Sebaceous carcinoma of the breast

We report on a rare distinctive variant of infiltrating ductal carcinoma ch aracterized by sebaceous differentiation of tumor cells. The neoplasm was i dentified in a lumpectomy specimen from a 45-year-old woman with extensive metastatic disease. In addition to conventional in situ and invasive ductal components, approximately half of the tumor cells exhibited a phenotype re sembling tumors of the sebaceous skin appendage with coarsely vacuolated cy toplasm and peripherally displaced nuclei. The sebaceous moiety was also pr esent in the distant metastatic deposits. There was no evidence of mucin pr oduction by tumor cells. Ultrastructurally, empty-appearing non-membrane bo und vacuoles attested to the sebaceous cells' lipid content. The immunoprof ile of the lesion included positivity for cytokeratin and epithelial membra ne antigen. Vimentin, S100 protein and carcinoembryonic antigen were not ex pressed. Most tumor cell nuclei reacted with antibodies to oestrogen and pr ogesterone receptors but failed to show overexpression of the HER2/neu prot ein. The MIB-1 labeling index averaged 16%. At variance with sebaceous brea st carcinomas on record, the present case is notable for its prolonged clin ical course.