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The incidence of gastric cancer is higher in men than women. Epidemiological studies suggest that female hormones reduce gastric cancer risk. We examined the effect of ovarian-dependent female hormones on Helicobacter pylori-induced gastric cancer in hypergastrinemic INS-GAS mice. Male and female sexually intact or ovariectomized (OVX) mice were inoculated with H.pylori SS1 or vehicle-only at 10 weeks of age, and tissues were evaluated at 16 or 28 weeks post-infection (WPI). A subset of OVX females were supplemented with 17β-estradiol (E2), beginning at 16 WPI. Stomachs were evaluated by histopathology, Ki-67 proliferation index, H.pylori quantitative culture and quantitative polymerase chain reaction for messenger RNA expression of inducible nitric oxide synthase (iNOS) and inflammatory cytokines. Infected OVX females developed significantly more severe gastritis (P H.pylori-induced gastric cancer in a mouse model. [ABSTRACT FROM AUTHOR]