Choriocarcinoma of the colon: report of a case and review of the literature.

Primary choriocarcinoma of the colon is a very rare tumor, with only six reported cases in the world literature, all but one of which was associated with an adjacent adenocarcinoma. This has led to the suggestion that colonic choriocarcinomas may arise from the more typical adenocarcinoma a process of further dedifferentiation. This article reviews the above cases and adds a further case from a 73-year-old male in whom no associated adenocarcinoma could be found despite careful postmortem examination. This finding gives support to the hypothesis that, rather than arising as a result of further dedifferentiation of an existing tumor, primary choriocarcinomas may also develop in the large intestine.