Carcinosarcoma of the Breast

Carcinosarcoma of the breast is rare and accounts for less than 0.1% of all breast malignancies. Carcinosarcomas have traditionally been distinguished from other forms of metaplastic breast carcinoma because they are aggressive and have an ominous prognosis. Metaplastic tumors that show both carcinomatous and sarcomatous features occur in various anatomical sites and, in spite of differences in terminology and exact microscopic composition, evidence suggests these all are similar tumors that develop through a peculiar phenotypic transformation of carcinoma cells into sarcoma. In the breast, the most popular theories regarding the histogenesis of the sarcomatous component of carcinosarcomas and sarcomatoid carcinomas propose the malignant transformation of myoepithelial cells or myofibroblastic metaplasia of malignant epithelial cells. In this chapter, we review the limited published clinical experience with carcinosarcomas of the breast and make therapy recommendations on the basis of available data. In addition, we explore some potentially targetable molecular mechanisms that need to be further explored for their potential to improve the outcomes of patients with these aggressive tumors.