A cutaneous myoepithelial carcinoma arising in a papillary eccrine adenoma

Cutaneous myoepithelial neoplasms and papillary eccrine adenomas (PEA) are rare conditions. Malignant tumors within a PEA are even rarer, with only one case reported to date. Herein, we present an extremely rare case of a cutaneous myoepithelial carcinoma arising in a PEA in a 70- year-old man presenting a solid mass in the left buttock. Histopathologically, most of the resected tumor revealed features consistent with the diagnosis of PEA. Some small nests and nodules were intermixed with the PEA and were present adjacent to the PEA. The tumor cells of nests and nodules showed ovoid to spindle shaped nuclei and slightly eosinophilic cytoplasm. Immunohistochemically, they were positive for both epithelial and myogenic markers, consistent with myoepithelioma. An inguinal lymph node with a metastatic lesion showed the same findings of myoepithelioma despite inconspicuous atypia. Our case showed malignant transformation of the myoepithelial cells at the outermost layers of the PEA.