Abstract Background Previous studies have found that polymorphisms of the DNA repair gene X-ray repair cross-complementing group 1(XRCC1) and environmental factors are both associated with an increased risk of stomach cancer, but no study has reported on the potential additive effect of these factors among Thai people. The aim of this study was to investigate whether the risk of stomach cancer from XRCC1 gene polymorphisms was modified by environmental factors in the Thai population. Methods Hospital-based matched case-control study data were collected from 101 new stomach cancer cases and 202 controls, which were recruited from2002 to 2006 and were matched for gender and age. Genotype analysis was performed using real-time PCR-HRM. The data were analysed by the chi-square test and conditional logistic regression. Results The Arg/Arg homozygote polymorphism of the XRCC1 gene was associated with an increased risk of stomach cancer in the Thai population (OR adj, 3.7; 95%CI, 1.30–10.72) compared with Gln/Gln homozygosity. The effect of the XRCC1gene on the risk of stomach cancer was modified by both a high intake of vegetable oils and salt (p = 0.036 and p = 0.014), particularly for the Arg/Arg homozygous genotype. There were, however, no additive effects on the risk of stomach cancer between variants of the XRCC1gene and smoking,alcohol or pork oil consumption. Conclusions The effect of the XRCC1 gene homozygosity, particularly Arg/Arg, on the risk for stomach cancer was elevated by a high intake of vegetable oils and salt.
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