Subtype classification of hepatocellular adenoma.

Hepatocellular adenomas (HCA) are rare benign tumours occurring mainly in women under oral contraceptives. HCA bleed frequently and transform rarely into hepatocellular carcinoma. Identification of genes recurrently mutated in HCA and good genotype/phenotype correlations provided the basis of a pathomolecular classification of different HCA subgroups, characterized using immunohistochemical markers. HNF1A-mutated HCA: Biallelic-inactivating mutations of HNF1A gene are identified in 35-40% of HCA. HNF1alpha-inactivated HCA display characteristic pathological features, including marked steatosis. The expression of FABP1 (which is a HNF1A target gene) is downregulated and the absence of L-FABP expression diagnosed this subgroup. beta-Catenin-mutated HCA: beta-catenin mutations leading to activation of the Wnt/beta-catenin pathway represented 10-15% of HCA. They are characterized by overexpression of glutamine synthetase and aberrant nuclear beta-catenin staining. These beta-catenin-activated HCA are at greater risk of malignant transformation; they are difficult to differentiate from well-differentiated HCC. Inflammatory HCA (50%): These are defined by the presence of inflammatory infiltrates, sinusoidal dilatation and thick-walled arteries. Small in-frame deletions that target the binding site of gp130 for IL-6 have been reported in 60% of inflammatory HCA. There is an overexpression of the inflammatory proteins serum amyloid A and C-reactive protein in tumour hepatocytes both at mRNA and protein levels. Inflammatory HCA occurred more frequently in patients with high body mass index; they can be also mutated for beta-catenin and therefore are probably at risk of HCC. Unclassified HCA: Less than 10% of HCA do not express any of the above-mentioned phenotypic markers. Taking into account noticeable differences between the HCA subgroups, in terms of clinical and prognostic features, phenotyping may become an important tool for HCA management strategy.