“…Mismatch repair defects are the basis for the microsatellite instability found in hereditary nonpolyposis colorectal cancer (HNPCC) and in a significant fraction of sporadic colorectal cancers and certain other sporadic tumors [Ionov et al, 1993;Fishel et al, 1993;Parsons et al, 1993;Peltomaki et al, 1993;Thibodeau et al, 1993;Aaltonen et al, 1994;Umar et al, 1994;Li and Modrich, 1995]. The majority of these defects are in the hMLH1 or hMSH2 genes [Bronner et al, 1994;Hemminki et al, 1994;Koike et al, 1997;Benanchenhou et al, 1998;Cunningham et al, 1998;Guerrette et al, 1998;Herman et al, 1998]. …”