Histologic features of microcystic adnexal carcinoma

(A) Microcystic adnexal carcinoma (MAC) is a locally aggressive adnexal carcinoma with divergent differentiation. Follicular differentiation in the form of keratin (horn) cysts is present in the superficial dermis (H&E 20x).
(B) Deeper in the dermis, smaller aggregations of keratinocytes with sweat duct formation infiltrate between deep dermal collagen and into the subcutis. Dystrophic calcium deposition (fragmented purple material) is common (H&E 100x).