Carcinosarcoma of the colon: report of a rare tumor.

Carcinosarcoma is a rare tumor that shows both epithelial and stromal malignant differentiation. Most reported cases of carcinosarcoma affect the female genital tract (and are called malignant mixed müllerian tumors), but there are also some isolated reports of cases affecting the lung and the head and neck area. Carcinosarcomas only rarely affect the gastrointestinal tract, mainly the esophagus. To the best of our knowledge, only eight cases of carcinosarcoma of the colon have been reported to date. For some lesions, the term 'sarcomatoid carcinoma' is preferred to 'carcinosarcoma', as both stromal and epithelial cells have shown cytokeratin expression on immunohistochemistry. The expression 'carcinosarcoma' should be applied only to those lesions, the stromal elements of which do not express epithelial markers. We report a new case of carcinosarcoma affecting the left colon. The most unique feature of this tumor is that it shows chondro-and osteosarcomatous differentiation, a feature that has been described previously in only one colonic carcinosarcoma. We discuss the histopathological and immunohistochemical features of this lesion as well as its possible histogenesis.