Coexistence of adenocarcinoma and choriocarcinoma in the sigmoid colon

A rare case of a colon carcinoma that developed in a 50-year-old woman is documented. Histologically, the removed tumor was composed of two distinctive elements, i.e., well-differentiated papillary adenocarcinoma and choriocarcinoma. It was strongly suggested that the latter malignancy derived from the pre-existing colonic carcinoma through metaplastic proliferation. A very high human chorionic gonadotropin level was noted in the patient's serum obtained at the preoperative stage. Autopsy materials revealed that metastatic foci in the liver, lungs, and lymph nodes were exclusively composed of choriocarcinoma.