Sebaceous carcinoma of the breast: case report and review of the literature.

Sebaceous differentiation has been described in only limited examples of benign and malignant epithelial lesions of the breast. We report a rare case of mammary sebaceous carcinoma to further delineate its morphologic features. Microscopically, the tumor, arising in the right mammary gland of a 63-year-old woman, was composed of well-defined solid sheets or lobules of atypical epithelial cells including many large pale or clear cells with often scalloped nuclei and coarsely vacuolated cytoplasm, in which abundant lipid droplets were identified with oil-red-O staining. Immunohistochemical expressions of cytokeratin, epithelial membrane antigen, and receptors of estrogen and progesterone were detected, whereas GCDFP-15, S-100 protein, vimentin, alpha-smooth muscle actin, p63, androgen receptor, and the HER2/neu protein were not expressed. Besides, a subset of the tumor cells co-expressed synaptophysin, neurofilament, and PGP9.5, suggesting neuroendocrine differentiation that is a hitherto undescribed phenomenon in the mammary tumors with sebaceous features. This case would expand the morphologic diversity of carcinoma of the breast.