Primary cutaneous adenoid cystic carcinoma: case report, immunohistochemistry, and review of the literature.

We report a case of primary cutaneous adenoid cystic carcinoma in a 75-year-old man. Electron microscopy revealed similar features to those previously described in adenoid cystic carcinomas of salivary gland origin: wide intercellular spaces, pseudocysts containing replicated basement membrane-like material and true lumina lined by cytoplasmic membranes with numerous microvilli. Immunohistochemistry using antibodies to several cytoskeletal proteins (keratins and actin) indicated the presence of two epithelial tumour cell populations, one with the phenotype of myoepithelial cells, lining the pseudocysts and the periphery of the tumour fields, and another with the phenotype of acinar cells of the secretory coil of sweat glands. In addition, the tumour showed immunoreactivity for epithelial membrane antigen, but not carcinoembryonic antigen. A review of the literature on other cases of primary cutaneous adenoid cystic carcinoma showed that this tumour generally affects older patients with a female to male ratio of 4:1. The most common tumour site appears to be the scalp (40%), and the recurrence rate is 50%. Surgical treatment with extensive resection margins is recommended.