Immature hepatic tumor of bimodal differentiation in a young adult patient: a novel lesion expressing beta-catenin and mimicking a distinct phase of hepatogenesis.

A large right-sided liver tumor was incidentally discovered and totally resected in a 21-year-old female patient without chronic liver disease. Histopathologic examination revealed that this malignant tumor does not fit any of the known types of primary liver tumors reported thus far. The lesion chiefly consisted of numerous solid nests composed of immature epithelial cells disclosing a marker profile typical for hepatocytes and strongly expressing beta-catenin. These nests were tightly associated with abnormal duct-like profiles exhibiting features of bile duct cells. The finding of numerous neoplastic hepatobiliary units ('liverlets') suggests that this tumor may mimic a distinct developmental phase of hepatogenesis close to ductal plate formation.