Yolk sac tumor of the stomach with an adenocarcinomatous component: A casereport with immunohistochemical analysis

A 56-year-old male treated for a gastric yolk sac tumor with an adenocarcin omatous component is described. A mixed area of reticular and glandular neo plastic components was morphologically identified in this tumor. Immunohist ochemically, the yolk sac tumor expressed alpha-fetoprotein (AFP), placenta l alkaline phosphatase (PLAP), and cytokeratin, but was negative for carcin oembryonic antigen (CEA). The adenocarcinoma was positive for CEA and cytok eratin, partially positive for FLAP, and negative for AFP. In the mixed are a, the tumor cells were positive for cytokeratin, weakly expressed AFP and FLAP, and sporadically stained for CEA both in the reticular and glandular components. This area was identified as a transitional area of the yolk sac tumor and adenocarcinoma. These findings demonstrate that the yolk sac and adenocarcinomatous components are closely related. It also suggests that t he tumor arose from multipotential neoplastic mucosal epithelial cells with both yolk sac and gastric mucosal phenotypes.