Skin metastasis from the spindle cell component in rectal carcinosarcoma.

Carcinosarcomas are rare tumors, which are usually composed of carcinomatous areas close to or intermixed with sarcomatous components. Only 6 cases of carcinosarcoma of the colon have been reported in the English literature previously. We describe the 7th case, an 82-year-old man with a skin metastasis from the spindle cell component of a rectal carcinosarcoma. On rectal exploration, a large, firm tumor was palpated 2 cm from the anal verge. Endoscopic examination revealed a tumor projecting into the lumen, and hemorrhage from the tumor surface. We performed a low anterior resection. The resected specimen contained an ulcerative lesion with a round wall in continuity with a papillary tumor. Carcinoma and sarcoma components existed concomitantly along with transitional features. Immunohistochemistry disclosed immunoreactivity for vimentin in most of the spindle cell areas. Carcinoembryonic antigen was positive in the adenocarcinomatous component. One month after surgery, the patient developed a skin metastasis on the back. The skin biopsy specimen contained proliferating spindle cells almost identical to those of the primary lesion. The patient died of carcinosarcoma 6 months after surgery. In this paper, we review 7 cases of colorectal carcinosarcoma, including our patient, who is only the 7th such reported case.