MUTATIONAL ANALYSIS OF THE P53 AND K-RAS GENES AND ALLELOTYPE STUDY OF THE RB-1 GENE FOR INVESTIGATING THE PATHOGENESIS OF COMBINED HEPATOCELLULAR-CHOLANGIO-CELLULAR CARCINOMAS

Because combined hepatocellular-cholangiocellular carcinoma is rare an d its biological features and pathogenesis have not been well establis hed, we investigated alterations of the p53, K-ras and Rb-1 genes, as well as expression patterns: of carcinoembryonic antigen and keratin, in seven combined hepatocellular-cholangiocarcinomas out of 557 hepato cellular carcinomas autopsied at Tokyo University during 30 years. Mut ations of the p53 gene were found in two cases, at codon 244 (GGC to T GC) in the cholangiocellular carcinoma component of case I (mixed type , showing an intimate intermingling of both elements) and at codon 234 (TAG to AAC) in both components of case 5 (combined type, consisting of contiguous but independent masses of both elements). Mutation of th e Ei-ras gene (codon 12, GGT to GAT) was seen only in the cholangiocel lular carcinoma component of clinically apparent double cancer, case 6 . Allelic alteration of the Rb-1 gene was observed in two cases, delet ion of both alleles in the hepatocellular carcinoma component of case 3 (combined type) and replication error of the same pattern in both co mponents of case 4 (mixed type). Immunohistochemical analysis showed t hat the hepatocellular carcinoma components of five cases (cases 2, 3, 5, 6, 7) were immunoreactive for keratin, suggesting biliary epitheli al transformation. In four of the five cases (cases 3 and 5 combined, case 7 mixed and case 6 double cancer), cholangiocellular carcinoma co mponents were also positive for keratin. These results suggest that bo th components of combined hepatocellular-cholangio-carcinoma have the same genetic and phenotypic character and might have arisen from the s ame origin in some cases.