Microcystic Adnexal Carcinoma

Abstract

Microcystic adnexal carcinoma (MAC) is an uncommon, locally aggressive neoplasm of the skin appendages that exhibits eccrine and follicular differentiation. The tumor is typically described as slow growing but destructive. Histologic sections demonstrate keratinized cysts, eccrine ducts, and bland tumor cords within a desmoplastic stroma. MAC is characteristically devoid of striking atypia, mitotic figures, and necrosis. The deeply invasive process starts in the superficial dermis but may extend into the subcutaneous tissue and skeletal muscle. Bland clinical and histologic features combined with characteristically superficial or small incomplete biopsies often result in a misdiagnosis and delay curative treatment. In this article, we report a case of MAC followed by a comparative discussion of the most common histologic differential diagnoses.