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 from 20 microdissected tumor samples mere investigated. Nucleotide sequence analysis of subcloned polymerase chain reaction-fragments of the conserved domain exons 5-8 was performed in order to detect heterogeneous distribution of p53 mutated cells within the tumors. In a screening procedure four clones of each exon 5-8 were analyzed. To confirm the observed mutations polymerase chain reaction and subcloning was repeated. Results: Sequence analysis cofirmed a mutation in only two cases (10%). 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 CGG 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 step were artefacts due to the infidelity of the taq-polymerase. All tumors had mild type sequence at the reported hot spot codon 249. The minor importance of p53 gene alterations in European hepatocarcinogenesis 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 tumors showed higher levels of p53 expression. Conclusions: We therefore conclude that the incidence of p53 mutations in European hepatocellular carcinomas is very low Generally there may be no heterogeneous distribution of p53 mutated cells within a tumor. The contribution of this genetic alteration to hepatocarcinogenesis in Europe seems of little importance.