Assessing tumor mutations to gain insight into base excision repair sequence polymorphisms and smoking in colon cancer.

DNA repair enzymes function in major pathways to reverse DNA damage, including base excision repair (BER). Missense polymorphisms in BER repair genes may contribute to differences in DNA repair capacity, specific mutations, and susceptibility to cancer in the presence of exposure to carcinogens such as cigarette smoking. In a study of 1,604 incident colon cancer cases and 1,969 matched population-based controls genotyped for BER variants OGG1 (S326C) and XRCC1 (R194W, R280H, and R399Q), we found no associations with colon cancer overall. However, a 2-fold increased risk of BRAF V600E tumor mutation was observed in current and former cigarette smokers homozygous for the OGG1 polymorphism (odds ratio, 2.2; 95% confidence interval, 1.02-4.9, recessive model); similar associations were not observed for microsatellite instability, CpG island methylator phenotype, KRAS2 mutations, or TP53 mutations. The XRCC1 R194W polymorphism was associated with a modest increased risk of TP53 tumor mutations in those who regularly smoked cigarettes (odds ratio, 1.4; 95% confidence interval, 1.02-1.9). These findings point to the importance of studying tumor mutations when examining DNA repair polymorphisms and cigarette smoke exposure to identify potentially relevant associations with colorectal cancer.