To evaluate contribution of polymorphisms of the XRCC1 gene to the risk of colorectal cancer, we conducted a case-control study of 209 colorectal cancer cases and 209 age-and gender-matched controls in the Korean population. We tested the hypothesis by constructing allele combinations with known SNP. Allelic variants of the XRCC1 gene at codons 194, 280 and 399 were analyzed in lymphocyte DNA by PCR-RFLP. We observed an increased risk of colorectal cancer associated with the 399Gln allele. The odds ratio (OR) was 1.61 (95% confidence interval [CI] 1.09-2.39) for the 399Gln allele. When combined allele-specific OR were calculated after estimating frequencies, 3 common allele combinations were found to be associated with an increased risk of colorectal cancer. The OR for the 194Trp-280Arg-399Arg was 1.48 (95% CI 5 1.06-2.07) using 194Arg-280Arg-399Arg as the reference. The OR for the 194Arg-280His-399Arg and the 194Arg-280Arg-399Gln were 1.78 (95% CI 5 1.09-2.89) and 1.78 (95% CI 5 1.23-2.59), respectively. Analysis after controlling for smoking, exercise and dietary habits indicated that alcohol consumption ( 80 g/week) is a significant risk factor of colorectal cancer (OR 5 2.60, 95% CI 5 1. 46-4.62). An increased risk for colorectal cancer was identified in alcohol drinkers with the risky allele combinations. Our results suggest that polymorphisms in the XRCC1 genes may contribute to colorectal cancer susceptibility, and some evidence was obtained of a genetic modification for the relationship between alcohol intake and colorectal cancer. ' 2005 Wiley-Liss, Inc.Key words: polymorphisms; XRCC1; genotype; allele; colorectal cancer; alcohol Colorectal cancer is one of the most commonly diagnosed cancers in North America and Western Europe, 1 and is the fourth most common cause of cancer in South Korea. 2 Inherited deficiencies in DNA repair have been associated with an individual's susceptibility to cancer. 3 Therefore, polymorphisms of DNA repair genes may increase the risk of colorectal cancer.The human XRCC1 gene, one of the DNA repair genes, was identified because of its ability to restore DNA repair activity in a Chinese hamster ovary mutant cell line EM9. 4 The XRCC1 protein is involved in base-excision repair, and interacts with DNA ligase III, DNA polymerase b, poly(ADP-ribose)polymerase (PARP), polynucleotide kinase and AP endonuclease I. 5-8 The base-excision repair pathway is designed to remove non-bulky base adducts, which are produced by methylation, oxidation or reduction by ionizing radiation or oxidative damage. 9,10 Three coding polymorphisms of the DNA repair gene XRCC1 (Arg194Trp, Arg280His and Arg399Gln) have been identified in man, suggesting altered efficiency due to amino acid substitutions. 11,12 Alcohol consumption has been associated with the production of reactive oxygen species, which are known to cause DNA lesions that can be removed by the DNA base-excision repair pathway. 13 Meta-analyses of alcohol consumption in relation to colorectal cancer have reported a small or moderate addit...