Sebaceous epithelioma with sweat gland differentiation.

We examined a neoplasm of > 10 years' duration on the head of a woman. Light microscopically, the neoplasm was composed of multiple epithelial lobules in the dermis. The islands were mainly made up of basaloid cells and sebaceous cells; the latter cells were focally grouped in the lobules. Neither a palisade arrangement of peripheral cells nor the formation of peritumoral clefts were seen. Ductal spaces were scattered in the lobules and their luminal surfaces showed keratinization. Furthermore, in the peripheral parts of some lobules, there were sweat-gland-like structures. Immunohistochemically, most of the lobules were shown to have stratified squamous epithelium-type keratins, while the sweat-gland-like structures were shown to have simple epithelium-type keratins and stained positive for carcinoembryonic antigen. Ultrastructurally, many cells had lipid formation in their cytoplasm, and some cells formed luminal walls keratinizing without microvilli and keratohyaline granules. Although most of this neoplasm showed sebaceous differentiation, it partially differentiated to secretory cells of sweat gland apparatus.