Polymorphism of Xeroderma Pigmentosum group G and the risk of lung cancer and squamous cell carcinomas of the oropharynx, larynx and esophagus

Coffee and tea intake and risk of head and neck cancer: pooled analysis in the international head and neck cancer epidemiology consortium

BACKGROUND

Only a few studies have explored the relation between coffee and tea intake and head and neck cancers, with inconsistent results.

METHODS

We pooled individual-level data from nine case-control studies of head and neck cancers, including 5,139 cases and 9,028 controls. Logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (95% CI), adjusting for potential confounders.

RESULTS

Caffeinated coffee intake was inversely related with the risk of cancer of the oral cavity and pharynx: the ORs were 0.96 (95% CI, 0.94-0.98) for an increment of 1 cup per day and 0.61 (95% CI, 0.47-0.80) in drinkers of >4 cups per day versus nondrinkers. This latter estimate was consistent for different anatomic sites (OR, 0.46; 95% CI, 0.30-0.71 for oral cavity; OR, 0.58; 95% CI, 0.41-0.82 for oropharynx/hypopharynx; and OR, 0.61; 95% CI, 0.37-1.01 for oral cavity/pharynx not otherwise specified) and across strata of selected covariates. No association of caffeinated coffee drinking was found with laryngeal cancer (OR, 0.96; 95% CI, 0.64-1.45 in drinkers of >4 cups per day versus nondrinkers). Data on decaffeinated coffee were too sparse for detailed analysis, but indicated no increased risk. Tea intake was not associated with head and neck cancer risk (OR, 0.99; 95% CI, 0.89-1.11 for drinkers versus nondrinkers).

CONCLUSIONS

This pooled analysis of case-control studies supports the hypothesis of an inverse association between caffeinated coffee drinking and risk of cancer of the oral cavity and pharynx.

IMPACT

Given widespread use of coffee and the relatively high incidence and low survival of head and neck cancers, the observed inverse association may have appreciable public health relevance.

Replication of lung cancer susceptibility loci at chromosomes 15q25, 5p15, and 6p21: a pooled analysis from the International Lung Cancer Consortium

BACKGROUND

Genome-wide association studies have identified three chromosomal regions at 15q25, 5p15, and 6p21 as being associated with the risk of lung cancer. To confirm these associations in independent studies and investigate heterogeneity of these associations within specific subgroups, we conducted a coordinated genotyping study within the International Lung Cancer Consortium based on independent studies that were not included in previous genome-wide association studies.

METHODS

Genotype data for single-nucleotide polymorphisms at chromosomes 15q25 (rs16969968, rs8034191), 5p15 (rs2736100, rs402710), and 6p21 (rs2256543, rs4324798) from 21 case-control studies for 11 645 lung cancer case patients and 14 954 control subjects, of whom 85% were white and 15% were Asian, were pooled. Associations between the variants and the risk of lung cancer were estimated by logistic regression models. All statistical tests were two-sided.

RESULTS

Associations between 15q25 and the risk of lung cancer were replicated in white ever-smokers (rs16969968: odds ratio [OR] = 1.26, 95% confidence interval [CI] = 1.21 to 1.32, P(trend) = 2 x 10(-26)), and this association was stronger for those diagnosed at younger ages. There was no association in never-smokers or in Asians between either of the 15q25 variants and the risk of lung cancer. For the chromosome 5p15 region, we confirmed statistically significant associations in whites for both rs2736100 (OR = 1.15, 95% CI = 1.10 to 1.20, P(trend) = 1 x 10(-10)) and rs402710 (OR = 1.14, 95% CI = 1.09 to 1.19, P(trend) = 5 x 10(-8)) and identified similar associations in Asians (rs2736100: OR = 1.23, 95% CI = 1.12 to 1.35, P(trend) = 2 x 10(-5); rs402710: OR = 1.15, 95% CI = 1.04 to 1.27, P(trend) = .007). The associations between the 5p15 variants and lung cancer differed by histology; odds ratios for rs2736100 were highest in adenocarcinoma and for rs402710 were highest in adenocarcinoma and squamous cell carcinomas. This pattern was observed in both ethnic groups. Neither of the two variants on chromosome 6p21 was associated with the risk of lung cancer.

CONCLUSIONS

In this international genetic association study of lung cancer, previous associations found in white populations were replicated and new associations were identified in Asian populations. Future genetic studies of lung cancer should include detailed stratification by histology.

Associations between NBS1 polymorphisms, haplotypes and smoking-related cancers

Constituents of tobacco smoke can cause DNA double-strand breaks (DSBs), leading to tumorigenesis. The NBS1 gene product is a vital component in DSB detection and repair, thus genetic variations may influence cancer development. We examined the associations between NBS1 polymorphisms and haplotypes and newly incident smoking-related cancers in three case-control studies (Los Angeles: 611 lung and 601 upper aero-digestive tract (UADT) cancer cases and 1040 controls; Memorial Sloan-Kettering Cancer Center: 227 bladder cancer cases and 211 controls and Taixing, China: 218 esophagus, 206 stomach, 204 liver cancer cases and 415 controls). rs1061302 was associated with cancers of the lung [adjusted odds ratio (OR(adj)) = 1.6, 95% confidence interval (CI): 1.2, 2.4], larynx (OR(adj) = 0.56, 95% CI: 0.32, 0.97) and liver (OR(adj) = 1.7, 95% CI: 1.0, 2.9). Additionally, positive associations were found for rs709816 with bladder cancer (OR(adj) = 4.2, 95% CI: 1.4, 12) and rs1063054 with lung cancer (OR(adj) = 1.6, 95% CI: 1.0, 2.3). Some associations in lung and stomach cancers varied with smoking status. CAC haplotype was positively associated with smoking-related cancers: lung (OR(adj) = 1.7, 95% CI: 1.1, 2.9) and UADT (OR(adj) = 2.0, 95% CI: 1.1, 3.7), specifically, oropharynx (OR(adj) = 2.1, 95% CI: 1.0, 4.2) and larynx (OR(adj) = 4.8, 95% CI: 1.7, 14). Bayesian false-discovery probabilities were calculated to assess Type I error. It appears that NBS1 polymorphisms and haplotypes may be associated with smoking-related cancers and that these associations may differ by smoking status. Our findings also suggest that single-nucleotide polymorphisms located in the binding region of the MRE-RAD50-NBS1 complex or microRNA targeted pathways may influence tumor development. These hypotheses should be further examined in functional studies.

International Lung Cancer Consortium: coordinated association study of 10 potential lung cancer susceptibility variants

BACKGROUND

Analysis of candidate genes in individual studies has had only limited success in identifying particular gene variants that are conclusively associated with lung cancer risk. In the International Lung Cancer Consortium (ILCCO), we conducted a coordinated genotyping study of 10 common variants selected because of their prior evidence of an association with lung cancer. These variants belonged to candidate genes from different cancer-related pathways including inflammation (IL1B), folate metabolism (MTHFR), regulatory function (AKAP9 and CAMKK1), cell adhesion (SEZL6) and apoptosis (FAS, FASL, TP53, TP53BP1 and BAT3).

METHODS

Genotype data from 15 ILCCO case-control studies were available for a total of 8431 lung cancer cases and 11 072 controls of European descent and Asian ethnic groups. Unconditional logistic regression was used to model the association between each variant and lung cancer risk.

RESULTS

Only the association between a non-synonymous variant of TP53BP1 (rs560191) and lung cancer risk was significant (OR = 0.91, P = 0.002). This association was more striking for squamous cell carcinoma (OR = 0.86, P = 6 x 10(-4)). No heterogeneity by center, ethnicity, smoking status, age group or sex was observed. In order to confirm this association, we included results for this variant from a set of independent studies (9966 cases/11,722 controls) and we reported similar results. When combining all these studies together, we reported an overall OR = 0.93 (0.89-0.97) (P = 0.001). This association was significant only for squamous cell carcinoma [OR = 0.89 (0.85-0.95), P = 1 x 10(-4)].

CONCLUSION

This study suggests that rs560191 is associated to lung cancer risk and further highlights the value of consortia in replicating or refuting published genetic associations.

Total exposure and exposure rate effects for alcohol and smoking and risk of head and neck cancer: a pooled analysis of case-control studies

Although cigarette smoking and alcohol consumption increase risk for head and neck cancers, there have been few attempts to model risks quantitatively and to formally evaluate cancer site-specific risks. The authors pooled data from 15 case-control studies and modeled the excess odds ratio (EOR) to assess risk by total exposure (pack-years and drink-years) and its modification by exposure rate (cigarettes/day and drinks/day). The smoking analysis included 1,761 laryngeal, 2,453 pharyngeal, and 1,990 oral cavity cancers, and the alcohol analysis included 2,551 laryngeal, 3,693 pharyngeal, and 3,116 oval cavity cancers, with over 8,000 controls. Above 15 cigarettes/day, the EOR/pack-year decreased with increasing cigarettes/day, suggesting that greater cigarettes/day for a shorter duration was less deleterious than fewer cigarettes/day for a longer duration. Estimates of EOR/pack-year were homogeneous across sites, while the effects of cigarettes/day varied, indicating that the greater laryngeal cancer risk derived from differential cigarettes/day effects and not pack-years. EOR/drink-year estimates increased through 10 drinks/day, suggesting that greater drinks/day for a shorter duration was more deleterious than fewer drinks/day for a longer duration. Above 10 drinks/day, data were limited. EOR/drink-year estimates varied by site, while drinks/day effects were homogeneous, indicating that the greater pharyngeal/oral cavity cancer risk with alcohol consumption derived from the differential effects of drink-years and not drinks/day.

Association and impact of XPG Asp 1104 His gene polymorphism in HIV 1 disease progression to AIDS among north Indian HIV seropositive individuals

Various efforts made to stop the deadly epidemic of HIV since its discovery in 1983 remain unsuccessful and this virus still continues to claim the lives of millions of individuals every year. The viral effect in the cell is complicated and the overall disease outcome is the result of interaction between a few viral proteins and complex host immune response. Because it has been reported that XPG (Xeroderma pigementesum group G) gene does play a role in reducing UV induced apoptosis and participate in Nucleotide Excision Repair (NER) process of DNA damage, it was hypothesized that polymorphism in this gene may have a role in HIV 1 disease progression to AIDS. The aim of the present study, therefore, was to find out the association between XPG gene polymorphism and its effect on the rate of HIV 1 disease progression to AIDS. 300 HIV seropositive cases and an equal number of age and sex matched controls were recruited for the study from north Indian population. The PCR-RFLP method was utilized to genotype 600 study subject for the XPG Asp (1104) His gene polymorphism. There was significant difference in the frequency of the His/His variant genotype (OR 1.95, 95% CI = 1.93-3.63, P = 0.04) between cases and controls indicating a probable role of this gene in host viral interactions.

International Lung Cancer Consortium: pooled analysis of sequence variants in DNA repair and cell cycle pathways

BACKGROUND

The International Lung Cancer Consortium was established in 2004. To clarify the role of DNA repair genes in lung cancer susceptibility, we conducted a pooled analysis of genetic variants in DNA repair pathways, whose associations have been investigated by at least 3 individual studies.

METHODS

Data from 14 studies were pooled for 18 sequence variants in 12 DNA repair genes, including APEX1, OGG1, XRCC1, XRCC2, XRCC3, ERCC1, XPD, XPF, XPG, XPA, MGMT, and TP53. The total number of subjects included in the analysis for each variant ranged from 2,073 to 13,955 subjects.

RESULTS

Four of the variants were found to be weakly associated with lung cancer risk with borderline significance: these were XRCC3 T241M [heterozygote odds ratio (OR), 0.89; 95% confidence interval (95% CI), 0.79-0.99 and homozygote OR, 0.84; 95% CI, 0.71-1.00] based on 3,467 cases and 5,021 controls from 8 studies, XPD K751Q (heterozygote OR, 0.99; 95% CI, 0.89-1.10 and homozygote OR, 1.19; 95% CI, 1.02-1.39) based on 6,463 cases and 6,603 controls from 9 studies, and TP53 R72P (heterozygote OR, 1.14; 95% CI, 1.00-1.29 and homozygote OR, 1.20; 95% CI, 1.02-1.42) based on 3,610 cases and 5,293 controls from 6 studies. OGG1 S326C homozygote was suggested to be associated with lung cancer risk in Caucasians (homozygote OR, 1.34; 95% CI, 1.01-1.79) based on 2,569 cases and 4,178 controls from 4 studies but not in Asians. The other 14 variants did not exhibit main effects on lung cancer risk.

DISCUSSION

In addition to data pooling, future priorities of International Lung Cancer Consortium include coordinated genotyping and multistage validation for ongoing genome-wide association studies.

Associations between variants of the 8q24 chromosome and nine smoking-related cancer sites

Recent genome-wide association studies identified key single nucleotide polymorphisms (SNPs) in the 8q24 region to be associated with prostate cancer. 8q24 SNPs have also been associated with colorectal cancer, suggesting that this region may not be specifically associated to just prostate cancer. To date, the association between these polymorphisms and tobacco smoking-related cancer sites remains unknown. Using epidemiologic data and biological samples previously collected in three case-control studies from U.S. and Chinese populations, we selected and genotyped one SNP from each of the three previously determined "regions" within the 8q24 loci, rs1447295 (region 1), rs16901979 (region 2), and rs6983267 (region 3), and examined their association with cancers of the lung, oropharynx, nasopharynx, larynx, esophagus, stomach, liver, bladder, and kidney. We observed noteworthy associations between rs6983267 and upper aerodigestive tract cancers [adjusted odds ratio (ORadj), 1.69; 95% confidence interval (95% CI), 1.28-2.24], particularly in oropharynx (ORadj, 1.80; 95% CI, 1.30-2.49) and larynx (ORadj, 2.04; 95% CI, 1.12-3.72). We also observed a suggestive association between rs6983267 and liver cancer (ORadj, 1.51; 95% CI, 0.99-2.31). When we stratified our analysis by smoking status, rs6983267 was positively associated with lung cancer among ever-smokers (ORadj, 1.45; 95% CI, 1.05-2.00) and inversely associated with bladder cancer among ever-smokers (ORadj, 0.35; 95% CI, 0.14-0.83). Associations were observed between rs16901979 and upper aerodigestive tract cancer among never-smokers and between rs1447295 and liver cancer among ever-smokers. Our results suggest variants of the 8q24 chromosome may play an important role in smoking-related cancer development. Functional and large epidemiologic studies should be conducted to further investigate the association of 8q24 SNPs with smoking-related cancers.

Interaction between tobacco and alcohol use and the risk of head and neck cancer: pooled analysis in the International Head and Neck Cancer Epidemiology Consortium

BACKGROUND

The magnitude of risk conferred by the interaction between tobacco and alcohol use on the risk of head and neck cancers is not clear because studies have used various methods to quantify the excess head and neck cancer burden.

METHODS

We analyzed individual-level pooled data from 17 European and American case-control studies (11,221 cases and 16,168 controls) participating in the International Head and Neck Cancer Epidemiology consortium. We estimated the multiplicative interaction parameter (psi) and population attributable risks (PAR).

RESULTS

A greater than multiplicative joint effect between ever tobacco and alcohol use was observed for head and neck cancer risk (psi = 2.15; 95% confidence interval, 1.53-3.04). The PAR for tobacco or alcohol was 72% (95% confidence interval, 61-79%) for head and neck cancer, of which 4% was due to alcohol alone, 33% was due to tobacco alone, and 35% was due to tobacco and alcohol combined. The total PAR differed by subsite (64% for oral cavity cancer, 72% for pharyngeal cancer, 89% for laryngeal cancer), by sex (74% for men, 57% for women), by age (33% for cases <45 years, 73% for cases >60 years), and by region (84% in Europe, 51% in North America, 83% in Latin America).

CONCLUSIONS

Our results confirm that the joint effect between tobacco and alcohol use is greater than multiplicative on head and neck cancer risk. However, a substantial proportion of head and neck cancers cannot be attributed to tobacco or alcohol use, particularly for oral cavity cancer and for head and neck cancer among women and among young-onset cases.

Family history of cancer: pooled analysis in the International Head and Neck Cancer Epidemiology Consortium

Alcohol and tobacco consumption are well-recognized risk factors for head and neck cancer (HNC). Evidence suggests that genetic predisposition may also play a role. Only a few epidemiologic studies, however, have considered the relation between HNC risk and family history of HNC and other cancers. We pooled individual-level data across 12 case-control studies including 8,967 HNC cases and 13,627 controls. We obtained pooled odds ratios (OR) using fixed and random effect models and adjusting for potential confounding factors. All statistical tests were two-sided. A family history of HNC in first-degree relatives increased the risk of HNC (OR=1.7, 95% confidence interval, CI, 1.2-2.3). The risk was higher when the affected relative was a sibling (OR=2.2, 95% CI 1.6-3.1) rather than a parent (OR=1.5, 95% CI 1.1-1.8) and for more distal HNC anatomic sites (hypopharynx and larynx). The risk was also higher, or limited to, in subjects exposed to tobacco. The OR rose to 7.2 (95% CI 5.5-9.5) among subjects with family history, who were alcohol and tobacco users. A weak but significant association (OR=1.1, 95% CI 1.0-1.2) emerged for family history of other tobacco-related neoplasms, particularly with laryngeal cancer (OR=1.3, 95% CI 1.1-1.5). No association was observed for family history of nontobacco-related neoplasms and the risk of HNC (OR=1.0, 95% CI 0.9-1.1). Familial factors play a role in the etiology of HNC. In both subjects with and without family history of HNC, avoidance of tobacco and alcohol exposure may be the best way to avoid HNC.

Type of alcoholic beverage and risk of head and neck cancer--a pooled analysis within the INHANCE Consortium

The authors pooled data from 15 case-control studies of head and neck cancer (9,107 cases, 14,219 controls) to investigate the independent associations with consumption of beer, wine, and liquor. In particular, they calculated associations with different measures of beverage consumption separately for subjects who drank beer only (858 cases, 986 controls), for liquor-only drinkers (499 cases, 527 controls), and for wine-only drinkers (1,021 cases, 2,460 controls), with alcohol never drinkers (1,124 cases, 3,487 controls) used as a common reference group. The authors observed similar associations with ethanol-standardized consumption frequency for beer-only drinkers (odds ratios (ORs) = 1.6, 1.9, 2.2, and 5.4 for < or =5, 6-15, 16-30, and >30 drinks per week, respectively; P(trend) < 0.0001) and liquor-only drinkers (ORs = 1.6, 1.5, 2.3, and 3.6; P < 0.0001). Among wine-only drinkers, the odds ratios for moderate levels of consumption frequency approached the null, whereas those for higher consumption levels were comparable to those of drinkers of other beverage types (ORs = 1.1, 1.2, 1.9, and 6.3; P < 0.0001). Study findings suggest that the relative risks of head and neck cancer for beer and liquor are comparable. The authors observed weaker associations with moderate wine consumption, although they cannot rule out confounding from diet and other lifestyle factors as an explanation for this finding. Given the presence of heterogeneity in study-specific results, their findings should be interpreted with caution.

Involuntary smoking and head and neck cancer risk: pooled analysis in the International Head and Neck Cancer Epidemiology Consortium

Although active tobacco smoking has been identified as a major risk factor for head and neck cancer, involuntary smoking has not been adequately evaluated because of the relatively low statistical power in previous studies. We took advantage of data pooled in the International Head and Neck Cancer Epidemiology Consortium to evaluate the role of involuntary smoking in head and neck carcinogenesis. Involuntary smoking exposure data were pooled across six case-control studies in Central Europe, Latin America, and the United States. Adjusted odds ratios (OR) and 95% confidence interval (95% CI) were estimated for 542 cases and 2,197 controls who reported never using tobacco, and the heterogeneity among the study-specific ORs was assessed. In addition, stratified analyses were done by subsite. No effect of ever involuntary smoking exposure either at home or at work was observed for head and neck cancer overall. However, long duration of involuntary smoking exposure at home and at work was associated with an increased risk (OR for >15 years at home, 1.60; 95% CI, 1.12-2.28; P(trend) < 0.01; OR for >15 years at work, 1.55; 95% CI, 1.04-2.30; P(trend) = 0.13). The effect of duration of involuntary smoking exposure at home was stronger for pharyngeal and laryngeal cancers than for other subsites. An association between involuntary smoking exposure and the risk of head and neck cancer, particularly pharyngeal and laryngeal cancers, was observed for long duration of exposure. These results are consistent with those for active smoking and suggest that elimination of involuntary smoking exposure might reduce head and neck cancer risk among never smokers.

Nucleotide excision repair genes and risk of lung cancer among San Francisco Bay Area Latinos and African Americans

Few studies on the association between nucleotide excision repair (NER) variants and lung cancer risk have included Latinos and African Americans. We examine variants in 6 NER genes (ERCC2, ERCC4, ERCC5, LIG1, RAD23B and XPC) in association with primary lung cancer risk among 113 Latino and 255 African American subjects newly diagnosed with primary lung cancer from 1998 to 2003 in the San Francisco Bay Area and 579 healthy controls (299 Latinos and 280 African Americans). Individual single nucleotide polymorphism and haplotype analyses, multifactor dimensionality reduction (MDR) and principal components analysis (PCA) were performed to assess the association between 6 genes in the NER pathway and lung cancer risk. Among Latinos, ERCC2 haplotype CGA (rs238406, rs11878644, rs6966) was associated with reduced lung cancer risk [odds ratio (OR) of 0.65 and 95% confidence interval (CI): 0.44-0.97], especially among nonsmokers (OR = 0.29; 95% CI: 0.12-0.67). From MDR analysis, in Latinos, smoking and 3 SNPs (ERCC2 rs171140, ERCC5 rs17655 and LIG1 rs20581) together had a prediction accuracy of 67.4% (p = 0.001) for lung cancer. Among African Americans, His/His genotype of ERCC5 His1104Asp (rs17655) was associated with increased lung cancer risk (OR = 1.78; 95% CI: 1.09-2.91), and LIG1 haplotype GGGAA (rs20581, rs156641, rs3730931, rs20579 and rs439132) was associated with reduced lung cancer risk (OR = 0.61; 95% CI: 0.42-0.88). Our study suggests different elements of the NER pathway may be important in the different ethnic groups resulting either from different linkage relationship, genetic backgrounds and/or exposure histories.

Association between nucleotide excision repair gene polymorphisms and chromosomal damage in coke-oven workers

The associations between several genetic polymorphisms of nucleotide excision repair genes (NER) and chromosome damage level were studied among 140 coke-oven workers exposed to a high level of polyaromatic hydrocarbons (PAHs) and 66 non-exposed workers. Seven polymorphisms with functional potential in five NER genes (ERCC1, ERCC2, ERCC4, ERCC5 and ERCC6) were genotyped in the 206 study subjects. Multivariate analysis of covariance revealed that coke-oven workers with the ERCC1 19007 CC genotype had significantly higher cytokinesis-block micronucleus frequency (CBMN) (10.5 +/- 6.8 per thousand) than those with CT (8.1 +/- 6.6 per thousand, p = 0.01) or TT (6.6 +/- 3.7-/ per thousand p = 0.05) or CT+TT genotypes (7.5 +/- 6.3 per thousand, p = 0.004). The ERCC6 A3368G polymorphism was also associated with CBMN frequency among coke-oven workers. Subjects with the AA genotype have a significantly higher CBMN frequency (10.0 +/- 6.9 per thousand) than those with AG (6.7 +/- 4.2 per thousand, p = 0.05) or AG+GG genotypes (6.6 +/- 4.1 per thousand, p = 0.02). Stratification analysis revealed the significant associations between ERCC1 C19007T and ERCC6 A3368G, and the CBMN frequencies were only found among older workers. In addition, a significant association between ERCC2 G23591A polymorphism and CBMN frequencies was also found among older coke-oven workers. The results suggest that polymorphisms of ERCC1 C19007T, ERCC6 A3368G and ERCC2 G23591A are associated with the CBMN frequencies among coke-oven workers.

Dietary flavonoid intake and lung cancer--a population-based case-control study

BACKGROUND

Laboratory studies suggest that flavonoids are antimutagenic and anticarcinogenic. To investigate the associations between commonly consumed flavonoid compounds and lung cancer, the authors conducted a population-based case-control study of 558 lung cancer cases and a group of 837 controls.

METHODS

Dietary intakes of flavonoids were estimated by combining the intake frequency (collected by a food frequency questionnaire), portion size, and food composition data. Unconditional logistic regression analysis was used to estimate odds ratios (ORs) and 95% confidence limits (95% CLs) with an adjustment for potential confounders, including age, sex, race-ethnicity, years of schooling, smoking status, pack-years of tobacco smoking, and daily energy intake.

RESULTS

Lung cancer was associated inversely with the consumption of epicatechin (in 10 mg per day increment: OR, 0.64; 95% CL, 0.46-0.88), catechin (4 mg per day increment: OR, 0.49; 95% CL, 0.35-0.70), quercetin (9 mg per day increment: OR, 0.65; 95% CL, 0.44-0.95), and kaempferol (2 mg per day increment: OR, 0.68; 95% CL, 0.51-0.90) among tobacco smokers. There was little association between lung cancer and the flavonoid compounds mentioned above among nonsmokers. Regardless of smoking status, there was little association with total flavonoids: thearubigins, hesperetin, naringenin, and myricetin. In addition, consumption of vegetables, tea, and wine, all of which are rich sources of flavonoids, was associated inversely with lung cancer among tobacco smokers.

CONCLUSIONS

Certain flavonoid compounds, including epicatechin, catechin, quercetin, and kaempferol, were associated inversely with lung cancer among tobacco smokers, but not among nonsmokers. Further studies of these associations may be warranted.

A case-control study of the association of the polymorphisms and haplotypes of DNA ligase I with lung and upper-aerodigestive-tract cancers

Tobacco smoking is a major risk factor for lung and upper-aerodigestive-tract (UADT) cancers. One possible mechanism for the associations may be through DNA damage pathways. DNA Ligase I (LIG1) is a DNA repair gene involved in both the nucleotide excision repair (NER) and the base excision repair (BER) pathways. We examined the association of 4 LIG1 polymorphisms with lung and UADT cancers, and their potential interactions with smoking in a population-based case-control study in Los Angeles County. We performed genotyping using the SNPlex method from Applied Biosystems. Logistic regression analyses of 551 lung cancer cases, 489 UADT cancer cases and 948 controls showed the expected associations of tobacco smoking with lung and UADT cancers and new associations between the LIG1 haplotypes and these cancers. For lung cancer, when compared to the most common haplotype (rs20581-rs20580-rs20579-rs439132 = T-C-C-A), the adjusted odds ratio (OR) is 1.2 (95% confidence limits (CL) = 0.95, 1.5) for the CACA haplotype, 1.4 (1.0, 1.9) for the CATA haplotype and 1.8 (1.1, 2.8) for the CCCG haplotype, after controlling for age, gender, race/ethnicity, education and tobacco smoking. We observed weaker associations between the LIG1 haplotypes and UADT cancers. Our findings suggest the LIG1 haplotypes may affect the risk of lung and UADT cancers.

Correlating observed odds ratios from lung cancer case-control studies to SNP functional scores predicted by bioinformatic tools

Bioinformatic tools are widely utilized to predict functional single nucleotide polymorphisms (SNPs) for genotyping in molecular epidemiological studies. However, the extent to which these approaches are mirrored by epidemiological findings has not been fully explored. In this study, we first surveyed SNPs examined in case-control studies of lung cancer, the most extensively studied cancer type. We then computed SNP functional scores using four popular bioinformatics tools: SIFT, PolyPhen, SNPs3D, and PMut, and determined their predictive potential using the odds ratios (ORs) reported. Spearman's correlation coefficient (r) for the association with SNP score from SIFT, PolyPhen, SNPs3D, and PMut, and the summary ORs were r=-0.36 (p=0.007), r=0.25 (p=0.068), r=-0.20 (p=0.205), and r=-0.12 (p=0.370), respectively. By creating a combined score using information from all four tools we were able to achieve a correlation coefficient of r=0.51 (p<0.001). These results indicate that scores of predicted functionality could explain a certain fraction of the lung cancer risk detected in genetic association studies and more accurate predictions may be obtained by combining information from a variety of tools. Our findings suggest that bioinformatic tools are useful in predicting SNP functionality and may facilitate future genetic epidemiological studies.

Genetic polymorphisms and esophageal cancer risk

The aim of this paper is to review and evaluate, in a comprehensive manner, the published data regarding the contribution of genetic polymorphisms to risk of esophageal cancer, including squamous cell carcinoma (SCC) and adenocarcinoma, in humans. All relevant studies available in MEDLINE and published before February 2007 were identified. Studies carried out in humans and that compared esophageal cancer patients with at least 1 standard control group were considered for analysis. One-hundred studies and 3 meta-analyses were identified. Eighty (80%) studies were conducted in Asian countries, particularly China including Taiwan (60 (60%) studies). The most intensively examined genes were those encoding carcinogen metabolic enzymes. The most widely studied gene was GSTM1 (15 studies), followed by ALDH2 (11 studies). ALDH2, MTHFR C677T, CYP1A1 Ile/Val, CYP1A1MspI, CYP2E1, GSTP1, GSTM1 and GSTT1 were examined by meta-analyses and significant relations were found between ALDH2*1*2 and the CYP1A1 Val allele and increased risk of esophageal cancer. In addition, increased risk of esophageal SCC was consistently associated with the ADH2*1*2 and the p53 codon 72 Pro/Pro genotypes. Cohort studies that simultaneously consider multiple genetic and environmental factors possibly involved in esophageal carcinogenesis are needed to ascertain not only the relative contribution of these factors to tumor development but also the contributions of their putative interactions.

Potentially functional single nucleotide polymorphisms in the core nucleotide excision repair genes and risk of squamous cell carcinoma of the head and neck

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.

Alcohol drinking in never users of tobacco, cigarette smoking in never drinkers, and the risk of head and neck cancer: pooled analysis in the International Head and Neck Cancer Epidemiology Consortium

BACKGROUND

At least 75% of head and neck cancers are attributable to a combination of cigarette smoking and alcohol drinking. A precise understanding of the independent association of each of these factors in the absence of the other with the risk of head and neck cancer is needed to elucidate mechanisms of head and neck carcinogenesis and to assess the efficacy of interventions aimed at controlling either risk factor.

METHODS

We examined the extent to which head and neck cancer is associated with cigarette smoking among never drinkers and with alcohol drinking among never users of tobacco. We pooled individual-level data from 15 case-control studies that included 10,244 head and neck cancer case subjects and 15,227 control subjects, of whom 1072 case subjects and 5775 control subjects were never users of tobacco and 1598 case subjects and 4051 control subjects were never drinkers of alcohol. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using unconditional logistic regression models. All statistical tests were two-sided.

RESULTS

Among never drinkers, cigarette smoking was associated with an increased risk of head and neck cancer (OR for ever versus never smoking = 2.13, 95% CI = 1.52 to 2.98), and there were clear dose-response relationships for the frequency, duration, and number of pack-years of cigarette smoking. Approximately 24% (95% CI = 16% to 31%) of head and neck cancer cases among nondrinkers in this study would have been prevented if these individuals had not smoked cigarettes. Among never users of tobacco, alcohol consumption was associated with an increased risk of head and neck cancer only when alcohol was consumed at high frequency (OR for three or more drinks per day versus never drinking = 2.04, 95% CI = 1.29 to 3.21). The association with high-frequency alcohol intake was limited to cancers of the oropharynx/hypopharynx and larynx.

CONCLUSIONS

Our results represent the most precise estimates available of the independent association of each of the two main risk factors of head and neck cancer, and they exemplify the strengths of large-scale consortia in cancer epidemiology.

Gene prophylaxis by a DNA repair function

Gene therapy, the treatment of disorders or pathophysiologic states on the basis of the transfer of genetic information, has been thoroughly investigated for the treatment of lung illnesses, e.g. cystic fibrosis, alpha1-antitrypsin deficiency-related emphysema and cancer. Transfer of genetic information may be further used to elevate the level of protection of normal lung tissues in at risk individuals, with preventing purposes. This concept can be described by the term "gene prophylaxis". Lying at the gas-exchange interface, lung epithelia may be at risk of oxidation-induced mutagenesis. Further, inflammation processes possibly consequent on smoking liberate reactive oxygen species (ROS) that multiply the carcinogenic effects of tobacco. Some studies report in lung cancer patients an high frequency of variations of the 8-oxoguanine DNA glycosylase (hOGG1) gene that encodes a sluggish glycosylase for oxidized purines. Unlike dietary interventions with antioxidant drugs that only allow temporary oxy-radical scavenging, reinforcing the DNA repair capacity in lung epithelia may afford long-term, steady protection from ROS-generated mutagenesis and carcinogenesis. In this regard, the Escherichia coli formamidopyrimidine DNA glycosylase (FPG) is a possible tool. FPG is 80-fold faster than hOGG1 in repairing oxidized purines and has broader substrate specificity. Cell culture studies have shown that FPG can be expressed in mammalian cells where it accelerates DNA repair and abates mutagenicity of a wide range of DNA damaging agents. Spontaneous mutagenesis drops too. Prophylaxis of oxidative DNA damage and mutation could be achieved in lung epithelia and other tissues of at-risk individuals by FPG expression. Currently available vehicles for this peculiar type of gene therapy are briefly surveyed.

Genetic polymorphisms in the nucleotide excision repair pathway and lung cancer risk: a meta-analysis

Various DNA alterations can be caused by exposure to environmental and endogenous carcinogens. Most of these alterations, if not repaired, can result in genetic instability, mutagenesis and cell death. DNA repair mechanisms are important for maintaining DNA integrity and preventing carcinogenesis. Recent lung cancer studies have focused on identifying the effects of single nucleotide polymorphisms (SNPs) in candidate genes, among which DNA repair genes are increasingly being studied. Genetic variations in DNA repair genes are thought to modulate DNA repair capacity and are suggested to be related to lung cancer risk. We identified a sufficient number of epidemiologic studies on lung cancer to conduct a meta-analysis for genetic polymorphisms in nucleotide excision repair pathway genes, focusing on xeroderma pigmentosum group A (XPA), excision repair cross complementing group 1 (ERCC1), ERCC2/XPD, ERCC4/XPF and ERCC5/XPG. We found an increased risk of lung cancer among subjects carrying the ERCC2 751Gln/Gln genotype (odds ratio (OR) = 1.30, 95% confidence interval (CI) = 1.14 - 1.49). We found a protective effect of the XPA 23G/G genotype (OR = 0.75, 95% CI = 0.59 - 0.95). Considering the data available, it can be conjectured that if there is any risk association between a single SNP and lung cancer, the risk fluctuation will probably be minimal. Advances in the identification of new polymorphisms and in high-throughput genotyping techniques will facilitate the analysis of multiple genes in multiple DNA repair pathways. Therefore, it is likely that the defining feature of future epidemiologic studies will be the simultaneous analysis of large samples.