Adenocarcinoma of the colon with choriocarcinoma in its metastases.

A 49-year-old woman died from metastases from a colon carcinoma. This was predominantly an ordinary tubular adenocarcinoma but it included arease of much less differentiated appearance with giant cells, while the hepatic and pulmonary metastase were poorly differentiated and contained choriocarcinoma, as established by means of morphologic and immunocytochemical examination. The choriocarcinoma appeared to be due to metaplasia within the carcinomatous tissue. This and other similar cases of mixed tumours suggest that unexpected trophoblastic differentiation may result from aberrant differentiation of locally proliferating cells, rather than originating in ectopic germ cells or in foci of embryonic totipotent cells. Implications for possible origin and for classification of tumors are briefly discussed.