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Case ReportsAbstract
Myoepithelial cells are crucial supporters of glandular function and maintainers of the basement membrane. Myoepithelial neoplasms are well documented in organs such as the lungs, salivary glands, and breasts. Cutaneous myoepithelioma (CM) has only recently been recognized and is found to often arise near sweat glands. Cutaneous syncytial myoepithelioma (CSM), is a rare subtype of CM characterized by a syncytial growth pattern of histiocytoid or spindle cells with marked pale eosinophilic cytoplasm. CSM is positive for markers such as S100, epithelial membrane antigen (EMA), and smooth muscle actin (SMA), with absent expression of cytokeratin, p40, and p63. CSM presents as a well-circumscribed, painless nodule, primarily on the extremities. We present an interesting case of a 66-year-old woman who presented with an irregular multicolored macule on her thigh. Microscopic examination revealed a circumscribed, unencapsulated solid proliferation of cells within the dermis, extending up to the overlying epidermis without an intervening Grenz zone. The tumor was composed of epithelioid and spindled cells with finely vacuolated and gray to pink cytoplasm. Nuclei were mildly pleomorphic with visible nucleoli and occasional intranuclear vacuoles. Focal adipocytic metaplasia and scattered mast cells were identified. The stroma was scant ranging from eosinophilic to mildly myxoid. Immunohistochemistry stains demonstrated positivity for S100, EMA, and patchy SMA, with Ki-67 at 5%. Stains for SOX10, CD34, Factor XIIIa, CD68, HMB-45, CD45, and Melan-A were negative. This case demonstrates the importance of recognizing the histologic and immunochemical profile of CSM and contributes to the limited literature on this rare cutaneous neoplasm.