Inherited mutations in the MSH2 and MLH1 homologs of the bacterial DNA mismatch repair genes MutS and MutL were initially demonstrated at high frequency in HNPCC and were shown to be associated with microsatellite instability. The demonstration that 10-45% of pancreatic, gastric, breast, ovarian and small cell lung cancers also display microsatellite instability has been interpreted to s
