Carcinosarcoma, light micrograph. Carcinosarcoma of the uterus is now considered to be a variant of endometrial carcinoma with metaplastic sarcomatous elements. It was previously known as malignant mixed mullerian tumour. It usually occurs in postmenopausal women. Microscopically, it has a biphasic appearance consisting of carcinomatous areas admixed with sarcoma-like elements. The sarcomatous components may resemble endometrial stroma or they may contain skeletal muscle, bone, cartilage, or adipose tissue. This image shows malignant bone (osteosarcoma; pink areas) in a carcinosarcoma.