[Mutation of the mismatch repair genes for carcinogenesis of sporadic colorectal cancers with RER-positive phenotype].

Genetic instability, monitored by (a) replication error, is a feature of many hereditary and sporadic colorectal cancers. When such tumors are familial, the genetic instability is thought to be triggered by inherited mutations in DNA-mismatch repair genes but the mechanism by which sporadic tumors exhibit RER+ phenotypes is not as well understood. We examined RER in 129 sporadic colorectal tumors. In eight of them that exhibited RER+ at two or more loci, we screened for mutations of hMLH1 and hMSH2. We detected only two mutations; one was a constitutional mutation of hMLH1 and the other was a somatic mutation of hMSH2. These results suggest that RER in sporadic tumors does not always reflect germline mutation in genes associated with mismatch repair.