Apocrine carcinomas of the skin are rare and incompletely studied neoplasms. An immunohistochemical and ultrastructural study is reported of specimens from six patients with apocrine skin carcinoma in various body sites. Three tumors were in the axilla; one, the eyelid; one, the ear; and one, the scalp. There were three local recurrences and three regional lymph node metastases, but no patient died of cancer (follow-up, 2-10 years). The most reliable histopathologic criteria for identifying apocrine skin carcinoma appear to be decapitation secretion, periodic acid-Schiff-positive diastase-resistant material in the cells or lumen, and immunoreactivity with gross cystic disease fluid protein 15. All specimens expressed common epithelial antigens (cytokeratins, carcinoembryonic antigen, and epithelial membrane antigen) and histiocytic-secretive antigens (Leu-M1, lysozyme, LN5, alpha-1-antitrypsin, and alpha-1-antichymotrypsin). S-100 protein was found in the three nonaxillary tumors. Ultrastructurally, the primary tumors, and especially the secondary lesions, were dedifferentiated compared with normal apocrine glands. Apocrine differentiation in skin tumors does not indicate an exclusive origin from the apocrine sweat glands; these neoplasms usually have an indolent clinical course.
