Pilomatrix carcinoma.

A pilomatrix carcinoma presented as a large ulcerated mass in the left axilla. Histologically, irregular nests of basaloid matrix cells with cystic centers containing necrotic debris and "shadow cells" were seen. The tumor invaded adjacent structures and was characterized by areas of cellular pleomorphism, crowding of cells, and numerous mitotic figures. An occasional atypical mitosis was noted. A review of 16 cases reported in the world literature is included, with emphasis on epidemiology and treatment.