Hepatoid tumors of the gastrointestinal / pancreatobiliary district: morphology, immunohistochemistry and molecular profiles

Hepatoid tumors (HTs) histologically resemble hepatocellular carcinoma (HCC) but manifest outside the liver. Regarding immunohistochemistry (IHC), the classical markers of hepatoid differentiation are Hep Par-1, CD10, and arginase-1. This study provides a critical overview of HT in the gastrointestinal/biliopancreatic system, which is the most common site of origin. Gastric HTs are malignant neoplasms recognized by the current WHO classification as a variant of adenocarcinoma. In addition to the classic IHC markers, SALL4 and claudin-6 can help exclude a metastatic HCC at this site. Next-generation sequencing revealed the most common alterations, including TP53 mutation, microsatellite instability (MSI), and Her2 amplification. Esophageal HTs are exceptionally rare and usually arise in the context of Barrett's esophagus. In the intestine, HTs are classified within the adenocarcinoma spectrum and manifest more often in the background of inflammatory bowel disease. Regarding their molecular profile, recurrent alterations included MSI and NCOA4-RET fusions. In the pancreas, the current WHO classification acknowledges HT only as a possible variant of ductal adenocarcinoma, characterized by a poor prognosis. However, at this site, neuroendocrine tumors (NETs) and solid pseudopapillary neoplasms (SPNs) may also show hepatoid differentiation. Hepatoid NETs show aggressive behavior, whereas hepatoid SPNs harbor CTNNB1 mutations and are characterized by an indolent clinical course. Lastly, biliary HTs belong to the adenocarcinoma category and usually show a poor prognosis. In conclusion, gastrointestinal/pancreatobiliary HTs show specific histo-molecular features, which should be considered for improving routine diagnostic activity and clinical management.