RESUMO
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.