Microcystic adnexal carcinoma. Electron microscopic and immunohistochemical study.

We present a patient with microcystic adnexal carcinoma. The lesion was an indurated plaque on the skin of the right upper lip of a 58-year-old woman which was slowly growing during 27 years. Carcinoembryonic antigen was immunoreactive in the luminal contents of the tumor ducts and in the cytoplasm of cells surrounding ducts. S-100 protein was positive in the cytoplasm of a few cells at the lower dermis. These observations suggested that this tumor was related to sweat glands. Furthermore, electron microscopy revealed that tumor cells had features of eccrine ductal cells. These observations confirm that this tumor appeared at least capable of eccrine duct differentiation.