[Analysis of genetic changes in progression of colorectal cancer]

To investigate whether genetic changes of the p53 gene and genetic defects in DNA-mismatch repair systems are involved in progression of colorectal carcinomas (CRCs), we examined loss of heterozygosity (LOH) on 17p and mutations in exon 5 through 8 of the p53 gene as well as replication errors (RER) at four microsatellite loci in DNAs from 108 CRCs at all clinical stages (20 Dukes A, 40 Dukes b, 48 Dukes C). We observed that LOH on 17p and/or p53 mutation were detected in 93% of Dukes A carcinomas and in 84% of Dukes C carcinomas, suggesting that the p53 gene is mutated and/or deleted before carcinoma has been produced. RER-positive phenotype was observed in approximately 30% of CRCs, irrespective of clinical stage. These results suggest that genetic instability is likely to play an important role in development of a subpopulation of sporadic CRCs, but not in progression of CRCs. In addition, we found no significant association between genetic alterations and progression of CRCs. We consider that genetic defects in DNA-mismatch repair pathway do not necessarily promote genomic instability at the p53 sequences in CRCs.