Search

A recent hypothesis-free pathway-level analysis of genome-wide association study (GWAS) datasets suggested that the overall genetic variation measured by single nucleotide polymorphisms (SNPs) in the nucleotide excision repair (NER) pathway genes was associated with breast cancer (BC) risk, but no detailed SNP information was provided. To substantiate this finding, we performed a larger meta-analysis of 14 previously published GWAS datasets in the Discovery, Biology and Risk of Inherited Variants in Breast Cancer (DRIVE) study with 53,107 subjects of European descent. Using a hypothesis-driven approach, we selected 138 candidate genes from the NER pathway using the "Molecular Signatures Database (MsigDB)" and "PathCards". All SNPs were imputed using IMPUTE2 with the 1000 Genomes Project Phase 3. Logistic regression was used to estimate BC risk, and pooled ORs for each SNP were obtained from the meta-analysis using the false discovery rate for multiple test correction. RegulomeDB, HaploReg, SNPinfo and expression quantitative trait loci (eQTL) analysis were used to assess the SNP functionality. We identified four independent SNPs associated with BC risk, BIVM-ERCC5 rs1323697&#95;C (OR = 1.06, 95% CI = 1.03-1.10), GTF2H4 rs1264308&#95;T (OR = 0.93, 95% CI = 0.89-0.97), COPS2 rs141308737&#95;C deletion (OR = 1.06, 95% CI = 1.03-1.09) and ELL rs1469412&#95;C (OR = 0.93, 95% CI = 0.90-0.96). Their combined genetic score was also associated with BC risk (OR = 1.12, 95% CI = 1.08-1.16, p trend < 0.0001). The eQTL analysis revealed that BIVM-ERCC5 rs1323697 C and ELL rs1469412 C alleles were correlated with increased mRNA expression levels of their genes in 373 lymphoblastoid cell lines (p = 0.022 and 2.67 × 10 -22 , respectively). These SNPs might have roles in the BC etiology, likely through modulating their corresponding gene expression., (© 2019 UICC.)

The benefits of platinum-based chemotherapy (PBC) on survival of esophageal squamous cell carcinoma (ESCC) patients are inexplicit due to the varied therapeutic effects. Nucleotide excision repair (NER) pathway plays a vital role in removing platinum-DNA adducts in tumor cells and hence may modulate the therapeutic effect and survival outcome. The present study assessed the associations of 26 potentially functional regulatory single nucleotide polymorphisms (rSNPs) in nine core NER genes with disease-free survival (DFS) and overall survival (OS) in 339 ESCC patients. We found that ERCC2 rs2097215 T and rs3916788 A, ERCC5 rs3759497 A and XPC rs3731054 C alleles were associated with unfavorable DFS. Patients carrying high-risk allele group (HRG, 5-8 risk alleles) had a significantly shorter DFS, compared with those carrying low-risk alleles (LRG, 0-4 risk alleles) [adjusted hazards ratio (HR adj ) = 1.64, 95%CI = 1.23-2.19, P adj  < 0.001]. Three of these SNPs (ie, ERCC2 rs2097215 T and rs3916788 A and ERCC5 rs3759497 A) were also significantly associated with a poorer OS (HRG vs LRG: HR adj  = 1.75, 95%CI = 1.23-2.47, P adj  = 0.002). The expression quantitative trait loci (eQTL) analysis revealed significant genotype-expression correlations for ERCC5 rs3759497 and ERCC2 2097215 and rs3916788, which suggest regulatory roles of these SNPs. It appears that these NER variants may independently or jointly exert an impact on survival outcome of Chinese ESCC patients undergoing adjuvant platinum-based therapy. Large studies are warranted to validate these findings., (© 2018 Wiley Periodicals, Inc.)

The incidence of squamous cell carcinoma of the oropharynx (SCCOP) continues to rise because of increasing rates of human papillomavirus (HPV) infection. Inherited polymorphisms in DNA repair pathways may influence the risk of SCCOP development and the prognosis of SCCOP. We sought to determine whether polymorphisms in microRNA (miRNA)-binding sites within 3'-untranslated regions (3'UTRs) of genes in DNA repair pathways modulate the risk of SCCOP recurrence. We evaluated the associations between nine such polymorphisms and SCCOP recurrence in 1,008 patients with incident SCCOP using the log-rank test and multivariable Cox models. In an analysis of all the patients, patients with variant genotypes of BRCA1 rs12516 and RAD51 rs7180135 had better disease-free survival (log-rank, p = 0.0002 and p = 0.0003, respectively) and lower risk of SCCOP recurrence (hazard ratio [HR], 0.5, 95% confidence interval [CI], 0.2-0.8, and HR, 0.5, 95% CI, 0.3-0.9, respectively) than patients with common homozygous genotypes of the two polymorphisms after multivariable adjustment. Moreover, in tumor HPV16-positive patients, patients with variant genotypes of the same two polymorphisms also had better disease-free survival (log-rank, p = 0.004 and p = 0.003, respectively) and lower recurrence risk (HR, 0.2, 95% CI, 0.1-0.6, and HR, 0.2, 95% CI, 0.0-0.7, respectively) than patients with common homozygous genotypes of the two polymorphisms. No such significant associations were found for other polymorphisms. These findings support significant roles of BRCA1 rs12516 and RAD51 rs7180135 in modifying the risk of recurrence of SCCOP, particularly HPV16-positive SCCOP. However, these results must be validated in larger studies., (© 2017 UICC.)

Nucleotide excision repair (NER) plays a critical role in the development of smoking-related cancers. We hypothesize that mRNA expression levels of NER genes are associated with risk of the squamous cell carcinoma of head and neck (SCCHN). To test this hypothesis, we conducted a case-control study of 260 SCCHN patients and 246 cancer-free controls by measuring the mRNA expression levels of eight core NER genes in cultured peripheral lymphocytes. Compared with the controls, cases had statistically significantly lower expression levels of DDB1 and ERCC3 (P = 0.015 and 0.041, respectively). Because DDB1 and ERCC3 expression levels were highly correlated, we used DDB1 for further multivariate analyses and modeling. After dividing the subjects by controls' quartiles of expression levels, we found an association between an increased risk of SCCHN and low DDB1 expression levels [adjusted ORs and 95% CIs: 1.92 and 1.11-3.32, 1.48 and 0.85-2.59, 2.00 and 1.15-3.45 for the 2nd-4th quartiles, respectively, compared with the 1st quartile; Ptrend = 0.026]. We also identified a multiplicative interaction between sex and DDB1 expression levels (P = 0.007). Finally, the expanded model with gene expression levels, in addition to demographic and clinical variables, on SCCHN risk was significantly improved, especially among men. In conclusion, reduced DDB1 expression levels were associated with an increased risk of SCCHN. However, these results need to be validated in larger studies., (© The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Genetic variants of nucleotide excision repair (NER) genes have been extensively investigated for their roles in the development of prostate cancer (PCa); however, the published results have been inconsistent. In a hospital-based case-control study of 1,004 PCa cases and 1,055 cancer-free controls, we genotyped eight potentially functional single nucleotide polymorphisms (SNPs) of NER genes (i.e., XPC, rs2228001 T>G and rs1870134 G>C; XPD, rs13181 T>G and rs238406 G>T; XPG, rs1047768 T>C, rs751402 C>T, and rs17655 G>C; and XPF, rs2276464 G>C) and assessed their associations with risk of PCa by using logistic regression analysis. Among these eight SNPs investigated, only XPC rs1870134 CG/CC variant genotypes were associated with a decreased risk of prostate cancer under a dominant genetic model (adjusted odds ratio [OR] = 0.77, 95% confidence interval [CI] = 0.64-1.91, P = 0.003). Phenotype-genotype analysis also suggested that the XPC rs1870134 CG/CC variant genotypes were associated with significantly decreased expression levels of XPC mRNA in a mix population of different ethnicities. These findings suggested that XPC SNPs may contribute to risk of PCa in Eastern Chinese men.

Genetic polymorphisms at miRNA-binding sites may affect miRNA-mediated gene regulation. Thus, miRNA-binding site polymorphisms in double-strand break (DSB) repair genes may affect DNA repair capacity, which in turn could affect cancer prognosis. To determine whether miRNA-binding site polymorphisms in DSB repair genes are associated with the risk of recurrence of squamous cell carcinoma of the non-oropharynx (SCCNOP), we used a log-rank test and multivariable Cox models to evaluate the associations between miRNA-binding site polymorphisms in DSB repair genes and SCCNOP recurrence. Compared with patients without common homozygous genotypes, patients with the variant genotypes of ATM rs227091, LIG3 rs4796030, and RAD51 rs7180135 had significantly better disease-free survival (DFS) (log-rank P = 0.046, 0.002, and 0.041, respectively) and lower risk of disease recurrence [HR (95% CI) = 0.7 (0.6-0.9), 0.6 (0.5-0.9), and 0.7 (0.6-0.9), respectively]. Furthermore, patients with the variant genotypes of these 3 polymorphisms had significantly lower recurrence risk than those without common homozygous genotypes did [HR = 0.3 (95% CI = 0.2-0.7)]. Among patients who received chemoradiation, those with the individual or combined variant genotypes of the three polymorphisms had a significantly lower risk of disease recurrence than those with the individual or combined common homozygous genotypes did. The individual or combined variant genotypes of the ATM rs227091, LIG3 rs4796030, and RAD51 rs7180135 polymorphisms significantly modify the risk of SCCNOP recurrence, particularly for patients treated with chemoradiation. Future prospective studies with larger sample sizes are warranted to validate these findings to enable more effective personalized treatment for SCCNOP patients., (© The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Background: Adjuvant chemotherapy in patients with resected esophageal squamous cell cancer (ESCC) remains controversial for its uncertain role in improving overall survival (OS). Nucleotide excision repair (NER) removes DNA-adducts in tumor cells induced by the platinum-based chemotherapy and thus may modulate efficacy of the treatment. The present study evaluated if single nucleotide polymorphisms (SNPs) of NER genes were prognostic biomarkers in ESCC patients treated with platinum-based adjuvant chemotherapy (PAC)., Methods: The analysis included 572 patients, for whom six SNPs of NER genes [i.e., XPC (rs1870134 and rs2228001), ERCC2/XPD rs238406 and ERCC5/XPG (rs2094258, rs2296147 and rs873601)] were detected with the TaqMan assay. Kaplan-Meier analyses and Cox proportional hazards models were used to evaluate their associations with disease free survival (DFS) and OS of these ESCC patients receiving PAC. Receiving operating characteristic curve analysis was used to evaluate the role of the risk genotypes in the DFS and OS., Results: We found that ERCC5/XPG rs2094258 and rs873601 and ERCC2/XPD rs238406 SNPs were independently associated with poorer DFS and OS of ESCC patients [ERCC5/XPG rs2094258: CT+TT vs. CC: adjusted hazards ratio (adjHR) = 1.68 and P = 0.012 for DFS; adjHR = 1.99 and P = 0.0001 for OS; ERCC5/XPG rs873601: GA+GG vs. AA: adjHR = 1.59 and P = 0.024 for DFS; adjHR = 1.91 and P = 0.0005 for OS; ERCC2/XPD rs238406: TT vs. GG+GT: adjHR = 1.43 and P = 0.020 for DFS; adjHR = 1.52 and P = 0.008 for OS]. These HRs increased as the number of risk genotypes increased in the combined analysis. The model combining the risk genotypes with clinical characteristics or the TNM stage system was better in predicting outcomes in ESCC patients with PAC., Conclusion: SNPs of ERCC2/XPD and ERCC5/XPG may independently and jointly predict survival of ESCC patients treated with PAC in this study population. Further validation in other study populations is warranted.

Functional genetic variants of DNA repair genes may alter the host DNA repair capacity, and thus influence efficiency of therapies. We genotyped eight potentially functional single nucleotide polymorphisms (SNPs) in genes (i.e. ERCC1, XPA, XPC, XPD and XPG) involved in the nucleotide excision repair (NER) pathway in 496 Japanese gastric cancer patients, and assessed overall survival and recurrence-free survival. The combined effects of risk genotypes of these eight SNPs in Japanese patients were further replicated in 356 North-American gastric cancer patients. In Japanese patients, we found that the XPC rs2228000 TT genotype was associated with shorter overall survival [hazards ratio (HR) = 1.75, 95% confidence interval (95% CI) = 1.07-2.86] and recurrence-free survival (HR = 2.17, 95% CI = 1.19-3.95), compared with CC/CT genotypes, and the XPG rs17655 CC genotype was associated with shorter overall survival (HR = 1.60, 95% CI = 1.08-2.36), compared with GG/CG genotypes. The number of observed risk genotypes in the combined analysis was associated with shorter overall survival and recurrence-free survival in a dose-response manner (P(trend) = 0.006 and P(trend) < 0.000) in Japanese patients; specifically, compared with those with ≤1 risk genotypes, those with ≥2 risk genotypes showed markedly shorter overall survival (HR = 1.79, 95% CI = 1.18-2.70) and recurrence-free survival (HR = 2.80, 95% CI = 1.66-4.73). The association between ≥2 risk genotypes and shorter overall survival was not significant (HR = 1.26, 95% CI = 0.82-1.94) in North-American patients, but the trends were similar in these two groups of patients. These data show that functional SNPs in NER core genes may impact survival in Japanese gastric cancer patients., (© The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Genetically determined capacity for NER may modulate both cancer risk and prognosis. Thus, we evaluated associations of seven selected variants in the NER core genes with recurrence risk in 658 squamous cell carcinoma of the oropharynx (SCCOP) patients treated principally by radiation. The seven polymorphisms in the core NER genes (XPC-rs2228000, XPC-rs2228001, XPD-rs1799793, XPD-rs13181, XPG-rs17655, ERCC1-rs3212986 and XPA-rs1800975) were genotyped using PCR-RFLP method and log-rank test and multivariable Cox models were used to evaluate the associations in both dominant and recessive genetic models. In a dominant model, we found that polymorphisms of XPC-rs2228000, XPD-rs1799793 and XPG-rs17655 were significantly associated with disease-free survival (log-rank, p = 0.014; p = 0.00008; p = 0.0007, respectively), and these polymorphisms were significantly associated with recurrence risk of SCCOP (hazard ratio (HR) = 1.6, 95% confidence interval (CI) 1.1-2.3 for XPC-rs2228000; HR = 0.4, 95% 0.3-0.6 for XPD-rs1799793 and HR = 0.5, 95% CI 0.4-0.8 for XPG-rs17655) after multivariable adjustment. Moreover, the borderline significant or significant associations were also found for these three polymorphisms in HPV16/18-positive SCCOP patients (HR = 1.6, 95% CI 1.0-4.1 for XPC-rs2228000; HR = 0.2, 95% CI 0.1-0.5 for XPD-rs1799793 and HR = 0.1, 95% CI 0.0-0.9 for XPG-rs17655). However, similarly significant associations were not found for these polymorphisms in a recessive model. These findings suggest that polymorphisms of XPC-rs2228000, XPD-rs1799793 and XPG-rs17655 in the NER core genes may contribute to recurrence risk of SCCOP, particularly HPV-positive SCCOP, in a dominant but not in a recessive model. However, validation of these results is warranted., (Copyright © 2013 UICC.)

Melanoma is the most highly malignant skin cancer, and nucleotide excision repair (NER) is involved in melanoma susceptibility. In this analysis of 1,042 melanoma patients, we evaluated whether genetic variants of NER genes may predict survival outcome of melanoma patients. We used genotyping data of 74 tagging single-nucleotide polymorphisms (tagSNPs) in eight core NER genes from our genome-wide association study (including two in XPA, 14 in XPC, three in XPE, four in ERCC1, 10 in ERCC2, eight in ERCC3, 14 in ERCC4, and 19 in ERCC5) and evaluated their associations with prognosis of melanoma patients. Using the Cox proportional hazards model and Kaplan-Meier analysis, we found a predictive role of XPE rs28720291, ERCC5 rs4150314, XPC rs2470458, and ERCC2 rs50871 SNPs in the prognosis of melanoma patients (rs28720291: AG vs. GG, adjusted hazard ratio (adjHR)=11.2, 95% confidence interval (CI) 3.04-40.9, P=0.0003; rs4150314: AG vs. GG, adjHR=4.76, 95% CI 1.09-20.8, P=0.038; rs2470458: AA vs. AG/GG, adjHR=2.11, 95% CI 1.03-4.33, P=0.040; and rs50871: AA vs. AC/CC adjHR=2.27, 95% CI 1.18-4.35, P=0.015). Patients with an increasing number of unfavorable genotypes had markedly increased death risk. Genetic variants of NER genes, particularly XPE rs28720291, ERCC5 rs4150314, XPC rs2470458, and ERCC2 rs50871, may independently or jointly modulate survival outcome of melanoma patients. Because our results were based on a median follow-up of 3 years without multiple test corrections, additional large prospective studies are needed to confirm our findings.

Suboptimal cellular DNA repair capacity (DRC) has been shown to be associated with enhanced cancer risk, but genetic variants affecting the DRC phenotype have not been comprehensively investigated. In this study, with the available DRC phenotype data, we analyzed correlations between the DRC phenotype and genotypes detected by the Illumina 317K platform in 1,774 individuals of European ancestry from a Texas lung cancer genome-wide association study. The discovery phase was followed by a replication in an independent set of 1,374 cases and controls of European ancestry. We applied a generalized linear model with single nucleotide polymorphisms as predictors and DRC (a continuous variable) as the outcome. Covariates of age, sex, pack-years of smoking, DRC assay-related variables, and case-control status of the study participants were adjusted in the model. We validated that reduced DRC was associated with an increased risk of lung cancer in both independent datasets. Several suggestive loci that contributed to the DRC phenotype were defined in ERCC2/XPD, PHACTR2, and DUSP1. In summary, we determined that DRC is an independent risk factor for lung cancer, and we defined several genetic loci contributing to DRC phenotype.

In vitro benzo[a]pyrene diol epoxide (BPDE)-induced DNA adducts in cultured peripheral lymphocytes have been shown to be a phenotypic biomarker of individual's DNA repair phenotype that is associated with cancer risk. In this study, we explored associations between genotypes of base-excision repair genes (PARP1 Val762Ala, APEX1 Asp148Glu, and XRCC1 Arg399Gln) and in vitro BPDE-induced DNA adducts in cultured peripheral blood lymphocytes in 706 cancer-free non-Hispanic white subjects. We found that levels of BPDE-induced DNA adducts were significantly higher in ever smokers than in never smokers and that individuals with the Glu variant genotypes (i.e., Asp/Glu and Glu/Glu) exhibited lower levels of BPDE-induced DNA adducts than did individuals with the common Asp/Asp homozygous genotype (median RAL levels: 32.0 for Asp/Asp, 27.0 for Asp/Glu, and 17.0 for Glu/Glu, respectively; P(trend) = 0.030). Further stratified analysis showed that compared with individuals with the common APEX1-148 homozygous Asp/Asp genotype, individuals with the APEX1-148Asp/Glu genotype or the Glu/Glu genotype had a lower risk of having higher-level adducts (adjusted OR = 0.60, 95% CI: 0.36-0.98 and adjusted OR = 0.47, 95% CI: 0.26-0.86, respectively; P(trend) = 0.012) among smokers. Such an effect was not observed in non-smokers. However, there was no significant interaction between the APEX1 Asp148Glu polymorphism and smoking exposure in this study population (P = 0.512). Additional genotype-phenotype analysis found that the APEX1-148Glu allele had significantly increased expression of APEX1 mRNA in 270 Epstein-Barr virus-transformed lymphoblastoid cell lines, which is likely associated with more active repair activity. Our findings suggest that the functional APEX1-148Glu allele is associated with reduced risk of having high levels of BPDE-induced DNA adducts mediated with high levels of mRNA expression.

Purpose: Platinum-based regimens are the standard chemotherapy for patients with advanced non-small-cell lung cancer (NSCLC). DNA repair capacity (DRC) in tumor cells plays an important role in resistance to platinum-based drugs. We have previously reported that efficient DRC, as assessed by an in vitro lymphocyte-based assay, was a determinant of poor survival in patients with NSCLC in a relatively small data set. In this larger independent study of 591 patients with NSCLC, we further evaluated whether DRC in peripheral lymphocytes predicts survival of patients with NSCLC who receive platinum-based chemotherapy., Patients and Methods: All patients were recruited at The University of Texas MD Anderson Cancer Center and donated blood samples before the start of any chemotherapy. We measured DRC in cultured T lymphocytes by using the host-cell reactivation assay, and we assessed associations between DRC in peripheral lymphocytes and survival of patients with NSCLC who were treated with first-line platinum-based chemotherapy., Results: We found an inverse association between DRC in peripheral lymphocytes and patient survival. Compared with patients in the low tertile of DRC, patients with NSCLC in the high tertile of DRC had significantly worse overall and 3-year survival (adjusted hazard ratio [HR], 1.33; 95% CI, 1.04 to 1.71; P = .023; and HR, 1.35; 95% CI, 1.04 to 1.76; P = .025, respectively). This trend was more pronounced in patients with early-stage tumors, adenocarcinoma, or squamous cell carcinoma., Conclusion: We confirmed that DRC in peripheral lymphocytes is an independent predictor of survival for patients with NSCLC treated with platinum-based chemotherapy.

DNA repair genes are important for maintaining genomic stability and limiting carcinogenesis. We analyzed all single nucleotide polymorphisms (SNPs) of 125 DNA repair genes covered by the Illumina HumanHap300 (v1.1) BeadChips in a previously conducted genome-wide association study (GWAS) of 1154 lung cancer cases and 1137 controls and replicated the top-hits of XRCC4 SNPs in an independent set of 597 cases and 611 controls in Texas populations. We found that six of 20 XRCC4 SNPs were associated with a decreased risk of lung cancer with a P-value of 0.01 or lower in the discovery dataset, of which the most significant SNP was rs10040363 (P for allelic test=4.89 x 10⁻⁴). Moreover, the data in this region allowed us to impute a potentially functional SNP rs2075685 (imputed P for allelic test=1.3 x 10⁻³). A luciferase reporter assay demonstrated that the rs2075685G>T change in the XRCC4 promoter increased expression of the gene. In the replication study of rs10040363, rs1478486, rs9293329, and rs2075685, however, only rs10040363 achieved a borderline association with a decreased risk of lung cancer in a dominant model (adjusted OR=0.80, 95% CI=0.62-1.03 and P=0.079). In the final combined analysis of both the Texas GWAS discovery and replication datasets, the strength of the association was increased for rs10040363 (adjusted OR=0.77, 95% CI=0.66-0.89, P(dominant)=5 x 10⁻⁴ and P for trend=5 x 10⁻⁴) and rs1478486 (adjusted OR=0.82, 95% CI=0.71-0.94, P(dominant)=6 x 10⁻³ and P for trend=3.5 x 10⁻³). Finally, we conducted a meta-analysis of these XRCC4 SNPs with available data from published GWA studies of lung cancer with a total of 12,312 cases and 47,921 controls, in which none of these XRCC4 SNPs was associated with lung cancer risk. It appeared that rs2075685, although associated with increased expression of a reporter gene and lung cancer risk in the Texas populations, did not have an effect on lung cancer risk in other populations. This study underscores the importance of replication using published data in larger populations., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Mutagen challenge and DNA repair assays have been used in case-control studies for nearly three decades to assess human cancer risk. The findings still engender controversy because blood was drawn after cancer diagnosis so the results may be biased, a type called 'reverse causation'. We therefore used Epstein-Barr virus-transformed lymphoblastoid cell lines established from prospectively collected peripheral blood samples to evaluate lung cancer risk in relation to three DNA repair assays: alkaline Comet assay, host cell reactivation (HCR) assay with the mutagen benzo[a]pyrene diol epoxide and the bleomycin mutagen sensitivity assay. Cases (n = 117) were diagnosed with lung cancer between 0.3 and 6 years after blood collection and controls (n = 117) were frequency matched on calendar year and age at blood collection, gender and smoking history; all races were included. Case and control status was unknown to laboratory investigators. In unconditional logistic regression analyses, statistically significantly increased lung cancer odds ratios (OR(adjusted)) were observed for bleomycin mutagen sensitivity as quartiles of chromatid breaks/cell [relative to the lowest quartile, OR = 1.2, 95% confidence interval (CI): 0.5-2.5; OR = 1.4, 95% CI: 0.7-3.1; OR = 2.1, 95% CI: 1.0-4.4, respectively, P(trend) = 0.04]. The magnitude of the association between the bleomycin assay and lung cancer risk was modest compared with those reported in previous lung cancer studies but was strengthened when we included only incident cases diagnosed more than a year after blood collection (P(trend) = 0.02), supporting the notion the assay may be a measure of cancer susceptibility. The Comet and HCR assays were unrelated to lung cancer risk.

Methylating agents are involved in carcinogenesis, and the DNA repair protein O(6)-methylguanine-DNA methyltransferase (MGMT) removes methyl group from O(6)-methylguanine. Genetic variation in DNA repair genes has been shown to contribute to susceptibility to squamous cell carcinoma of the head and neck (SCCHN). We hypothesize that MGMT polymorphisms are associated with risk of SCCHN. In a hospital-based case-control study of 721 patients with SCCHN and 1234 cancer-free controls frequency-matched by age, sex and ethnicity, we genotyped four MGMT polymorphisms, two in exon 3, 16195C>T and 16286C>T and two in the promoter region, 45996G>T and 46346C>A. We found that none of these polymorphisms alone had a significant effect on risk of SCCHN. However, when these four polymorphisms were evaluated together by the number of putative risk genotypes (i.e. 16195CC, 16286CC, 45996GT+TT, and 46346CA+AA), a statistically significantly increased risk of SCCHN was associated with the combined genotypes with three to four risk genotypes, compared with those with zero to two risk genotypes (adjusted odds ratio (OR)=1.27; 95% confidence interval (CI)=1.05-1.53). This increased risk was also more pronounced among young subjects (OR=1.81; 95% CI=1.11-2.96), men (OR=1.24; 95% CI=1.00-1.55), ever smokers (OR=1.25; 95%=1.01-1.56), ever drinkers (OR=1.29; 95% CI=1.04-1.60), patients with oropharyngeal cancer (OR=1.45; 95% CI=1.12-1.87), and oropharyngeal cancer with regional lymph node metastasis (OR=1.52; 95% CI=1.16-1.89). In conclusion, our results suggest that any one of MGMT variants may not have a substantial effect on SCCHN risk, but a joint effect of several MGMT variants may contribute to risk and progression of SCCHN, particularly for oropharyngeal cancer, in non-Hispanic whites., ((c) 2010 Elsevier B.V. All rights reserved.)

Purpose: Although cigarette smoking and alcohol use are known risk factors for squamous cell carcinoma of head and neck (SCCHN), only a few exposed individuals develop this disease, suggesting an individual susceptibility. In this study, we investigated the associations between genetically determined DNA repair capacity (DRC) for removing tobacco-induced DNA adducts and risk of SCCHN and tumor characteristics., Experimental Design: We measured DRC in cultured T lymphocytes using the host-cell reactivation assay in a hospital-based case-control study of 744 SCCHN patients and 753 age-, sex-, and ethnicity-matched cancer-free controls recruited from The University of Texas M.D. Anderson Cancer Center., Results: Patients with SCCHN had significantly lower mean DRC (8.84% +/- 2.68%) than controls (9.97% +/- 2.61%; P < 0.0001), and the difference accounted for approximately 2-fold increased risk of SCCHN [adjusted odds ratio (OR), 1.91; 95% confidence interval (CI), 1.52-2.40] after adjustment for other covariates. Compared with the highest DRC quartile of controls, this increased risk was dose dependent (second highest quartile: OR, 1.40; 95% CI, 0.99-1.98; third quartile: OR, 1.87; 95% CI, 1.34-2.62; and fourth quartile: OR, 2.76; 95% CI, 1.98-3.84, respectively; P(trend) < 0.0001). We also assessed the performance of DRC in risk prediction models by calculating the area of under the receiver operating characteristic curve. The addition of DRC to the model significantly improved the sensitivity of the expanded model. However, we did not find the association between DRC and tumor sites and stages., Conclusion: DRC is an independent susceptibility biomarker for SCCHN risk but not a tumor marker.

The nucleotide excision repair (NER) pathway is central in response to damage induced by environmental carcinogens. Efficiency of this pathway, probably genetically determined, may modulate individual risk of developing squamous cell carcinoma of the head and neck (SCCHN) as well as second primary malignancy (SPM) after the index tumor. We hypothesized that common non-synonymous and regulatory single-nucleotide polymorphisms (SNPs) in the NER core genes individually, and more probably collectively, associated with the risk of SPM. We genotyped for seven selected SNPs in 1376 incident SCCHN patients who were prospectively recruited between 1995 and 2006 and followed for SPM development. We found that 110 patients (8%) developed SPM: 43 (39%) second SCCHN; 38 (35%) other tobacco-associated sites and 29 (26%) other non-tobacco-associated sites. The associations of these SNPs with SPM risk were assessed assuming a recessive genetic model. We did not find any significant associations of each or in combination of the seven SNPs with SPM risk in the recessive models. However, when we explored the combined effect based on an alternatively dominant genetic model, we found that the number of observed risk genotypes was associated with a significantly increased SPM risk in a dose-response manner (P = 0.005) and patients with five to seven risk genotypes had a significantly 2.4-fold increased SPM risk compared with patients with zero to two risk genotypes. These findings suggest that a profile of NER core gene polymorphisms might collectively contribute to risk of SPM not in a recessive model but in a dominant model among patients with an index primary SCCHN. These findings need to be validated in future studies with larger sample sizes and longer follow-up time.

Numerous prospective and retrospective studies have clearly demonstrated a dose-related increased lung cancer risk associated with cigarette smoking, with evidence also for a genetic component to risk. In this study, using the two-stage clonal expansion stochastic model framework, for the first time we investigated the roles of both genetic susceptibility and smoking history in the initiation, clonal expansion, and malignant transformation processes in lung carcinogenesis, integrating information collected by a case-control study and a large-scale prospective cohort study. Our results show that individuals with suboptimal DNA repair capacity have enhanced transition rates of key events in carcinogenesis., ((c) 2008 Wiley-Liss, Inc.)

DNA repair is a complicated biological process, consisting of several distinct pathways, that plays a fundamental role in the maintenance of genomic integrity. The very important field of DNA repair and cancer risk has developed rapidly in the past decades. In this review of selected published data from our laboratory, we describe mostly our work on the study of phenotypic markers of nucleotide excision repair (NER), as measured by the benzo(a)pyrene diol epoxide (BPDE)/ultraviolet (UV)-induced mutagen sensitivity assays, BPDE-induced adduct assay, host cell reactivation (HCR)-DNA repair capacity (DRC) assay, reverse transcription-polymerase chain reaction (RT-PCR) assay and reverse-phase protein lysate microarray (RPP) assay, by using peripheral blood lymphocytes in a series of molecular epidemiological studies. Results of our studies suggest that individuals with reduced DRC have an elevated cancer risk. This finding needs additional validation by other investigators, and we also discussed issues in conducting this kind of research in the future.

It is generally accepted that glioma develops through accumulation of genetic alterations. We hypothesized that polymorphisms of candidate genes involved in the DNA repair pathways may contribute to susceptibility to glioma. To address this possibility, we conducted a study on 373 Caucasian glioma cases and 365 cancer-free Caucasian controls to assess associations between glioma risk and 18 functional single-nucleotide polymorphisms in DNA repair genes. We evaluated potential gene-gene and gene-environment interactions using a multianalytic strategy combining logistic regression, multifactor dimensionality reduction and classification and regression tree approaches. In the single-locus analysis, six single-nucleotide polymorphisms [ERCC1 3' untranslated region (UTR), XRCC1 R399Q, APEX1 E148D, PARP1 A762V, MGMT F84L, and LIG1 5'UTR] showed a significant association with glioma risk. In the analysis of cumulative genetic risk of multiple single-nucleotide polymorphisms, a significant gene-dosage effect was found for increased glioma risk with increasing numbers of adverse genotypes involving the aforementioned six single-nucleotide polymorphisms (P(trend) = 0.0004). Furthermore, the multifactor dimensionality reduction and classification and regression tree analyses identified MGMT F84L as the predominant risk factor for glioma and revealed strong interactions among ionizing radiation exposure, PARP1 A762V, MGMT F84L, and APEX1 E148D. Interestingly, the risk for glioma was dramatically increased in ionizing radiation exposure individuals who had the wild-type genotypes of MGMT F84L and PARP1 A762V (adjusted odds ratios, 5.95; 95% confidence intervals, 2.21-16.65). Taken together, these results suggest that polymorphisms in DNA repair genes may act individually or together to contribute to glioma risk.

ERCC4/XPF protein plays an important role in the nucleotide excision repair (NER) pathway, and deficiencies in the gene encoding it can lead to a repair-deficiency syndrome, xeroderma pigmentosum group F (XP-F). Common variants on this gene are assumed to be foreboding markers for lung cancer, and 4 selected SNPs in the ERCC4 gene were genotyped in a multi-center case-control study involving 1010 lung cancer patients and 1011 cancer-free controls in a Chinese Han population to test the hypothesis. A significant association to decreased risk of lung cancer was observed in major allele C of rs3136038 carriers (adjusted OR=0.57, 95% CI=0.39-0.84 for CT; adjusted OR=0.75, 95% CI=0.52-1.10 for CC; adjusted OR=0.68, 95% CI=0.46-0.99 for CT+CC, compared with genotype TT), and additionally, referenced with homozygote TT, the heterozygous genotype CT showed a distinct protective effect in younger subjects (adjusted OR=0.47, 95% CI=0.26-0.86), in males (adjusted OR=0.59, 95% CI=0.37-0.93), in non-smokers (adjusted OR=0.38, 95% CI=0.20-0.72), in subjects without family history of cancer (adjusted OR=0.52, 95% CI=0.34-0.80) and in adenocarcinomas patients (adjusted OR=0.51, 95% CI=0.31-0.84). Our finding indicated, for the first time, the polymorphism rs3136038 on the promotor region of ERCC4 may contribute to the etiology of lung cancer. Further functional studies on this locus and/or other genetic variants in highly linkage disequilibrium with it are warranted to elucidate the underlying molecular mechanisms of the association.

Besides secondhand smoke exposure, few other risk factors for lung cancer in lifetime never smokers have been identified. We present the estimates of lung cancer risk associated with suboptimal DNA repair capacity (DRC) measured by the host-cell reactivation assay in lifetime never smokers using data from 219 cases and 309 matched controls enrolled in a case-control study. Suboptimal DRC level (below the control median) conferred a significantly increased lung cancer risk in never smokers [odds ratio, 1.92; 95% confidence interval (95% CI), 1.3-2.9; P = 0.0024]. There was a 3.38-fold risk for individuals with DRC below the first quartile (95% CI, 1.8-6.3) compared with individuals with DRC above the third quartile. Secondhand smoke exposure in individuals with DRC below the control median was associated with a 3.81-fold risk of lung cancer (95% CI, 2.3-6.4). A 2.49-fold (95% CI, 1.1-5.6) risk was noted for the joint effects of lung cancer family history in first-degree relatives and suboptimal DRC. Relatives of probands (cases and controls) with lowest DRC (below the first quartile) were significantly more likely to be diagnosed with lung cancer (odds ratio, 2.69; 95% CI, 1.1-6.7) compared with relatives of probands with the most proficient DRC (above the third quartile). Relatives of probands with suboptimal (below the control median) versus proficient DRC also had an earlier age at diagnosis with lung cancer, although the only statistically significant difference was in female relatives (55.4 versus 67.7 years; P = 0.03).

Magnesium (Mg) is required for maintenance of genomic stability; however, data on the relationship between dietary Mg intake and lung cancer are lacking. In an ongoing lung cancer case-control study, we identified 1139 cases and 1210 matched healthy controls with data on both diet and DNA repair capacity (DRC). Dietary intake was assessed using a modified Block-NCI food frequency questionnaire and DRC was measured using the host-cell reactivation assay to assess repair in lymphocyte cultures. After adjustment for potential confounding factors including DRC, the odds ratios (ORs) and 95% confidence intervals (CIs) for lung cancer with increasing quartiles of dietary Mg intake were 1.0, 0.83 (0.66-1.05), 0.64 (0.50-0.83) and 0.47 (0.36-0.61), respectively, for all subjects (P-trend < 0.0001). Similar results were observed by histology and clinical stage of lung cancer. Low dietary Mg intake was associated with poorer DRC and increased risk of lung cancer. In joint effects analyses, compared with those with high dietary Mg intake and proficient DRC, the OR (95% CI) for lung cancer in the presence of both low dietary Mg and suboptimal DRC was 2.36 (1.83-3.04). Similar results were observed for men and women. The effects were more pronounced among older subjects (>60 years), current or heavier smokers, drinkers, those with a family history of cancer in first-degree relatives, small cell lung cancer and late-stage disease. These intriguing results need to be confirmed in prospective studies.

Although the role of environmental risk factors in the etiology of gliomas remains to be elucidated, accumulative epidemiological evidence suggests that genetic factors, such as variants in genes involved in DNA repair, may also play an important role. LIG4 and XRCC4 are known to form a complex and are functionally linked in the repair of double-stranded DNA breaks. To determine whether LIG4 and XRCC4 polymorphisms are associated with susceptibility to glioma and whether there are interactions between LIG4 and XRCC4, we conducted a case-control study of 771 glioma patients and 752 cancer-free controls, assessed the associations between glioma risk and 20 tagging SNPs, and evaluated their potential gene-gene interactions using the multifactor dimensionality reduction (MDR), interaction dendrogram, and entropy analysis. In the single-locus analysis, only one variant, the LIG4 SNP2 rs3093739:T>C (P-permutation=0.009) was significantly associated with risk of developing glioma. Haplotype analysis revealed an association of glioma risk with genetic variants in LIG4 block 1 (global P=0.011), and XRCC4 blocks 2 and 4 (both global P<0.0001). Moreover, the MDR analysis suggested a significant three-locus interaction model involving LIG4 SNP4 rs1805388:C>T, XRCC4 SNP12 rs7734849:A>T, and SNP15 rs1056503:G>T. Further dendrogram and graph analysis indicated a more-than-additive effect among these three loci. These results suggested that these variants may contribute to glioma susceptibility.

DNA mismatch repair (MMR) plays an important role in maintaining genome stability. Defects in MMR genes have been involved in several types of sporadic and hereditary cancers. hMLH1 is considered one of central members of the MMR pathway. We conducted a hospital-based case-control study to investigate associations of common variations in the hMLH1 gene and risk of lung cancer. A total of 500 cases and 517 controls were genotyped for seven SNPs in hMLH1. Overall, the rs1799977 I219V polymorphism was marginally associated with the risk of lung cancer (P=0.055). This association was much stronger in younger patients (P=0.01; odds ratio, 5.28; 95% CI 1.45-19.21) and lung squamous cell carcinoma (P=0.006; odds ratio, 3.65; 95% CI 1.44-9.24). These findings indicate that the hMLH1 rs1799977 polymorphism may contribute to the etiology of early-onset lung cancer as well as some specific subtype of lung cancer. Larger association studies are warranted to validate our findings and mechanistic studies are needed to elucidate the underlying molecular mechanisms of the association.

In a large case-control study, we previously reported that dietary intakes of zinc (Zn) and copper (Cu), but not selenium (Se), were inversely associated with lung cancer risk. Because Zn, Cu, Se, iron (Fe), and calcium (Ca) are important for maintaining DNA stability, we examined their associations with DNA repair capacity (DRC) measured by the lymphocyte host-cell reactivation assay in 1,139 cases and 1,210 of the controls. Dietary intake was reported in a food frequency questionnaire. In multivariate analyses, compared to those with high dietary Cu + proficient DRC, the odds ratio (95% confidence interval) [OR (95% CI)] for lung cancer for low Cu + suboptimal DRC was 2.54 (1.97-3.27). Similar results were observed for men and women. These effects were more pronounced in older and lean subjects, those with late-stage disease, and those with a family history of cancer in first-degree relatives. Compared to subjects with high Zn + proficient DRC, the OR for lung cancer for low Zn + suboptimal DRC was 1.82 (95% CI, 1.41-2.34), with pronounced effects in men, current smokers, subjects with longer duration of smoking, those with late-stage disease, or those with a family history of cancer. An OR of 1.94 (95% CI, 1.51-2.48) was observed for low Fe + suboptimal DRC compared with high Fe + proficient DRC, and pronounced effects appeared in older, lean subjects, those with longer duration of smoking, are heavier smokers, those with a late-stage disease, and those with a family history of cancer. No significant joint associations were seen for Se or Ca and DRC. Our joint associations between Cu-DRC, Zn-DRC and Fe-DRC and lung cancer risk require confirmation in prospective studies.

Purpose: To examine the role of suboptimal DNA repair capacity (DRC) for UV light-induced DNA damage in the development of nonmelanoma skin cancer (NMSC) and tumor progression., Experimental Design: We conducted a hospital-based case-control study of 255 patients with newly diagnosed NMSC [146 with basal cell carcinoma (BCC) and 109 with squamous cell carcinoma (SCC)] and 333 cancer-free controls. We collected information on demographic variables and risk factors from questionnaires, tumor characteristics from medical records, and lymphocytic DRC phenotype by the host-cell reactivation assay. Multivariable logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals (95% CI)., Results: Overall, there was a relative 16% reduction in DRC in NMSC patients compared with controls (P < 0.001 for BCC and for SCC, respectively). DRC below the controls' median value was associated with increased risk significantly for BCC (OR, 1.62; 95% CI, 1.07-2.45) but borderline for SCC (OR, 1.63; 95% CI, 0.95-2.79) after adjustment for age, sex, and other assay-related covariates. When the highest tertile of controls' DRC was used as the reference, the intermediate and low DRC were associated with a statistically significant trend for increasing risk for both BCC (P(trend) = 0.007) and SCC (P(trend) = 0.020). However, patients with aggressive or multiple SCC tended to have a higher DRC than those with nonaggressive or single SCC., Conclusions: Reduced DRC is an independent risk factor for BCC and single or nonaggressive SCC but not for multiple primaries, local aggressiveness, or recurrence of NMSC.

Susceptibility to cancer has been associated with DNA repair capacity, a global reflection of all functional variants, most of which are relatively rare. Among the 1,098 single nucleotide polymorphisms (SNP) identified in the eight core nucleotide excision repair genes, only a few are common nonsynonymous or regulatory SNPs that are potentially functional. We tested the hypothesis that seven selected common nonsynonymous and regulatory variants in the nucleotide excision repair core genes are associated with risk of squamous cell carcinoma of the head and neck (SCCHN) in a hospital-based, case-control study of 829 SCCHN cases and 854 cancer-free controls. Assuming a recessive genetic model, we found that only carriers of the XPC 499Val/Val genotype had a significantly increased SCCHN risk (adjusted odds ratio, 1.65; 95% confidence interval, 1.16-2.36). In analysis of the joint effects, the number of observed risk genotypes was associated with SCCHN risk in a dose-response manner (P for trend = 0.017) and those who carried four or more risk genotypes exhibited a borderline significant 1.23-fold increased SCCHN risk (adjusted odds ratio, 1.23; 95% confidence interval, 0.99-1.53). In the stratified analysis, the dichotomized combined effect of the seven SNPs was slightly more evident among older subjects, women, and laryngeal cancer. These findings suggest that these potentially functional SNPs may collectively contribute to susceptibility to SCCHN. These findings need to be validated in larger, independent studies.

The nicotine-derived nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) induces lung adenocarcinoma through formation of DNA adducts. Our previous research on susceptibility to tobacco-induced carcinogenesis focused on benzo[a]pyrene diol epoxide (BPDE) as the in vitro mutagen for phenotype measurements of DNA repair capacity (DRC) in mammalian cells. Here, we present a modified host-cell reactivation (HCR) assay to measure lymphocytic DRC for alkylating DNA damage as is induced by the tobacco-specific nitrosamine, NNK. We substituted dimethyl sulfate (DMS) to create alkylating damage in pCMVluc plasmid DNA and established the damage-repair dose-response curves in both normal and nucleotide excision repair-deficient lymphoblastoid cell lines and in phytohemagglutinin (PHA)-stimulated primary lymphocytes. We then successfully measured the DRC in PHA-stimulated lymphocytes from 48 patients with lung adenocarcinoma and 45 cancer-free controls and tested our hypothesis that lower DRC for alkylating damage is associated with an increased risk of lung adenocarcinoma. The cases exhibited a lower mean DRC than did the controls. A >3-fold increased risk (odds ratio = 3.21; 95% confidence interval = 1.25-8.21) was found for those with DRC levels below the control median. There was no correlation between the DRC measured with this DMS-HCR assay and that from the parallel BPDE-HCR assay. Interestingly, risk increased to >10-fold for those with sub-optimal DRC measured by both DMS- and BPDE-HCR assays. We conclude that variability in DRC is a risk factor for lung cancer and our results provide proof of principle for a new assay that can assess DRC for NNK-induced DNA damage.

Background: The nucleotide excision repair (NER) protein, xeroderma pigmentosum C (XPC), participates in recognizing DNA lesions and initiating DNA repair in response to DNA damage. Because mutations in XPC cause a high risk of cancer in XP patients, we hypothesized that inherited sequence variations in XPC may alter DNA repair and thus susceptibility to cancer., Methods: In this hospital-based case-control study, we investigated five XPC tagging, common single nucleotide polymorphisms (tagging SNPs) in 1,010 patients with newly diagnosed lung cancer and 1,011 matched cancer free controls in a Chinese population., Results: In individual tagging SNP analysis, we found that rs3731055AG+AA variant genotypes were associated with a significantly decreased risk of lung adenocarcinoma [adjusted odds ratio (OR), 0.71; 95% confidence interval (CI), 0.56-0.90] but an increased risk of small cell carcinomas [adjusted OR, 1.79; 95% CI, 1.05-3.07]. Furthermore, we found that haplotype ACCCA was associated with a decreased risk of lung adenocarcinoma [OR, 0.78; 95% CI, 0.62-0.97] but an increased risk of small cell carcinomas [OR, 1.68; 95% CI, 1.04-2.71], which reflected the presence of rs3731055A allele in this haplotype. Further stratified analysis revealed that the protective effect of rs3731055AG+AA on risk of lung adenocarcinoma was more evident among young subjects (age < or= 60) and never smokers., Conclusion: These results suggest that inherited sequence variations in XPC may modulate risk of lung cancer, especially lung adenocarcinoma, in Chinese populations. However, these findings need to be verified in larger confirmatory studies with more comprehensively selected tagging SNPs.

DNA repair should occur after cells sense DNA damage signals and undergo cell-cycle arrest to provide sufficient time for DNA repair, and suboptimal DNA repair capacity (DRC) in peripheral lymphocytes has been suggested as a cancer susceptibility marker. Numerous studies showed a functional link between DNA damage sensing, cell-cycle checkpoint, and DNA repair. We hypothesized that in vitro cell-cycle checkpoint-related protein expression levels in stimulated lymphocytes predict DRC levels. To test this hypothesis, we performed the host-cell reactivation assay for DRC by transfecting stimulated peripheral blood lymphocytes from 120 normal donors with transient expression plasmids damaged by benzo[a]pyrene diol epoxide (BPDE). The same cells were assessed for protein expression induction of eight cell-cycle checkpoint-related genes using the reverse-phase protein lysate microarray assay. In multivariate linear regression analysis adjusting for age, sex, blastogenic rate, and sample storage duration, the association between DRC and expression levels of cell-cycle checkpoint-related proteins induced by BPDE-adducts was statistically significant for p27, CCND1, ATM, and MDM2 (P = 0.00, 0.03, 0.03, and 0.03, respectively), borderline for p73 and p21 (P = 0.07 and 0.09, respectively), but not for p53 and p16 (P = 0.13 and 0.18, respectively). Because the relative expression levels of all these eight proteins were highly correlated, we further performed the principal component analysis and identified ATM as the most important predictor of DRC, followed by MDM2 and p27. Our results provide population-based in vitro evidence demonstrating that cell-cycle checkpoint-related proteins play essential roles in regulating DNA repair, at least in unaffected human peripheral blood lymphocytes. Further studies are warranted to investigate the role of interindividual variation in the expression levels of these proteins in cancer susceptibility.

Sunlight causes DNA damage, including bulky lesions that are removed effectively by the nucleotide-excision repair (NER) pathway. There are at least eight core NER proteins participating in the pathway, and genetic variations in their genes may alter NER functions. We hypothesized that some NER variants are associated with risk of cutaneous melanoma. In a hospital-based case-control study of 602 non-Hispanic White patients with cutaneous melanoma and 603 age- and sex-matched cancer-free controls, we genotyped five common non-synonymous single-nucleotide polymorphisms identified to date and assessed their associations with risk of cutaneous melanoma. We found that a significantly increased risk of cutaneous melanoma was associated with XPD 751Lys/Gln [adjusted odds ratio (OR), 1.55 and 95% confidence interval (95% CI), 1.12-2.16] and XPD 751Gln/Gln (OR, 1.66; 95% CI, 1.03-2.68) genotypes compared with the XPD 751Lys/Lys genotype as well as XPD312Asp/Asn (OR, 1.54; 95% CI, 1.11-2.12) and XPD312Asn/Asn (OR, 1.75; 95% CI, 1.05-2.90) genotypes compared with the XPD 312Asp/Asp genotype. This increased risk was not observed in the other three XPC and XPG single-nucleotide polymorphisms. Moreover, the number of the observed XPD at-risk genotypes (i.e., 312Asn/Asn+Asn/Asp and 751Gln/Gln+Lys/Gln) was associated with cutaneous melanoma risk in a dose-response manner (OR, 1.47; 95% CI, 0.97-2.23 for one at-risk genotype; OR, 1.83; 95% CI, 1.29-2.61 for two at-risk genotypes; P(trend) < 0.001). However, we found no evidence of any interaction between XPD genotypes with XPC and XPG genotypes or the known risk factors. We concluded that genetic variants of the XPD gene might serve as biomarkers for susceptibility to cutaneous melanoma.

The transcript levels of nucleotide excision repair (NER) genes were shown to be associated with risk of squamous cell carcinomas of the head and neck (SCCHN). However, this association may be biased, because the transcript level does not necessarily reflect the level of protein expression. To address this issue, we did a pilot study to test the hypothesis that the expression of six core NER proteins is associated with risk of SCCHN. We obtained cultured lymphocytes from 57 patients with newly diagnosed SCCHN patients and 63 cancer-free controls. We transfected some of the lymphocytes with both damaged and undamaged plasmid DNA and quantified NER protein levels in these lymphocytes using a reverse-phase protein microarray. The relative NER protein levels in the 63 controls were highly correlated with each other (P<0.001 for all). Compared with the controls, the cases had lower expression levels for all the NER proteins, particularly XPC and XPF, which were reduced by about 25% (P<0.01). When we used the median expression levels of the NER proteins in the controls as cutoff values, we found that a significantly increased risk of SCCHN was associated with low expression of XPA [odds ratio (OR), 2.99; 95% confidence interval (CI), 1.22-7.47], XPC (OR, 2.46; 95% CI, 1.04-5.87), XPD (OR, 3.02; 95% CI, 1.18-7.76), and XPF (OR, 5.29; 95% CI, 2.01-13.9), but not ERCC1 and XPG, after adjustment for age, sex, ethnicity, smoking, alcohol use, and sample storage time. In a multivariate logistic regression model that included all covariates and NER proteins, however, only low expression of XPF remained a significant risk factor for SCCHN (OR, 11.5; 95% CI, 2.32-56.6). These results suggest that XPF may be a crucial rate-limiting factor in DNA repair and that the reverse-protein microarray assay may be a useful tool for measuring protein markers of susceptibility to cancer.

Purpose: ERCC4 (XPF) plays a role in both recombinant DNA repair and nucleotide excision repair, which involve repairing radiation-induced genetic damage. We hypothesized that two ERCC4 single-nucleotide polymorphisms are associated with normal-tissue toxicity in patients treated with radiotherapy for oropharyngeal squamous cell carcinoma (OPSCC)., Methods and Materials: A retrospective review of the medical records of 130 patients with OPSCC who were prospectively recruited into a molecular epidemiologic study was performed to determine whether a long-term percutaneous feeding gastrostomy (LPFG) tube (a tube required for more than 180 days) had been used during and after definitive radiotherapy. We determined the genotype of the ERCC4 G1244A and T2505C polymorphisms using standard polymerase chain reaction-restriction fragment-length polymorphism techniques on DNA extracted from peripheral blood lymphocytes., Results: Of 130 patients, 100 (77%) were evaluable for the ERCC4 G1244A polymorphism in exon 8, and 122 (94%) were evaluable for the ERCC4 T2505C polymorphism in exon 11. The ERCC4 G1244A polymorphism was associated with a decreased need for LPFG, but this was not statistically significant (adjusted odds ratio = 0.53; 95% confidence interval, 0.10-2.78). Sixteen (32%), 9 (14%), and 1 (10%) of patients with the wild-type homozygous TT genotype of ERCC4 T2505C, the heterozygous TC genotype, and the homozygous CC polymorphic genotype, respectively, required LPFG. These results suggest that the ERCC4 2505C allele was associated with a reduced need for LPFG (adjusted odds ratio = 0.20; 95% confidence interval, 0.06-0.67). Furthermore, the need for LPFG was reduced by having more than 1 ERCC4 2505C allele and further for having both the ERCC4 1244A and 2505C polymorphic alleles, but this was not statistically significant. In addition, the actual time of gastrostomy dependence was associated with the T2505C polymorphism based on the Kaplan-Meier method (p = 0.03)., Conclusions: Our findings suggest that the ERCC4 T2505C polymorphism may be associated with improved recovery from radiation treatment toxicity in patients with OPSCC. Further study with larger sample sizes and prospective measure of radiotherapy-induced toxicity is warranted.

X-ray repair cross complementing group 1 (XRCC1) is one of the major DNA repair proteins involved in the base-excision repair pathway. Functional Polymorphisms in the XRCC1 gene may lead to decreased DNA repair capacity and thus confer inherited predisposition to cancer risk. In this case-control study of 710 patients with incident lung cancer and 710 cancer-free controls who were frequency matched on age, sex and residential area, we genotyped a novel T>C transition at the promoter region (-77T>C) of XRCC1 and other two common non-synonymous polymorphisms (Arg194Trp and Arg399Gln) to determine their associations with risk of lung cancer. We found that compared with the -77TT wild-type homozygote, the variant genotypes were associated with significantly increased risk of lung cancer [adjusted odds ratio (OR)=1.51; 95% confidence interval (CI)=1.17-1.94 for -77TC; OR=2.98; 95% CI=0.93-9.59 for -77CC; and OR=1.55; 95% CI=1.21-1.98 for -77TC/CC]. By contrast, no significant associations were observed between the other two exonic variants (Arg194Trp and Arg399Gln) and lung cancer risk. Furthermore, we observed a 9.82-fold increased risk (95% CI=5.66-17.02) for heavy smokers carrying the -77C variant (-77TC/CC) and a 4.07-fold increased risk (95% CI=2.85-5.81) for heavy smokers not carrying the variant. However, the interaction between the -77T>C variant and cumulative smoking was not statistically significant (P=0.1560). These findings indicate that the new XRCC1 -77T>C polymorphism may contribute to the aetiology of lung cancer. Further functional studies are warranted to elucidate the underlying molecular mechanisms of the association.

DNA repair is central to normal cellular functions, and polymorphisms of DNA repair genes may cause variation in DNA repair capacity in the general population. Newly identified polymorphisms of xeroderma pigmentosum group C (XPC), one of the nucleotide excision repair genes, were shown to contribute to genetic susceptibility to cancer. In this study, we hypothesized that 2 exonic variants C499T and A939C and their haplotypes in XPC are associated with lung cancer risk. To test this hypothesis, we performed a case-control study of 320 histologically confirmed lung cancer patients and 322 age and sex frequency-matched cancer-free controls in a Chinese population. Multivariate logistic regression analyses revealed that the risks [adjusted odds ratios (ORs) and 95% confidence intervals (CIs)] associated with the XPC variant genotypes were 1.57 (95% CI = 1.13-2.19) for 499CT/TT and 1.21 (95% CI = 0.87-1.69) for 939AC/CC compared with the 499CC and 939AA wild-type homozygotes, respectively. Individuals with both putative risk genotypes (499CT/TT and 939AC/CC) had a greater risk of lung cancer (adjusted OR = 2.37; 95% CI = 1.33-4.21) compared with individuals with both wild-type genotypes (499CC and 939AA). When we performed the haplotype analysis and assumed the XPC 499T and 939C as risk alleles, the adjusted ORs increased as the number of variants in the haplotype genotypes increased (p(trend) < 0.001). In the stratified analysis, the greatest risk was found in smokers having the combined variant genotypes (adjusted OR = 7.36; 95% CI = 3.19-17.00) compared with nonsmokers having both wild-type genotypes and in smokers with 2 or 3 haplotype variants (adjusted OR = 7.27; 95% CI = 3.37-15.68) compared with nonsmokers having 0 haplotype variant. These findings indicate that XPC exonic variants may contribute to the risk of lung cancer in the Chinese population, and these variant genotypes may modulate the risk of lung cancer associated with smoking., ((c) 2005 Wiley-Liss, Inc.)

Purpose: Genetic polymorphisms of DNA repair genes seem to determine the DNA repair capacity, which in turn may affect the risk of breast cancer. To evaluate the role of genetic polymorphisms of DNA repair genes in breast cancer, we conducted a hospital-based case-control study of Korean women., Experimental Design: We included 872 incident breast cancer cases and 671 controls recruited from several teaching hospitals in Seoul from 1995 to 2002. Twelve loci of selected DNA repair genes were genotyped by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (XRCC2 Arg188His, XRCC4 921G > T, XRCC6 1796G > T, LIG4 1977T/C, RAD51 135G > C, 172G > T, RAD52 2259C > T, LIG1 551A > C, ERCC1 8092A > C, 354C > T, hMLH1 -93G > A, and Ile219Val)., Results: We found that the RAD52 2259 CT or TT, hMLH1 -93 GG, and ERCC1 8092 AA genotypes were associated with breast cancer risk after adjustment for known risk factors [odds ratio (OR), 1.33; 95% confidence interval (95% CI), 1.02-1.75; OR, 1.31; 95% CI, 0.99-1.74; and OR, 0.58; 95% CI, 0.38-0.89, respectively]. When Bonferroni's method was used to correct for multiple comparisons for nine polymorphisms with P = 0.005, all of these associations were not significant. However, the effects of RAD52 2259 CT or TT and ERCC1 354 CT or TT genotypes were more evident for the estrogen/progesterone receptor-negative cases (OR, 2.03; 95% CI, 1.24-3.34 and OR, 1.99; 95% CI, 1.35-2.94, respectively)., Conclusion: Our findings suggest that genetic polymorphisms of RAD52, ERCC1, and hMLH1 may be associated with breast cancer risk in Korean women.

Adenosine diphosphate ribosyl transferase (ADPRT) and X-ray repair cross-complementing 1 (XRCC1) are two major DNA base excision repair (BER) proteins and act interactively in stimulating and executing BER processes. Polymorphisms of ADPRT Val762Ala and XRCC1 Arg399Gln have been associated with altered protein function and BER activity. This case-control study examined the contribution of these two polymorphisms, alone and in combination, or in interaction with smoking, to the risk of developing lung cancer. We estimated the risk of lung cancer associated with these polymorphisms in 1,000 cases and 1,000 cancer-free controls using logistic regression models. Subjects having the ADPRT Ala/Ala genotype had an odds ratio (OR) of 1.68 [95% confidence interval (95% CI), 1.27-2.23] compared with those having the Val/Val genotype. A greater than multiplicative joint effect between the ADPRT polymorphism and smoking was observed. The ORs (95% CI) of the Ala/Ala genotype for nonsmokers and smokers who smoked < or =16, 16 to 28, or >28 pack-years were 1.13 (0.79-1.62), 1.35 (0.68-2.70), 2.46 (1.35-4.51) or 17.09 (8.15-35.83), respectively (P trend test < 0.001). Gene-gene interaction of ADPRT and XRCC1 polymorphisms increased risk of lung cancer in a supermultiplicative manner (OR for the presence of both ADPRT 762Ala/Ala and XRCC1 399Gln/Gln genotypes, 5.91; 95% CI, 2.09-16.72), although the XRCC1 polymorphism itself was not associated with the risk. In conclusion, the ADPRT Val762Ala polymorphism plays an important role in smoking-related lung cancer and the XRCC1 Arg399Gln polymorphism may serve as a risk modifier.

DNA repair is a complicated biological process consisting of several distinct pathways that play a central role in maintaining genomic stability. Research on DNA repair and cancer risk is a vital, emerging field that recently has seen rapid advances facilitated by the completion of the Human Genome Project. In this review, we described phenotypic and genotypic markers of nucleotide excision repair (NER) that have been used in molecular epidemiology studies. We summarized the population-based studies to date that have examined the association between DNA repair capacity phenotype and genetic polymorphisms of the NER genes and risk of tobacco-related cancers, including cancers of the lung, head and neck, prostate, bladder, breast, and esophagus. We also included studies of melanoma and nonmelanoma skin cancers because individuals with defective NER, such as patients with xeroderma pigmentosum (XP) are highly susceptible to ultraviolet light (UV)-induced melanoma and nonmelanoma skin cancers. The published data provide emerging evidence that DNA repair capacity may contribute to genetic susceptibility to cancers in the general population. However, many of the studies are limited in terms of the size of the study populations. Furthermore, all published findings are still considered preliminary, the assays used in the studies have yet to be validated, and the results need to be confirmed. Large and well-designed population-based studies are warranted to assess gene-gene and gene-environment interactions and to ultimately determine, which biomarkers of DNA repair capacity are useful for screening high-risk populations for primary prevention and early detection of tobacco-related cancers.

DNA repair capacity in a cell could be detected by a host-cell reactivation assay (HCR). Since relation between DNA repair and genetic susceptibility to cancer remains unclear, it is necessary to identify DNA repair defects in human cancer cells. To assess DNA repair for breast cancer susceptibility, we developed a modified HCR assay using a plasmid containing a firefly luciferase gene damaged by mitomycin C (MMC), which forms interstrand cross-link (ICL) adducts. In particular, interstrand cross-link is thought to induce strand breaks being repaired by homologous recombination. The MMC-ICLs were verified by electrophoresis. Damaged plasmids were transfected into apparently normal human lymphocytes and NER-deficient XP cell lines and the DNA repair capacity of the cells were measured by quantifying the activity of the firefly luciferase. MMC lesion was repaired as much as UV adducts in normal lymphocytes and the XPC cells. However, the XPA cells have a lower repair capacity for MMC lesion than the XPC cell, indicating that the XPA protein may be involved in initial damage recognition of MMC-ICL adducts. Since several repair pathways including NER and recombination participate in MMC-ICL removal, this host cell reactivation assay using MMC-ICLs can be used in exploring DNA repair defects in human cancer cells.

Environmental chemicals are thought to play a role in the etiology of breast cancer, because polycyclic acromatic hydrocarbon (PAH)-DNA adducts are detectable in normal and malignant breast tissues. Peripheral blood lymphocytes (PBLs) from female breast cancer patients were more sensitive to in vitro exposure to benzo[a]pyrene diol epoxide (BPDE) than those from healthy controls. Therefore, we hypothesized that reduced DNA repair is associated with risk of breast cancer in women and the risk may be modulated by polymorphisms of DNA repair genes. In a case-control pilot study, we included 69 previously untreated female breast cancer patients and 79 controls frequency matched to the cases on age and ethnicity. The PBLs were used to measure DNA repair capacity (DRC) by using the host-cell reactivation (HCR) assay with a reporter gene damaged by exposure to 60 micro M BPDE prior to transfection. We also genotyped for two common XPD polymorphisms Lys751Gln and Asp312Asn. We found that the mean DRC level was significantly lower in breast cancer patients (10.1%) than in controls (11.1%) (P = 0.008). Subjects with DRC lower than the median level of controls (11.0%) had >3-fold increased risk (OR = 3.36, 95% CI = 1.15-9.80) for breast cancer than did those with higher DRC after adjustment for age, smoking status and assay-related variables. None of the genotypes was statistically significantly associated with an increased risk of breast cancer, which may be due to the small number of observations in each subgroup. The XPD variant genotypes in general predicted the DRC better in the controls than in the cases, suggesting genetic variants of other DNA repair genes may be involved in these breast cancer patients. These findings suggest that women with reduced DRC may be at an increased risk of developing breast cancer. Large studies are warranted to confirm these preliminary findings.

DNA repair genes play a major role in maintaining genomic stability through different repair pathways that are mediated by cell cycle control genes such as p53. We found previously that glioma patients were susceptible to gamma-ray-induced chromosomal breaks, which may be influenced by genetic variation in genes involved in DNA strand breaks, such as XRCC1 in single-strand break repair, XRCC3 and RAD51 in homologous recombination repair, and XRCC7 in nonhomologous end joining double-strand break repair. Therefore, we tested the hypothesis that genetic polymorphisms in XRCC1, XRCC3, RAD51, XRCC7, and p53 were associated with risk of glioma in 309 patients with newly diagnosed glioma and 342 cancer-free control participants frequency matched on age (+/- 5 years), sex, and self-reported ethnicity. We did not find any statistically significant differences in the distributions of XRCC1 Arg399Gln, XRCC3 Thr241Met, RAD51 G135C, and P53 Arg72Pro polymorphisms between the cases and the controls. However, the XRCC7 G6721T variant T allele and TT genotype were more common in the cases (0.668 and 43.4%, respectively) than in the controls (0.613 and 38.9%, respectively), and the differences were statistically significant (P = 0.045 and 0.040, respectively). The adjusted odds ratios were 1.78 (95% confidence interval, 1.08-2.94) and 1.86 (95% confidence interval, 1.12-3.09) for the GT heterozygotes and TT homozygotes, respectively. The combined T variant genotype (GT+TT) was associated with a 1.82-fold increased risk of glioma (95% confidence interval, 1.13-2.93). These results suggest that the T allele may be a risk allele, and this XRCC7 polymorphism may be a marker for the susceptibility to glioma. Larger studies are needed to confirm our findings and unravel the underlying mechanisms.

The etiology of esophageal squamous cell carcinoma (ESCC) has been shown to be associated with genetic and certain environmental factors that produce DNA damage. Base excision repair (BER) genes are responsible for repair of DNA damage caused by reactive oxygen species and other electrophiles and therefore are good candidate susceptibility genes for ESCC. We first screened eight BER genes for new and potential functional polymorphisms by resequencing 27 DNA samples. We then identified and genotyped for important tagging single nucleotide polymorphisms (SNPs) in a case-control study of 419 patients with newly diagnosed esophageal cancer and 480 healthy controls by frequency matching on age and sex. The association between genotypes and ESCC risk was estimated by unconditional multivariate logistic regression analysis, and stepwise regression procedure was used for constructing the final logistic regression model. We identified 129 SNPs in the eight BER genes, including 18 SNPs that cause amino acid changes. In the final model, 4 SNPs, including 2 in the coding regions (ADPRT Val762Ala and MBD4 Glu346Lys) and others in noncoding regions (LIG3 A3704G and XRCC1 T-77C), remained as significant predictors for the risk of ESCC. The adjusted odd ratios were 1.25 [95% confidence interval (CI) 1.02-1.53] for the ADPRT 762Ala allele, 1.25 (95% CI 1.02-1.53) for the MBD4 346 Lys allele, 0.78 (95% CI 0.63-0.97) for the LIG3 3704G allele, and 1.38 (95% CI 1.01-1.89) for the XRCC1-77C allele. In addition, we observed a significant gene-gene interaction between XRCC1 Gln399Arg and ADPRT Val762Ala. The results suggest that the polymorphisms in five BER genes may be associated with the susceptibility to ESCC in a Chinese population.

Mammalian cells are constantly exposed to a wide variety of genotoxic agents from both endogenous and exogenous sources. Genetic variability in DNA repair may contribute to human cancer risk. In this population-based case-control study in China, we tested the hypothesis that a C to T variant (Thr241Met) of DNA repair gene XRCC3 (X-ray repair cross-complementing group 3) is associated with risk of developing gastric cancer. We genotyped for this variant using polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLP) in 188 histologically confirmed gastric cancer patients and 166 frequency-matched cancer-free controls. The XRCC3 genotype and allele frequencies were not significantly different between cases and controls (P = 0.99 for genotype; P = 0.76 for allele). The XRCC3 241Met allele frequency (4.8%) was significantly lower in healthy Chinese controls than previously reported healthy US Caucasian controls (38.9%). Compared with the XRCC3 241Thr/Thr genotype, the variant XRCC3241Thr/Met and Met/Met genotypes were not associated with an increased risk of gastric cancer (adjusted odds ratio (OR(a)), 1.06; 95% confidence interval (CI), 0.52-2.16). These findings suggest that polymorphisms of XRCC3 Thr241Met may not play a role in the etiology of gastric cancer. Further studies with a larger number of subjects and simultaneous measurement of different polymorphisms in DNA repair genes in the same pathway are needed to confirm these findings.

Tobacco-related carcinogens cause a variety of DNA damage that is repaired by different enzymatic pathways, suggesting that DNA repair plays an important role in tobacco-induced carcinogenesis. In a large hospital-based case-control study, we investigated DNA repair capacity (DRC) as a biomarker for susceptibility to nonsmall cell lung cancer (NSCLC) and evaluated the possible interaction between DRC and tobacco smoke in 467 newly diagnosed NSCLC patients and 488 cancer-free controls. We measured DRC in cultured peripheral lymphocytes using the host-cell reactivation assay with a reporter gene damaged by an activated tobacco carcinogen, benzo[a]pyrene diol epoxide. The results showed that current smokers exhibited the highest DRCs as compared to former and nonsmokers both among patients and control subjects. There were no differences of DRC among 3 different histopathologic types of NSCLC. Logistic regression analysis revealed that suboptimal DRC and pack-years smoked were independent predictors of NSCLC risk. The overall 15.5% reduction in DRC observed in the cases (7.84%) compared to the controls (9.28%) (p<0.001) was associated with an approximately 2-fold increased risk of NSCLC (adjusted odds ratio (OR) = 1.85, 95% confidence interval (CI) 1.42-2.42). There was a significant dose-response association between decreased DRC and increased risk of lung cancer. Furthermore, we observed a nonstatistically significant additive but not multiplicative interaction between DRC and pack-years smoked on lung cancer risk, particularly in the histopathologic types of NSCLC other than adenocarcinoma. The results suggest that suboptimal DRC is associated with increased risk of NSCLC and DRC may modulate the risk of lung cancer associated with smoking but the latter needs to be verified in larger studies., (Copyright 2003 Wiley-Liss, Inc.)

Both reduced DNA repair capacity (DRC) and folate deficiency are associated with increased cancer risk. Furthermore, folate is involved in DNA repair through de novo DNA synthesis and methylation. To determine whether low dietary folate intake is associated with low cellular DRC in humans, we assessed total dietary folate intake using a food frequency questionnaire in 559 non-Hispanic white cancer-free subjects enrolled from 1995 through 2001 as controls for ongoing molecular epidemiological studies from among enrollees in a community-based multispecialty physician practice in the Houston metropolitan area. We assessed cellular DRC using the host-cell reactivation assay that measures nucleotide-excision repair capacity in peripheral blood lymphocytes. The distribution of DRC was approximately normal in this study population. In univariate analysis, subjects in the lowest tertile of total dietary folate intake (<170 microg/1000 kcal/day) exhibited a significant reduction (-18%) in DRC compared with those in the upper tertile (>225 microg/1000 kcal/day; P < 0.001). In multivariate linear regression analysis, calorie-adjusted total folate intake remained an independent predictor of DRC (P < 0.001). Additional stratification analysis indicated that this association was more pronounced in those who did not use folate supplementation (n = 230; P < 0.001) compared with those who did (n = 329; P = 0.177). Our findings suggest that low dietary folate intake is associated with suboptimal cellular DRC. Once replicated by other investigators, this finding has public health implications by reinforcing the need for folate supplementation or dietary modification for the at-risk population.

XPA, a DNA binding protein in the nucleotide excision repair (NER) pathway, modulates damage recognition. Recently, a common single-nucleotide polymorphism (A --> G) of unknown function was identified in the 5' non-coding region of the XPA gene. Because a deficiency in NER is associated with an increased risk of lung cancer, we evaluated the role of this polymorphism in 695 lung cancer case patients and 695 age-, sex-, ethnicity- and smoking-matched control subjects. We also studied the effect of this polymorphism on NER capacity in a subset sample for whom the host cell reactivation data were available. The presence of one or two copies of the G allele was associated with a reduced lung cancer risk for Caucasians [adjusted odds ratio (ORadj) = 0.69 [95% confidence interval (CI) = 0.53-0.90]], Mexican-Americans [ORadj = 0.32 (95% CI = 0.12-0.83)] and African-Americans [ORadj = 0.45 (95% CI = 0.16-1.22)]. In Caucasians, ever smokers with one or more copies of the G allele were observed to have a significantly reduced risk of lung cancer. Control subjects with one or two copies of the G allele demonstrated more efficient DRC than did those with the homozygous A allele. Our data suggest that the XPA 5' non-coding region polymorphism modulates NER capacity and is associated with decreased lung cancer risk, especially in the presence of exposure to tobacco carcinogens.

Background: The mechanism underlying the role of UV light exposure from sunlight in the etiology of cutaneous malignant melanoma (CMM) is unclear. Patients with xeroderma pigmentosum, a disease characterized by severe sensitivity to UV radiation and a defect in nucleotide excision repair, have a high incidence of CMM, which suggests that DNA repair capacity (DRC) plays a role in sunlight-induced CMM in the general population as well., Methods: We conducted a hospital-based case-control study of DRC and CMM among 312 non-Hispanic white CMM patients who had no prior chemotherapy or radiation therapy, and 324 cancer-free control subjects who were frequency-matched to case patients on age, sex, and ethnicity. Information on demographic variables, risk factors, and tumor characteristics was obtained from questionnaires and medical records. We used the host-cell reactivation assay to measure the DRC in study subjects' lymphocytes. All statistical tests were two sided., Results: Case patients had a 19% lower mean (+/- standard deviation [SD]) DRC (8.5 +/- 3.4%) than control subjects (10.5 +/- 5.1%), a statistically significant difference (P<.001). DRC that was at or below the median value (i.e., 9.4%) in control subjects was associated with increased risk for CMM after adjustment for age, sex, and other covariates (odds ratio [OR] = 2.02, 95% confidence interval [CI] = 1.45 to 2.82). We observed a dose-response relationship between decreased DRC and increased risk of CMM (P(trend)<.001). Patients with tumors on sun-exposed skin had statistically significantly lower DRC than patients with tumors on unexposed skin (8.2 +/- 3.3% versus 9.5 +/- 3.5%; P =.004)., Conclusions: Reduced DRC is an independent risk factor for CMM and may contribute to susceptibility to sunlight-induced CMM among the general population.