Gastric choriocarcinoma and yolk sac tumor in a man: observations about its possible origin.

The case of a 65-year-old man who had a gastric tumor with components of choriocarcinoma and yolk sac tumor is presented. The presence of a small component of adenocarcinoma in the primary tumor and the absence of any gonadal or other primary tumor at autopsy confirm its origin. Despite the common association of embryonal and trophoblastic elements in gonadal tumors, this is the first case in which such an association was clearly depicted in the stomach. This and the usual coexistence of adenocarcinoma with choriocarcinoma in the stomach suggest the possibility of a different mode of development of these tumors in the two sites: forward differentiation of neoplastic germ cells in the gonads and retrodifferentiation (opisthoplasia) of neoplastic mucosal epithelial cells in the stomach.