Sebaceous
carcinoma of the breast is an exceedingly rare
neoplasm. Little is known about the behavior and prognosis of this type of
breast cancer. We report clinical, histological and immunohistochemical features of four cases of
breast carcinoma with prominent (at least 50%) sebaceous differentiation. The
tumors occurred in four women, aged 25-66, and were composed of cords, lobules and solid sheets of
tumor cells with sebaceous differentiation, comprising 50-90% of the
tumor mass. The second component consisted of cells with non-vacuolated cytoplasm, present mostly around the periphery of the lobules, or which formed separate
tumor sheets with no evidence of sebaceous differentiation and were indistinguishable from a classical
ductal carcinoma. Immunohistochemically, three
tumors expressed
hormone receptors; all cases were HER2-negative and had retained expression of the DNA mismatch repair
proteins. Three patients had axillary
lymph node metastases, and two patients had distant
metastases: one in the liver, lung and bones, and one in the mediastinal and supraclavicular lymph nodes. One patient died 28 months after diagnosis, indicating that mammary sebaceous
carcinoma is a potentially aggressive
neoplasm. In contrast to extraocular cutaneous sebaceous
carcinomas, mammary sebaceous
carcinoma is probably unrelated to
Muir-Torre syndrome. It should be differentiated from morphologically similar but biologically distinct
lipid-rich
carcinoma.