[Microsatellite instability--a new aspects in genetics and molecular biology of hereditary nonpolyposis and sporadic colorectal tumors]

Microsatellite instability (or replication error phenotyp) is a new molecular phenotyp of a substantial fraction of human cancers. The microsatellite instability in these cancers arises from alterations in normal regions of the genome consisting short sequences of repeated DNA. Ubiquitous changes in length of microsatellite sequences between constitutional and tumor DNA occur in about 90% of cases of HNPCC and in about 15% of cases of non-familial, sporadic colorectal cancer. Microsatellite instability is also found in a substantial percentage of sporadic endometrial, and gastric cancer, as well as in additional sporadic cancers, such as lung cancer which is usually not associated with HNPCC. Thus far, four different mismatch repair genes (hPMS1, hPMS2, hMLH1 hMSH2), all homologous to bacterial DNA repair genes have been identified as involved in HNPCC kindreds, and consequently they are associated with microsatellite instability. In conclusion, these basic genetic informations provide new insights into a new molecular pathway in oncogenesis, i.e. the occurrence of mutations in genomic stability genes leading to an increased cellular mutation rate (replication error phenotyp) and thus to cancer.