Microcystic adnexal carcinoma: a case report with immunohistochemical and electron microscopical examinations.

Microcystic adnexal carcinoma (MAC) is an unusual cutaneous neoplasm comprised of pilar and sweat duct structures. We report here a 66-year-old Japanese woman with MAC on her left nasolabial fold with more prominent calcified keratinous cysts than ductal differentiated structures which stained positively for carcinoembryonic antigen (CEA). The clinical appearance and statistical characteristics of MAC are reported to be different from those of other adnexal tumors. Desmoplastic trichoepithelioma (DTE) is the most difficult tumor to differentiate from MAC, unless positive reactivity for CEA in differentiated ductal structures in MAC can be demonstrated. We compare the differences between the clinical, histological, immunohistochemical, and electron microscopical features of DTE and MAC. It seems probable that these differences could be explained by biological differences in the characteristics of the cells from which these tumors originate, hair follicle cells and eccrine sweat cells, respectively.