Malignant mediastinal germ cell tumor with pure hepatoid differentiation.

We describe a germ cell tumor of anterior mediastinal origin, with pure hepatoid differentiation and elevated serum AFP in a 41-year-old man. This is the first report of such a neoplasm analyzed by conventional stains and immunohistochemistry. Hepatocellular differentiation was proved by immunoreactivity with HepPar-1 and alpha-fetoproein (AFP), membranous expression of carcinoembryonic antigen (CEA-poly) in a canalicuar pattern, and focal expression of cytokeratin 19 in abortive ductular structures. Our investigation shows that mediastinal germ cell tumors with hepatoid components typically arise in middle-aged men; they are of pure hepatoid differentiation, as demonstrated here, or exclusively associated with yolk sac structures.