Yolk sac tumor of the liver combined with hepatocellular carcinoma.

Hepatic yolk sac tumor is extremely rare, and only nine cases have been reported previously to our knowledge. We report the occurrence of a tumor combining hepatocellular carcinoma and yolk sac tumor. The clinical, pathologic, and immunohistochemical findings are presented. The patient was a 62-year-old Japanese man who died of hepatic failure and uncontrolled ascites. On autopsy, a large hepatic tumor was observed, which microscopically was composed of hepatocellular carcinoma and yolk sac tumor. The two components were intermingled, and transition zones were evident. Immunohistochemically, both components were positive for alpha-fetoprotein, but only the yolk sac tumor component was positive for carcinoembryonic antigen, epithelial membrane antigen, stage specific embryonic antigen-1, placental alkaline phosphatase, and keratin. To our knowledge, this is the first reported case of hepatic yolk sac tumor associated with hepatocellular carcinoma. The present tumor is best considered a variant of hepatocellular carcinoma showing yolk sac differentiation, and it provides another explanation for the histogenesis of extragonadal yolk sac tumor.