Carcinosarcoma of the colon. Report of a unique case with light and immunohistochemical studies.

A unique case of carcinosarcoma of the colon is reported. The tumor invaded the bowel wall deeply, metastasized widely, resisted multi-agent chemotherapy, and caused the patient's death 4 years later. The tumor was composed of adenosquamous carcinoma admixed with sarcoma showing osseous, cartilaginous, and nonspecific spindle-cell differentiation. Although carcinoembryonic antigen appeared limited to carcinoma cells, cytokeratin immunoreactivity was observed in both carcinoma and sarcoma cells. Like carcinosarcomas at other body sites, the finding of cytokeratin in sarcoma cells supports partial epithelial differentiation in this component, likely retained from carcinoma precursor cells.