Assessment of interaction and confounding effects in logistic regression model: An application in a case-control study of stomach cancer

Stomach cancer (SC) is a major cause of cancer death worldwide. Stomach cancer is the second most common cancer in men and third in women in Turkey. Glutathione S-transferases (GSTs) appear to play a critical role in the protection from the effects of carcinogens. The contribution of GSTM1 and GSTT1 genotypes to susceptibility to the risk of SC and their interaction with cigarette smoking are still unclear in Turkish population. The aim of this study was to determine whether there was any association between genetic polymorphisms of GSTM1 and GSTT1 and SC as well as any interaction between polymorphisms and smoking.The case-control study was carried out in İzmir, Turkey. The data were collected by questionnaire from 127 SC cases and 101 healthy controls. The relationships between SC and determined risk factors were assessed using ORs and 95 percent CIs derived from univariate, stratified and multivariate analyses.The finding of the study showed that the prevalences of GSTM1 and GSTT1 null genotypes were 58.2 percent and 22.8 percent in cases, 46.5 percent and 22.2 percent in controls, respectively. In stratified analysis, we found that gender and age were confounder. There were no interactions in all multivariate analysis. This study revealed that GSTM1 polymorphism in SC has a potential role for interaction between this polymorphism and smoking. Our data suggested an increased risk for GSTM1 genotype although a significant association was not found. There was no association for GSTT1 genotype in cases and controls.