Hypermethylation of the hMLH1 gene promoter is associated with microsatellite instability in early human gastric neoplasia

A significant portion of gastric cancers exhibit defective DNA mismatch rep air, manifested as microsatellite instability (MSI). High-frequency MSI (MS I-H) is associated with hypermethylation of the human mut-L homologue 1 (hM LH1) mismatch repair gene promoter and diminished hMLH1 expression in advan ced gastric cancers, However, the relationship between MSI and hMLH1 hyperm ethylation has not been studied in early gastric neoplasms, We therefore in vestigated hMLH1 hypermethylation, hMLH1 expression and MSI in a group of e arly gastric cancers and gastric adenomas, Sixty-four early gastric neoplas ms mere evaluated, comprising 28 adenomas, 18 mucosal carcinomas, and 18 ca rcinomas with superficial submucosal invasion but clear margins, MSI was ev aluated using multiplex fluorescent PCR to amplify loci D2S123, D5S346, D17 S250, BAT 25 and BAT 26, Methylation-specific PCR was performed to determin e the methylation status of hMLH1. In two hypermethylated MSI-H cancers, hM LH1 protein expression was also evaluated by immunohistochemistry. Six of s ixty-four early gastric lesions were MSI-H, comprising 1 adenoma, 4 mucosal carcinomas, and 1 carcinoma with superficial submucosal invasion, Two lesi ons tone adenoma and one mucosal carcinoma) demonstrated low-frequency MSI (MSI-L), The remaining 56 neoplasms were MSI-stable (MSI-S), Six of six MSI -H, one of two MSI-L, and none of thirty MSI-S lesions showed hMLH1 hyperme thylation (P < 0.001), Diminished hMLH1 protein expression was demonstrated by immunohistochemistry in two of two MSI-H hypermethylated lesions, hMLH1 promoter hypermethylation is significantly associated with MSI and diminis hed hMLH1 expression in early gastric neoplasms, MSI and hypermethylation-a ssociated inactivation of hMLH1 are more prevalent in early gastric cancers than in gastric adenomas, Thus, hypermethylation-associated inactivation o f the hMLH1 gene can occur early in gastric carcinogenesis.