Nucleotide excision repair gene polymorphisms and risk of advanced colorectal adenoma: XPC polymorphisms modify smoking-related risk.

OBJECTIVES

Nucleotide excision repair enzymes remove bulky damage caused by environmental agents, including carcinogenic polycyclic aromatic hydrocarbons found in cigarette smoke, a risk factor for colorectal adenoma. Among participants randomized to the screening arm of the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial, we studied the risk of advanced colorectal adenoma in relation to cigarette smoking and selected single nucleotide polymorphisms (SNP) in the nucleotide excision repair pathway.

METHODS

Cases (n = 772) were subjects with left-sided advanced adenoma (>1 cm in size, high-grade dysplasia, or villous characteristics). Controls (n = 777) were screen-negative for left-sided polyps by sigmoidoscopy. DNA was extracted from blood samples and 15 common nonsynonymous SNPs in seven-nucleotide excision repair genes [XPC, RAD23B (hHR23B), CSB (ERCC6), XPD (ERCC2), CCNH, XPF (ERCC4), and XPG (ERCC5)] were genotyped.

RESULTS

None of the studied SNPs were independently associated with advanced adenoma risk. Smoking was related to adenoma risk and XPC polymorphisms (R492H, A499V, K939Q) modified these effects (P(interaction) from 0.03-0.003). Although the three XPC variants were in linkage disequilibrium, a multivariate logistic regression tended to show independent protective effects for XPC 499V (P(trend) = 0.06), a finding supported by haplotype analysis (covariate-adjusted global permutation P = 0.03).

CONCLUSIONS

Examining a spectrum of polymorphic variants in nucleotide excision repair genes, we found evidence that smoking-associated risks for advanced colorectal adenoma are modified by polymorphisms in XPC, particularly haplotypes containing XPC 499V.