Microcystic Adnexal Carcinoma: An Uncommon Tumor with Debatable Origin

BACKGROUND: Microcystic adnexal carcinoma is an uncommon skin appendage neoplasm exhibiting both pilar and sweat duct differentiation. This tumor remains a subject of controversy as to its differentiation profile, histogenesis, and classification which is reflected in the nomenclature used to designate the neoplasm in question. Beyond this controversy the tumor remains a diagnostic challenge because of its rarity, the histologic mimicry it may display, and its banal cytologic appearance; it also poses a therapeutic challenge, as it is characterized by slow but aggressive and destructive local growth extending beyond clinical margins together with a high tendency for perineural invasion and recurrence. OBJECTIVE: We report two cases of this unusual tumor illustrating some of its characteristics. Our review emphasizes the divergent opinions concerning its differentiation profile and its origin. An organoid nevus as the origin of microcystic adnexal carcinoma in one of our patients is discussed in this context.