Basal cell tumor with apocrine differentiation: apocrine epithelioma

A locally invasive tumor developed in a 71-year-old woman on the right retroauricular skin, involving cartilage and parotid glands. Histologically, the tumor displayed characteristic features of basal cell epithelioma accompanied by stromal fibrosis. Histochemically, an apocrine pattern in enzyme reactions was detected in tumor cells. Ultrastructurally, the tumor cells showed the features of apocrine-type secretory cells and ductlike structures, and the peripheral cells revealed the characteristics of myoepithelial cells. A large number of myofibroblasts was observed in the connective tissue surrounding the tumor nests. From these findings, the woman's tumor was considered to represent a basal cell tumor with apocrine differentiation.