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Aim: Hepatocellular adenoma (HCA) represents a heterogeneous entity, and recently four major subgroups were identified based on genotype and phenotype classification from Europe. HCA is rare in Asian countries including Japan and there has been no study regarding the subgroups of HCA in Japan. Methods: We took advantage of the reported genotype/phenotype classification to analyze 14 HCA (seven women) in Japan. Results: We identified one hepatocyte nuclear factor (HNF)1α-inactivated HCA (one woman), two β-catenin-activated HCA (one woman), seven inflammatory HCA (IHCA, two women); four additional cases (three women) had no known phenotypic marker (unclassified HCA). The use of oral contraceptives was found only in two unclassified HCA (29%) cases. Fatty change of the background liver was seen in one β-catenin-activated HCA cases, four IHCA (57%) and two unclassified HCA (50%). Hepatic fibrosis was seen in five IHCA (71%) and two unclassified HCA (50%) cases. Four IHCA patients (one woman) were alcohol drinkers and one had alcoholic steatofibrosis and three had alcoholic cirrhosis. Eight HCA (57%) were multiple; one HNF1α-inactivated HCA (100%), four IHCA (57%) and three unclassified HCA (75%). The tumor was significantly larger in β-catenin-activated HCA than in other subgroups. The association of hepatocellular carcinoma was seen only in one case of unclassified HCA. Conclusion: This study suggests that IHCA arising in men with alcoholic liver disease may be a major subtype of HCA in Japan. [ABSTRACT FROM AUTHOR]