The cohort of 37 index patients at risk for HNPCC screened in this study for LGRs has been established mainly on the basis of clinico-genetical criteria for HNPCC (AC-I and II, BG and RBG) and a lack of a germline mutation in the major MMR genes (MLH1 and MSH2) by conventional mutation screening techniques. This evidence concerns the gene MRC1 and hereditary nonpolyposis colon cancer.