Mammary carcinosarcoma presenting as rhabdomyosarcoma: an ultrastructural and immunocytochemical study.

A mass in the left breast of a 32-year-old woman was first diagnosed as sarcoma with rhabdomyosarcomatous differentiation. Subsequent studies demonstrated a malignant epithelial component to be present, changing the diagnosis to carcinosarcoma. This course of events supports the concept that many, if not all, sarcomas of the breast would be mixed tumors with a malignant epithelial component, if search for the epithelial component was extensive. Carcinosarcomas with rhabdomyosarcomatous differentiation in the breast are rare, but like sarcomas elsewhere, they do not metastasize to regional lymph nodes, but disseminate hematogenously, primarily to the lungs.