Disruption of mismatch repair system in human cancers

It is known that transformation of normal cells to cancer cells is caused by the accumulation of successive mutations in oncogenes and/or tumor suppressor genes. Since four DNA mismatch repair genes (hMSH2, hMLH1, hPMS1 and hPMS2) have been identified as the cause of hereditary nonpolyposis colorectal cancer (HNPCC), the role of defective mismatch repair system in the development of sporadic cancers with microsatellite instability has also been discussed. Defects in mismatch repair genes would contribute to mutations in genes, including oncogenes and tumor suppressor genes, at an increased rate. Furthermore, recent investigations suggested that this mechanism was also involved in the development of multiple primary cancers as well.