Arginase-1 is frequently positive in hepatoid adenocarcinomas

Summary Hepatoid adenocarcinoma is a rare extrahepatic tumor, which shows morphological and immunohistochemical similarities to hepatocellular carcinoma (HCC). Hence, hepatoid adenocarcinoma can cause diagnostic confusion with HCC. Arginase-1 immunostain has been recently shown to be an excellent marker of normal hepatocytes and is a sensitive and specific marker for HCC. However, the expression of Arginase-1 in hepatoid adenocarcinoma has not been evaluated in detail. Eight cases of hepatoid adenocarcinoma were immunostained with Arginase-1, Hepar-1, Glypican-3, CK7, CK20, CK19, polyclonal carcinoembryonic antigen, α-fetoprotein, CDX2, and TTF-1. Albumin in situ hybridization was performed in 4 cases. All 8 cases were positive for Hepar-1. Arginase-1 was positive in 5 (62.5%) of 8 cases; 2 of these cases showed diffuse staining, while 3 showed patchy staining. Glypican-3, CK7 and α-fetoprotein were each positive in 4 (50%) of 8 cases. CK19 was positive in 3 (37.5%) of 8 cases. polyclonal carcinoembryonic antigen showed canalicular staining in 3 (37.5%) of 8 cases and albumin in situ hybridization was positive in 3 (75%) of 4 cases. CDX2 was positive in 2 (25%) of 8 cases, both arising from the stomach. CK20 was positive in 1 (12.5%) of 8 case while TTF-1 was negative in all cases. Hepatoid adenocarcinoma has a similar immunostaining profile as HCC. Arginase-1 expression is common (62.5%) in hepatoid adenocarcinoma and hence it is not useful in distinguishing HCC from hepatoid adenocarcinoma.