Background: The rate of human T lymphotropic virus type 1 (HTLV-1) positivity among residents of Kamigoto, Japan, is extremely high (15%). Although the rate of Helicobacter pylori positivity in Kamigoto is almost the same as that in other areas of Japan, the incidence of gastric cancer in Kamigoto is lower. This study examined whether HTLV-1 infection affects H. pylori infection and the development of gastric cancer.
Methods: The study involved 5686 patients >40 years of age who provided serum specimens for HTLV-1 antibody testing during 1989-1992. A total of 1812 patients underwent gastric endoscopy during the follow-up period. Of these, 497 were HTLV-1 seropositive. Data for these patients were compared with those for 497 HTLV-1-seronegative control patients matched for age, sex, and follow-up duration. We followed these groups until 2003 and determined the cumulative incidence rate of gastric cancer.
Results: The rate of H. pylori positivity was 61.7% in the HTLV-1-positive group and 71.6% in the HTLV-1-negative group (P = .07). Fourteen HTLV-1-positive patients (2.8%) had gastric cancer, compared with 35 patients (7.0%) in the HTLV-1-negative group (odds ratio, 0.38; 95% confidence interval, 0.21-0.70; P = .0028).
Conclusion: HTLV-1 infection likely reduces the risk of H. pylori infection and proliferation and, thereby, the risk of gastric cancer.