Genomic Analysis in the Categorization of Poorly Differentiated Primary Liver Carcinomas

A subset of primary liver carcinomas (PLCs) cannot be classified as hepatocellular carcinoma (HCC) or intrahepatic cholangiocarcinoma (iCCA) based on morphology and immunohistochemistry (IHC). This includes tumors with morphology suggestive of HCC but lacking hepatocellular marker expression, tumors with ambiguous morphology characterized by co-expression of hepatocellular and cholangiocytic markers, and undifferentiated pleomorphic carcinomas with no discernible line of differentiation on morphology or IHC. This study examines the role of genomic analysis in the categorization of these tumors. Genomic analysis was performed on 16 PLCs that could not be definitely classified as HCC or iCCA based on morphology and IHC using a capture-based next-generation sequencing assay (n=15) or single gene mutational analysis (n=1). Genomic alterations in TERT promoter were seen in 9/16 cases (56%) and strongly favored HCC. Genomic alterations favoring iCCA were seen in 5/16 cases (31%) and included mutations in IDH1, PBRM1, BAP1, and ERBB2, as well as FGFR2 fusion. Genomic changes were helpful in classifying 14/16 (87%) PLCs. Though not specific, these genomic alterations can provide valuable diagnostic clues in selected morphologically and immunohistochemically unclassifiable cases. Given the important differences in management between HCC and iCCA, routine use of genomic analysis in diagnostically challenging settings should be considered.