Abnormal methylation of the CDH1, RASSF1A, MLH1, N33, and DAPK genes in the tumor and morphologically intact (nontumor) gastric epithelium

Abnormal methylation of the CDH1, RASSF1A, MLH1, N33, and DAPK genes was studied in the intraoperative specimens of gastric carcinomas and adjacent nontumor tissues from 47 patients with gastric cancer. For comparison, methylation of these genes was examined in 25 specimens of the nontumor gastric mucosa obtained by endoscopic biopsy from patients with esophageal cancer or burn. A surgical material comprising 3-5 tissue samples from each patient was obtained by a definitive procedure. The N33 and CDH1 genes were methylated in the tumor significantly more frequently than were the RASSF1A and MLH1 genes (p < 0.01). Abnormal methylation of the N33, CDH1, and DAPK genes were more often detectable in all gastric tissue segments (1, 2, 3, 4), including morphologically intact tissue with the upper and lower resection margins. The RASSF1A and MLH1 genes had low methylation rates (19 and 17%, respectively). Their methylation was found mainly in the tumor samples (2, 2e) and was not in the samples obtained from the resection margin.