LOW INCIDENCE OF P53 MUTATIONS IN EUROPEAN HEPATOCELLULAR CARCINOMAS WITH HETEROGENEOUS MUTATION AS A RARE EVENT

Background/Aims: The aim of this study was to evaluate the role of p53 mutations in European hepatocarcinogenesis. Methods: DNA extracts fro m 20 microdissected tumor samples mere investigated. Nucleotide sequen ce analysis of subcloned polymerase chain reaction-fragments of the co nserved domain exons 5-8 was performed in order to detect heterogeneou s distribution of p53 mutated cells within the tumors. In a screening procedure four clones of each exon 5-8 were analyzed. To confirm the o bserved mutations polymerase chain reaction and subcloning was repeate d. Results: Sequence analysis cofirmed a mutation in only two cases (1 0%). One at codon 220 (exon 6) was a homogeneous transition in nearly all clones from TAT to TGT. The other mutation was a transition from C GG to CAG at the known hot spot codon 248 (exon 7). It was found in 30 % of the clones. We conclude that the other mutations from the first s tep were artefacts due to the infidelity of the taq-polymerase. All tu mors had mild type sequence at the reported hot spot codon 249. The mi nor importance of p53 gene alterations in European hepatocarcinogenesi s was further confirmed at the protein level by immunohistochemistry. Only the tumor,vith the heterogeneous p53 mutation at codon 248 showed a p53 overexpression in nearly 30% of the nuclei. None of the other t umors showed higher levels of p53 expression. Conclusions: We therefor e conclude that the incidence of p53 mutations in European hepatocellu lar carcinomas is very low Generally there may be no heterogeneous dis tribution of p53 mutated cells within a tumor. The contribution of thi s genetic alteration to hepatocarcinogenesis in Europe seems of little importance.