Solid adenoma with exclusive hepatocellular differentiation: a new variant among pancreatic benign neoplasms?

We report a unique, previously unreported pancreatic tumor with hepatoid differentiation associated with serous microcystic adenoma in a 70-year-old man. These two lesions localized, respectively, at the body and the tail of the pancreas, were found incidentally on abdominal ultrasonography. Serum alpha-fetoprotein was not increased and no hepatic lesion was displayed on computed tomography. A subtotal pancreatectomy with splenectomy was performed. The patient is alive and well 12 months after resection. Pathological examination showed a very unusual encapsulated solid tumor with hepatocytic differentiation, bile production and immunoreactivity for hepatocyte paraffin-1 antibody. The tumor cells were negative for endocrine (neuron-specific enolase, chromogranin A, synaptophysin) and acinar (amylase, trypsin) markers. Ultrastructurally, zymogen and neurosecretory granules were absent. The features of the tumor were almost indistinguishable from those of hepatocellular adenoma; therefore, we believe that this solid hepatoid tumor may represent a variant of pancreatic adenoma. Recognition of this entity is important because the only reported pancreatic hepatoid tumors to date have been malignant. The main differential diagnoses include hepatoid ductal adenocarcinoma, hepatoid acinar cell carcinoma, primitive hepatoid endocrine tumor, and metastatic hepatocellular carcinoma.