Squamoid eccrine ductal carcinoma: a case report and review of the literature.

Eccrine ductal carcinoma is a rare adnexal tumor. Squamoid eccrine ductal carcinoma (SEDC) represents an exceptionally rare variant with only 6 cases reported to date. This neoplasm is deeply infiltrative and may provide a diagnostic challenge in superficial shave biopsies of skin. We present a case of SEDC in an immunocompromised patient, who, after an initial shave biopsy for diagnostic purposes, underwent a complete excision of his tumor by Mohs micrographic surgery. A combined histologic and immunohistochemical approach is necessary to identify and confirm the unique characteristics of SEDC. Because this cancer is very rare and little is known about its biologic behavior, optimal diagnostic and treatment guidelines need to be developed.