Microcystic adnexal carcinoma arising in the setting of previous radiationtherapy

While there are several reports of microcystic adnexal carcinoma developing in patients within sites of previous therapeutic irradiation, this relatio nship is not well described in the dermatologic literature. We report a cas e of a 42-year-old man with a remote history of therapeutic irradiation fol lowing surgical resection of periorbital rhabdomyosarcoma. Subsequently, he developed multiple basal cell carcinomas and a microcystic adnexal carcino ma within the held of irradiation. The histologic features were those of a classic microcystic adnexal carcinoma, with well differentiated nests and c ords of keratinocytes displaying follicular and ductular differentiation in filtrating diffusely into the reticular dermis. Dense fibrosis was present surrounding the neoplastic keratinocytes. Nuclear atypia and mitotic figure s were not identified. A carcinoembryonic antigen (CEA) stain demonstrated glandular differentiation. It is important for dermatologists to be aware o f the apparent relationship between the rare microcystic adnexal carcinoma with its innocuous scar-like clinical appearance and prior local radiation therapy.