Abstract

Microcystic adnexal carcinoma (MAC), is a rare adnexal tumor, accounting for less than 0.5% of all skin cancers. MAC is a slow growing, locally aggressive, and frequently recurring entity with debatable origin. Few cases of MAC with germinative follicle differentiation (GFD) have been reported in the literature. We present an additional case of MAC with GFD and apocrine differentiation. 

A 67-year-old-male presented with a 1 cm polypoid mass of left nasal ala.  Microscopic examination of the resection specimen demonstrated a poorly circumscribed tumor characterized by superficial keratocysts and deeply infiltrating nests of bland-appearing epithelial cells with focal epidermal and follicular involvement, focal mitoses (2 per square mm), skeletal muscle infiltration and multifocal perineural invasion.  Additional findings included areas of solid nests comprised of undifferentiated basaloid cells resembling trichoblastoma and focal nests with apocrine and complex ductal differentiation (positive for GCDFP-15). 

This case illustrates the broad and mixed morphologic spectrum of MAC and suggests a combined follicular-sebaceous-apocrine origin.  It is important to be aware of the expanded morphologic features seen in MAC particularly when evaluating partial samples of clinically larger lesions in which characteristic infiltrative growth and perineural invasion may not be seen due to limited sampling.