DNA repair gene XRCC3 codon 241 polymorphism, its interaction with smoking and XRCC1 polymorphisms, and bladder cancer risk. 
DNA repair efficiency varies among individuals, with reduced repair capacity as a risk factor for various cancers.  This variability could be partly explained by allelic variants for different DNA repair genes.  We examined the role of a common polymorphism in the XRCC3 gene (codon 241: threonine to methionine change) and bladder cancer risk.  This gene plays a role in the homologous recombination pathway, which repairs double-strand breaks.  The functional consequences of the XRCC3 codon 241 polymorphism are still unknown.  We hypothesized that this polymorphism could affect repair of smoking-associated DNA damage and could thereby affect bladder cancer risk.  We genotyped 233 bladder cancer cases and 209 controls who had been frequency matched to cases on age, sex, and ethnicity.  We observed little evidence of a positive association between subjects who carried at least one copy of the codon 241 Met allele and bladder cancer (odds ratio: 1.3; 95% confidence interval: 0.9-1.9).  Among heavy smokers, individuals with the Met allele had about twice the risk of those without it; however, a test of interaction was not statistically significant (P = 0.26).  Previously, we observed in these subjects an association between bladder cancer risk and allelic variants of the XRCC1 gene, which is involved in the repair of base damage and single-strand breaks.  In this study, we found some evidence for a gene-gene interaction between the XRCC1 codon 194 and XRCC3 codon 241 polymorphisms (P = 0.09) and some support for a possible gene-gene-smoking three-way interaction (P = 0.08).