Most sporadic gastric cancers with MSI have been demonstrated to be caused by somatic hypermethylation of the MLH1 promoter region, resulting in the downregulation of MLH1 gene expression (Fleisher et al, 1999,2001; Kang et al, 1999; Leung et al, 1999; Suzuki et al, 1999). This evidence concerns the gene MLH1 and gastric cancer.