AIM:To investigate the effects of Helicobacter pylori (H pylori)eradication therapy for treatment of peptic ulcer on the incidence of gastric cancer. METHODS:A multicenter prospective cohort study was conducted between November 2000 and December 2007 in Yamagata Prefecture,Japan.The study included patients with H pylori-positive peptic ulcer who decided themselves whether to receive H pylori eradication(eradication group)or conventional antacid therapy(non-eradication group).Incidence of gastric cancer in the two groups was determined based on the results of annual endoscopy and questionnaire surveys,as well as Yamagata Prefectural Cancer Registry data,and was compared between the two groups and by results of H pylori therapy.RESULTS:A total of 4133 patients aged between 13 and 91 years(mean 52.9 years)were registered,and 56 cases of gastric cancer were identified over a mean follow-up of 5.6 years.The sex-and age-adjusted incidence ratio of gastric cancer in the eradication group, as compared with the non-eradication group,was 0.58 (95%CI:0.28-1.19)and ratios by follow-up period(<1 year,1-3 years,>3 years)were 1.16(0.27-5.00),0.50 (0.17-1.49),and 0.34(0.09-1.28),respectively.Longer follow-up tended to be associated with better prevention of gastric cancer,although not to a significant extent.No significant difference in incidence of gastric cancer was observed between patients with successful eradication therapy(32/2451 patients,1.31%)and those with treatment failure(11/639 patients,1.72%).Among patients with duodenal ulcer,which is known to be more prevalent in younger individuals,the incidence of gastric cancer was significantly less in those with successful eradication therapy(2/845 patients,0.24%)than in those with treatment failure(3/216 patients,1.39%). CONCLUSION:H pylori eradication therapy for peptic ulcer patients with a mean age of 52.9 years at registration did not significantly decrease the incidence of gastric cancer. AIM: To investigate the effects of Helicobacter pylori (H pylori) eradication therapy for treatment of peptic ulcer on the incidence of gastric cancer. METHODS: A multicenter prospective cohort study was conducted between November 2000 and December 2007 in Yamagata Prefecture, Japan. The study included patients with H pylori-positive peptic ulcer who decided themselves whether to receive H pylori eradication (eradication group) or conventional antacid therapy (non-eradication group) .Inidence of gastric cancer in the two groups was determined based on the results of annual endoscopy and questionnaire surveys, as well as Yamagata Prefectural Cancer Registry data, and was compared between the two groups and by results of H pylori therapy .RESULTS: A total of 4133 patients aged between 13 and 91 years (mean 52.9 years) were registered, and 56 cases of gastric cancer were identified over a mean follow-up of 5.6 years.The sex-and age-adjusted incidence ratio of gastric cancer in the eradication group, as compared with the non-eradication group was was 0.58 (95% CI: 0.28-1.19) and ratios by follow-up period (<1 year, 1-3 years,> 3 years) were 1.16 (0.27-5.00), 0.50 0.17-1.49), and 0.34 (0.09-1.28), respectively. Longer follow-up tended to be associated with better prevention of gastric cancer, although not to a significant extent. No significant difference in incidence of gastric cancer was observed between patients with Among patients with duodenal ulcer, which is known to be more prevalent in younger individuals, the incidence of gastric cancer was (32/2451 patients, 1.31%) and those with treatment failure (11/639 patients, 1.72% significantly less in those with successful eradication therapy (2/845 patients, 0.24%) than in those with treatment failure (3/216 patients, 1.39%). CONCLUSION: H pylori eradication therapy for peptic ulcer patients with a mean age of 52.9 years at registration did not significantly decrease the incidence of gastric cancer.