Focal β‐catenin mutation identified on formalin‐fixed and paraffin‐embedded inflammatory hepatocellular adenomas

The identification of hepatocellular adenoma (HCA) with mutation in exon 3 of the CTNNB1 gene encoding for β‐catenin is clinically relevant due to a higher risk of malignant transformation. Inflammatory HCA (IHCA) can exhibit β‐catenin activation (β‐IHCA). We report two cases with multiple IHCA in which focal β‐catenin activation has been found in one of the IHCA. In both cases, the diagnosis of IHCA was confirmed on the resected nodules by routine stains, immunohistochemical detection of C‐reactive protein (CRP) and molecular biology on frozen material. An additional molecular analysis was performed on formalin‐fixed paraffin‐embedded (FFPE) material that showed focal glutamine synthetase (GS) staining, the surrogate marker of β‐catenin activation. In case 1, it was a 1.8‐cm area within the 7.5 cm IHCA, and in case 2 a small 0.3‐cm area within a 1.8 cm resected IHCA located close to a larger IHCA, negative for GS. In both cases, nuclear β‐catenin expression and decreased reticulin network were observed in the GS expressing foci, together with cholestasis and diffuse CD34 expression in case 1. Molecular analysis by pyrosequencing on FFPE material using the GS‐stained slides as reference to select areas with/without positive staining revealed a CTNNB1 exon 3 mutation restricted to the areas exhibiting both positive GS and CRP expression, whereas wild‐type CTNNB1 was found in areas showing only CRP staining. These two cases illustrate focal β‐catenin activation that can occur within IHCAs. Additional data are needed to determine if β‐catenin mutation is a secondary event in IHCA.