Track

Case Reports

Abstract

Sweat gland carcinoma with neuroendocrine differentiation is a recently proposed diagnostic entity, distinct from both endocrine mucin-producing sweat gland carcinoma (EMPSGC) and Merkel cell carcinoma. Formerly referred to as low-grade neuroendocrine carcinoma of the skin, the updated terminology reflects findings from a recent case series identifying tumors with high-grade cytologic atypia and a significant potential for lymph node and distant metastasis, particularly in lesions exceeding 2 cm. We present the case of an 80-year-old woman with a lesion on the right posterior shoulder, initially suspected to be a cyst. Histopathologic examination revealed a poorly circumscribed malignant epithelial neoplasm (1.8 cm) involving the dermis and subcutis, composed of infiltrative nests, cords, and single cells with focal ductal differentiation and frequent atypical mitoses. No apocrine features or mucin were identified. By immunohistochemistry, tumor cells were positive for pan-cytokeratin, BerEP4, CK19, GATA-3, ER, CEA, EMA, and synaptophysin, with patchy CK7 and chromogranin expression. P63 highlighted a focal myoepithelial component in the center of the lesion, providing some support for a primary cutaneous origin, although metastatic breast carcinoma could not be definitively excluded.  All the other tested markers were negative. The findings were most consistent with sweat gland carcinoma with neuroendocrine differentiation. Surgical excision and sentinel lymph node biopsy revealed metastasis in one of ten axillary lymph nodes. Breast imaging excluded a breast primary. This case underscores the importance of recognizing this emerging entity in the differential diagnosis of cutaneous carcinomas with ductal and neuroendocrine differentiation to guide appropriate management and follow-up.