Objective: There are a number of susceptible factors for an increased risk of gastric cancer. Nitric oxide (NO) is considered to be associated with the development of a range of cancers. In particular, inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase (eNOS) are known to play a central role in the production of NO. Published studies relating to the association between eNOS  rs1799983, rs2070744, and iNOS  rs2297518 polymorphisms and the risk of gastric cancer risk are conflicting and inconclusive and require further analysis.
Materials and methods: This study involved a meta-analysis of case–control studies relating to eNOS  rs1799983, rs2070744, and iNOS  rs2297518 polymorphisms published prior to January 2018. Literature searches were carried out in PubMed, Embase, Web of Science, the Cochrane Library databases, and the Chinese National Knowledge Infrastructure. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were used to evaluate the strength of association based on genotype data. 
Results: A total of 1,356 cases and 1,791 controls were included from nine case–control studies involving eNOS  rs1799983 (G894T), rs2070744 (T-786C), and iNOS  rs2297518 (C150T) polymorphisms. Data analysis indicated that iNOS  rs2297518 was a risk factor for Helicobacter pylorus -positive gastric cancer when compared with H. pylorus -negative gastric cancer (p =0.003, OR [95% CI] =2.19 [1.31–3.66]). In addition, the allelic, dominant, and recessive models of eNOS  rs2070744 were significantly associated with a risk of gastric cancer (allelic model: p <0.00001, OR [95% CI] =0.23 [0.16–0.34]; dominant model: p <0.00001, OR [95% CI] =0.25 [0.15–0.42]; recessive model: p <0.00001, OR [95% CI] =0.16 [0.08–0.30]). No association was identified between eNOS  rs1799983 and the risk of gastric cancer (p >0.05).
Conclusion: iNOS  rs2297518 and eNOS  rs2070744 polymorphisms may represent susceptible factors for gastric cancer.
Keywords: inducible nitric oxide synthase, iNOS, endothelial nitric oxide synthase, eNOS, gastric cancer, meta-analysis