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Background: The association of ABO blood groups with gastric cancer risk was proposed decades ago, but the results have been inconsistent.Methods: We used two single nucleotide polymorphisms to determine ABO genotype in 4932 gastric cancer cases and 6158 controls of Chinese descent, and evaluated the associations of ABO blood groups and genotypes with risk of gastric cancer using multivariable logistic regression models. We also systematically reviewed published literature and performed a meta-analysis of all relevant studies.Results: In the case-control study, compared with blood group O, both blood group A and AB were associated with increased gastric cancer risk (for group A, odds ratio (OR) = 1.13, 95% confidence interval (CI): 1.02-1.24; for group AB, OR = 1.18, 95% CI: 1.02-1.36, respectively). Analyses of ABO genotypes revealed associations of AO and AB with risk of gastric cancer compared with OO genotype. Consistent with the case-control study, meta-analysis of 40 studies including 33,613 cases and 2,431,327 controls demonstrated that blood group A (OR = 1.19, 95% CI: 1.13-1.25) and AB (OR = 1.09, 95% CI: 1.03-1.16) were associated with increased risk of gastric cancer.Conclusions: Our analyses validated the association of blood group A with risk of gastric cancer, and suggested that blood group AB was also associated with gastric cancer risk. Functional investigations are warranted to elucidate the exact mechanism of ABO blood groups in gastric carcinogenesis. [ABSTRACT FROM AUTHOR]