Multiple retrospective studies (Halling et al., 1999; Gaf et al., 2000; Lanza et al., 2006; Sinicrope et al., 2006), including a population-based study (Samowitz et al., 2001) and a meta-analysis (Popat et al., 2005), have demonstrated that patients with MMR-deficient colon cancers have a more favorable stage-adjusted prognosis compared with patients whose tumors have intact MMR. This evidence concerns the gene MRC1 and colonic neoplasm.