Complex adnexal tumor of the primary epithelial germ with distinct patterns of superficial epithelioma with sebaceous differentiation, immature trichoepithelioma, and apocrine adenocarcinoma.

A 60-year-old man came for treatment of a sharply outlined erythematous plaque on the gluteal area (45 x 20 mm) of 20 years' duration. Eccentrically located on the plaque was a nodule, 20 mm in diameter. Histological study of the plaque showed a superficial platelike tumor with basaloid bland cytology and sebaceous gland differentiation. Histologic study of the nodule found an undifferentiated adenocarcinoma whose ductlike glandular structures opened to the skin surface and infiltrated the whole depth of the dermis. Study of other areas of the lesion detected two more neoplasms. A nodule of squamous cell carcinoma was found within the superficial band of the benign sebaceous tumor. The fourth neoplastic pattern consisted of epithelial islands composed of basaloid cells within a fibroblastic stroma. There was prominent palisading of epithelial cell nuclei at the periphery of the islands, which usually were surrounded by a sheath of mesenchymal cells. In this complex adnexal tumor of the primary epithelial germ, sebaceous and follicular differentiation both simulate neoplastic patterns recently described as separate entities: superficial epithelioma with sebaceous differentiation and immature trichoepithelioma. The undifferentiated adenocarcinoma may represent differentiation toward the third component of the germ, that is, the apocrine gland.