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

Patient and methods: 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. Results: The lesion chiefly consisted of numerous solid nests composed of immature epithelial cells disclosing a marker profile typical for hepatocytes and strongly expressing β-catenin. These nests were tightly associated with abnormal duct-like profiles exhibiting features of bile duct cells. Conclusions: 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.