should be positive for S-100 and SOX-10 with IHC staining. Unlike other melanomas, human melanoma black 45 and Melan-A often are negative or only focally positive. Treatment of DM is similar to non-DM in that wide local excision usually is employed. A systematic review evaluating sentinel lymph node biopsy (SLNB) recommended consideration of SLNB in mixed DM but not for pure DM, as rates of positive SLNB were much lower in the latter.¹⁵

Patients with malignant peripheral nerve sheath tumor (MPNST) usually present with an enlarging mass, pain, or neurologic symptoms. Most cases of MPNST are located on the trunk or extremities.¹⁶ Plexiform neurofibromas, especially in adults with NF1, have the potential to transform into an MPNST.⁴ In fact, MPNST is the most common malignancy in patients with NF1.¹⁷ Pediatric cancer survivors also are predisposed to MPNST, with a 40-fold increase in incidence compared to the general population.¹⁸ Transformation from schwannoma to MPNST is rare but has been reported.⁸ Histologically, spindle cells easily can be appreciated with a fasciculated growth pattern (Figure 5). Mitotic activity and tumor necrosis may be present. Diagnosis of these tumors historically has been challenging, though recent research has identified inactivation of polycomb repressive complex 2 in 70% to 90% of MPNSTs. Because of polycomb repressive complex 2 inactivation, there is loss of stone H3K27 trimethylation that can be capitalized on for MPNST diagnosis.¹⁹ Negative IHC staining for H3K27 trimethylation has been found to be highly specific for MPNST. Negative staining for different cytokeratin and melanoma markers can be helpful in differentiating it from carcinomas and melanoma. The only curative treatment for MPNST is complete excision, leaving patients with recurrent, refractory, and metastatic cases to be encouraged for enrollment in clinical trials. The 5-year survival rates for patients with MPNST reported in the literature range from 20% to 50%.²⁰

The Diagnosis: Hybrid Schwannoma-Perineurioma

Hybrid nerve sheath tumors are rare entities that display features of more than one nerve sheath tumor such as neurofibromas, schwannomas, and perineuriomas.¹ These tumors often are found in the dermis or subcutaneous tissue of the extremities and abdomen²; however, cases of hybrid peripheral nerve sheath tumors have been reported in many anatomical locations without a gender predilection.³ The most common type of hybrid nerve sheath tumor is a schwannoma-perineurioma.^3,4 Histologically, they are well-circumscribed lesions composed of both spindled Schwann cells with plump nuclei and spindled perineural cells with more elongated thin nuclei.⁵ Although the Schwann cell component tends to predominate, the 2 cell populations interdigitate, making it challenging to definitively distinguish them by hematoxylin and eosin staining alone.4 However, immunohistochemical (IHC) staining can be used to help distinguish the 2 separate cell populations. Staining for S-100 and SRY-box transcription factor 10 (SOX-10) will be positive in the Schwann cell component, and staining for epithelial membrane antigen, Claudin-1, or glucose transporter-1 (Figure 1) will be positive in the perineural component. Other hybrid forms of benign nerve sheath tumors include neurofibroma-schwannoma and neurofibromaperineurioma.⁴ Neurofibroma-schwannomas usually have a schwannoma component containing Antoni A areas with palisading Verocay bodies. The neurofibroma cells typically have wavy elongated nuclei, fibroblasts, and mucinous myxoid material.³ Neurofibroma-perineurioma is the least common hybrid tumor. These hybrid tumors have a plexiform neurofibroma appearance with areas of perineural differentiation, which can be difficult to identify on routine histology and typically will require IHC staining to appreciate. The neurofibroma component will stain positive for S-100 and negative for markers of perineural differentiation, including epithelial membrane antigen, glucose transporter-1, and Claudin-1.³ Although schwannoma-perineuriomas are benign sporadic tumors not associated with neurofibromatosis, neurofibromaschwannomas are associated with neurofibromatosis types 1 and 2 (NF1 and NF2). Neurofibroma-perineurioma tumors usually are associated with only NF1.^3,6

Schwannomas typically present in middle-aged patients as tumors located on flexor surfaces.⁷ Although perineural cells can be seen at the periphery of a schwannoma forming a capsule, they do not interdigitate between the Schwann cells. Schwannomas are composed almost entirely of well-differentiated Schwann cells.^1,4,8 Schwannomas classically are well-circumscribed, encapsulated, biphasic lesions with alternating compact areas (Antoni A) and loosely arranged areas (Antoni B). The spindled cells occasionally may display nuclear palisading within the Antoni A areas, known as Verocay bodies (Figure 2). Antoni B areas are more disorganized and hypocellular with variable macrophage infiltrate.^1,4,8 The Schwann cells predominantly will have bland cytologic features, but scattered areas of degenerative nuclear atypia (also known as ancient change) may be present.⁴ Multiple schwannomas are associated with NF2 gene mutations and loss of merlin protein.8 There are different subtypes of schwannomas, including cellular and plexiform schwannomas.⁴ Because schwannomas are benign nerve sheath lesions, treatment typically consists of excision with careful dissection around the involved nerve.⁹

Neurofibromas are the most common peripheral nerve sheath tumors of the skin with no notable anatomic prediction, though one study found them to be more prevalent in the upper extremities.¹⁰ They typically present as sporadic solitary lesions, but multiple lesions may appear as superficial pedunculated growths that present in those aged 20 to 30 years.¹¹ Microscopically, neurofibromas typically are not well circumscribed and have an infiltrative growth pattern. Neurofibromas are composed of cytologically bland spindled Schwann cells with thin wavy nuclei in a variable myxoid stroma (Figure 3). In addition to Schwann cells, neurofibromas contain other cell components, including fibroblasts, mast cells, perineurial-like cells, and residual axons.⁴ Neurofibromas typically are located in the dermis but may extend into the subcutaneous tissue. Clinically, the overlying skin may show hyperpigmentation.8 Neurofibromas can be localized, diffuse, or plexiform, with the majority being localized. Diffuse neurofibromas clinically have a raised plaque appearance. Treatment is unnecessary because these lesions are benign.⁷

Desmoplastic melanoma (DM) is another diagnosis in the differential for this case. Patients with DM are older compared to non-DM melanoma patients, with a male predilection.¹² Desmoplastic melanomas are more likely to be located on the head and neck. In approximately one-third of cases, no in situ component will be identified, leading to confusion of the dermal lesion as a neural lesion or an area of scar formation. Microscopically, DM presents as a variable cellular infiltrative tumor composed of spindle cells with varying degrees of nuclear atypia. The spindled melanocytes are within a collagenous (desmoplastic) stroma (Figure 4).¹³ Desmoplastic melanoma has been described with a low mitotic index, leading to misdiagnosis with benign spindle cell neoplasms.¹⁴ The spindle cells should be positive for S-100 and SOX-10 with IHC staining. Unlike other melanomas, human melanoma black 45 and Melan-A often are negative or only focally positive. Treatment of DM is similar to non-DM in that wide local excision usually is employed. A systematic review evaluating sentinel lymph node biopsy (SLNB) recommended consideration of SLNB in mixed DM but not for pure DM, as rates of positive SLNB were much lower in the latter.¹⁵

Patients with malignant peripheral nerve sheath tumor (MPNST) usually present with an enlarging mass, pain, or neurologic symptoms. Most cases of MPNST are located on the trunk or extremities.¹⁶ Plexiform neurofibromas, especially in adults with NF1, have the potential to transform into an MPNST.⁴ In fact, MPNST is the most common malignancy in patients with NF1.¹⁷ Pediatric cancer survivors also are predisposed to MPNST, with a 40-fold increase in incidence compared to the general population.¹⁸ Transformation from schwannoma to MPNST is rare but has been reported.⁸ Histologically, spindle cells easily can be appreciated with a fasciculated growth pattern (Figure 5). Mitotic activity and tumor necrosis may be present. Diagnosis of these tumors historically has been challenging, though recent research has identified inactivation of polycomb repressive complex 2 in 70% to 90% of MPNSTs. Because of polycomb repressive complex 2 inactivation, there is loss of stone H3K27 trimethylation that can be capitalized on for MPNST diagnosis.¹⁹ Negative IHC staining for H3K27 trimethylation has been found to be highly specific for MPNST. Negative staining for different cytokeratin and melanoma markers can be helpful in differentiating it from carcinomas and melanoma. The only curative treatment for MPNST is complete excision, leaving patients with recurrent, refractory, and metastatic cases to be encouraged for enrollment in clinical trials. The 5-year survival rates for patients with MPNST reported in the literature range from 20% to 50%.²⁰

The Diagnosis: Hybrid Schwannoma-Perineurioma

Hybrid nerve sheath tumors are rare entities that display features of more than one nerve sheath tumor such as neurofibromas, schwannomas, and perineuriomas.¹ These tumors often are found in the dermis or subcutaneous tissue of the extremities and abdomen²; however, cases of hybrid peripheral nerve sheath tumors have been reported in many anatomical locations without a gender predilection.³ The most common type of hybrid nerve sheath tumor is a schwannoma-perineurioma.^3,4 Histologically, they are well-circumscribed lesions composed of both spindled Schwann cells with plump nuclei and spindled perineural cells with more elongated thin nuclei.⁵ Although the Schwann cell component tends to predominate, the 2 cell populations interdigitate, making it challenging to definitively distinguish them by hematoxylin and eosin staining alone.4 However, immunohistochemical (IHC) staining can be used to help distinguish the 2 separate cell populations. Staining for S-100 and SRY-box transcription factor 10 (SOX-10) will be positive in the Schwann cell component, and staining for epithelial membrane antigen, Claudin-1, or glucose transporter-1 (Figure 1) will be positive in the perineural component. Other hybrid forms of benign nerve sheath tumors include neurofibroma-schwannoma and neurofibromaperineurioma.⁴ Neurofibroma-schwannomas usually have a schwannoma component containing Antoni A areas with palisading Verocay bodies. The neurofibroma cells typically have wavy elongated nuclei, fibroblasts, and mucinous myxoid material.³ Neurofibroma-perineurioma is the least common hybrid tumor. These hybrid tumors have a plexiform neurofibroma appearance with areas of perineural differentiation, which can be difficult to identify on routine histology and typically will require IHC staining to appreciate. The neurofibroma component will stain positive for S-100 and negative for markers of perineural differentiation, including epithelial membrane antigen, glucose transporter-1, and Claudin-1.³ Although schwannoma-perineuriomas are benign sporadic tumors not associated with neurofibromatosis, neurofibromaschwannomas are associated with neurofibromatosis types 1 and 2 (NF1 and NF2). Neurofibroma-perineurioma tumors usually are associated with only NF1.^3,6

Schwannomas typically present in middle-aged patients as tumors located on flexor surfaces.⁷ Although perineural cells can be seen at the periphery of a schwannoma forming a capsule, they do not interdigitate between the Schwann cells. Schwannomas are composed almost entirely of well-differentiated Schwann cells.^1,4,8 Schwannomas classically are well-circumscribed, encapsulated, biphasic lesions with alternating compact areas (Antoni A) and loosely arranged areas (Antoni B). The spindled cells occasionally may display nuclear palisading within the Antoni A areas, known as Verocay bodies (Figure 2). Antoni B areas are more disorganized and hypocellular with variable macrophage infiltrate.^1,4,8 The Schwann cells predominantly will have bland cytologic features, but scattered areas of degenerative nuclear atypia (also known as ancient change) may be present.⁴ Multiple schwannomas are associated with NF2 gene mutations and loss of merlin protein.8 There are different subtypes of schwannomas, including cellular and plexiform schwannomas.⁴ Because schwannomas are benign nerve sheath lesions, treatment typically consists of excision with careful dissection around the involved nerve.⁹

Neurofibromas are the most common peripheral nerve sheath tumors of the skin with no notable anatomic prediction, though one study found them to be more prevalent in the upper extremities.¹⁰ They typically present as sporadic solitary lesions, but multiple lesions may appear as superficial pedunculated growths that present in those aged 20 to 30 years.¹¹ Microscopically, neurofibromas typically are not well circumscribed and have an infiltrative growth pattern. Neurofibromas are composed of cytologically bland spindled Schwann cells with thin wavy nuclei in a variable myxoid stroma (Figure 3). In addition to Schwann cells, neurofibromas contain other cell components, including fibroblasts, mast cells, perineurial-like cells, and residual axons.⁴ Neurofibromas typically are located in the dermis but may extend into the subcutaneous tissue. Clinically, the overlying skin may show hyperpigmentation.8 Neurofibromas can be localized, diffuse, or plexiform, with the majority being localized. Diffuse neurofibromas clinically have a raised plaque appearance. Treatment is unnecessary because these lesions are benign.⁷

Desmoplastic melanoma (DM) is another diagnosis in the differential for this case. Patients with DM are older compared to non-DM melanoma patients, with a male predilection.¹² Desmoplastic melanomas are more likely to be located on the head and neck. In approximately one-third of cases, no in situ component will be identified, leading to confusion of the dermal lesion as a neural lesion or an area of scar formation. Microscopically, DM presents as a variable cellular infiltrative tumor composed of spindle cells with varying degrees of nuclear atypia. The spindled melanocytes are within a collagenous (desmoplastic) stroma (Figure 4).¹³ Desmoplastic melanoma has been described with a low mitotic index, leading to misdiagnosis with benign spindle cell neoplasms.¹⁴ The spindle cells should be positive for S-100 and SOX-10 with IHC staining. Unlike other melanomas, human melanoma black 45 and Melan-A often are negative or only focally positive. Treatment of DM is similar to non-DM in that wide local excision usually is employed. A systematic review evaluating sentinel lymph node biopsy (SLNB) recommended consideration of SLNB in mixed DM but not for pure DM, as rates of positive SLNB were much lower in the latter.¹⁵

Patients with malignant peripheral nerve sheath tumor (MPNST) usually present with an enlarging mass, pain, or neurologic symptoms. Most cases of MPNST are located on the trunk or extremities.¹⁶ Plexiform neurofibromas, especially in adults with NF1, have the potential to transform into an MPNST.⁴ In fact, MPNST is the most common malignancy in patients with NF1.¹⁷ Pediatric cancer survivors also are predisposed to MPNST, with a 40-fold increase in incidence compared to the general population.¹⁸ Transformation from schwannoma to MPNST is rare but has been reported.⁸ Histologically, spindle cells easily can be appreciated with a fasciculated growth pattern (Figure 5). Mitotic activity and tumor necrosis may be present. Diagnosis of these tumors historically has been challenging, though recent research has identified inactivation of polycomb repressive complex 2 in 70% to 90% of MPNSTs. Because of polycomb repressive complex 2 inactivation, there is loss of stone H3K27 trimethylation that can be capitalized on for MPNST diagnosis.¹⁹ Negative IHC staining for H3K27 trimethylation has been found to be highly specific for MPNST. Negative staining for different cytokeratin and melanoma markers can be helpful in differentiating it from carcinomas and melanoma. The only curative treatment for MPNST is complete excision, leaving patients with recurrent, refractory, and metastatic cases to be encouraged for enrollment in clinical trials. The 5-year survival rates for patients with MPNST reported in the literature range from 20% to 50%.²⁰

The Diagnosis: Tuberous Xanthoma

The skin biopsy revealed a nodular collection of foam cells (quiz image [bottom]). Tuberous xanthoma was the most likely diagnosis based on the patient’s history as well as the clinical and histologic findings. Tuberous xanthomas are flat or elevated nodules in the dermis and subcutaneous tissue, commonly occurring on the skin over the joints.¹ Smaller nodules and papules often are referred to as tuberoeruptive xanthomas and exist on a continuum with the larger tuberous xanthomas. All xanthomas appear histologically similar, with collections of foam cells present within the dermis.² Foam cells form when serum lipoproteins diffuse through capillary walls, deposit in the skin or tendons, and are scavenged by monocytes.3 Tuberous xanthomas, along with tendinous, eruptive, and planar xanthomas, are the most likely to be associated with hyperlipidemia.⁴ They may indicate an underlying disorder of lipid metabolism, such as familial hypercholesterolemia.^1,3 This is the most common cause of inheritable cardiovascular disease, with a prevalence of approximately 1:250.² Premature cardiovascular disease risk increases 2 to 4 times in patients with familial hypercholesterolemia and tendinous xanthomas,¹ illustrating that recognition of cutaneous lesions can lead to earlier diagnosis and prevention of patient morbidity and mortality.

Juvenile xanthogranuloma typically presents as smooth yellow papules or nodules on the head and neck, with a characteristic “setting-sun” appearance (ie, yellow center with an erythematous halo) on dermoscopy.⁵ Histologically, juvenile xanthogranulomas are composed of foam cells and a mixed lymphohistiocytic infiltrate with eosinophils within the dermis. Giant cells with a ring of nuclei surrounded by cytoplasm containing lipid vacuoles (called Touton giant cells) are characteristic (Figure 1). In contrast to tuberous xanthomas, juvenile xanthogranulomas often present within the first year of life.⁶

Keloid scars are more prevalent in patients with skin of color. They are characterized by eosinophilic keloidal collagen with a whorled proliferation of fibroblasts on histology (Figure 2).⁷ They occur spontaneously or at sites of injury and present as bluish-red or flesh-colored firm papules or nodules.⁸ In our patient, keloid scars were an unlikely diagnosis due to the lack of trauma and the absence of keloidal collagen on histology.

Necrobiosis lipoidica diabeticorum typically presents as an erythematous, yellow-brown, circular plaque on the anterior lower leg in patients with diabetes mellitus; it rarely occurs in children.⁹ Microscopy shows palisaded granulomas surrounding necrobiotic collagen arranged horizontally in a layer cake–like fashion (Figure 3).^9,10 The etiology of necrobiosis lipoidica diabeticorum currently is unknown, though immune complex deposition may contribute to its pathology. It has been associated with type 1 diabetes mellitus, though severity of the lesions is not associated with extent of glycemic control.¹⁰

Rosai-Dorfman disease is an uncommon disorder characterized by a proliferation of histiocytes that most often presents as bilateral cervical lymphadenopathy in children and young adults but rarely can present with cutaneous lesions when extranodal involvement is present.^11,12 The cutaneous form most commonly presents as red papules or nodules. On histology, the lesions exhibit a nodular dermal proliferation of histiocytes and smaller lymphocytoid cells with a marbled or starry sky–like appearance on low power (Figure 4). On higher magnification, the characteristic finding of emperipolesis can be seen.11 On immunohistochemistry, the histiocytes stain positively for CD68 and S-100. Although the pathogenesis currently is unknown, evidence of clonality indicates the disease may be related to a neoplastic process.¹²

The Diagnosis: Tuberous Xanthoma

The skin biopsy revealed a nodular collection of foam cells (quiz image [bottom]). Tuberous xanthoma was the most likely diagnosis based on the patient’s history as well as the clinical and histologic findings. Tuberous xanthomas are flat or elevated nodules in the dermis and subcutaneous tissue, commonly occurring on the skin over the joints.¹ Smaller nodules and papules often are referred to as tuberoeruptive xanthomas and exist on a continuum with the larger tuberous xanthomas. All xanthomas appear histologically similar, with collections of foam cells present within the dermis.² Foam cells form when serum lipoproteins diffuse through capillary walls, deposit in the skin or tendons, and are scavenged by monocytes.3 Tuberous xanthomas, along with tendinous, eruptive, and planar xanthomas, are the most likely to be associated with hyperlipidemia.⁴ They may indicate an underlying disorder of lipid metabolism, such as familial hypercholesterolemia.^1,3 This is the most common cause of inheritable cardiovascular disease, with a prevalence of approximately 1:250.² Premature cardiovascular disease risk increases 2 to 4 times in patients with familial hypercholesterolemia and tendinous xanthomas,¹ illustrating that recognition of cutaneous lesions can lead to earlier diagnosis and prevention of patient morbidity and mortality.

Juvenile xanthogranuloma typically presents as smooth yellow papules or nodules on the head and neck, with a characteristic “setting-sun” appearance (ie, yellow center with an erythematous halo) on dermoscopy.⁵ Histologically, juvenile xanthogranulomas are composed of foam cells and a mixed lymphohistiocytic infiltrate with eosinophils within the dermis. Giant cells with a ring of nuclei surrounded by cytoplasm containing lipid vacuoles (called Touton giant cells) are characteristic (Figure 1). In contrast to tuberous xanthomas, juvenile xanthogranulomas often present within the first year of life.⁶

Keloid scars are more prevalent in patients with skin of color. They are characterized by eosinophilic keloidal collagen with a whorled proliferation of fibroblasts on histology (Figure 2).⁷ They occur spontaneously or at sites of injury and present as bluish-red or flesh-colored firm papules or nodules.⁸ In our patient, keloid scars were an unlikely diagnosis due to the lack of trauma and the absence of keloidal collagen on histology.

Necrobiosis lipoidica diabeticorum typically presents as an erythematous, yellow-brown, circular plaque on the anterior lower leg in patients with diabetes mellitus; it rarely occurs in children.⁹ Microscopy shows palisaded granulomas surrounding necrobiotic collagen arranged horizontally in a layer cake–like fashion (Figure 3).^9,10 The etiology of necrobiosis lipoidica diabeticorum currently is unknown, though immune complex deposition may contribute to its pathology. It has been associated with type 1 diabetes mellitus, though severity of the lesions is not associated with extent of glycemic control.¹⁰

Rosai-Dorfman disease is an uncommon disorder characterized by a proliferation of histiocytes that most often presents as bilateral cervical lymphadenopathy in children and young adults but rarely can present with cutaneous lesions when extranodal involvement is present.^11,12 The cutaneous form most commonly presents as red papules or nodules. On histology, the lesions exhibit a nodular dermal proliferation of histiocytes and smaller lymphocytoid cells with a marbled or starry sky–like appearance on low power (Figure 4). On higher magnification, the characteristic finding of emperipolesis can be seen.11 On immunohistochemistry, the histiocytes stain positively for CD68 and S-100. Although the pathogenesis currently is unknown, evidence of clonality indicates the disease may be related to a neoplastic process.¹²

The Diagnosis: Tuberous Xanthoma

The skin biopsy revealed a nodular collection of foam cells (quiz image [bottom]). Tuberous xanthoma was the most likely diagnosis based on the patient’s history as well as the clinical and histologic findings. Tuberous xanthomas are flat or elevated nodules in the dermis and subcutaneous tissue, commonly occurring on the skin over the joints.¹ Smaller nodules and papules often are referred to as tuberoeruptive xanthomas and exist on a continuum with the larger tuberous xanthomas. All xanthomas appear histologically similar, with collections of foam cells present within the dermis.² Foam cells form when serum lipoproteins diffuse through capillary walls, deposit in the skin or tendons, and are scavenged by monocytes.3 Tuberous xanthomas, along with tendinous, eruptive, and planar xanthomas, are the most likely to be associated with hyperlipidemia.⁴ They may indicate an underlying disorder of lipid metabolism, such as familial hypercholesterolemia.^1,3 This is the most common cause of inheritable cardiovascular disease, with a prevalence of approximately 1:250.² Premature cardiovascular disease risk increases 2 to 4 times in patients with familial hypercholesterolemia and tendinous xanthomas,¹ illustrating that recognition of cutaneous lesions can lead to earlier diagnosis and prevention of patient morbidity and mortality.

Juvenile xanthogranuloma typically presents as smooth yellow papules or nodules on the head and neck, with a characteristic “setting-sun” appearance (ie, yellow center with an erythematous halo) on dermoscopy.⁵ Histologically, juvenile xanthogranulomas are composed of foam cells and a mixed lymphohistiocytic infiltrate with eosinophils within the dermis. Giant cells with a ring of nuclei surrounded by cytoplasm containing lipid vacuoles (called Touton giant cells) are characteristic (Figure 1). In contrast to tuberous xanthomas, juvenile xanthogranulomas often present within the first year of life.⁶

Keloid scars are more prevalent in patients with skin of color. They are characterized by eosinophilic keloidal collagen with a whorled proliferation of fibroblasts on histology (Figure 2).⁷ They occur spontaneously or at sites of injury and present as bluish-red or flesh-colored firm papules or nodules.⁸ In our patient, keloid scars were an unlikely diagnosis due to the lack of trauma and the absence of keloidal collagen on histology.

Necrobiosis lipoidica diabeticorum typically presents as an erythematous, yellow-brown, circular plaque on the anterior lower leg in patients with diabetes mellitus; it rarely occurs in children.⁹ Microscopy shows palisaded granulomas surrounding necrobiotic collagen arranged horizontally in a layer cake–like fashion (Figure 3).^9,10 The etiology of necrobiosis lipoidica diabeticorum currently is unknown, though immune complex deposition may contribute to its pathology. It has been associated with type 1 diabetes mellitus, though severity of the lesions is not associated with extent of glycemic control.¹⁰

Rosai-Dorfman disease is an uncommon disorder characterized by a proliferation of histiocytes that most often presents as bilateral cervical lymphadenopathy in children and young adults but rarely can present with cutaneous lesions when extranodal involvement is present.^11,12 The cutaneous form most commonly presents as red papules or nodules. On histology, the lesions exhibit a nodular dermal proliferation of histiocytes and smaller lymphocytoid cells with a marbled or starry sky–like appearance on low power (Figure 4). On higher magnification, the characteristic finding of emperipolesis can be seen.11 On immunohistochemistry, the histiocytes stain positively for CD68 and S-100. Although the pathogenesis currently is unknown, evidence of clonality indicates the disease may be related to a neoplastic process.¹²

The Diagnosis: Metastatic Carcinoid Tumor

Carcinoid tumors are derived from neuroendocrine cell compartments and generally arise in the gastrointestinal tract, with a quarter of carcinoids arising in the small bowel.¹ Carcinoid tumors have an incidence of approximately 2 to 5 per 100,000 patients.² Metastasis of carcinoids is approximately 31.2% to 46.7%.¹ Metastasis to the skin is uncommon; we present a rare case of a carcinoid tumor of the terminal ileum with metastasis to the scalp.

Unlike our patient, most patients with carcinoid tumors have an indolent clinical course. The most common cutaneous symptom is flushing, which occurs in 75% of patients.³ Secreted vasoactive peptides such as serotonin may cause other symptoms such as tachycardia, diarrhea, and bronchospasm; together, these symptoms comprise carcinoid syndrome. Carcinoid syndrome requires metastasis of the tumor to the liver or a site outside of the gastrointestinal tract because the liver will metabolize the secreted serotonin. However, even in patients with liver metastasis, carcinoid syndrome only occurs in approximately 10% of patients.⁴ Common skin findings of carcinoid syndrome include pellagralike dermatitis, flushing, and sclerodermalike changes.⁵ Our patient experienced several episodes of presyncope with symptoms of dyspnea, lightheadedness, and flushing but did not have bronchospasm or recurrent diarrhea. Intramuscular octreotide improved some symptoms.

The scalp accounts for approximately 15% of cutaneous metastases, the most common being from the lung, renal, and breast cancers.⁶ Cutaneous metastases of carcinoid tumors are rare. A PubMed search of articles indexed for MEDLINE using the terms metastatic AND [carcinoid OR neuroendocrine] tumors AND [skin OR cutaneous] revealed 47 cases.^7-11 Similar to other skin metastases, cutaneous metastases of carcinoid tumors commonly present as firm erythematous nodules of varying sizes that may be asymptomatic, tender, or pruritic (Figure 1). Cases of carcinoid tumors with cutaneous metastasis as the initial and only presenting sign are exceedingly rare.¹²

Histology of carcinoid tumors reveals a dermal neoplasm composed of loosely cohesive, mildly atypical, polygonal cells with salt-and-pepper chromatin and eosinophilic cytoplasm, which are similar findings to the primary tumor. The cells may grow in the typical trabecular or organoid neuroendocrine pattern or exhibit a pseudoglandular growth pattern with prominent vessels (quiz image, top).¹² Positive chromogranin and synaptophysin immunostaining are the most common and reliable markers used for the diagnosis of carcinoid tumors.

An important histopathologic differential diagnosis is the aggressive Merkel cell carcinoma, which also demonstrates homogenous salt-and-pepper chromatin but exhibits a higher mitotic rate and positive cytokeratin 20 staining (Figure 2).¹³ Basal cell carcinoma (BCC) also may display similar features, including a blue tumor at scanning magnification and nodular or infiltrative growth patterns. The cell morphology of BCC is characterized by islands of basaloid cells with minimal cytoplasm and frequent apoptosis, connecting to the epidermis with peripheral palisading, retraction artifact, and a myxoid stroma; BCC lacks the salt-and-pepper chromatin commonly seen in carcinoid tumors (Figure 3). Basal cell carcinoma is characterized by positive BerEP4 (epithelial cell adhesion molecule immunostain), cytokeratin 5/6, and cytokeratin 14 uptake. Cytokeratin 20, often used to diagnose Merkel cell carcinoma, is negative in BCC. Chromogranin and synaptophysin occasionally may be positive in BCC.¹⁴

The superficial Ewing sarcoma family of tumors also may be included in the differential diagnosis of small round cell tumors of the skin, but they are very rare. These tumors possess strong positive membranous staining of cytokeratin 99 and also can stain positively for synaptophysin and chromogranin.¹⁵ Epithelial membrane antigen, which is negative in Ewing sarcomas, is positive in carcinoid tumors.¹⁶ Neuroendocrine tumors of all sites share similar basic morphologic patterns, and multiple primary tumors should be considered, including small cell lung carcinoma (Figure 4).^17,18 Red granulations and true glandular lumina typically are not seen in the lungs but are common in gastrointestinal carcinoids.¹⁸ Regarding immunohistochemistry, TTF-1 is negative and CDX2 is positive in gastroenteropancreatic carcinoids, suggesting that these 2 markers can help distinguish carcinoids of unknown primary origin.¹⁹

Metastases in carcinoid tumors are common, with one study noting that the highest frequency of small intestinal metastases was from the ileal subset.²⁰ At the time of diagnosis, 58% to 64% of patients with small intestine carcinoid tumors already had nonlocalized disease, with frequent sites being the lymph nodes (89.8%), liver (44.1%), lungs (13.6%), and peritoneum (13.6%). Regional and distant metastases are associated with substantially worse prognoses, with survival rates of 71.7% and 38.5%, respectively.¹ Treatment of symptomatic unresectable disease focuses on symptomatic management with somatostatin analogs that also control tumor growth.²¹

We present a rare case of scalp metastasis of a carcinoid tumor of the terminal ileum. Distant metastasis is associated with poorer prognosis and should be considered in patients with a known history of a carcinoid tumor.

Acknowledgment—We would like to acknowledge the Research Histology and Tissue Imaging Core at University of Illinois Chicago Research Resources Center for the immunohistochemistry studies.

The Diagnosis: Metastatic Carcinoid Tumor

Carcinoid tumors are derived from neuroendocrine cell compartments and generally arise in the gastrointestinal tract, with a quarter of carcinoids arising in the small bowel.¹ Carcinoid tumors have an incidence of approximately 2 to 5 per 100,000 patients.² Metastasis of carcinoids is approximately 31.2% to 46.7%.¹ Metastasis to the skin is uncommon; we present a rare case of a carcinoid tumor of the terminal ileum with metastasis to the scalp.

Unlike our patient, most patients with carcinoid tumors have an indolent clinical course. The most common cutaneous symptom is flushing, which occurs in 75% of patients.³ Secreted vasoactive peptides such as serotonin may cause other symptoms such as tachycardia, diarrhea, and bronchospasm; together, these symptoms comprise carcinoid syndrome. Carcinoid syndrome requires metastasis of the tumor to the liver or a site outside of the gastrointestinal tract because the liver will metabolize the secreted serotonin. However, even in patients with liver metastasis, carcinoid syndrome only occurs in approximately 10% of patients.⁴ Common skin findings of carcinoid syndrome include pellagralike dermatitis, flushing, and sclerodermalike changes.⁵ Our patient experienced several episodes of presyncope with symptoms of dyspnea, lightheadedness, and flushing but did not have bronchospasm or recurrent diarrhea. Intramuscular octreotide improved some symptoms.

The scalp accounts for approximately 15% of cutaneous metastases, the most common being from the lung, renal, and breast cancers.⁶ Cutaneous metastases of carcinoid tumors are rare. A PubMed search of articles indexed for MEDLINE using the terms metastatic AND [carcinoid OR neuroendocrine] tumors AND [skin OR cutaneous] revealed 47 cases.^7-11 Similar to other skin metastases, cutaneous metastases of carcinoid tumors commonly present as firm erythematous nodules of varying sizes that may be asymptomatic, tender, or pruritic (Figure 1). Cases of carcinoid tumors with cutaneous metastasis as the initial and only presenting sign are exceedingly rare.¹²

Histology of carcinoid tumors reveals a dermal neoplasm composed of loosely cohesive, mildly atypical, polygonal cells with salt-and-pepper chromatin and eosinophilic cytoplasm, which are similar findings to the primary tumor. The cells may grow in the typical trabecular or organoid neuroendocrine pattern or exhibit a pseudoglandular growth pattern with prominent vessels (quiz image, top).¹² Positive chromogranin and synaptophysin immunostaining are the most common and reliable markers used for the diagnosis of carcinoid tumors.

An important histopathologic differential diagnosis is the aggressive Merkel cell carcinoma, which also demonstrates homogenous salt-and-pepper chromatin but exhibits a higher mitotic rate and positive cytokeratin 20 staining (Figure 2).¹³ Basal cell carcinoma (BCC) also may display similar features, including a blue tumor at scanning magnification and nodular or infiltrative growth patterns. The cell morphology of BCC is characterized by islands of basaloid cells with minimal cytoplasm and frequent apoptosis, connecting to the epidermis with peripheral palisading, retraction artifact, and a myxoid stroma; BCC lacks the salt-and-pepper chromatin commonly seen in carcinoid tumors (Figure 3). Basal cell carcinoma is characterized by positive BerEP4 (epithelial cell adhesion molecule immunostain), cytokeratin 5/6, and cytokeratin 14 uptake. Cytokeratin 20, often used to diagnose Merkel cell carcinoma, is negative in BCC. Chromogranin and synaptophysin occasionally may be positive in BCC.¹⁴

The superficial Ewing sarcoma family of tumors also may be included in the differential diagnosis of small round cell tumors of the skin, but they are very rare. These tumors possess strong positive membranous staining of cytokeratin 99 and also can stain positively for synaptophysin and chromogranin.¹⁵ Epithelial membrane antigen, which is negative in Ewing sarcomas, is positive in carcinoid tumors.¹⁶ Neuroendocrine tumors of all sites share similar basic morphologic patterns, and multiple primary tumors should be considered, including small cell lung carcinoma (Figure 4).^17,18 Red granulations and true glandular lumina typically are not seen in the lungs but are common in gastrointestinal carcinoids.¹⁸ Regarding immunohistochemistry, TTF-1 is negative and CDX2 is positive in gastroenteropancreatic carcinoids, suggesting that these 2 markers can help distinguish carcinoids of unknown primary origin.¹⁹

Metastases in carcinoid tumors are common, with one study noting that the highest frequency of small intestinal metastases was from the ileal subset.²⁰ At the time of diagnosis, 58% to 64% of patients with small intestine carcinoid tumors already had nonlocalized disease, with frequent sites being the lymph nodes (89.8%), liver (44.1%), lungs (13.6%), and peritoneum (13.6%). Regional and distant metastases are associated with substantially worse prognoses, with survival rates of 71.7% and 38.5%, respectively.¹ Treatment of symptomatic unresectable disease focuses on symptomatic management with somatostatin analogs that also control tumor growth.²¹

We present a rare case of scalp metastasis of a carcinoid tumor of the terminal ileum. Distant metastasis is associated with poorer prognosis and should be considered in patients with a known history of a carcinoid tumor.

Acknowledgment—We would like to acknowledge the Research Histology and Tissue Imaging Core at University of Illinois Chicago Research Resources Center for the immunohistochemistry studies.

The Diagnosis: Metastatic Carcinoid Tumor

Carcinoid tumors are derived from neuroendocrine cell compartments and generally arise in the gastrointestinal tract, with a quarter of carcinoids arising in the small bowel.¹ Carcinoid tumors have an incidence of approximately 2 to 5 per 100,000 patients.² Metastasis of carcinoids is approximately 31.2% to 46.7%.¹ Metastasis to the skin is uncommon; we present a rare case of a carcinoid tumor of the terminal ileum with metastasis to the scalp.

Unlike our patient, most patients with carcinoid tumors have an indolent clinical course. The most common cutaneous symptom is flushing, which occurs in 75% of patients.³ Secreted vasoactive peptides such as serotonin may cause other symptoms such as tachycardia, diarrhea, and bronchospasm; together, these symptoms comprise carcinoid syndrome. Carcinoid syndrome requires metastasis of the tumor to the liver or a site outside of the gastrointestinal tract because the liver will metabolize the secreted serotonin. However, even in patients with liver metastasis, carcinoid syndrome only occurs in approximately 10% of patients.⁴ Common skin findings of carcinoid syndrome include pellagralike dermatitis, flushing, and sclerodermalike changes.⁵ Our patient experienced several episodes of presyncope with symptoms of dyspnea, lightheadedness, and flushing but did not have bronchospasm or recurrent diarrhea. Intramuscular octreotide improved some symptoms.

The scalp accounts for approximately 15% of cutaneous metastases, the most common being from the lung, renal, and breast cancers.⁶ Cutaneous metastases of carcinoid tumors are rare. A PubMed search of articles indexed for MEDLINE using the terms metastatic AND [carcinoid OR neuroendocrine] tumors AND [skin OR cutaneous] revealed 47 cases.^7-11 Similar to other skin metastases, cutaneous metastases of carcinoid tumors commonly present as firm erythematous nodules of varying sizes that may be asymptomatic, tender, or pruritic (Figure 1). Cases of carcinoid tumors with cutaneous metastasis as the initial and only presenting sign are exceedingly rare.¹²

Histology of carcinoid tumors reveals a dermal neoplasm composed of loosely cohesive, mildly atypical, polygonal cells with salt-and-pepper chromatin and eosinophilic cytoplasm, which are similar findings to the primary tumor. The cells may grow in the typical trabecular or organoid neuroendocrine pattern or exhibit a pseudoglandular growth pattern with prominent vessels (quiz image, top).¹² Positive chromogranin and synaptophysin immunostaining are the most common and reliable markers used for the diagnosis of carcinoid tumors.

An important histopathologic differential diagnosis is the aggressive Merkel cell carcinoma, which also demonstrates homogenous salt-and-pepper chromatin but exhibits a higher mitotic rate and positive cytokeratin 20 staining (Figure 2).¹³ Basal cell carcinoma (BCC) also may display similar features, including a blue tumor at scanning magnification and nodular or infiltrative growth patterns. The cell morphology of BCC is characterized by islands of basaloid cells with minimal cytoplasm and frequent apoptosis, connecting to the epidermis with peripheral palisading, retraction artifact, and a myxoid stroma; BCC lacks the salt-and-pepper chromatin commonly seen in carcinoid tumors (Figure 3). Basal cell carcinoma is characterized by positive BerEP4 (epithelial cell adhesion molecule immunostain), cytokeratin 5/6, and cytokeratin 14 uptake. Cytokeratin 20, often used to diagnose Merkel cell carcinoma, is negative in BCC. Chromogranin and synaptophysin occasionally may be positive in BCC.¹⁴

The superficial Ewing sarcoma family of tumors also may be included in the differential diagnosis of small round cell tumors of the skin, but they are very rare. These tumors possess strong positive membranous staining of cytokeratin 99 and also can stain positively for synaptophysin and chromogranin.¹⁵ Epithelial membrane antigen, which is negative in Ewing sarcomas, is positive in carcinoid tumors.¹⁶ Neuroendocrine tumors of all sites share similar basic morphologic patterns, and multiple primary tumors should be considered, including small cell lung carcinoma (Figure 4).^17,18 Red granulations and true glandular lumina typically are not seen in the lungs but are common in gastrointestinal carcinoids.¹⁸ Regarding immunohistochemistry, TTF-1 is negative and CDX2 is positive in gastroenteropancreatic carcinoids, suggesting that these 2 markers can help distinguish carcinoids of unknown primary origin.¹⁹

Metastases in carcinoid tumors are common, with one study noting that the highest frequency of small intestinal metastases was from the ileal subset.²⁰ At the time of diagnosis, 58% to 64% of patients with small intestine carcinoid tumors already had nonlocalized disease, with frequent sites being the lymph nodes (89.8%), liver (44.1%), lungs (13.6%), and peritoneum (13.6%). Regional and distant metastases are associated with substantially worse prognoses, with survival rates of 71.7% and 38.5%, respectively.¹ Treatment of symptomatic unresectable disease focuses on symptomatic management with somatostatin analogs that also control tumor growth.²¹

We present a rare case of scalp metastasis of a carcinoid tumor of the terminal ileum. Distant metastasis is associated with poorer prognosis and should be considered in patients with a known history of a carcinoid tumor.

Acknowledgment—We would like to acknowledge the Research Histology and Tissue Imaging Core at University of Illinois Chicago Research Resources Center for the immunohistochemistry studies.

The Diagnosis: Cutaneous Lymphoid Hyperplasia

Cutaneous lymphoid hyperplasia (CLH)(also known as pseudolymphoma or lymphocytoma cutis) is a benign inflammatory condition that typically presents as a flesh-colored to erythematous or violaceous papule or nodule on the head or neck. Cutaneous lymphoid hyperplasia may arise in response to an antigenic stimulus, such as an insect bite, infectious agent (eg, Borrelia species), medication, or foreign body (eg, tattoos and piercings).^1,2 Given the benign nature and potential for spontaneous resolution, treatment is conservative; however, high-potency topical steroids, cryosurgery, surgical excision, or local radiotherapy may lead to improvement.³ Our patient was started on clobetasol ointment 0.05% and topical tacrolimus 0.1%. After 3 months of use, she reported lesion improvement, but a new lesion appeared on the nose superior to the original. She was offered a steroid injection and liquid nitrogen freezing but was lost to follow-up.

The histopathologic features of CLH are variable and can resemble a cutaneous B- or T-cell lymphoma (quiz images). If there is B-cell predominance, histopathology typically shows a dense dermal infiltrate of lymphocytes admixed with sparse histiocytes, eosinophils, and plasma cells. Multiple germinal-center phenotype lymphoid follicles also may be seen.⁴ Histopathology of T-cell–predominant CLH commonly shows CD4⁺ T helper lymphocytes admixed with CD8⁺ T cells within the dermis with possible papillary dermal edema and red cell extravasation.⁵ Immunohistochemical stains for CD3, CD4, CD8, and CD20 usually are positive. Most lymphocytes are CD3⁺ T cells. Admixed clusters of CD20⁺ B cells may be present.

Angiolymphoid hyperplasia with eosinophilia is a vascular tumor of the skin composed of endothelial cells and inflammatory cells.^6,7 The condition presents as single or multiple flesh-colored to purple papules most commonly on the face, scalp, and ears.⁸ Histologically, lesions appear as well-circumscribed collections of blood vessels composed of plump endothelial cells and an inflammatory infiltrate with lymphocytes and eosinophils (Figure 1A). Endothelial cells also may have an epithelioid appearance.⁷ Apparent fenestrations—holes within endothelial cells—may be present (Figure 1B). Surgical excision is the preferred treatment of angiolymphoid hyperplasia with eosinophilia. Success with laser and cryosurgery also has been reported.

Granuloma faciale typically presents as a solitary redbrown papule or plaque on the face. Linear arborizing vessels and dilated follicular openings with brown globules frequently are seen on dermoscopy.⁹ Although it may resemble CLH clinically, the histopathology of granuloma faciale is characterized by a perivascular and interstitial dermal infiltrate of numerous eosinophils admixed with lymphocytes, plasma cells, and neutrophils underneath a grenz zone (Figure 2).¹⁰ Leukocytoclastic vasculitis may be seen in early lesions, and lesions can show variable angiocentric fibrosis.¹¹ Treatment options include intralesional triamcinolone, topical steroids or calcineurin inhibitors, topical psoralen plus UVA, surgical excision, and laser therapy, but outcomes are variable.¹²

Leukemia cutis is a malignant hematopoietic skin infiltration that presents as multiple pink to red-brown, firm, hemorrhagic papules most frequently involving the head, neck, and trunk.¹³ Rarely, lesions of leukemia cutis may present as ulcers or bullae. Most lesions occur at presentation of systemic leukemia or in the setting of established leukemia. The cutaneous involvement portends a poor prognosis, strongly correlating with additional extramedullary leukemic involvement.¹⁴ Histologic features vary based on the specific type of leukemia (eg, acute myelogenous leukemia). Generally, neoplastic infiltration of the dermis and subcutaneous tissue in a nodular, diffuse, perivascular, or interstitial pattern is seen (Figure 3).¹⁵ Leukemia cutis typically resolves after successful treatment of the underlying leukemia.

Mycosis fungoides (MF) is the most common type of cutaneous T-cell lymphoma. In its early stages, MF presents as erythematous, brown, scaly patches and plaques. With progression to the tumor stage of disease, clonal expansion of CD4⁺ T cells leads to the development of purple papules and nodules.¹⁶ Microscopic findings of MF are dependent on the stage of disease. Early patch lesions show superficial or lichenoid lymphocytic infiltration of the epidermal basal layer.¹⁷ In the plaque stage, dermal infiltrates and epidermotropism become more pronounced, with increased atypical lymphocytes with cerebriform nuclei and interspersed inflammatory cells (Figure 4). In the tumor stage, lymphocytic infiltrates may involve the entirety of the dermis or extend into the subcutaneous tissue, and malignant cells become larger in size.¹⁷ Mycosis fungoides lesions typically stain positive for helper T-cell markers with a minority staining positive for CD8.

The Diagnosis: Cutaneous Lymphoid Hyperplasia

Cutaneous lymphoid hyperplasia (CLH)(also known as pseudolymphoma or lymphocytoma cutis) is a benign inflammatory condition that typically presents as a flesh-colored to erythematous or violaceous papule or nodule on the head or neck. Cutaneous lymphoid hyperplasia may arise in response to an antigenic stimulus, such as an insect bite, infectious agent (eg, Borrelia species), medication, or foreign body (eg, tattoos and piercings).^1,2 Given the benign nature and potential for spontaneous resolution, treatment is conservative; however, high-potency topical steroids, cryosurgery, surgical excision, or local radiotherapy may lead to improvement.³ Our patient was started on clobetasol ointment 0.05% and topical tacrolimus 0.1%. After 3 months of use, she reported lesion improvement, but a new lesion appeared on the nose superior to the original. She was offered a steroid injection and liquid nitrogen freezing but was lost to follow-up.

The histopathologic features of CLH are variable and can resemble a cutaneous B- or T-cell lymphoma (quiz images). If there is B-cell predominance, histopathology typically shows a dense dermal infiltrate of lymphocytes admixed with sparse histiocytes, eosinophils, and plasma cells. Multiple germinal-center phenotype lymphoid follicles also may be seen.⁴ Histopathology of T-cell–predominant CLH commonly shows CD4⁺ T helper lymphocytes admixed with CD8⁺ T cells within the dermis with possible papillary dermal edema and red cell extravasation.⁵ Immunohistochemical stains for CD3, CD4, CD8, and CD20 usually are positive. Most lymphocytes are CD3⁺ T cells. Admixed clusters of CD20⁺ B cells may be present.

Angiolymphoid hyperplasia with eosinophilia is a vascular tumor of the skin composed of endothelial cells and inflammatory cells.^6,7 The condition presents as single or multiple flesh-colored to purple papules most commonly on the face, scalp, and ears.⁸ Histologically, lesions appear as well-circumscribed collections of blood vessels composed of plump endothelial cells and an inflammatory infiltrate with lymphocytes and eosinophils (Figure 1A). Endothelial cells also may have an epithelioid appearance.⁷ Apparent fenestrations—holes within endothelial cells—may be present (Figure 1B). Surgical excision is the preferred treatment of angiolymphoid hyperplasia with eosinophilia. Success with laser and cryosurgery also has been reported.

Granuloma faciale typically presents as a solitary redbrown papule or plaque on the face. Linear arborizing vessels and dilated follicular openings with brown globules frequently are seen on dermoscopy.⁹ Although it may resemble CLH clinically, the histopathology of granuloma faciale is characterized by a perivascular and interstitial dermal infiltrate of numerous eosinophils admixed with lymphocytes, plasma cells, and neutrophils underneath a grenz zone (Figure 2).¹⁰ Leukocytoclastic vasculitis may be seen in early lesions, and lesions can show variable angiocentric fibrosis.¹¹ Treatment options include intralesional triamcinolone, topical steroids or calcineurin inhibitors, topical psoralen plus UVA, surgical excision, and laser therapy, but outcomes are variable.¹²

Leukemia cutis is a malignant hematopoietic skin infiltration that presents as multiple pink to red-brown, firm, hemorrhagic papules most frequently involving the head, neck, and trunk.¹³ Rarely, lesions of leukemia cutis may present as ulcers or bullae. Most lesions occur at presentation of systemic leukemia or in the setting of established leukemia. The cutaneous involvement portends a poor prognosis, strongly correlating with additional extramedullary leukemic involvement.¹⁴ Histologic features vary based on the specific type of leukemia (eg, acute myelogenous leukemia). Generally, neoplastic infiltration of the dermis and subcutaneous tissue in a nodular, diffuse, perivascular, or interstitial pattern is seen (Figure 3).¹⁵ Leukemia cutis typically resolves after successful treatment of the underlying leukemia.

Mycosis fungoides (MF) is the most common type of cutaneous T-cell lymphoma. In its early stages, MF presents as erythematous, brown, scaly patches and plaques. With progression to the tumor stage of disease, clonal expansion of CD4⁺ T cells leads to the development of purple papules and nodules.¹⁶ Microscopic findings of MF are dependent on the stage of disease. Early patch lesions show superficial or lichenoid lymphocytic infiltration of the epidermal basal layer.¹⁷ In the plaque stage, dermal infiltrates and epidermotropism become more pronounced, with increased atypical lymphocytes with cerebriform nuclei and interspersed inflammatory cells (Figure 4). In the tumor stage, lymphocytic infiltrates may involve the entirety of the dermis or extend into the subcutaneous tissue, and malignant cells become larger in size.¹⁷ Mycosis fungoides lesions typically stain positive for helper T-cell markers with a minority staining positive for CD8.

The Diagnosis: Cutaneous Lymphoid Hyperplasia

Cutaneous lymphoid hyperplasia (CLH)(also known as pseudolymphoma or lymphocytoma cutis) is a benign inflammatory condition that typically presents as a flesh-colored to erythematous or violaceous papule or nodule on the head or neck. Cutaneous lymphoid hyperplasia may arise in response to an antigenic stimulus, such as an insect bite, infectious agent (eg, Borrelia species), medication, or foreign body (eg, tattoos and piercings).^1,2 Given the benign nature and potential for spontaneous resolution, treatment is conservative; however, high-potency topical steroids, cryosurgery, surgical excision, or local radiotherapy may lead to improvement.³ Our patient was started on clobetasol ointment 0.05% and topical tacrolimus 0.1%. After 3 months of use, she reported lesion improvement, but a new lesion appeared on the nose superior to the original. She was offered a steroid injection and liquid nitrogen freezing but was lost to follow-up.

The histopathologic features of CLH are variable and can resemble a cutaneous B- or T-cell lymphoma (quiz images). If there is B-cell predominance, histopathology typically shows a dense dermal infiltrate of lymphocytes admixed with sparse histiocytes, eosinophils, and plasma cells. Multiple germinal-center phenotype lymphoid follicles also may be seen.⁴ Histopathology of T-cell–predominant CLH commonly shows CD4⁺ T helper lymphocytes admixed with CD8⁺ T cells within the dermis with possible papillary dermal edema and red cell extravasation.⁵ Immunohistochemical stains for CD3, CD4, CD8, and CD20 usually are positive. Most lymphocytes are CD3⁺ T cells. Admixed clusters of CD20⁺ B cells may be present.

Angiolymphoid hyperplasia with eosinophilia is a vascular tumor of the skin composed of endothelial cells and inflammatory cells.^6,7 The condition presents as single or multiple flesh-colored to purple papules most commonly on the face, scalp, and ears.⁸ Histologically, lesions appear as well-circumscribed collections of blood vessels composed of plump endothelial cells and an inflammatory infiltrate with lymphocytes and eosinophils (Figure 1A). Endothelial cells also may have an epithelioid appearance.⁷ Apparent fenestrations—holes within endothelial cells—may be present (Figure 1B). Surgical excision is the preferred treatment of angiolymphoid hyperplasia with eosinophilia. Success with laser and cryosurgery also has been reported.

Granuloma faciale typically presents as a solitary redbrown papule or plaque on the face. Linear arborizing vessels and dilated follicular openings with brown globules frequently are seen on dermoscopy.⁹ Although it may resemble CLH clinically, the histopathology of granuloma faciale is characterized by a perivascular and interstitial dermal infiltrate of numerous eosinophils admixed with lymphocytes, plasma cells, and neutrophils underneath a grenz zone (Figure 2).¹⁰ Leukocytoclastic vasculitis may be seen in early lesions, and lesions can show variable angiocentric fibrosis.¹¹ Treatment options include intralesional triamcinolone, topical steroids or calcineurin inhibitors, topical psoralen plus UVA, surgical excision, and laser therapy, but outcomes are variable.¹²

Leukemia cutis is a malignant hematopoietic skin infiltration that presents as multiple pink to red-brown, firm, hemorrhagic papules most frequently involving the head, neck, and trunk.¹³ Rarely, lesions of leukemia cutis may present as ulcers or bullae. Most lesions occur at presentation of systemic leukemia or in the setting of established leukemia. The cutaneous involvement portends a poor prognosis, strongly correlating with additional extramedullary leukemic involvement.¹⁴ Histologic features vary based on the specific type of leukemia (eg, acute myelogenous leukemia). Generally, neoplastic infiltration of the dermis and subcutaneous tissue in a nodular, diffuse, perivascular, or interstitial pattern is seen (Figure 3).¹⁵ Leukemia cutis typically resolves after successful treatment of the underlying leukemia.

Mycosis fungoides (MF) is the most common type of cutaneous T-cell lymphoma. In its early stages, MF presents as erythematous, brown, scaly patches and plaques. With progression to the tumor stage of disease, clonal expansion of CD4⁺ T cells leads to the development of purple papules and nodules.¹⁶ Microscopic findings of MF are dependent on the stage of disease. Early patch lesions show superficial or lichenoid lymphocytic infiltration of the epidermal basal layer.¹⁷ In the plaque stage, dermal infiltrates and epidermotropism become more pronounced, with increased atypical lymphocytes with cerebriform nuclei and interspersed inflammatory cells (Figure 4). In the tumor stage, lymphocytic infiltrates may involve the entirety of the dermis or extend into the subcutaneous tissue, and malignant cells become larger in size.¹⁷ Mycosis fungoides lesions typically stain positive for helper T-cell markers with a minority staining positive for CD8.

The Diagnosis: Leiomyosarcoma

Cutaneous leiomyosarcomas are relatively rare neoplasms that favor the head, neck, and extremities of older adults.¹ Dermal leiomyosarcomas originate from arrector pili and are locally aggressive, whereas subcutaneous leiomyosarcomas arise from vascular smooth muscle and metastasize in 30% to 60% of cases.² Clinically, leiomyosarcomas present as solitary, firm, well-circumscribed nodules with possible ulceration and crusting.³ Histopathology of leiomyosarcoma shows fascicles of atypical spindle cells with blunt-ended nuclei and perinuclear glycogen vacuoles, variable atypia, and mitotic figures (quiz images). Definitive diagnosis is based on positive immunohistochemical staining for desmin and smooth muscle actin.⁴ Treatment entails complete removal via wide local excision or Mohs micrographic surgery.⁵

Atypical fibroxanthoma (AFX) is a malignant fibrohistiocytic neoplasm that arises in the dermis and preferentially affects the head and neck in older individuals.³ Atypical fibroxanthoma presents as a nonspecific, pinkred, sometimes ulcerated papule on sun-damaged skin that may clinically resemble a squamous cell carcinoma (SCC) or basal cell carcinoma.6 Histopathology shows pleomorphic spindle cells with hyperchromatic nuclei and abundant cytoplasm mixed with multinucleated giant cells and scattered mitotic figures (Figure 1). Immunohistochemistry is essential for distinguishing AFX from other spindle cell neoplasms. Atypical fibroxanthoma stains positively for vimentin, procollagen-1, CD10, and CD68 but is negative for S-100, human melanoma black 45, Melan-A, desmin, cytokeratin, p40, and p63.⁶ Treatment includes wide local excision or Mohs micrographic surgery.

Melanoma is an aggressive cancer with the propensity to metastasize. Both desmoplastic and spindle cell variants demonstrate atypical spindled melanocytes on histology, and desmoplasia is seen in the desmoplastic variant (Figure 2). In some cases, evaluation of the epidermis for melanoma in situ may aid in diagnosis.⁷ Clinical and prognostic features differ between the 2 variants. Desmoplastic melanomas usually present on the head and neck as scarlike nodules with a low rate of nodal involvement, while spindle cell melanomas can occur anywhere on the body, often are amelanotic, and are associated with widespread metastatic disease at the time of presentation.⁸ SOX10 (SRY-box transcription factor 10) and S-100 may be the only markers that are positive in desmoplastic melanoma.^9,10 Treatment depends on the thickness of the lesion.¹¹

Spindle cell SCC is a histologic variant of SCC characterized by spindled epithelial cells. Spindle cell SCC typically presents as an ulcerated or exophytic mass in sun-exposed areas or areas exposed to ionizing radiation, or in immunocompromised individuals. Histopathology shows spindled pleomorphic keratinocytes with elongated nuclei infiltrating the dermis and minimal keratinization (Figure 3).¹² Immunohistochemistry is necessary to distinguish spindle cell SCC from other spindle cell tumors such as spindle cell melanoma, AFX, and leiomyosarcoma. Spindle cell SCC is positive for high-molecular-weight cytokeratin, p40, and p63. Mohs micrographic surgery provides the highest cure rate, and radiation therapy may be considered when clear surgical margins cannot be obtained.⁶

Undifferentiated pleomorphic sarcoma (UPS) (formerly known as malignant fibrous histiocytoma) describes tumors that resemble AFX but are more invasive. They commonly involve the soft tissue with a higher risk for both recurrence and metastasis than AFX.¹³ Histopathology shows marked cytologic pleomorphism, bizarre cellular forms, atypical mitoses, and ulceration (Figure 4).¹⁴ Diagnosis of UPS is by exclusion and is dependent on immunohistochemical studies. In contrast to AFX, UPS is more likely to be positive for LN-2 (CD74).⁶ Undifferentiated pleomorphic sarcoma has been treated with surgical excision in combination with chemical and radiation therapy, but due to limited data, optimal management is less clear compared to AFX.¹⁵ There is a substantial risk for local recurrence and metastasis, and the lungs are the most common sites of distant metastasis.¹³ In a study of 23 individuals with high-grade UPS, 5-year metastasis-free survival and local recurrence-free survival were 26% and 16%, respectively.¹⁰

The Diagnosis: Leiomyosarcoma

Cutaneous leiomyosarcomas are relatively rare neoplasms that favor the head, neck, and extremities of older adults.¹ Dermal leiomyosarcomas originate from arrector pili and are locally aggressive, whereas subcutaneous leiomyosarcomas arise from vascular smooth muscle and metastasize in 30% to 60% of cases.² Clinically, leiomyosarcomas present as solitary, firm, well-circumscribed nodules with possible ulceration and crusting.³ Histopathology of leiomyosarcoma shows fascicles of atypical spindle cells with blunt-ended nuclei and perinuclear glycogen vacuoles, variable atypia, and mitotic figures (quiz images). Definitive diagnosis is based on positive immunohistochemical staining for desmin and smooth muscle actin.⁴ Treatment entails complete removal via wide local excision or Mohs micrographic surgery.⁵

Atypical fibroxanthoma (AFX) is a malignant fibrohistiocytic neoplasm that arises in the dermis and preferentially affects the head and neck in older individuals.³ Atypical fibroxanthoma presents as a nonspecific, pinkred, sometimes ulcerated papule on sun-damaged skin that may clinically resemble a squamous cell carcinoma (SCC) or basal cell carcinoma.6 Histopathology shows pleomorphic spindle cells with hyperchromatic nuclei and abundant cytoplasm mixed with multinucleated giant cells and scattered mitotic figures (Figure 1). Immunohistochemistry is essential for distinguishing AFX from other spindle cell neoplasms. Atypical fibroxanthoma stains positively for vimentin, procollagen-1, CD10, and CD68 but is negative for S-100, human melanoma black 45, Melan-A, desmin, cytokeratin, p40, and p63.⁶ Treatment includes wide local excision or Mohs micrographic surgery.

Melanoma is an aggressive cancer with the propensity to metastasize. Both desmoplastic and spindle cell variants demonstrate atypical spindled melanocytes on histology, and desmoplasia is seen in the desmoplastic variant (Figure 2). In some cases, evaluation of the epidermis for melanoma in situ may aid in diagnosis.⁷ Clinical and prognostic features differ between the 2 variants. Desmoplastic melanomas usually present on the head and neck as scarlike nodules with a low rate of nodal involvement, while spindle cell melanomas can occur anywhere on the body, often are amelanotic, and are associated with widespread metastatic disease at the time of presentation.⁸ SOX10 (SRY-box transcription factor 10) and S-100 may be the only markers that are positive in desmoplastic melanoma.^9,10 Treatment depends on the thickness of the lesion.¹¹

Spindle cell SCC is a histologic variant of SCC characterized by spindled epithelial cells. Spindle cell SCC typically presents as an ulcerated or exophytic mass in sun-exposed areas or areas exposed to ionizing radiation, or in immunocompromised individuals. Histopathology shows spindled pleomorphic keratinocytes with elongated nuclei infiltrating the dermis and minimal keratinization (Figure 3).¹² Immunohistochemistry is necessary to distinguish spindle cell SCC from other spindle cell tumors such as spindle cell melanoma, AFX, and leiomyosarcoma. Spindle cell SCC is positive for high-molecular-weight cytokeratin, p40, and p63. Mohs micrographic surgery provides the highest cure rate, and radiation therapy may be considered when clear surgical margins cannot be obtained.⁶

Undifferentiated pleomorphic sarcoma (UPS) (formerly known as malignant fibrous histiocytoma) describes tumors that resemble AFX but are more invasive. They commonly involve the soft tissue with a higher risk for both recurrence and metastasis than AFX.¹³ Histopathology shows marked cytologic pleomorphism, bizarre cellular forms, atypical mitoses, and ulceration (Figure 4).¹⁴ Diagnosis of UPS is by exclusion and is dependent on immunohistochemical studies. In contrast to AFX, UPS is more likely to be positive for LN-2 (CD74).⁶ Undifferentiated pleomorphic sarcoma has been treated with surgical excision in combination with chemical and radiation therapy, but due to limited data, optimal management is less clear compared to AFX.¹⁵ There is a substantial risk for local recurrence and metastasis, and the lungs are the most common sites of distant metastasis.¹³ In a study of 23 individuals with high-grade UPS, 5-year metastasis-free survival and local recurrence-free survival were 26% and 16%, respectively.¹⁰

The Diagnosis: Leiomyosarcoma

Cutaneous leiomyosarcomas are relatively rare neoplasms that favor the head, neck, and extremities of older adults.¹ Dermal leiomyosarcomas originate from arrector pili and are locally aggressive, whereas subcutaneous leiomyosarcomas arise from vascular smooth muscle and metastasize in 30% to 60% of cases.² Clinically, leiomyosarcomas present as solitary, firm, well-circumscribed nodules with possible ulceration and crusting.³ Histopathology of leiomyosarcoma shows fascicles of atypical spindle cells with blunt-ended nuclei and perinuclear glycogen vacuoles, variable atypia, and mitotic figures (quiz images). Definitive diagnosis is based on positive immunohistochemical staining for desmin and smooth muscle actin.⁴ Treatment entails complete removal via wide local excision or Mohs micrographic surgery.⁵

Atypical fibroxanthoma (AFX) is a malignant fibrohistiocytic neoplasm that arises in the dermis and preferentially affects the head and neck in older individuals.³ Atypical fibroxanthoma presents as a nonspecific, pinkred, sometimes ulcerated papule on sun-damaged skin that may clinically resemble a squamous cell carcinoma (SCC) or basal cell carcinoma.6 Histopathology shows pleomorphic spindle cells with hyperchromatic nuclei and abundant cytoplasm mixed with multinucleated giant cells and scattered mitotic figures (Figure 1). Immunohistochemistry is essential for distinguishing AFX from other spindle cell neoplasms. Atypical fibroxanthoma stains positively for vimentin, procollagen-1, CD10, and CD68 but is negative for S-100, human melanoma black 45, Melan-A, desmin, cytokeratin, p40, and p63.⁶ Treatment includes wide local excision or Mohs micrographic surgery.

Melanoma is an aggressive cancer with the propensity to metastasize. Both desmoplastic and spindle cell variants demonstrate atypical spindled melanocytes on histology, and desmoplasia is seen in the desmoplastic variant (Figure 2). In some cases, evaluation of the epidermis for melanoma in situ may aid in diagnosis.⁷ Clinical and prognostic features differ between the 2 variants. Desmoplastic melanomas usually present on the head and neck as scarlike nodules with a low rate of nodal involvement, while spindle cell melanomas can occur anywhere on the body, often are amelanotic, and are associated with widespread metastatic disease at the time of presentation.⁸ SOX10 (SRY-box transcription factor 10) and S-100 may be the only markers that are positive in desmoplastic melanoma.^9,10 Treatment depends on the thickness of the lesion.¹¹

Spindle cell SCC is a histologic variant of SCC characterized by spindled epithelial cells. Spindle cell SCC typically presents as an ulcerated or exophytic mass in sun-exposed areas or areas exposed to ionizing radiation, or in immunocompromised individuals. Histopathology shows spindled pleomorphic keratinocytes with elongated nuclei infiltrating the dermis and minimal keratinization (Figure 3).¹² Immunohistochemistry is necessary to distinguish spindle cell SCC from other spindle cell tumors such as spindle cell melanoma, AFX, and leiomyosarcoma. Spindle cell SCC is positive for high-molecular-weight cytokeratin, p40, and p63. Mohs micrographic surgery provides the highest cure rate, and radiation therapy may be considered when clear surgical margins cannot be obtained.⁶

Undifferentiated pleomorphic sarcoma (UPS) (formerly known as malignant fibrous histiocytoma) describes tumors that resemble AFX but are more invasive. They commonly involve the soft tissue with a higher risk for both recurrence and metastasis than AFX.¹³ Histopathology shows marked cytologic pleomorphism, bizarre cellular forms, atypical mitoses, and ulceration (Figure 4).¹⁴ Diagnosis of UPS is by exclusion and is dependent on immunohistochemical studies. In contrast to AFX, UPS is more likely to be positive for LN-2 (CD74).⁶ Undifferentiated pleomorphic sarcoma has been treated with surgical excision in combination with chemical and radiation therapy, but due to limited data, optimal management is less clear compared to AFX.¹⁵ There is a substantial risk for local recurrence and metastasis, and the lungs are the most common sites of distant metastasis.¹³ In a study of 23 individuals with high-grade UPS, 5-year metastasis-free survival and local recurrence-free survival were 26% and 16%, respectively.¹⁰

The Diagnosis: Borrelial Lymphocytoma (Lymphocytoma Cutis)

A punch biopsy revealed an atypical lobular lymphoid infiltrate within the dermis and subcutaneous tissue with a mixed composition of CD3⁺ T cells and CD20⁺ B cells (quiz image, bottom). Immunohistochemical studies revealed a normal CD4:CD8 ratio with preservation of CD5 and CD7. CD30 was largely negative. CD21 failed to detect follicular dendritic cell networks, and κ/λ light chain staining confirmed a preserved ratio of polytypic plasma cells. There was limited staining with B-cell lymphoma (Bcl-2 and Bcl-6). Polymerase chain reaction studies for both T- and B-cell receptors were negative (polyclonal).

Lyme disease is the most frequently reported vectorborne infectious disease in the United States, and borrelial lymphocytoma (BL) is a rare clinical sequela. Borrelial lymphocytoma is a variant of lymphocytoma cutis (also known as benign reactive lymphoid hyperplasia), which is an inflammatory lesion that can mimic malignant lymphoma clinically and histologically. Lymphocytoma cutis is considered the prototypical example of cutaneous B-cell pseudolymphoma.¹ Due to suspicion for lymphocytoma cutis based on the histologic findings and characteristic location of the lesions in our patient, Lyme serologies were ordered and were positive for IgM antibodies against p23, p39, and p41 antigens in high titers. Our patient was treated with doxycycline 100 mg twice daily for 3 weeks with complete resolution of the lesions at 3-month follow-up.

Clinically, BL appears as erythematous papules, plaques, or nodules commonly on the lobules of the ears (quiz image, top). Most cases of lymphocytoma cutis are idiopathic but may be triggered by identifiable associated etiologies including Borrelia burgdorferi, Leishmania donovani, molluscum contagiosum, herpes zoster virus, vaccinations, tattoos, insect bites, and drugs. The main differential diagnosis of lymphocytoma cutis is cutaneous B-cell lymphoma. Pseudolymphoma of the skin can mimic nearly all immunohistochemical staining patterns of true B-cell lymphomas.²

Primary cutaneous follicle center lymphoma frequently occurs on the head and neck. This true lymphoma of the skin can demonstrate prominent follicle centers with centrocytes and fragmented germinal centers (Figure 1) or show a diffuse pattern.³ Most cases show conspicuous Bcl-6 staining, and IgH gene rearrangements can detect a clonal B-cell population in more than 50% of cases.⁴

Diffuse large B-cell lymphoma can occur as a primary cutaneous malignancy or as a manifestation of systemic disease.4 When arising in the skin, lesions tend to affect the extremities, and the disease is classified as diffuse large B-cell lymphoma, leg type. Histologically, sheets of large atypical lymphocytes with numerous mitoses are seen (Figure 2). These cells stain positively with Bcl-2 and frequently demonstrate Bcl-6 and MUM-1, none of which were seen in our case.4 Lymphomatoid papulosis (LyP) tends to present with relapsing erythematous papules. Patients occasionally develop LyP in association with mycosis fungoides or other lymphomas. Both LyP and primary cutaneous anaplastic large cell lymphoma demonstrate conspicuous CD30+ large cells that can be multinucleated or resemble the Reed-Sternberg cells seen in Hodgkin lymphoma (Figure 3).4 Arthropod bite reactions are common but may be confused with lymphomas and pseudolymphomas. The perivascular lymphocytic infiltrate seen in arthropod bite reactions may be dense and usually is associated with numerous eosinophils (Figure 4). Occasional plasma cells also can be seen, and if the infiltrate closely adheres to vascular structures, a diagnosis of erythema chronicum migrans also can be considered. Patients with chronic lymphocytic leukemia/lymphoma may demonstrate exaggerated or persistent arthropod bite reactions, and atypical lymphocytes can be detected admixed with the otherwise reactive infiltrate.⁴

Borrelia burgdorferi is primarily endemic to North America and Europe. It is a spirochete bacterium spread by the Ixodes tick that was first recognized as the etiologic agent in 1975 in Old Lyme, Connecticut, where it received its name.⁵ Most reported cases of Lyme disease occur in the northeastern United States, which correlates with this case given our patient’s place of residence.⁶ Borrelial lymphocytoma cutis occurs in areas endemic for the Ixodes tick in Europe and North America.⁷ When describing the genotyping of Borrelia seen in BL, the strain B burgdorferi previously was grouped with Borrelia afzelii and Borrelia garinii.² In the contemporary literature, however, B burgdorferi is referred to as sensu stricto when specifically talking about the strain B burgdorferi, and the term sensu lato is used when referencing the combination of strains (B burgdorferi, B afzelii, B garinii).

A 2016 study by Maraspin et al⁸ comprising 144 patients diagnosed with BL showed that the lesions mainly were located on the breast (106 patients [73.6%]) and the earlobe (27 patients [18.8%]), with the remaining cases occurring elsewhere on the body (11 patients [7.6%]). The Borrelia strains isolated from the BL lesions included B afzelii, Borrelia bissettii, and B garinii, with B afzelii being the most commonly identified (84.6% [11/13]).⁸

Borrelial lymphocytoma usually is categorized as a form of early disseminated Lyme disease and is treated as such. The treatment of choice for early disseminated Lyme disease is doxycycline 100 mg twice daily for 14 to 21 days. Ceftriaxone and azithromycin are reasonable treatment options for patients who have tetracycline allergies or who are pregnant.⁹

In conclusion, the presentation of red papules or nodules on the ears should prompt clinical suspicion of Lyme disease, particularly in endemic areas. Differentiating pseudolymphomas from true lymphomas and other reactive conditions can be challenging.

The Diagnosis: Borrelial Lymphocytoma (Lymphocytoma Cutis)

A punch biopsy revealed an atypical lobular lymphoid infiltrate within the dermis and subcutaneous tissue with a mixed composition of CD3⁺ T cells and CD20⁺ B cells (quiz image, bottom). Immunohistochemical studies revealed a normal CD4:CD8 ratio with preservation of CD5 and CD7. CD30 was largely negative. CD21 failed to detect follicular dendritic cell networks, and κ/λ light chain staining confirmed a preserved ratio of polytypic plasma cells. There was limited staining with B-cell lymphoma (Bcl-2 and Bcl-6). Polymerase chain reaction studies for both T- and B-cell receptors were negative (polyclonal).

Lyme disease is the most frequently reported vectorborne infectious disease in the United States, and borrelial lymphocytoma (BL) is a rare clinical sequela. Borrelial lymphocytoma is a variant of lymphocytoma cutis (also known as benign reactive lymphoid hyperplasia), which is an inflammatory lesion that can mimic malignant lymphoma clinically and histologically. Lymphocytoma cutis is considered the prototypical example of cutaneous B-cell pseudolymphoma.¹ Due to suspicion for lymphocytoma cutis based on the histologic findings and characteristic location of the lesions in our patient, Lyme serologies were ordered and were positive for IgM antibodies against p23, p39, and p41 antigens in high titers. Our patient was treated with doxycycline 100 mg twice daily for 3 weeks with complete resolution of the lesions at 3-month follow-up.

Clinically, BL appears as erythematous papules, plaques, or nodules commonly on the lobules of the ears (quiz image, top). Most cases of lymphocytoma cutis are idiopathic but may be triggered by identifiable associated etiologies including Borrelia burgdorferi, Leishmania donovani, molluscum contagiosum, herpes zoster virus, vaccinations, tattoos, insect bites, and drugs. The main differential diagnosis of lymphocytoma cutis is cutaneous B-cell lymphoma. Pseudolymphoma of the skin can mimic nearly all immunohistochemical staining patterns of true B-cell lymphomas.²

Primary cutaneous follicle center lymphoma frequently occurs on the head and neck. This true lymphoma of the skin can demonstrate prominent follicle centers with centrocytes and fragmented germinal centers (Figure 1) or show a diffuse pattern.³ Most cases show conspicuous Bcl-6 staining, and IgH gene rearrangements can detect a clonal B-cell population in more than 50% of cases.⁴

Diffuse large B-cell lymphoma can occur as a primary cutaneous malignancy or as a manifestation of systemic disease.4 When arising in the skin, lesions tend to affect the extremities, and the disease is classified as diffuse large B-cell lymphoma, leg type. Histologically, sheets of large atypical lymphocytes with numerous mitoses are seen (Figure 2). These cells stain positively with Bcl-2 and frequently demonstrate Bcl-6 and MUM-1, none of which were seen in our case.4 Lymphomatoid papulosis (LyP) tends to present with relapsing erythematous papules. Patients occasionally develop LyP in association with mycosis fungoides or other lymphomas. Both LyP and primary cutaneous anaplastic large cell lymphoma demonstrate conspicuous CD30+ large cells that can be multinucleated or resemble the Reed-Sternberg cells seen in Hodgkin lymphoma (Figure 3).4 Arthropod bite reactions are common but may be confused with lymphomas and pseudolymphomas. The perivascular lymphocytic infiltrate seen in arthropod bite reactions may be dense and usually is associated with numerous eosinophils (Figure 4). Occasional plasma cells also can be seen, and if the infiltrate closely adheres to vascular structures, a diagnosis of erythema chronicum migrans also can be considered. Patients with chronic lymphocytic leukemia/lymphoma may demonstrate exaggerated or persistent arthropod bite reactions, and atypical lymphocytes can be detected admixed with the otherwise reactive infiltrate.⁴

Borrelia burgdorferi is primarily endemic to North America and Europe. It is a spirochete bacterium spread by the Ixodes tick that was first recognized as the etiologic agent in 1975 in Old Lyme, Connecticut, where it received its name.⁵ Most reported cases of Lyme disease occur in the northeastern United States, which correlates with this case given our patient’s place of residence.⁶ Borrelial lymphocytoma cutis occurs in areas endemic for the Ixodes tick in Europe and North America.⁷ When describing the genotyping of Borrelia seen in BL, the strain B burgdorferi previously was grouped with Borrelia afzelii and Borrelia garinii.² In the contemporary literature, however, B burgdorferi is referred to as sensu stricto when specifically talking about the strain B burgdorferi, and the term sensu lato is used when referencing the combination of strains (B burgdorferi, B afzelii, B garinii).

A 2016 study by Maraspin et al⁸ comprising 144 patients diagnosed with BL showed that the lesions mainly were located on the breast (106 patients [73.6%]) and the earlobe (27 patients [18.8%]), with the remaining cases occurring elsewhere on the body (11 patients [7.6%]). The Borrelia strains isolated from the BL lesions included B afzelii, Borrelia bissettii, and B garinii, with B afzelii being the most commonly identified (84.6% [11/13]).⁸

Borrelial lymphocytoma usually is categorized as a form of early disseminated Lyme disease and is treated as such. The treatment of choice for early disseminated Lyme disease is doxycycline 100 mg twice daily for 14 to 21 days. Ceftriaxone and azithromycin are reasonable treatment options for patients who have tetracycline allergies or who are pregnant.⁹

In conclusion, the presentation of red papules or nodules on the ears should prompt clinical suspicion of Lyme disease, particularly in endemic areas. Differentiating pseudolymphomas from true lymphomas and other reactive conditions can be challenging.

The Diagnosis: Borrelial Lymphocytoma (Lymphocytoma Cutis)

A punch biopsy revealed an atypical lobular lymphoid infiltrate within the dermis and subcutaneous tissue with a mixed composition of CD3⁺ T cells and CD20⁺ B cells (quiz image, bottom). Immunohistochemical studies revealed a normal CD4:CD8 ratio with preservation of CD5 and CD7. CD30 was largely negative. CD21 failed to detect follicular dendritic cell networks, and κ/λ light chain staining confirmed a preserved ratio of polytypic plasma cells. There was limited staining with B-cell lymphoma (Bcl-2 and Bcl-6). Polymerase chain reaction studies for both T- and B-cell receptors were negative (polyclonal).

Lyme disease is the most frequently reported vectorborne infectious disease in the United States, and borrelial lymphocytoma (BL) is a rare clinical sequela. Borrelial lymphocytoma is a variant of lymphocytoma cutis (also known as benign reactive lymphoid hyperplasia), which is an inflammatory lesion that can mimic malignant lymphoma clinically and histologically. Lymphocytoma cutis is considered the prototypical example of cutaneous B-cell pseudolymphoma.¹ Due to suspicion for lymphocytoma cutis based on the histologic findings and characteristic location of the lesions in our patient, Lyme serologies were ordered and were positive for IgM antibodies against p23, p39, and p41 antigens in high titers. Our patient was treated with doxycycline 100 mg twice daily for 3 weeks with complete resolution of the lesions at 3-month follow-up.

Clinically, BL appears as erythematous papules, plaques, or nodules commonly on the lobules of the ears (quiz image, top). Most cases of lymphocytoma cutis are idiopathic but may be triggered by identifiable associated etiologies including Borrelia burgdorferi, Leishmania donovani, molluscum contagiosum, herpes zoster virus, vaccinations, tattoos, insect bites, and drugs. The main differential diagnosis of lymphocytoma cutis is cutaneous B-cell lymphoma. Pseudolymphoma of the skin can mimic nearly all immunohistochemical staining patterns of true B-cell lymphomas.²

Primary cutaneous follicle center lymphoma frequently occurs on the head and neck. This true lymphoma of the skin can demonstrate prominent follicle centers with centrocytes and fragmented germinal centers (Figure 1) or show a diffuse pattern.³ Most cases show conspicuous Bcl-6 staining, and IgH gene rearrangements can detect a clonal B-cell population in more than 50% of cases.⁴

Diffuse large B-cell lymphoma can occur as a primary cutaneous malignancy or as a manifestation of systemic disease.4 When arising in the skin, lesions tend to affect the extremities, and the disease is classified as diffuse large B-cell lymphoma, leg type. Histologically, sheets of large atypical lymphocytes with numerous mitoses are seen (Figure 2). These cells stain positively with Bcl-2 and frequently demonstrate Bcl-6 and MUM-1, none of which were seen in our case.4 Lymphomatoid papulosis (LyP) tends to present with relapsing erythematous papules. Patients occasionally develop LyP in association with mycosis fungoides or other lymphomas. Both LyP and primary cutaneous anaplastic large cell lymphoma demonstrate conspicuous CD30+ large cells that can be multinucleated or resemble the Reed-Sternberg cells seen in Hodgkin lymphoma (Figure 3).4 Arthropod bite reactions are common but may be confused with lymphomas and pseudolymphomas. The perivascular lymphocytic infiltrate seen in arthropod bite reactions may be dense and usually is associated with numerous eosinophils (Figure 4). Occasional plasma cells also can be seen, and if the infiltrate closely adheres to vascular structures, a diagnosis of erythema chronicum migrans also can be considered. Patients with chronic lymphocytic leukemia/lymphoma may demonstrate exaggerated or persistent arthropod bite reactions, and atypical lymphocytes can be detected admixed with the otherwise reactive infiltrate.⁴

Borrelia burgdorferi is primarily endemic to North America and Europe. It is a spirochete bacterium spread by the Ixodes tick that was first recognized as the etiologic agent in 1975 in Old Lyme, Connecticut, where it received its name.⁵ Most reported cases of Lyme disease occur in the northeastern United States, which correlates with this case given our patient’s place of residence.⁶ Borrelial lymphocytoma cutis occurs in areas endemic for the Ixodes tick in Europe and North America.⁷ When describing the genotyping of Borrelia seen in BL, the strain B burgdorferi previously was grouped with Borrelia afzelii and Borrelia garinii.² In the contemporary literature, however, B burgdorferi is referred to as sensu stricto when specifically talking about the strain B burgdorferi, and the term sensu lato is used when referencing the combination of strains (B burgdorferi, B afzelii, B garinii).

A 2016 study by Maraspin et al⁸ comprising 144 patients diagnosed with BL showed that the lesions mainly were located on the breast (106 patients [73.6%]) and the earlobe (27 patients [18.8%]), with the remaining cases occurring elsewhere on the body (11 patients [7.6%]). The Borrelia strains isolated from the BL lesions included B afzelii, Borrelia bissettii, and B garinii, with B afzelii being the most commonly identified (84.6% [11/13]).⁸

Borrelial lymphocytoma usually is categorized as a form of early disseminated Lyme disease and is treated as such. The treatment of choice for early disseminated Lyme disease is doxycycline 100 mg twice daily for 14 to 21 days. Ceftriaxone and azithromycin are reasonable treatment options for patients who have tetracycline allergies or who are pregnant.⁹

In conclusion, the presentation of red papules or nodules on the ears should prompt clinical suspicion of Lyme disease, particularly in endemic areas. Differentiating pseudolymphomas from true lymphomas and other reactive conditions can be challenging.

The Diagnosis: Proximal-Type Epithelioid Sarcoma

Proximal-type epithelioid sarcoma (PES) is a rare high-grade sarcoma of uncertain histogenesis that may present with a benign clinical appearance. Proximal-type epithelioid sarcoma peaks at 20 to 40 years of age and has a slight male predominance. This tumor exhibits aggressive behavior with both local recurrence and metastasis.¹ The average overall survival is poor; however, tumor size less than 5 cm and complete excision with tumor-free margin status improves the prognosis.² Proximal-type epithelioid sarcoma should not be confused with distal-type epithelioid sarcoma, which has a better prognosis and occurs in younger patients.¹ Treatment of PES is wide excision, and chemotherapy trials with tazemetostat are ongoing.³

The deceptively banal clinical appearance of PES may delay appropriate diagnosis and treatment. Proximal-type epithelioid sarcoma often grows in sheets (quiz image [top] inset) and loose nests1 but also may take on a more corded appearance mimicking myoepithelial carcinoma. The cells themselves are plump dyscohesive epithelioid cells (quiz image [top]) with large nucleoli and eosinophilic cytoplasm or hyaline globules1 (quiz image [bottom]), but cells also may be focally spindled. Myxoid stroma, hemorrhage, and necrosis often are prominent features. Epithelioid sarcomas characteristically demonstrate positive immunostaining for both epithelial and mesenchymal markers (pan-cytokeratin and vimentin),¹ with the majority having loss of expression of integrase interactor 1 (INI-1).² Histology in this case was positive for cytokeratin monoclonal antibodies CAM5.2 and OSCAR, epithelial membrane antigen, and vimentin; it showed loss of INI-1 staining (quiz image [bottom]). Negative stains included S-100, p63, cytokeratins 7 and 20, CD34, CD31, ERG, glial fibrillary acidic protein, transducin-like enhancer of split 1, CD117, myogenin, synaptophysin, chromogranin, CD10, inhibin, CD99, and estrogen receptor.

The differential diagnosis of PES includes poorly differentiated squamous cell carcinoma (Figure 1 [inset]), melanoma, myoepithelial carcinoma, and epithelioid angiosarcoma. Primary squamous cell carcinoma of the vulva presents as an endophytic or exophytic mass with raised borders. Vulvar cancer is uncommon among gynecologic malignancies, with squamous cell carcinoma being the most commonly encountered.⁴ Vulvar intraepithelial neoplasia (VIN) is increasing in incidence, while the occurrence of invasive squamous cell carcinoma remains stable.⁵ Human papillomavirus–related VIN (usual-type VIN) is less likely to progress to squamous cell carcinoma than differentiated VIN (d-VIN), a dysplasia that is unrelated to human papillomavirus that frequently harbors p53 mutations.⁴ The presence of histologic epidermal involvement can help distinguish squamous cell carcinoma from PES (Figure 1). As opposed to PES, metastatic squamous cell carcinoma is characterized by intercellular bridges and often at least focal keratinization (Figure 1). Squamous cell carcinoma demonstrates positivity with p63 and p40 immunohistochemical stains, while PES rarely stains for either.⁶

Melanoma is the second most common vulvar malignancy. Vulvar melanoma tends to occur in women of advanced age but has been reported in girls as young as 10 years old.⁷ There is some evidence that patients with lichen sclerosus may be at an increased risk for the development of vulvar melanoma.⁸ Compared to PES, primary vulvar melanoma usually demonstrates epidermal involvement as well as clinical findings of a pigmented lesion (Figure 2). A notable minority of vulvar melanomas are amelanotic.⁹ Melanoma may be distinguished from PES with a panel of melanocytic markers—human melanoma black 45, Melan-A, SRY-box transcription factor 10, S-100, and microphthalmia transcription factor—that rarely are expressed in the latter. Both PES and rhabdoid melanoma have eosinophilic and tinctorial cytoplasmic inclusions.¹⁰ Melanin pigment and more cohesive nests are helpful clues that may point to melanoma when present.

Myoepithelial carcinoma of the vulva is rare.¹¹ Myoepithelial carcinoma of soft tissue is more aggressive than its benign counterpart, with up to a 50% metastasis rate.¹² The presence of prominent corded or trabecular growth in a myxoid or hyaline background may point to the diagnosis (Figure 3). Similar to PES, myoepithelial carcinoma may lose expression of nuclear INI-1, while myoepithelial carcinoma is more likely to express S-100 and glial fibrillary acidic protein.¹³ Rearrangements of EWS RNA binding protein 1, EWSR1, have been found in half of myoepithelial neoplasms.¹²

Angiosarcomas represent 5% of cutaneous sarcomas and rarely have been reported in the vulva, primarily occurring in the setting of long-standing lymphedema and radiation.¹⁴ Angiosarcoma more often occurs on the head and neck, breasts, or extremities. Additional risk factors for the development of angiosarcoma include toxin exposure (eg, polyvinyl chloride, thorium dioxide, arsenic), anabolic steroids, and filariasis, as well as genetic disorders (eg, neurofibromatosis type 1, BRCA gene mutations, Maffucci syndrome).¹⁵ Epithelioid angiosarcoma is an infiltrative tumor composed of irregular anastomosing vascular channels with extravasated erythrocytes (Figure 4). Solid growth and necrosis may be present in more aggressive tumors. The cells themselves are pleomorphic endothelial cells with vesicular chromatin and prominent nucleoli. Epithelioid angiosarcoma may resemble carcinoma and have focal keratin expression. However, the characteristic eosinophilic cytoplasm seen in PES should not be identified in epithelioid angiosarcoma. Unlike PES, epithelioid angiosarcoma is positive for CD31 and has retained expression for INI-1. Both angiosarcoma and proximal-type epithelioid sarcoma may express vascular markers CD34 and FLI-1¹⁶; thus an expanded panel of immunohistochemical studies may be of utility.

The Diagnosis: Proximal-Type Epithelioid Sarcoma

Proximal-type epithelioid sarcoma (PES) is a rare high-grade sarcoma of uncertain histogenesis that may present with a benign clinical appearance. Proximal-type epithelioid sarcoma peaks at 20 to 40 years of age and has a slight male predominance. This tumor exhibits aggressive behavior with both local recurrence and metastasis.¹ The average overall survival is poor; however, tumor size less than 5 cm and complete excision with tumor-free margin status improves the prognosis.² Proximal-type epithelioid sarcoma should not be confused with distal-type epithelioid sarcoma, which has a better prognosis and occurs in younger patients.¹ Treatment of PES is wide excision, and chemotherapy trials with tazemetostat are ongoing.³

The deceptively banal clinical appearance of PES may delay appropriate diagnosis and treatment. Proximal-type epithelioid sarcoma often grows in sheets (quiz image [top] inset) and loose nests1 but also may take on a more corded appearance mimicking myoepithelial carcinoma. The cells themselves are plump dyscohesive epithelioid cells (quiz image [top]) with large nucleoli and eosinophilic cytoplasm or hyaline globules1 (quiz image [bottom]), but cells also may be focally spindled. Myxoid stroma, hemorrhage, and necrosis often are prominent features. Epithelioid sarcomas characteristically demonstrate positive immunostaining for both epithelial and mesenchymal markers (pan-cytokeratin and vimentin),¹ with the majority having loss of expression of integrase interactor 1 (INI-1).² Histology in this case was positive for cytokeratin monoclonal antibodies CAM5.2 and OSCAR, epithelial membrane antigen, and vimentin; it showed loss of INI-1 staining (quiz image [bottom]). Negative stains included S-100, p63, cytokeratins 7 and 20, CD34, CD31, ERG, glial fibrillary acidic protein, transducin-like enhancer of split 1, CD117, myogenin, synaptophysin, chromogranin, CD10, inhibin, CD99, and estrogen receptor.

The differential diagnosis of PES includes poorly differentiated squamous cell carcinoma (Figure 1 [inset]), melanoma, myoepithelial carcinoma, and epithelioid angiosarcoma. Primary squamous cell carcinoma of the vulva presents as an endophytic or exophytic mass with raised borders. Vulvar cancer is uncommon among gynecologic malignancies, with squamous cell carcinoma being the most commonly encountered.⁴ Vulvar intraepithelial neoplasia (VIN) is increasing in incidence, while the occurrence of invasive squamous cell carcinoma remains stable.⁵ Human papillomavirus–related VIN (usual-type VIN) is less likely to progress to squamous cell carcinoma than differentiated VIN (d-VIN), a dysplasia that is unrelated to human papillomavirus that frequently harbors p53 mutations.⁴ The presence of histologic epidermal involvement can help distinguish squamous cell carcinoma from PES (Figure 1). As opposed to PES, metastatic squamous cell carcinoma is characterized by intercellular bridges and often at least focal keratinization (Figure 1). Squamous cell carcinoma demonstrates positivity with p63 and p40 immunohistochemical stains, while PES rarely stains for either.⁶

Melanoma is the second most common vulvar malignancy. Vulvar melanoma tends to occur in women of advanced age but has been reported in girls as young as 10 years old.⁷ There is some evidence that patients with lichen sclerosus may be at an increased risk for the development of vulvar melanoma.⁸ Compared to PES, primary vulvar melanoma usually demonstrates epidermal involvement as well as clinical findings of a pigmented lesion (Figure 2). A notable minority of vulvar melanomas are amelanotic.⁹ Melanoma may be distinguished from PES with a panel of melanocytic markers—human melanoma black 45, Melan-A, SRY-box transcription factor 10, S-100, and microphthalmia transcription factor—that rarely are expressed in the latter. Both PES and rhabdoid melanoma have eosinophilic and tinctorial cytoplasmic inclusions.¹⁰ Melanin pigment and more cohesive nests are helpful clues that may point to melanoma when present.

Myoepithelial carcinoma of the vulva is rare.¹¹ Myoepithelial carcinoma of soft tissue is more aggressive than its benign counterpart, with up to a 50% metastasis rate.¹² The presence of prominent corded or trabecular growth in a myxoid or hyaline background may point to the diagnosis (Figure 3). Similar to PES, myoepithelial carcinoma may lose expression of nuclear INI-1, while myoepithelial carcinoma is more likely to express S-100 and glial fibrillary acidic protein.¹³ Rearrangements of EWS RNA binding protein 1, EWSR1, have been found in half of myoepithelial neoplasms.¹²

Angiosarcomas represent 5% of cutaneous sarcomas and rarely have been reported in the vulva, primarily occurring in the setting of long-standing lymphedema and radiation.¹⁴ Angiosarcoma more often occurs on the head and neck, breasts, or extremities. Additional risk factors for the development of angiosarcoma include toxin exposure (eg, polyvinyl chloride, thorium dioxide, arsenic), anabolic steroids, and filariasis, as well as genetic disorders (eg, neurofibromatosis type 1, BRCA gene mutations, Maffucci syndrome).¹⁵ Epithelioid angiosarcoma is an infiltrative tumor composed of irregular anastomosing vascular channels with extravasated erythrocytes (Figure 4). Solid growth and necrosis may be present in more aggressive tumors. The cells themselves are pleomorphic endothelial cells with vesicular chromatin and prominent nucleoli. Epithelioid angiosarcoma may resemble carcinoma and have focal keratin expression. However, the characteristic eosinophilic cytoplasm seen in PES should not be identified in epithelioid angiosarcoma. Unlike PES, epithelioid angiosarcoma is positive for CD31 and has retained expression for INI-1. Both angiosarcoma and proximal-type epithelioid sarcoma may express vascular markers CD34 and FLI-1¹⁶; thus an expanded panel of immunohistochemical studies may be of utility.

The Diagnosis: Proximal-Type Epithelioid Sarcoma

Proximal-type epithelioid sarcoma (PES) is a rare high-grade sarcoma of uncertain histogenesis that may present with a benign clinical appearance. Proximal-type epithelioid sarcoma peaks at 20 to 40 years of age and has a slight male predominance. This tumor exhibits aggressive behavior with both local recurrence and metastasis.¹ The average overall survival is poor; however, tumor size less than 5 cm and complete excision with tumor-free margin status improves the prognosis.² Proximal-type epithelioid sarcoma should not be confused with distal-type epithelioid sarcoma, which has a better prognosis and occurs in younger patients.¹ Treatment of PES is wide excision, and chemotherapy trials with tazemetostat are ongoing.³

The deceptively banal clinical appearance of PES may delay appropriate diagnosis and treatment. Proximal-type epithelioid sarcoma often grows in sheets (quiz image [top] inset) and loose nests1 but also may take on a more corded appearance mimicking myoepithelial carcinoma. The cells themselves are plump dyscohesive epithelioid cells (quiz image [top]) with large nucleoli and eosinophilic cytoplasm or hyaline globules1 (quiz image [bottom]), but cells also may be focally spindled. Myxoid stroma, hemorrhage, and necrosis often are prominent features. Epithelioid sarcomas characteristically demonstrate positive immunostaining for both epithelial and mesenchymal markers (pan-cytokeratin and vimentin),¹ with the majority having loss of expression of integrase interactor 1 (INI-1).² Histology in this case was positive for cytokeratin monoclonal antibodies CAM5.2 and OSCAR, epithelial membrane antigen, and vimentin; it showed loss of INI-1 staining (quiz image [bottom]). Negative stains included S-100, p63, cytokeratins 7 and 20, CD34, CD31, ERG, glial fibrillary acidic protein, transducin-like enhancer of split 1, CD117, myogenin, synaptophysin, chromogranin, CD10, inhibin, CD99, and estrogen receptor.

The differential diagnosis of PES includes poorly differentiated squamous cell carcinoma (Figure 1 [inset]), melanoma, myoepithelial carcinoma, and epithelioid angiosarcoma. Primary squamous cell carcinoma of the vulva presents as an endophytic or exophytic mass with raised borders. Vulvar cancer is uncommon among gynecologic malignancies, with squamous cell carcinoma being the most commonly encountered.⁴ Vulvar intraepithelial neoplasia (VIN) is increasing in incidence, while the occurrence of invasive squamous cell carcinoma remains stable.⁵ Human papillomavirus–related VIN (usual-type VIN) is less likely to progress to squamous cell carcinoma than differentiated VIN (d-VIN), a dysplasia that is unrelated to human papillomavirus that frequently harbors p53 mutations.⁴ The presence of histologic epidermal involvement can help distinguish squamous cell carcinoma from PES (Figure 1). As opposed to PES, metastatic squamous cell carcinoma is characterized by intercellular bridges and often at least focal keratinization (Figure 1). Squamous cell carcinoma demonstrates positivity with p63 and p40 immunohistochemical stains, while PES rarely stains for either.⁶

Melanoma is the second most common vulvar malignancy. Vulvar melanoma tends to occur in women of advanced age but has been reported in girls as young as 10 years old.⁷ There is some evidence that patients with lichen sclerosus may be at an increased risk for the development of vulvar melanoma.⁸ Compared to PES, primary vulvar melanoma usually demonstrates epidermal involvement as well as clinical findings of a pigmented lesion (Figure 2). A notable minority of vulvar melanomas are amelanotic.⁹ Melanoma may be distinguished from PES with a panel of melanocytic markers—human melanoma black 45, Melan-A, SRY-box transcription factor 10, S-100, and microphthalmia transcription factor—that rarely are expressed in the latter. Both PES and rhabdoid melanoma have eosinophilic and tinctorial cytoplasmic inclusions.¹⁰ Melanin pigment and more cohesive nests are helpful clues that may point to melanoma when present.

Myoepithelial carcinoma of the vulva is rare.¹¹ Myoepithelial carcinoma of soft tissue is more aggressive than its benign counterpart, with up to a 50% metastasis rate.¹² The presence of prominent corded or trabecular growth in a myxoid or hyaline background may point to the diagnosis (Figure 3). Similar to PES, myoepithelial carcinoma may lose expression of nuclear INI-1, while myoepithelial carcinoma is more likely to express S-100 and glial fibrillary acidic protein.¹³ Rearrangements of EWS RNA binding protein 1, EWSR1, have been found in half of myoepithelial neoplasms.¹²

Angiosarcomas represent 5% of cutaneous sarcomas and rarely have been reported in the vulva, primarily occurring in the setting of long-standing lymphedema and radiation.¹⁴ Angiosarcoma more often occurs on the head and neck, breasts, or extremities. Additional risk factors for the development of angiosarcoma include toxin exposure (eg, polyvinyl chloride, thorium dioxide, arsenic), anabolic steroids, and filariasis, as well as genetic disorders (eg, neurofibromatosis type 1, BRCA gene mutations, Maffucci syndrome).¹⁵ Epithelioid angiosarcoma is an infiltrative tumor composed of irregular anastomosing vascular channels with extravasated erythrocytes (Figure 4). Solid growth and necrosis may be present in more aggressive tumors. The cells themselves are pleomorphic endothelial cells with vesicular chromatin and prominent nucleoli. Epithelioid angiosarcoma may resemble carcinoma and have focal keratin expression. However, the characteristic eosinophilic cytoplasm seen in PES should not be identified in epithelioid angiosarcoma. Unlike PES, epithelioid angiosarcoma is positive for CD31 and has retained expression for INI-1. Both angiosarcoma and proximal-type epithelioid sarcoma may express vascular markers CD34 and FLI-1¹⁶; thus an expanded panel of immunohistochemical studies may be of utility.

The Diagnosis: Metastatic Clear Cell Renal Cell Carcinoma

Renal cell carcinoma (RCC) is a common genitourinary system malignancy with incidence peaking between 50 and 70 years of age and a male predominance.¹ The clear cell variant is the most common subtype of RCC, accounting for 70% to 75% of all cases. It is known to be a highly aggressive malignancy that frequently metastasizes to the lungs, lymphatics, bones, liver, and brain.^2,3 Approximately 20% to 50% of patients with RCC eventually will develop metastasis after nephrectomy.⁴ Survival with metastatic RCC to any site typically is in the range of 10 to 22 months.^5,6 Cutaneous metastases of RCC rarely have been reported in the literature (3%–6% of cases⁷) and most commonly are found on the scalp, followed by the chest or abdomen. ⁸ Cutaneous metastases generally are regarded as a late manifestation of the disease with a very poor prognosis. ⁹ It is unusual to identify cutaneous RCC metastasis without known RCC or other symptoms consistent with advanced RCC, such as hematuria or abdominal/flank pain. Renal cell carcinoma accounts for an estimated 6% to 7% of all cutaneous metastatic lesions.¹⁰ Cutaneous metastatic lesions of RCC often are solitary and grow rapidly, with the clinical appearance of an erythematous or violaceous, nodular, highly vascular, and often hemorrhagic growth.^9,11,12

Following the histologic diagnosis of metastatic clear cell RCC, our patient was referred to medical oncology for further workup. Magnetic resonance imaging and a positron emission tomography scan demonstrated widespread disease with a 7-cm left renal mass, liver and lung metastases, and bilateral mediastinal lymphadenopathy. The patient was started on combination immunotherapy as a palliative treatment given the widespread disease.

Histologically, clear cell RCC is characterized by lipid and glycogen-rich cells with ample cytoplasm and a well-developed vascular network, which often is thin walled with a chicken wire–like architecture. Metastatic clear cell RCC tumor cells may form glandular, acinar, or papillary structures with variable lymphocytic inflammatory infiltrates and abundant capillary formation. Immunohistochemically, the tumor cells should demonstrate positivity for paired box gene 8, PAX8, and RCC marker antigen.¹³ Vimentin and carcinoembryonic antigen may be utilized to distinguish from hidradenoma as carcinoembryonic antigen will be positive in hidradenoma and vimentin will be negative.¹⁴ Renal cell carcinoma also has a common molecular signature of von Hippel-Lindau tumor suppressor gene inactivation as well as upregulation of hypoxia inducible factor and vascular endothelial growth factor.¹⁵

Balloon cell nevi often clinically present in young patients as bicolored nevi that sometimes are polypoid or verrucous in appearance with central yellow globules surrounded by a peripheral reticular pattern on dermoscopy. Histologically, balloon cell nevi are characterized by large cells with small, round, centrally located basophilic nuclei and clear foamy cytoplasm (Figure 1), which are thought to be formed by progressive vacuolization of melanocytes due to the enlargement and disintegration of melanosomes. This ballooning change reflects an seen in malignant melanoma, in which case nuclear pleomorphism, atypia, and increased mitotic activity also are observed. The prominent vascular network characteristic of RCC typically is not present.¹⁶

Clear cell hidradenomas are benign skin appendage tumors that often present as small, firm, solitary dermal nodules that may extend into the subcutaneous fat. They have a predilection for the head, face, and arms and demonstrate 2 predominant cell types, including a polyhedral cell with a rounded nucleus and slightly basophilic cytoplasm as well as a round cell with clear cytoplasm and bland nuclei (Figure 2). The latter cell type is less common, representing the predominant cell type in less than one-third of hidradenomas, and can present a diagnostic quandary based on histologic similarity to other clear cell neoplasms. The clear cells contain glycogen but no lipid. Ductlike structures often are present, and the intervening stroma varies from delicate vascularized cords of fibrous tissue to dense hyalinized collagen. Immunohistochemistry may be required for definitive diagnosis, and clear cell hidradenomas should react with monoclonal antibodies that label both eccrine and apocrine secretory elements, such as cytokeratins 6/18, 7, and 8/18.¹⁷

Pyogenic granulomas (also referred to as lobular capillary hemangiomas) are common and present clinically as rapidly growing, polypoid, red masses surrounded by a thickened epidermis that often are found on the fingers or lips. This entity is benign and often regresses spontaneously. Histologically, pyogenic granulomas are characterized by a lobular pattern of vascular proliferation associated with edema and inflammation resembling granulation tissue, with acanthosis and hyperkeratosis at the edges of the lesion (Figure 3).¹⁸

Sebaceous carcinoma is a locally aggressive malignant neoplasm arising from the cells of the sebaceous glands and occurring most commonly in the periorbital area. This neoplasm most often affects older adults, with a mean age at diagnosis of 63 to 77 years. It commonly presents as a solitary nodule with yellowish discoloration and madarosis, which is a key distinguishing feature to differentiate this entity from a chalazion or hordeolum. Histologically, sebaceous carcinoma is a dermal-based infiltrative, nodular tumor with varying degrees of clear cell changes—well-differentiated tumors show more clear cell change as compared to more poorly differentiated variants—along with basaloid or squamous features and abundant mitotic activity (Figure 4), which may be useful in distinguishing it from the other entities in the clear cell neoplasm differential.^19-22

The Diagnosis: Metastatic Clear Cell Renal Cell Carcinoma

Renal cell carcinoma (RCC) is a common genitourinary system malignancy with incidence peaking between 50 and 70 years of age and a male predominance.¹ The clear cell variant is the most common subtype of RCC, accounting for 70% to 75% of all cases. It is known to be a highly aggressive malignancy that frequently metastasizes to the lungs, lymphatics, bones, liver, and brain.^2,3 Approximately 20% to 50% of patients with RCC eventually will develop metastasis after nephrectomy.⁴ Survival with metastatic RCC to any site typically is in the range of 10 to 22 months.^5,6 Cutaneous metastases of RCC rarely have been reported in the literature (3%–6% of cases⁷) and most commonly are found on the scalp, followed by the chest or abdomen. ⁸ Cutaneous metastases generally are regarded as a late manifestation of the disease with a very poor prognosis. ⁹ It is unusual to identify cutaneous RCC metastasis without known RCC or other symptoms consistent with advanced RCC, such as hematuria or abdominal/flank pain. Renal cell carcinoma accounts for an estimated 6% to 7% of all cutaneous metastatic lesions.¹⁰ Cutaneous metastatic lesions of RCC often are solitary and grow rapidly, with the clinical appearance of an erythematous or violaceous, nodular, highly vascular, and often hemorrhagic growth.^9,11,12

Following the histologic diagnosis of metastatic clear cell RCC, our patient was referred to medical oncology for further workup. Magnetic resonance imaging and a positron emission tomography scan demonstrated widespread disease with a 7-cm left renal mass, liver and lung metastases, and bilateral mediastinal lymphadenopathy. The patient was started on combination immunotherapy as a palliative treatment given the widespread disease.

Histologically, clear cell RCC is characterized by lipid and glycogen-rich cells with ample cytoplasm and a well-developed vascular network, which often is thin walled with a chicken wire–like architecture. Metastatic clear cell RCC tumor cells may form glandular, acinar, or papillary structures with variable lymphocytic inflammatory infiltrates and abundant capillary formation. Immunohistochemically, the tumor cells should demonstrate positivity for paired box gene 8, PAX8, and RCC marker antigen.¹³ Vimentin and carcinoembryonic antigen may be utilized to distinguish from hidradenoma as carcinoembryonic antigen will be positive in hidradenoma and vimentin will be negative.¹⁴ Renal cell carcinoma also has a common molecular signature of von Hippel-Lindau tumor suppressor gene inactivation as well as upregulation of hypoxia inducible factor and vascular endothelial growth factor.¹⁵

Balloon cell nevi often clinically present in young patients as bicolored nevi that sometimes are polypoid or verrucous in appearance with central yellow globules surrounded by a peripheral reticular pattern on dermoscopy. Histologically, balloon cell nevi are characterized by large cells with small, round, centrally located basophilic nuclei and clear foamy cytoplasm (Figure 1), which are thought to be formed by progressive vacuolization of melanocytes due to the enlargement and disintegration of melanosomes. This ballooning change reflects an seen in malignant melanoma, in which case nuclear pleomorphism, atypia, and increased mitotic activity also are observed. The prominent vascular network characteristic of RCC typically is not present.¹⁶

Clear cell hidradenomas are benign skin appendage tumors that often present as small, firm, solitary dermal nodules that may extend into the subcutaneous fat. They have a predilection for the head, face, and arms and demonstrate 2 predominant cell types, including a polyhedral cell with a rounded nucleus and slightly basophilic cytoplasm as well as a round cell with clear cytoplasm and bland nuclei (Figure 2). The latter cell type is less common, representing the predominant cell type in less than one-third of hidradenomas, and can present a diagnostic quandary based on histologic similarity to other clear cell neoplasms. The clear cells contain glycogen but no lipid. Ductlike structures often are present, and the intervening stroma varies from delicate vascularized cords of fibrous tissue to dense hyalinized collagen. Immunohistochemistry may be required for definitive diagnosis, and clear cell hidradenomas should react with monoclonal antibodies that label both eccrine and apocrine secretory elements, such as cytokeratins 6/18, 7, and 8/18.¹⁷

Pyogenic granulomas (also referred to as lobular capillary hemangiomas) are common and present clinically as rapidly growing, polypoid, red masses surrounded by a thickened epidermis that often are found on the fingers or lips. This entity is benign and often regresses spontaneously. Histologically, pyogenic granulomas are characterized by a lobular pattern of vascular proliferation associated with edema and inflammation resembling granulation tissue, with acanthosis and hyperkeratosis at the edges of the lesion (Figure 3).¹⁸

Sebaceous carcinoma is a locally aggressive malignant neoplasm arising from the cells of the sebaceous glands and occurring most commonly in the periorbital area. This neoplasm most often affects older adults, with a mean age at diagnosis of 63 to 77 years. It commonly presents as a solitary nodule with yellowish discoloration and madarosis, which is a key distinguishing feature to differentiate this entity from a chalazion or hordeolum. Histologically, sebaceous carcinoma is a dermal-based infiltrative, nodular tumor with varying degrees of clear cell changes—well-differentiated tumors show more clear cell change as compared to more poorly differentiated variants—along with basaloid or squamous features and abundant mitotic activity (Figure 4), which may be useful in distinguishing it from the other entities in the clear cell neoplasm differential.^19-22

The Diagnosis: Metastatic Clear Cell Renal Cell Carcinoma

Renal cell carcinoma (RCC) is a common genitourinary system malignancy with incidence peaking between 50 and 70 years of age and a male predominance.¹ The clear cell variant is the most common subtype of RCC, accounting for 70% to 75% of all cases. It is known to be a highly aggressive malignancy that frequently metastasizes to the lungs, lymphatics, bones, liver, and brain.^2,3 Approximately 20% to 50% of patients with RCC eventually will develop metastasis after nephrectomy.⁴ Survival with metastatic RCC to any site typically is in the range of 10 to 22 months.^5,6 Cutaneous metastases of RCC rarely have been reported in the literature (3%–6% of cases⁷) and most commonly are found on the scalp, followed by the chest or abdomen. ⁸ Cutaneous metastases generally are regarded as a late manifestation of the disease with a very poor prognosis. ⁹ It is unusual to identify cutaneous RCC metastasis without known RCC or other symptoms consistent with advanced RCC, such as hematuria or abdominal/flank pain. Renal cell carcinoma accounts for an estimated 6% to 7% of all cutaneous metastatic lesions.¹⁰ Cutaneous metastatic lesions of RCC often are solitary and grow rapidly, with the clinical appearance of an erythematous or violaceous, nodular, highly vascular, and often hemorrhagic growth.^9,11,12

Following the histologic diagnosis of metastatic clear cell RCC, our patient was referred to medical oncology for further workup. Magnetic resonance imaging and a positron emission tomography scan demonstrated widespread disease with a 7-cm left renal mass, liver and lung metastases, and bilateral mediastinal lymphadenopathy. The patient was started on combination immunotherapy as a palliative treatment given the widespread disease.

Histologically, clear cell RCC is characterized by lipid and glycogen-rich cells with ample cytoplasm and a well-developed vascular network, which often is thin walled with a chicken wire–like architecture. Metastatic clear cell RCC tumor cells may form glandular, acinar, or papillary structures with variable lymphocytic inflammatory infiltrates and abundant capillary formation. Immunohistochemically, the tumor cells should demonstrate positivity for paired box gene 8, PAX8, and RCC marker antigen.¹³ Vimentin and carcinoembryonic antigen may be utilized to distinguish from hidradenoma as carcinoembryonic antigen will be positive in hidradenoma and vimentin will be negative.¹⁴ Renal cell carcinoma also has a common molecular signature of von Hippel-Lindau tumor suppressor gene inactivation as well as upregulation of hypoxia inducible factor and vascular endothelial growth factor.¹⁵

Balloon cell nevi often clinically present in young patients as bicolored nevi that sometimes are polypoid or verrucous in appearance with central yellow globules surrounded by a peripheral reticular pattern on dermoscopy. Histologically, balloon cell nevi are characterized by large cells with small, round, centrally located basophilic nuclei and clear foamy cytoplasm (Figure 1), which are thought to be formed by progressive vacuolization of melanocytes due to the enlargement and disintegration of melanosomes. This ballooning change reflects an seen in malignant melanoma, in which case nuclear pleomorphism, atypia, and increased mitotic activity also are observed. The prominent vascular network characteristic of RCC typically is not present.¹⁶

Clear cell hidradenomas are benign skin appendage tumors that often present as small, firm, solitary dermal nodules that may extend into the subcutaneous fat. They have a predilection for the head, face, and arms and demonstrate 2 predominant cell types, including a polyhedral cell with a rounded nucleus and slightly basophilic cytoplasm as well as a round cell with clear cytoplasm and bland nuclei (Figure 2). The latter cell type is less common, representing the predominant cell type in less than one-third of hidradenomas, and can present a diagnostic quandary based on histologic similarity to other clear cell neoplasms. The clear cells contain glycogen but no lipid. Ductlike structures often are present, and the intervening stroma varies from delicate vascularized cords of fibrous tissue to dense hyalinized collagen. Immunohistochemistry may be required for definitive diagnosis, and clear cell hidradenomas should react with monoclonal antibodies that label both eccrine and apocrine secretory elements, such as cytokeratins 6/18, 7, and 8/18.¹⁷

Pyogenic granulomas (also referred to as lobular capillary hemangiomas) are common and present clinically as rapidly growing, polypoid, red masses surrounded by a thickened epidermis that often are found on the fingers or lips. This entity is benign and often regresses spontaneously. Histologically, pyogenic granulomas are characterized by a lobular pattern of vascular proliferation associated with edema and inflammation resembling granulation tissue, with acanthosis and hyperkeratosis at the edges of the lesion (Figure 3).¹⁸

Sebaceous carcinoma is a locally aggressive malignant neoplasm arising from the cells of the sebaceous glands and occurring most commonly in the periorbital area. This neoplasm most often affects older adults, with a mean age at diagnosis of 63 to 77 years. It commonly presents as a solitary nodule with yellowish discoloration and madarosis, which is a key distinguishing feature to differentiate this entity from a chalazion or hordeolum. Histologically, sebaceous carcinoma is a dermal-based infiltrative, nodular tumor with varying degrees of clear cell changes—well-differentiated tumors show more clear cell change as compared to more poorly differentiated variants—along with basaloid or squamous features and abundant mitotic activity (Figure 4), which may be useful in distinguishing it from the other entities in the clear cell neoplasm differential.^19-22