Atypical hepatocellular adenoma-like neoplasms with β-catenin activation show cytogenetic alterations similar to well-differentiated hepatocellular carcinomas.

The distinction of hepatocellular adenoma from well-differentiated hepatocellular carcinoma (HCC) arising in noncirrhotic liver can be challenging, particularly when tumors histologically resembling hepatocellular adenoma occur in unusual clinical settings such as in a man or an older woman or show focal atypical morphologic features. In this study, we examine the morphologic, immunohistochemical, and cytogenetic features of hepatocellular adenoma-like neoplasms occurring in men, women 50 years or older or younger than 15 years, and/or those with focal atypia (small cell change, pseudogland formation, and/or nuclear atypia), designated atypical hepatocellular neoplasms, where the distinction of hepatocellular adenoma versus HCC could not be clearly established. Immunohistochemistry was performed for β-catenin, glutamine synthetase, and serum amyloid A in 31 hepatocellular adenomas, 20 well-differentiated HCCs, and 40 atypical hepatocellular neoplasms. Chromosomal gains/losses had previously been determined in 37 cases using comparative genomic hybridization or fluorescence in situ hybridization. β-Catenin activation was observed in 35% of atypical hepatocellular neoplasms compared with 10% of typical hepatocellular adenomas (P < .05) and 55% of well-differentiated HCCs (P = .14). Cytogenetic changes typically observed in HCC were present in all atypical hepatocellular neoplasms with β-catenin activation. β-Catenin activation in atypical hepatocellular neoplasms was also associated with atypical morphologic features. Follow-up data were limited, but adverse outcome was observed in 2 atypical hepatocellular neoplasms with β-catenin activation (1 recurrence, 1 metastasis); transition to areas of HCC was observed in 1 case. The similarity in morphologic and cytogenetic features of β-catenin-activated hepatocellular adenoma-like tumors and HCC suggests that the former tumors represent an extremely well-differentiated variant of HCC.