Abstract 886: Germline variation in nucleotide excision repair genes and lung cancer risk in smokers

Nucleotide excision repair (NER) is the primary mechanism for detecting and repairing bulky DNA lesions, which in the respiratory tract can be induced by tobacco smoke and other environmental exposures. By altering DNA repair capacity, single nucleotide polymorphisms (SNPs) in NER protein-encoding genes may affect lung cancer risk, especially in smokers. Although meta-analyses have suggested some associations between NER SNPs and lung cancer (e.g., ERCC2 rs13181 and XPA rs1800975), they are largely built upon studies that have examined a limited number of SNPs in a few genes in fairly small samples. To comprehensively assess the influence of NER gene variation on lung cancer risk, we genotyped 78 SNPs tagging the regions spanning ±2500 base pairs of the ERCC1, ERCC2, ERCC3, ERCC4, ERCC5, LIG1, POLE, XPA and XPC genes in lung cancer cases and controls selected from the Beta-Carotene and Retinol Efficacy Trial, a randomized chemoprevention trial in smokers. Controls were matched to cases on age, sex, race, enrollment year, and baseline measures of smoking status and occupational asbestos exposure. Gene coverage by the tag SNPs selected using HapMap CEU data (dbSNP build 129, ≫5% minor allele frequency, pairwise r2 >0.8) ranged from 91.7% to 100%. To assess SNP-level associations, we computed odds ratios (OR) and 95% confidence intervals (CI) adjusted for matching variables using logistic regression. To assess gene-level associations, we computed global p-values for likelihood ratio tests comparing each model with all SNPs in a given gene to that with no SNPs. Analyses were limited to Caucasians (746 cases, 1477 controls). At the gene level, XPA (pglobal=0.008) and LIG1 (pglobal=0.039) were associated with lung cancer risk. Associations were detected for two of the nine XPA SNPs examined, rs3176683 (OR per G allele: 0.77, 95% CI: 0.58-1.00, p=0.05) and rs3176658 (OR per A allele: 0.83, 95% CI: 0.69-1.00, p=0.05), and three of the eleven LIG1 SNPs examined, rs156640 (OR per G allele: 1.2, 95% CI: 1.1-1.4, p=0.002), rs156641 (OR per A allele: 1.2, 95% CI: 1.1-1.4, p=0.003), and rs8100261 (OR per A allele: 0.87, 95% CI: 0.77-0.99, p=0.03). The two XPA SNPs (r2=0.01) exhibited stronger associations when included together in a single regression model. In diplotype analyses, lung cancer risk was lower for those carrying the homozygous major genotypes of rs3176683 and rs3176658, relative to both heterozygous genotypes (OR: 0.38, 95% CI: 0.17-0.87). Lung cancer risk was higher for those carrying the homozygous minor genotypes of rs156640 and rs156641 and homozygous major genotype of rs8100261, relative to the homozygous major genotypes of rs156640 and 156641 and homozygous minor genotype of rs8100261 (OR: 1.7, 95% CI: 1.2-2.3). Although reported ERCC2 rs13181 and XPA rs1800975 associations could not be confirmed, our data nonetheless support the hypothesis that germline variation in NER genes influences lung cancer risk.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 886. doi:10.1158/1538-7445.AM2011-886

Abstract 4593: Telomere length measured prior to lung cancer diagnosis and survival by histologic type

Short telomere length is thought to be a marker of increased cumulative cellular aging, and has been reported to be associated with poor survival from a variety of cancer types, including lung cancer. We examined associations between telomere length and overall survival for the major lung cancer histologic types in very heavy smokers from the Beta Carotene and Retinol Trial (CARET). CARET was a randomized, double-blinded, placebo-controlled chemoprevention trial of daily β-carotene and retinyl palmitate in smokers with ≥20 pack-years, and smokers who were occupationally exposed to asbestos. Individuals who provided blood and were later diagnosed with lung cancer were included in the study. Telomere length was successfully measured on average 5 years prior to diagnosis for 711 lung cancer cases, of whom 648 died during follow up (median survival 1.5 years). Telomere length was negatively associated with increasing age (p<0.0001), but was not associated with any aspect of smoking exposure. Hazard ratios (HRs) for decreasing quintiles of telomere length were calculated using Cox proportional hazards regression. After controlling for age at blood draw, sex, race, enrollment year, placebo/active intervention, asbestos exposure, current/former smoking and time since quit, pack years, average number of cigarettes per day, tumor stage and histologic type, shorter telomere length was associated with decreased survival. Overall, HRs and 95% confidence intervals (CIs) for decreasing quintiles of telomere length and risk of death were: 1.0 (reference), 1.40 (1.08-1.83), 1.21 (0.94-1.54), 1.46 (1.13-1.89), and 1.37 (1.05-1.78), p trend = 0.02. Associations were considerably stronger for small cell carcinoma (HRs (95% CIs): 1.0, 3.39 (1.45-7.94), 1.88 (0.95-3.72), 3.62 (1.68-7.81), 2.91 (1.37-6.22), p = 0.01) and adenocarcinoma (HRs (95% CIs): 1.0, 1.00 (0.57-1.78), 1.23 (0.72-2.11), 1.78 (1.02-3.10), 1.77 (1.03-3.05), p = 0.01), than for squamous cell carcinoma (HRs (95% CIs): 1.0, 2.58 (1.29-5.15), 0.97 (0.52-1.82), 1.24 (0.65-2.34), 1.17 (0.58-2.35), p = 0.99), and stronger for stage III/IV disease (HRs (95% CIs): 1.0, 1.55 (1.07-2.23), 1.21 (0.88-1.67), 1.74 (1.23-2.47), 1.48 (1.05-2.08), p = 0.02) than for early stage disease (HRs (95% CIs): 1.0, 1.05 (0.55-2.03), 0.68 (0.37-1.26), 1.11 (0.60-2.05), 1.06 (0.53-2.09), p = 0.88). As well, short telomere length was associated with particularly poor survival among individuals <65 years at diagnosis (HRs (95% CIs): 1.0, 2.37 (1.35-4.15), 1.99 (1.16-3.44), 2.31 (1.21-4.40), 2.93 (1.61-5.33), p = 0.0007) but not among individuals ages 65 and older (HRs (95% CIs): 1.0, 1.15 (0.85-1.56), 0.98 (0.74-1.30), 1.26 (0.94-1.68), 1.09 (0.81-1.47), p = 0.39). Short telomere length measured prior to diagnosis may be a marker for poor survival after a diagnosis of lung cancer, particularly for small cell carcinoma and adenocarcinoma, and for individuals diagnosed before age 65.

Citation Format: Jennifer A. Doherty, John Houck, Matt J. Barnett, Jean DD Tapsoba, Liberto Julianto, Mark D. Thornquist, Ching-Yun Wang, Chu Chen, Gary E. Goodman. Telomere length measured prior to lung cancer diagnosis and survival by histologic type. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4593. doi:10.1158/1538-7445.AM2015-4593

DNA repair genotype and lung cancer risk in the beta-carotene and retinol efficacy trial

Many carcinogens in tobacco smoke cause DNA damage, and some of that damage can be mitigated by the actions of DNA repair enzymes. In a case-control study nested within the Beta-Carotene and Retinol Efficacy Trial, a randomized chemoprevention trial in current and former heavy smokers, we examined whether lung cancer risk was associated with variation in 26 base excision repair, mismatch repair, and homologous recombination repair genes. Analyses were limited to Caucasians (744 cases, 1477 controls), and logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs) for individual SNPs and common haplotypes, with adjustment for matching factors. Lung cancer associations were observed (p<0.05) with SNPs in MSH5 (rs3131379, rs707938), MSH2 (rs2303428), UNG (rs246079), and PCNA (rs25406). MSH5 rs3131379 is a documented lung cancer susceptibility locus in complete linkage disequilibrium with rs3117582 in BAT3, and we observed associations similar in magnitude to those in prior studies (per A allele OR 1.37, 95% CI 1.13-1.65). UNG was associated with lung cancer risk at the gene level (p=0.02), and the A allele of rs246079 was associated with an increased risk (per A allele OR 1.15, 95% CI1.01-1.31). We observed stronger associations with UNG rs246079 among individuals who carried the risk genotypes (AG/AA) for MSH5 rs3131379 (pinteraction= 0.038). Our results provide additional evidence to suggest that the MSH5/BAT3 locus is associated with increased lung cancer risk among smokers, and that associations with other SNPs may vary depending upon MSH5/BAT3 genotype. Future studies to examine this possibility are warranted.

Germ line variation in nucleotide excision repair genes and lung cancer risk in smokers

Since nucleotide excision repair (NER) is primarily responsible for detecting and removing bulky DNA lesions induced by tobacco smoke in the respiratory tract, single nucleotide polymorphisms (SNPs) in NER protein-encoding genes may influence lung cancer risk, particularly in smokers. Studies testing this hypothesis have produced inconsistent results, with most analyzing a few SNPs in relatively small population samples. In a study nested in the Beta- Carotene and Retinol Efficacy Trial, we examined 79 tag and previously reported risk-associated SNPs in the ERCC1, ERCC2, ERCC3, ERCC4, ERCC5, LIG1, POLE, XPA, and XPC genes in 744 lung cancer cases and 1,477 controls, all of whom were non-Hispanic white smokers. Using logistic regression, odds ratios (OR) and 95% confidence intervals (95% CI) were calculated to estimate lung cancer risk associated with SNP genotypes and haplotypes, adjusting for case-control matching factors. Lung cancer risk was modestly associated with LIG1 rs156640 (OR per G allele, 1.23; 95% CI, 1.08-1.40), rs156641 (OR per A allele, 1.23; 95% CI, 1.08-1.40), and rs8100261 (OR per A allele, 0.83; 95% CI, 0.76-0.98); XPA rs3176658 (OR per A allele, 0.83; 95% CI, 0.69-1.00); and ERCC2 rs50871 (OR per C allele, 1.15; 95% CI: 1.01-1.30). Associations with LIG1 and XPA, but not ERCC2, haplotypes were found. The results of this study and others suggest that inherited variants in LIG1 and possibly other NER genes may predispose to smoking-related lung cancer. Given that chance likely accounts for one or more of the associations observed, replication of our findings is needed.