Immunoreactivity for hepatocyte paraffin 1 antibody in hepatoid adenocarcinomas of the gastrointestinal tract

Hepatocyte paraffin 1 (Hep Par 1) is a monoclonal antibody considered almos t specific for normal and neoplastic hepatocytes, that can be used on forma lin-fixed paraffin-embedded tissues. Hep Par 1 reactivity has been demonstr ated consistently in hepatocellular carcinomas and hepatoblastomas but only rarely in cholangiocarcinomas and metastatic tumors to the liver. Although its role as a marker of hepatocytic differentiation in primary liver tumor s has been studied extensively, Hep Par 1 expression has not been explored in extrahepatic lesions, especially rare adenocarcinomas with hepatoid morp hologic features. We studied 7 hepatoid adenocarcinomas of the gastrointest inal tract (6 gastric and 1 from the gallbladder) for Hep Par 1 immunoreact ivity. Focal Hep Par 1 expression was seen in 6 of 7 tumors. These hepatoid adenocarcinomas also showed reactivity for alpha-fetoprotein and carcinoem bryonic antigen. The presence of Hep Par 1 reactivity in extrahepatic hepat oid adenocarcinomas underscores the fact that Hep Par 1 expression is not u nique to primary hepatocellular neoplasms. Adenocarcinomas with hepatoid fe atures must be considered in the differential diagnosis of Hep Par 1-positi ve lesions.