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XRCC1 polymorphisms, cooking oil fume and lung cancer in Chinese women nonsmokers
Lung Cancer (2008) 62, 145—151
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XRCC1 polymorphisms, cooking oil fume and lung cancer in Chinese women nonsmokers Mingchuan Li a, Zhihua Yin a, Peng Guan a, Xuelian Li a, Zeshi Cui b, Jun Zhang c, Weijun Bai d, Qincheng He a, Baosen Zhou a,∗ a
Department of Epidemiology, School of Public Health, China Medical University, Shenyang 110001, Liaoning Province, PR China The Third Center of Laboratory Technology and Experimental Medicine, China Medical University, Shenyang 110001, Liaoning Province, PR China c Department of Thoracic Surgery, The First Affiliated Hospital of China Medical University, Shenyang 110001, Liaoning Province, PR China d Department of Internal Medicine, Liaoning Cancer Hospital & Institute, Shenyang 110042, Liaoning Province, PR China b
Received 9 November 2007; received in revised form 29 February 2008; accepted 1 March 2008
KEYWORDS XRCC1; Lung cancer; Nonsmoker; Susceptibility; Single nucleotide polymorphism; Oils
∗
Summary X-ray repair cross-complementing group 1 (XRCC1) is one of the major DNA repair proteins involved in the base excision repair (BER) and single-strand break repair (SSBR) pathway. Single nucleotide polymorphisms (SNPs) in XRCC1 may alter protein function and repair capacity, thus lead to genetic instability and carcinogenesis. To establish our understanding of possible relationships between XRCC1 polymorphisms (5 UTR -77T>C, Arg194Trp, Arg280His and Arg399Gln) and the susceptibility to lung cancer among women nonsmokers, we performed a hospital-based case-control study of 350 patients with newly diagnosed lung cancer and 350 cancer-free controls, frequency matched by age. Our results showed that exposure to cooking oil fume was associated with increased risk of lung cancer in Chinese women nonsmokers [odds ratio (OR) = 2.51, 95% confidence interval (CI) [1.80—3.51], P < 0.001]. Individuals with homozygous XRCC1 399Gln/Gln genotype (OR = 1.75, 95% CI [1.02—3.01]) and XRCC1 -77 combined TC and CC genotype (OR = 1.66, 95% CI [1.13—2.42]) showed a slightly higher risk for lung cancer overall. In the subgroup of adenocarcinoma cases, adjusted ORs were increased for individuals with homozygous XRCC1 399Gln/Gln genotype (OR = 2.62, 95% CI [1.44—4.79]) and XRCC1 -77 combined TC and CC genotype (OR = 1.85, 95% CI [1.19—2.86]). Haplotype analysis showed that T—Trp—Arg—Gln haplotypes were associated with an increased risk of lung cancer among women nonsmokers (OR = 2.26, 95% CI [1.38—3.68]), however, we did not observe a statistically significant joint effect of cooking oil fume and 399Gln or -77C variant allele on lung cancer among women nonsmokers. In conclusion, XRCC1 Arg399Gln and T-77C polymorphisms may alter the risk of lung cancer in women nonsmokers in China. © 2008 Elsevier Ireland Ltd. All rights reserved.
Corresponding author. Tel.: +86 24 23258982; fax: +86 24 23258982. E-mail address: [email protected] (B. Zhou).
0169-5002/$ — see front matter © 2008 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.lungcan.2008.03.002
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1. Introduction Lung cancer incidence has increased rapidly in China, especially in females. A study of cancer mortality trends between 1973 and 2002 in 30 cities or counties, conducted by the National Center for Cancer Registry, showed that over the last 30 years, mortality rates from lung cancer in women increased more than 100% in some cities of northeast China [1]. Although cigarette smoking remains the predominant cause of lung cancer, it cannot fully explain epidemiologic characteristics of lung cancer in nonsmokers. The latter constitute a special subset of patients which include a higher proportion of women, presence of adenocarcinoma, as well as an earlier age at diagnosis [2]. Why do lung cancers occur in nonsmokers? Data on this topic, particularly the etiology of lung cancer in women nonsmokers, are limited. Recent genetic association studies on cancer risk have focused on assessing effects of single nucleotide polymorphisms (SNPs) in candidate genes, among which DNA repair genes are increasingly studied because of their pivotal role in maintaining genome integrity. Sequence variants in DNA repair genes are thought to modulate DNA repair capacity and consequently are suggested to be associated with altered cancer risk [3]. The X-ray repair cross-complementing group 1 (XRCC1) protein plays a central role in two interconnected DNA repair pathways: base excision repair (BER) and single-strand break repair (SSBR). The former consists of two sub-pathways: a short-patch pathway that replaces 1 nucleotide and a long-patch pathway that replaces 2—15 nucleotides [4]. In the BER and SSBR pathways, XRCC1 interacts directly with at least seven other proteins. In short-patch BER, XRCC1 interacts with 8-oxoguanine glycosylase (OGG1) [5], apurinic/apyrimidinic endonuclease(APE1) [6], polymerase (pol) [7—9], and DNA ligaseIII␣ (LigIII␣) [10]. In long-patch BER, XRCC1 interacts with some of the same proteins, as well as proliferating cell nuclear antigen [11]. In SSBR, XRCC1 interacts with PARP1 [9,12] and polynucleotide kinase/phosphatase [13]. More than 60 validated single nucleotide polymorphisms have been found in XRCC1, among which approximately 30 variants are located in exons or promoter regions. The most extensively studied single nucleotide polymorphisms are Arg194Trp on exon 6, Arg280His on exon 9, and Arg399Gln on exon 10. The Arg194Trp variant has been shown to be associated with lower bleomycin and benzo(␣)pyrene diolepoxide sensitivity in vitro [14]. The Arg280His is located in the proliferating cell nuclear antigen binding region [11]. The Arg280His variant protein is defective in its efficient localization of a damaged site in the chromosome, thereby reducing the cellular BER/SSBR efficiency [15]. The 399Gln allele is situated within the BRCT-1 region harboring the ADPRT binding domain that is likely to affect functional interaction between XRCC1 and ADPRT [16]. An altered DNA repair activity has been suggested to be associated with this polymorphism [17—19]. 5 UTR-77T>C is a novel polymorphism identified in the XRCC1 gene located in the 5 untranslated region. Hao et al. have reported that functional SNP-77T>C decreased transcriptional activity of C-allelecontaining promoter with higher affinity to Sp1 binding [20].
M. Li et al. In this study including a relatively large number of women nonsmokers, we investigated the possible association of four polymorphisms with susceptibility to lung cancer. We also evaluated other possible etiological factors for lung cancer in women nonsmokers.
2. Materials and methods 2.1. Study subjects This was a hospital-based case-control study in the northeast of China, comprising 350 primary lung cancer cases and 350 cancer-free hospital controls. All subjects were unrelated ethnic Han Chinese. Cases were recruited from January 2002 to January 2006 at the First Affiliated Hospital of China Medical University and the Liaoning Cancer Hospital & Institute. They were all newly diagnosed with histopathologically confirmed primary lung cancer and surgically treated, before any radiotherapy and chemotherapy. Cancer-free controls were selected from the same hospital during the same period as the cases. The selection criteria included no previous or present history of malignant disease and they were frequency matched to case subjects by age (±5 years). Controls suffered mainly from bronchitis, pneumonias, fibrosis, sarcoidosis, chronic obstructive pulmonary disease and emphysema.
2.2. Data collection All study participants signed an informed consent form and completed a detailed questionnaire on personal history, information on demographic characteristics and environmental exposure factors such as passive smoking, cooking oil fume, occupational exposures and family history of cancer. Those who had consumed as much as one cigarette per day for 1 month in their lifetime were defined as smokers, otherwise they were considered as nonsmokers. Subjects were defined as passive smokers if they were exposed to the smoke from more than one cigarette per day for at least 1 year. This same criterion was set either for home or the workplace. For cooking oil fume exposure, participants were asked about the frequency of using various cooking methods, particularly stir-frying and types of oils as their usual practice 20—30 years. Subjects were also asked ‘‘How often did the air in your kitchen become filled with oily ‘smoke’ during frying?’’ For each of these cooking exposures, there were four possible responses ranging from ‘‘never’’, ‘‘seldom’’, ‘‘sometimes’’, and ‘‘frequently’’. Exposure for cooking oil fume was categorized as an indicator variable equal to 1 if participants reported frequently or sometimes and equal to 0 otherwise. Family history of cancer refers to history of lung cancer or other kinds of cancer in first-degree relatives. Coal is the most common fuel used in northeast China. Subjects were considered fuel smoke exposure if they used coal-fuel-burning stoves or Kang without flues.
2.3. Genotype analysis Genomic DNA samples from cases were isolated from surgically resected normal tissues adjacent to the tumors of
XRCC1 polymorphisms, cooking oil fume and lung cancer in Chinese women nonsmokers lung cancer patients using trizol reagent. In controls, we collected approximately 5-ml venous blood and extracted genomic DNA by the guanidine hydrochloride (Gu·HCl) method. XRCC1 genotypes were analysed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) methods as described previously [21]. The PCR primers (Takara Biotechnology Dalian Co. Ltd., China) for amplifying DNA fragment containing the -77T>C (rs3213245), Arg194Trp (rs1799782), Arg280His (rs25489), or Arg399Gln (rs25487) site were 77F5 GAG GAA ACG CTC GTT GCT AAG 3 , R5 TCC TCA TTA ATT CCC TCA CGT C 3 ; 194F5 GCC AGG GCC CCT CCT TCA A 3 , R5 TAC CCT CAG ACC CAC GAG T 3 ; 280F5 CCA GTG GTG CTA ACC TAA TC 3 , R5 CCTA CAT GAG GTG CGT GCT GT 3 ; 399F5 TTG TGC TTT CTC TGT GTC CA 3 , R5 TCC TCC AGC CTT TTC TGA TA 3 , respectively. The PCR products were digested with restriction enzyme (New England Biolabs, Beverly, MA) BsrBI (for -77T>C), PvuII (for Arg194Trp), RsaI (for Arg280His), or MspI (for Arg399Gln) to determine the genotypes. A masked, random sample of 10% of cases and controls was tested twice by different persons, and the results were found to be concordant for all of the masked duplicate sets.
2.4. Statistical analysis The chi-square test was used to examine differences in demographic variables and distribution of genotypes, alleles and haplotypes between cases and controls. The associations between genotype and risk of lung cancer were estimated by calculating crude and adjusted odds ratio (OR) and 95% confidence interval (95% CI) with unconditional logistic models. The Hardy—Weinberg equilibrium for each SNP was tested with Pearson’s 2 test. On the basis of the observed frequencies of the selected SNPs, we calculated linkage disequilibrium index (D and r2 ) and inferred haplotype frequencies by using the SHEsis analysis platform [22]. To evaluate gene—environment interaction, the risks were estimated by a logistic regression model. Data were analysed with Statistical Product and Service Solutions (SPSS) software, Version 10.0, if not otherwise specified.
3. Results 3.1. Subject characteristics The demographic data for cases and controls are presented in Table 1, with mean ages of cases and controls (mean ± S.D.) being almost identical (55.5 ± 11.3 and 57.5 ± 9.4 years, respectively). Cases included 203 adenocarcinomas, 78 squamous cell carcinomas and 69 other tumors with a variety of different pathologies (including large-cell and small-cell carcinomas, carcinoids and mixed types). No significant differences were found between cases and controls regarding passive smoking (P = 0.2), family history of cancer (P = 0.08) and fuel smoke exposure (P = 0.08). However, cases have a higher prevalence of cooking oil fume exposure compared with controls (crude OR = 2.60, 95% CI [1.87—3.61], P < 0.001).
Table 1
147
Characteristics of lung cancer cases and controls
Variable
Case N (%)
Control N (%)
P value
Female Age (years) Passive smoking Family history of cancer Fuel smoke exposure Cooking oil fume exposure Histological type Adenocarcinoma Squamous cell carcinoma Other
350 55.5 ± 11.3 215 (61.4) 48 (13.7)
350 57.5 ± 9.4 199 (56.8) 33 (9.4)
0.705 0.219 0.076
103 (29.4)
100 (28.6)
0.075
148 (42.3)
77 (22.0)
<0.001
203 (58.0) 78 (22.3) 69 (19.7)
3.2. SNPs frequencies and association with lung cancer In the controls, frequencies of the variant alleles were as follows: XRCC1 -77C = 0.09; XRCC1 194Trp = 0.25; XRCC1 280His = 0.11; XRCC1 399Gln = 0.25. All allele distributions were consistent with Hardy—Weinberg equilibrium. Genotype frequencies and ORs related to the variant alleles are shown in Table 2 for controls and cases. Among these SNPs, homozygous carriers of the XRCC1 399Gln/Gln variant genotype had a 1.73-fold risk of lung cancer compared with the homozygous wild genotype (95% CI [1.01—2.97], P = 0.01). Individuals carrying the XRCC1 -77TC heterozygote genotype had a 1.51-fold increased risk of lung cancer compared with the wild genotype (OR = 1.51, 95% CI [1.01—2.24], P = 0.04) and those carrying the -77CC homozygote genotype had a 3.14-fold (non-significant) increased risk (95% CI [0.96—10.30], P = 0.091). In the adenocarcinoma (AC) subgroup, we found that the impact of 399Gln and -77C variant alleles was more evident than the analysis included all cases. Other SNPs including Arg194Trp and Arg280His were not associated with lung cancer in this study. Because the -77CC genotype was rare in this population, it was combined with the -77TC genotype for subsequent estimation of lung cancer risk. As a result, the combined -77TC/CC genotypes were associated with an increased risk of lung cancer with an adjusted OR of 1.61 for overall cases and 1.81 for AC. In the subgroup of squamous cell carcinoma (SCC) and other types, the distribution of genotypes was very similar among cases and controls for all polymorphisms (data not shown). In multivariate analysis, we first eliminated the statistically non-significant SNPs (P > 0.1) observed at individual SNP analyses. Thus only two SNPs were selected in the logistic regression model in which two non-genetic covariates (age and cooking oil expose) remained. As shown in Table 3, the environmental factor cooking oil fume was the main risk factor in this model (OR = 2.51 for overall cases and 2.75 for AC), and in the presence of cooking oil fume exposure in the same model, genetic factors appeared to have a relatively
148 Table 2
M. Li et al. Case-control distribution of genotypes and ORs for all lung cancer and adenocarcinoma
Genotype
Controls
Overall cases
Cases with adenocarcinoma
N (%)
N (%)
OR (95% CI)a
N (%)
OR (95% CI)a
XRCC1 T-77C TT TC CC TC+CC
291 (83.1) 55 (15.7) 4 (1.1) 59 (16.8)
264 (75.4) 75 (21.4) 11 (3.1) 86 (24.5)
1.00 1.51 (1.01—2.24) 3.14 (0.96—10.30) 1.61 (1.12—2.39)
149 (73.4) 47 (23.2) 7 (3.4) 54 (26.6)
1.00 1.66 (1.06—2.6) 4.15 (1.17—14.73) 1.81 (1.18—2.79)
XRCC1 codon 194 Arg/Arg Arg/Trp Trp/Trp
196 (56.0) 133 (38.0) 21 (6.0)
184 (52.6) 136 (38.9) 30 (8.6)
1.00 0.94(0.68—1.30) 1.53(0.84—2.81)
104 (51.2) 83 (40.9) 16 (7.9)
1.00 1.01(0.69—1.47) 1.38(0.68—2.82)
XRCC1 codon 280 Arg/Arg Arg/His His/His
74 (78.3) 72 (20.6) 4 (1.1)
266 (76.0) 79 (22.6) 5 (1.4)
1.00 1.15(0.80—1.67) 1.78(0.47—6.75)
149 (73.4) 52 (25.6) 2 (1.0)
1.00 1.36(0.89—2.07) 1.33(0.24—7.44)
XRCC1 codon 399 Arg/Arg Arg/Gln Gln/Gln
201 (57.4) 123 (35.1) 26 (7.4)
168 (48.0) 139 (39.7) 43 (12.3)
1.00 1.26 (0.91—1.75) 1.73 (1.01—2.97)
84 (41.4) 88 (43.3) 31 (15.0)
1.00 1.61 (1.09—2.36) 2.58 (1.42—4.69)
Boldfaced letters: P values <0.05. a Data were calculated by unconditional logistic regression and adjusted for age, cooking oil fume.
moderate effect on risk of female nonsmoker lung cancer. An increased risk of lung cancer was found for 399Gln/Gln genotype carriers (Gln/Gln versus Arg/Arg, OR = 1.75, 95% CI [1.02—3.01]) and -77C variant allele carriers (TT+TC versus TT: OR = 1.66, 95% CI [1.13—2.42]). The analysis of the histological subtype AC revealed slightly higher differences between cases and controls than the analysis including all cancer cases with an OR for the 399Arg/Gln genotype of 1.63 (95% CI [1.11—2.40], P = 0.014).
lung cancer in women nonsmokers. Six possible haplotypes represented 86.0% of the chromosomes for the cases and 93.9% for the controls. Comparisons of overall haplotype distribution profiles revealed a statistically significant difference between cases and controls (global test: P < 0.0001). The T—Trp—Arg—Arg and T—Arg—His—Arg haplotypes were associated with (non-significantly) reduced risks of lung cancer (OR = 0.75 and 0.67, respectively), compared with the T—Arg—Arg—Arg haplotype, whereas T—Trp—Arg—Gln was associated with a significantly increased risk (OR = 2.26).
3.3. Association with haplotypes 3.4. Analysis of gene—environment interactions We estimated haplotype frequencies for cases and controls by the SHEsis analysis platform. Our analysis showed that the four SNPs are in linkage disequilibrium in this study population, the minimum D between any pair of SNPs analyzed being 0.72 (all P < 0.0001). We combined all haplotypes that had an allele frequency of less than 0.03. Table 4 summarizes the association between the haplotypes and risk of
Table 3
We analysed the interaction of XRCC1 Arg399Gln or XRCC1 T-77C with cooking oil fume on lung cancer among women nonsmokers in a logistic regression model. We combined the heterozygous and homozygous variant genotypes for analysis. Increased lung cancer risk for XRCC1 399Gln/Gln or Arg/Gln carriers (OR = 3.46, 95% CI [0.77—15.56]) or for
ORs and 95% CIs for the XRCC1 polymorphisms selected for the final logistic regression model
Variates retained in final model
All cases
Adenocarcinoma
OR (95% CI)
P
OR (95% CI)
P
Cooking oil
2.51 (1.80—3.51)
<0.001
2.75 (1.87—4.03)
<0.001
XRCC1 T-77C TC+CC
1.66 (1.13—2.42)
0.010
1.85 (1.19—2.86)
0.006
XRCC1 Arg399Gln Arg/Gln Gln/Gln
1.28 (0.92—1.78) 1.75 (1.02—3.01)
0.142 0.044
1.63 (1.11—2.40) 2.62 (1.44—4.79)
0.014 0.002
XRCC1 polymorphisms, cooking oil fume and lung cancer in Chinese women nonsmokers Table 4
149
Haplotype frequencies and their associations with risk of lung cancer among women nonsmokers
Haplotype (—77—194—280—399)
Case frequenciesa
Control frequenciesa
OR (95% CI)b
P value
T—Arg—Arg—Arg C—Arg—Arg—Arg T—Arg—Arg—Gln T—Arg—His—Arg T—Trp—Arg—Arg T—Trp—Arg—Gln
267 (38.1%) 44 (6.3%) 117 (16.7%) 36 (5.1%) 83 (11.9%) 55 (7.8%)
296 (42.3%) 34 (4.8%) 118 (16.9%) 60 (8.5%) 122 (17.4%) 27 (3.8%)
1.00 1.44(0.89—2.31) 1.10(0.81—1.49) 0.67(0.43—1.04) 0.75(0.54—1.04) 2.26(1.38—3.68)
— 0.137 0.543 0.071 0.088 0.001
a b
Haplotype frequency analysed by SHEsis software platform. Haplotypes with frequencies <0.03 in both case and control are dropped. Data were calculated by chi-square test with T—Arg—Arg—Arg haplotype as reference group.
XRCC1 -77TC or CC carriers (OR = 4.35, 95% CI [0.82—23.0]) among cooking oil fume exposure was observed, however, as these findings were not statistically significant, a further histological subgroup analysis was not performed in this paper.
4. Discussion Among lung cancer cases, women nonsmokers are an underrepresented subgroup. Nonetheless, they represent the ideal subjects to examine unknown, yet important, environmental and genetic factors besides tobacco smoking. In this case-control study of lung cancer, we investigated the associations between risk for development of lung cancer and multiple genetic polymorphisms in XRCC1 gene among Chinese women nonsmokers. Based on our results, -77C and 399Gln variant alleles of XRCC1 may contribute to lung cancer risk for women nonsmokers, whereas the variant 194Trp and 280His alleles have no association with lung cancer in women nonsmokers. As a novel polymorphism identified in the XRCC1 gene, XRCC1 -77T>C polymorphism has only been examined in a few studies [23—26]. Our results support some of the studies showing that -77T>C polymorphism may affect the carcinogenic process. For instance, -77C variant allele was significantly associated with a slightly increased risk of esophageal squamous cell carcinoma [23] and lung cancer [20,24], although these studies focused on smokers. The molecular mechanism by which the polymorphism affects lung cancer risk is not yet elucidated. It has been shown that T to C mutation greatly enhances the affinity of nuclear protein Sp1 to the promoter region, which may inhibit its transcription, therefore diminishes expression of this DNA repair protein and increases risk of lung cancer [20]. Our results, however, seem to be in disagreement with other studies in which no association with lung cancer was found for -77T>C polymorphism in Caucasians [25] and breast cancer in French women [26]. This may be attributed to the difference in study population. XRCC1 Arg399Gln has been extensively studied in many cancer sites in different populations, but the results are conflicting [27—39]. We found a significant association between the Gln/Gln genotype alone and risk of lung cancer in Chinese women nonsmokers (adjusted OR = 1.75 for overall cases, and 2.62 for the AC subgroup), which is consistent with our previous study [21]. Recently, a meta-analysis of 11 published studies of lung cancer showed that XRCC1
399Gln/Gln genotype was associated with an increased risk of lung cancer among Asians (OR = 1.34, 95% CI [1.16—1.54]) [40]. Conversely, this is not the case in other studies including a cohort study in nonsmokers [27] and large population-based case-control studies in Caucasians [33], which showed an opposite effect in lung cancer. The explanation for these differences is still unclear. Most previous studies on the association between lung cancer risk and genetic polymorphisms have been dominated by male smokers. Although we eliminated the effect of tobacco smoking, the results from this study show that exposure to cooking oil fume may be an environmental risk factor for women nonsmoker lung cancer (OR = 2.51, 95% CI [1.80—3.51]). Domestic exposures, such as to fumes from cooking oils, have been implicated as a possible risk factor in studies among Chinese women in Asia [41—43]. Some carcinogens, similar to tobacco smoke, have been identified in heated oils, including polycyclic aromatic hydrocarbons (PAH), aromatic amines, and nitro-polycyclic aromatic hydrocarbons [44], although the exact mechanism has not been clarified. Over 90% of women nonsmokers who participated in the present study stated that they cooked the family food regularly. Many of them were used to waiting until the cooking oil has been heated to a high temperature before cooking the food. Data obtained from this study suggest a potential modified action of XRCC1 399Gln and -77C variant alleles increasing lung cancer risk in the group who expose to cooking oil fume. In other words, inheritance of the 399Gln or -77C allele may further increase the risk for lung cancer if it is combined with carcinogenic environmental factors. As lung cancer is a multifactorial disease, on a genetic opinion, it is more likely that the combined effect of different SNPs in a gene produces a change in expression or protein function. Therefore, we further conducted haplotype analysis and found that the haplotype which contained variant alleles at codon 399 and 194 (T—Trp—Arg—Gln) are associated with increased lung cancer risk (OR = 2.26, 95% CI [1.38—3.68]), although we did not find the association between the single polymorphism in codon 194 or 280 and lung cancer among female nonsmokers. These findings further suggest that XRCC1 Arg399Gln polymorphism is a functional SNP that has an impact on lung cancer among women nonsmokers. Because it is just a statistical estimating method, biological validity warrants further studies. In addition, because we have used hospital controls with non-malignant lung diseases, some of them, especially those associated with chronic inflammatory processes, are sus-
150 pected to have predisposing factors for lung cancer [45]. The ORs we found may be underestimated, however, this study is one of the largest among female nonsmoker lung cancer patients to evaluate the connection between XRCC1 polymorphisms and risk of lung cancer in a non-tobacco exposure group. This study demonstrates several novel aspects on genetic susceptibility to lung cancer.
5. Conclusion In conclusion, our study revealed that XRCC1 Arg399Gln and T-77C polymorphisms may alter the risk of lung cancer in women nonsmokers in China. Moreover, because genetic polymorphisms often vary between ethnic groups, further studies are needed to clarify the association between XRCC1 polymorphisms and lung cancer in diverse ethnic women nonsmokers.
Conflict of interest None.
Acknowledgements This study was supported by grants no. 30471493 from National Nature Science Foundation of China, grant no. 00726 from China Medical Board. The authors are most grateful to Dr. Hugo De Vuyst (International Agency for Research on Cancer, Lyon) for revising the final manuscript.
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XRCC1 polymorphisms, cooking oil fume and lung cancer in Chinese women nonsmokers Mingchuan Li a, Zhihua Yin a, Peng Guan a, Xuelian Li a, Zeshi Cui b, Jun Zhang c, Weijun Bai d, Qincheng He a, Baosen Zhou a,∗ a
Department of Epidemiology, School of Public Health, China Medical University, Shenyang 110001, Liaoning Province, PR China The Third Center of Laboratory Technology and Experimental Medicine, China Medical University, Shenyang 110001, Liaoning Province, PR China c Department of Thoracic Surgery, The First Affiliated Hospital of China Medical University, Shenyang 110001, Liaoning Province, PR China d Department of Internal Medicine, Liaoning Cancer Hospital & Institute, Shenyang 110042, Liaoning Province, PR China b
Received 9 November 2007; received in revised form 29 February 2008; accepted 1 March 2008
KEYWORDS XRCC1; Lung cancer; Nonsmoker; Susceptibility; Single nucleotide polymorphism; Oils
∗
Summary X-ray repair cross-complementing group 1 (XRCC1) is one of the major DNA repair proteins involved in the base excision repair (BER) and single-strand break repair (SSBR) pathway. Single nucleotide polymorphisms (SNPs) in XRCC1 may alter protein function and repair capacity, thus lead to genetic instability and carcinogenesis. To establish our understanding of possible relationships between XRCC1 polymorphisms (5 UTR -77T>C, Arg194Trp, Arg280His and Arg399Gln) and the susceptibility to lung cancer among women nonsmokers, we performed a hospital-based case-control study of 350 patients with newly diagnosed lung cancer and 350 cancer-free controls, frequency matched by age. Our results showed that exposure to cooking oil fume was associated with increased risk of lung cancer in Chinese women nonsmokers [odds ratio (OR) = 2.51, 95% confidence interval (CI) [1.80—3.51], P < 0.001]. Individuals with homozygous XRCC1 399Gln/Gln genotype (OR = 1.75, 95% CI [1.02—3.01]) and XRCC1 -77 combined TC and CC genotype (OR = 1.66, 95% CI [1.13—2.42]) showed a slightly higher risk for lung cancer overall. In the subgroup of adenocarcinoma cases, adjusted ORs were increased for individuals with homozygous XRCC1 399Gln/Gln genotype (OR = 2.62, 95% CI [1.44—4.79]) and XRCC1 -77 combined TC and CC genotype (OR = 1.85, 95% CI [1.19—2.86]). Haplotype analysis showed that T—Trp—Arg—Gln haplotypes were associated with an increased risk of lung cancer among women nonsmokers (OR = 2.26, 95% CI [1.38—3.68]), however, we did not observe a statistically significant joint effect of cooking oil fume and 399Gln or -77C variant allele on lung cancer among women nonsmokers. In conclusion, XRCC1 Arg399Gln and T-77C polymorphisms may alter the risk of lung cancer in women nonsmokers in China. © 2008 Elsevier Ireland Ltd. All rights reserved.
Corresponding author. Tel.: +86 24 23258982; fax: +86 24 23258982. E-mail address: [email protected] (B. Zhou).
0169-5002/$ — see front matter © 2008 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.lungcan.2008.03.002
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1. Introduction Lung cancer incidence has increased rapidly in China, especially in females. A study of cancer mortality trends between 1973 and 2002 in 30 cities or counties, conducted by the National Center for Cancer Registry, showed that over the last 30 years, mortality rates from lung cancer in women increased more than 100% in some cities of northeast China [1]. Although cigarette smoking remains the predominant cause of lung cancer, it cannot fully explain epidemiologic characteristics of lung cancer in nonsmokers. The latter constitute a special subset of patients which include a higher proportion of women, presence of adenocarcinoma, as well as an earlier age at diagnosis [2]. Why do lung cancers occur in nonsmokers? Data on this topic, particularly the etiology of lung cancer in women nonsmokers, are limited. Recent genetic association studies on cancer risk have focused on assessing effects of single nucleotide polymorphisms (SNPs) in candidate genes, among which DNA repair genes are increasingly studied because of their pivotal role in maintaining genome integrity. Sequence variants in DNA repair genes are thought to modulate DNA repair capacity and consequently are suggested to be associated with altered cancer risk [3]. The X-ray repair cross-complementing group 1 (XRCC1) protein plays a central role in two interconnected DNA repair pathways: base excision repair (BER) and single-strand break repair (SSBR). The former consists of two sub-pathways: a short-patch pathway that replaces 1 nucleotide and a long-patch pathway that replaces 2—15 nucleotides [4]. In the BER and SSBR pathways, XRCC1 interacts directly with at least seven other proteins. In short-patch BER, XRCC1 interacts with 8-oxoguanine glycosylase (OGG1) [5], apurinic/apyrimidinic endonuclease(APE1) [6], polymerase (pol) [7—9], and DNA ligaseIII␣ (LigIII␣) [10]. In long-patch BER, XRCC1 interacts with some of the same proteins, as well as proliferating cell nuclear antigen [11]. In SSBR, XRCC1 interacts with PARP1 [9,12] and polynucleotide kinase/phosphatase [13]. More than 60 validated single nucleotide polymorphisms have been found in XRCC1, among which approximately 30 variants are located in exons or promoter regions. The most extensively studied single nucleotide polymorphisms are Arg194Trp on exon 6, Arg280His on exon 9, and Arg399Gln on exon 10. The Arg194Trp variant has been shown to be associated with lower bleomycin and benzo(␣)pyrene diolepoxide sensitivity in vitro [14]. The Arg280His is located in the proliferating cell nuclear antigen binding region [11]. The Arg280His variant protein is defective in its efficient localization of a damaged site in the chromosome, thereby reducing the cellular BER/SSBR efficiency [15]. The 399Gln allele is situated within the BRCT-1 region harboring the ADPRT binding domain that is likely to affect functional interaction between XRCC1 and ADPRT [16]. An altered DNA repair activity has been suggested to be associated with this polymorphism [17—19]. 5 UTR-77T>C is a novel polymorphism identified in the XRCC1 gene located in the 5 untranslated region. Hao et al. have reported that functional SNP-77T>C decreased transcriptional activity of C-allelecontaining promoter with higher affinity to Sp1 binding [20].
M. Li et al. In this study including a relatively large number of women nonsmokers, we investigated the possible association of four polymorphisms with susceptibility to lung cancer. We also evaluated other possible etiological factors for lung cancer in women nonsmokers.
2. Materials and methods 2.1. Study subjects This was a hospital-based case-control study in the northeast of China, comprising 350 primary lung cancer cases and 350 cancer-free hospital controls. All subjects were unrelated ethnic Han Chinese. Cases were recruited from January 2002 to January 2006 at the First Affiliated Hospital of China Medical University and the Liaoning Cancer Hospital & Institute. They were all newly diagnosed with histopathologically confirmed primary lung cancer and surgically treated, before any radiotherapy and chemotherapy. Cancer-free controls were selected from the same hospital during the same period as the cases. The selection criteria included no previous or present history of malignant disease and they were frequency matched to case subjects by age (±5 years). Controls suffered mainly from bronchitis, pneumonias, fibrosis, sarcoidosis, chronic obstructive pulmonary disease and emphysema.
2.2. Data collection All study participants signed an informed consent form and completed a detailed questionnaire on personal history, information on demographic characteristics and environmental exposure factors such as passive smoking, cooking oil fume, occupational exposures and family history of cancer. Those who had consumed as much as one cigarette per day for 1 month in their lifetime were defined as smokers, otherwise they were considered as nonsmokers. Subjects were defined as passive smokers if they were exposed to the smoke from more than one cigarette per day for at least 1 year. This same criterion was set either for home or the workplace. For cooking oil fume exposure, participants were asked about the frequency of using various cooking methods, particularly stir-frying and types of oils as their usual practice 20—30 years. Subjects were also asked ‘‘How often did the air in your kitchen become filled with oily ‘smoke’ during frying?’’ For each of these cooking exposures, there were four possible responses ranging from ‘‘never’’, ‘‘seldom’’, ‘‘sometimes’’, and ‘‘frequently’’. Exposure for cooking oil fume was categorized as an indicator variable equal to 1 if participants reported frequently or sometimes and equal to 0 otherwise. Family history of cancer refers to history of lung cancer or other kinds of cancer in first-degree relatives. Coal is the most common fuel used in northeast China. Subjects were considered fuel smoke exposure if they used coal-fuel-burning stoves or Kang without flues.
2.3. Genotype analysis Genomic DNA samples from cases were isolated from surgically resected normal tissues adjacent to the tumors of
XRCC1 polymorphisms, cooking oil fume and lung cancer in Chinese women nonsmokers lung cancer patients using trizol reagent. In controls, we collected approximately 5-ml venous blood and extracted genomic DNA by the guanidine hydrochloride (Gu·HCl) method. XRCC1 genotypes were analysed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) methods as described previously [21]. The PCR primers (Takara Biotechnology Dalian Co. Ltd., China) for amplifying DNA fragment containing the -77T>C (rs3213245), Arg194Trp (rs1799782), Arg280His (rs25489), or Arg399Gln (rs25487) site were 77F5 GAG GAA ACG CTC GTT GCT AAG 3 , R5 TCC TCA TTA ATT CCC TCA CGT C 3 ; 194F5 GCC AGG GCC CCT CCT TCA A 3 , R5 TAC CCT CAG ACC CAC GAG T 3 ; 280F5 CCA GTG GTG CTA ACC TAA TC 3 , R5 CCTA CAT GAG GTG CGT GCT GT 3 ; 399F5 TTG TGC TTT CTC TGT GTC CA 3 , R5 TCC TCC AGC CTT TTC TGA TA 3 , respectively. The PCR products were digested with restriction enzyme (New England Biolabs, Beverly, MA) BsrBI (for -77T>C), PvuII (for Arg194Trp), RsaI (for Arg280His), or MspI (for Arg399Gln) to determine the genotypes. A masked, random sample of 10% of cases and controls was tested twice by different persons, and the results were found to be concordant for all of the masked duplicate sets.
2.4. Statistical analysis The chi-square test was used to examine differences in demographic variables and distribution of genotypes, alleles and haplotypes between cases and controls. The associations between genotype and risk of lung cancer were estimated by calculating crude and adjusted odds ratio (OR) and 95% confidence interval (95% CI) with unconditional logistic models. The Hardy—Weinberg equilibrium for each SNP was tested with Pearson’s 2 test. On the basis of the observed frequencies of the selected SNPs, we calculated linkage disequilibrium index (D and r2 ) and inferred haplotype frequencies by using the SHEsis analysis platform [22]. To evaluate gene—environment interaction, the risks were estimated by a logistic regression model. Data were analysed with Statistical Product and Service Solutions (SPSS) software, Version 10.0, if not otherwise specified.
3. Results 3.1. Subject characteristics The demographic data for cases and controls are presented in Table 1, with mean ages of cases and controls (mean ± S.D.) being almost identical (55.5 ± 11.3 and 57.5 ± 9.4 years, respectively). Cases included 203 adenocarcinomas, 78 squamous cell carcinomas and 69 other tumors with a variety of different pathologies (including large-cell and small-cell carcinomas, carcinoids and mixed types). No significant differences were found between cases and controls regarding passive smoking (P = 0.2), family history of cancer (P = 0.08) and fuel smoke exposure (P = 0.08). However, cases have a higher prevalence of cooking oil fume exposure compared with controls (crude OR = 2.60, 95% CI [1.87—3.61], P < 0.001).
Table 1
147
Characteristics of lung cancer cases and controls
Variable
Case N (%)
Control N (%)
P value
Female Age (years) Passive smoking Family history of cancer Fuel smoke exposure Cooking oil fume exposure Histological type Adenocarcinoma Squamous cell carcinoma Other
350 55.5 ± 11.3 215 (61.4) 48 (13.7)
350 57.5 ± 9.4 199 (56.8) 33 (9.4)
0.705 0.219 0.076
103 (29.4)
100 (28.6)
0.075
148 (42.3)
77 (22.0)
<0.001
203 (58.0) 78 (22.3) 69 (19.7)
3.2. SNPs frequencies and association with lung cancer In the controls, frequencies of the variant alleles were as follows: XRCC1 -77C = 0.09; XRCC1 194Trp = 0.25; XRCC1 280His = 0.11; XRCC1 399Gln = 0.25. All allele distributions were consistent with Hardy—Weinberg equilibrium. Genotype frequencies and ORs related to the variant alleles are shown in Table 2 for controls and cases. Among these SNPs, homozygous carriers of the XRCC1 399Gln/Gln variant genotype had a 1.73-fold risk of lung cancer compared with the homozygous wild genotype (95% CI [1.01—2.97], P = 0.01). Individuals carrying the XRCC1 -77TC heterozygote genotype had a 1.51-fold increased risk of lung cancer compared with the wild genotype (OR = 1.51, 95% CI [1.01—2.24], P = 0.04) and those carrying the -77CC homozygote genotype had a 3.14-fold (non-significant) increased risk (95% CI [0.96—10.30], P = 0.091). In the adenocarcinoma (AC) subgroup, we found that the impact of 399Gln and -77C variant alleles was more evident than the analysis included all cases. Other SNPs including Arg194Trp and Arg280His were not associated with lung cancer in this study. Because the -77CC genotype was rare in this population, it was combined with the -77TC genotype for subsequent estimation of lung cancer risk. As a result, the combined -77TC/CC genotypes were associated with an increased risk of lung cancer with an adjusted OR of 1.61 for overall cases and 1.81 for AC. In the subgroup of squamous cell carcinoma (SCC) and other types, the distribution of genotypes was very similar among cases and controls for all polymorphisms (data not shown). In multivariate analysis, we first eliminated the statistically non-significant SNPs (P > 0.1) observed at individual SNP analyses. Thus only two SNPs were selected in the logistic regression model in which two non-genetic covariates (age and cooking oil expose) remained. As shown in Table 3, the environmental factor cooking oil fume was the main risk factor in this model (OR = 2.51 for overall cases and 2.75 for AC), and in the presence of cooking oil fume exposure in the same model, genetic factors appeared to have a relatively
148 Table 2
M. Li et al. Case-control distribution of genotypes and ORs for all lung cancer and adenocarcinoma
Genotype
Controls
Overall cases
Cases with adenocarcinoma
N (%)
N (%)
OR (95% CI)a
N (%)
OR (95% CI)a
XRCC1 T-77C TT TC CC TC+CC
291 (83.1) 55 (15.7) 4 (1.1) 59 (16.8)
264 (75.4) 75 (21.4) 11 (3.1) 86 (24.5)
1.00 1.51 (1.01—2.24) 3.14 (0.96—10.30) 1.61 (1.12—2.39)
149 (73.4) 47 (23.2) 7 (3.4) 54 (26.6)
1.00 1.66 (1.06—2.6) 4.15 (1.17—14.73) 1.81 (1.18—2.79)
XRCC1 codon 194 Arg/Arg Arg/Trp Trp/Trp
196 (56.0) 133 (38.0) 21 (6.0)
184 (52.6) 136 (38.9) 30 (8.6)
1.00 0.94(0.68—1.30) 1.53(0.84—2.81)
104 (51.2) 83 (40.9) 16 (7.9)
1.00 1.01(0.69—1.47) 1.38(0.68—2.82)
XRCC1 codon 280 Arg/Arg Arg/His His/His
74 (78.3) 72 (20.6) 4 (1.1)
266 (76.0) 79 (22.6) 5 (1.4)
1.00 1.15(0.80—1.67) 1.78(0.47—6.75)
149 (73.4) 52 (25.6) 2 (1.0)
1.00 1.36(0.89—2.07) 1.33(0.24—7.44)
XRCC1 codon 399 Arg/Arg Arg/Gln Gln/Gln
201 (57.4) 123 (35.1) 26 (7.4)
168 (48.0) 139 (39.7) 43 (12.3)
1.00 1.26 (0.91—1.75) 1.73 (1.01—2.97)
84 (41.4) 88 (43.3) 31 (15.0)
1.00 1.61 (1.09—2.36) 2.58 (1.42—4.69)
Boldfaced letters: P values <0.05. a Data were calculated by unconditional logistic regression and adjusted for age, cooking oil fume.
moderate effect on risk of female nonsmoker lung cancer. An increased risk of lung cancer was found for 399Gln/Gln genotype carriers (Gln/Gln versus Arg/Arg, OR = 1.75, 95% CI [1.02—3.01]) and -77C variant allele carriers (TT+TC versus TT: OR = 1.66, 95% CI [1.13—2.42]). The analysis of the histological subtype AC revealed slightly higher differences between cases and controls than the analysis including all cancer cases with an OR for the 399Arg/Gln genotype of 1.63 (95% CI [1.11—2.40], P = 0.014).
lung cancer in women nonsmokers. Six possible haplotypes represented 86.0% of the chromosomes for the cases and 93.9% for the controls. Comparisons of overall haplotype distribution profiles revealed a statistically significant difference between cases and controls (global test: P < 0.0001). The T—Trp—Arg—Arg and T—Arg—His—Arg haplotypes were associated with (non-significantly) reduced risks of lung cancer (OR = 0.75 and 0.67, respectively), compared with the T—Arg—Arg—Arg haplotype, whereas T—Trp—Arg—Gln was associated with a significantly increased risk (OR = 2.26).
3.3. Association with haplotypes 3.4. Analysis of gene—environment interactions We estimated haplotype frequencies for cases and controls by the SHEsis analysis platform. Our analysis showed that the four SNPs are in linkage disequilibrium in this study population, the minimum D between any pair of SNPs analyzed being 0.72 (all P < 0.0001). We combined all haplotypes that had an allele frequency of less than 0.03. Table 4 summarizes the association between the haplotypes and risk of
Table 3
We analysed the interaction of XRCC1 Arg399Gln or XRCC1 T-77C with cooking oil fume on lung cancer among women nonsmokers in a logistic regression model. We combined the heterozygous and homozygous variant genotypes for analysis. Increased lung cancer risk for XRCC1 399Gln/Gln or Arg/Gln carriers (OR = 3.46, 95% CI [0.77—15.56]) or for
ORs and 95% CIs for the XRCC1 polymorphisms selected for the final logistic regression model
Variates retained in final model
All cases
Adenocarcinoma
OR (95% CI)
P
OR (95% CI)
P
Cooking oil
2.51 (1.80—3.51)
<0.001
2.75 (1.87—4.03)
<0.001
XRCC1 T-77C TC+CC
1.66 (1.13—2.42)
0.010
1.85 (1.19—2.86)
0.006
XRCC1 Arg399Gln Arg/Gln Gln/Gln
1.28 (0.92—1.78) 1.75 (1.02—3.01)
0.142 0.044
1.63 (1.11—2.40) 2.62 (1.44—4.79)
0.014 0.002
XRCC1 polymorphisms, cooking oil fume and lung cancer in Chinese women nonsmokers Table 4
149
Haplotype frequencies and their associations with risk of lung cancer among women nonsmokers
Haplotype (—77—194—280—399)
Case frequenciesa
Control frequenciesa
OR (95% CI)b
P value
T—Arg—Arg—Arg C—Arg—Arg—Arg T—Arg—Arg—Gln T—Arg—His—Arg T—Trp—Arg—Arg T—Trp—Arg—Gln
267 (38.1%) 44 (6.3%) 117 (16.7%) 36 (5.1%) 83 (11.9%) 55 (7.8%)
296 (42.3%) 34 (4.8%) 118 (16.9%) 60 (8.5%) 122 (17.4%) 27 (3.8%)
1.00 1.44(0.89—2.31) 1.10(0.81—1.49) 0.67(0.43—1.04) 0.75(0.54—1.04) 2.26(1.38—3.68)
— 0.137 0.543 0.071 0.088 0.001
a b
Haplotype frequency analysed by SHEsis software platform. Haplotypes with frequencies <0.03 in both case and control are dropped. Data were calculated by chi-square test with T—Arg—Arg—Arg haplotype as reference group.
XRCC1 -77TC or CC carriers (OR = 4.35, 95% CI [0.82—23.0]) among cooking oil fume exposure was observed, however, as these findings were not statistically significant, a further histological subgroup analysis was not performed in this paper.
4. Discussion Among lung cancer cases, women nonsmokers are an underrepresented subgroup. Nonetheless, they represent the ideal subjects to examine unknown, yet important, environmental and genetic factors besides tobacco smoking. In this case-control study of lung cancer, we investigated the associations between risk for development of lung cancer and multiple genetic polymorphisms in XRCC1 gene among Chinese women nonsmokers. Based on our results, -77C and 399Gln variant alleles of XRCC1 may contribute to lung cancer risk for women nonsmokers, whereas the variant 194Trp and 280His alleles have no association with lung cancer in women nonsmokers. As a novel polymorphism identified in the XRCC1 gene, XRCC1 -77T>C polymorphism has only been examined in a few studies [23—26]. Our results support some of the studies showing that -77T>C polymorphism may affect the carcinogenic process. For instance, -77C variant allele was significantly associated with a slightly increased risk of esophageal squamous cell carcinoma [23] and lung cancer [20,24], although these studies focused on smokers. The molecular mechanism by which the polymorphism affects lung cancer risk is not yet elucidated. It has been shown that T to C mutation greatly enhances the affinity of nuclear protein Sp1 to the promoter region, which may inhibit its transcription, therefore diminishes expression of this DNA repair protein and increases risk of lung cancer [20]. Our results, however, seem to be in disagreement with other studies in which no association with lung cancer was found for -77T>C polymorphism in Caucasians [25] and breast cancer in French women [26]. This may be attributed to the difference in study population. XRCC1 Arg399Gln has been extensively studied in many cancer sites in different populations, but the results are conflicting [27—39]. We found a significant association between the Gln/Gln genotype alone and risk of lung cancer in Chinese women nonsmokers (adjusted OR = 1.75 for overall cases, and 2.62 for the AC subgroup), which is consistent with our previous study [21]. Recently, a meta-analysis of 11 published studies of lung cancer showed that XRCC1
399Gln/Gln genotype was associated with an increased risk of lung cancer among Asians (OR = 1.34, 95% CI [1.16—1.54]) [40]. Conversely, this is not the case in other studies including a cohort study in nonsmokers [27] and large population-based case-control studies in Caucasians [33], which showed an opposite effect in lung cancer. The explanation for these differences is still unclear. Most previous studies on the association between lung cancer risk and genetic polymorphisms have been dominated by male smokers. Although we eliminated the effect of tobacco smoking, the results from this study show that exposure to cooking oil fume may be an environmental risk factor for women nonsmoker lung cancer (OR = 2.51, 95% CI [1.80—3.51]). Domestic exposures, such as to fumes from cooking oils, have been implicated as a possible risk factor in studies among Chinese women in Asia [41—43]. Some carcinogens, similar to tobacco smoke, have been identified in heated oils, including polycyclic aromatic hydrocarbons (PAH), aromatic amines, and nitro-polycyclic aromatic hydrocarbons [44], although the exact mechanism has not been clarified. Over 90% of women nonsmokers who participated in the present study stated that they cooked the family food regularly. Many of them were used to waiting until the cooking oil has been heated to a high temperature before cooking the food. Data obtained from this study suggest a potential modified action of XRCC1 399Gln and -77C variant alleles increasing lung cancer risk in the group who expose to cooking oil fume. In other words, inheritance of the 399Gln or -77C allele may further increase the risk for lung cancer if it is combined with carcinogenic environmental factors. As lung cancer is a multifactorial disease, on a genetic opinion, it is more likely that the combined effect of different SNPs in a gene produces a change in expression or protein function. Therefore, we further conducted haplotype analysis and found that the haplotype which contained variant alleles at codon 399 and 194 (T—Trp—Arg—Gln) are associated with increased lung cancer risk (OR = 2.26, 95% CI [1.38—3.68]), although we did not find the association between the single polymorphism in codon 194 or 280 and lung cancer among female nonsmokers. These findings further suggest that XRCC1 Arg399Gln polymorphism is a functional SNP that has an impact on lung cancer among women nonsmokers. Because it is just a statistical estimating method, biological validity warrants further studies. In addition, because we have used hospital controls with non-malignant lung diseases, some of them, especially those associated with chronic inflammatory processes, are sus-
150 pected to have predisposing factors for lung cancer [45]. The ORs we found may be underestimated, however, this study is one of the largest among female nonsmoker lung cancer patients to evaluate the connection between XRCC1 polymorphisms and risk of lung cancer in a non-tobacco exposure group. This study demonstrates several novel aspects on genetic susceptibility to lung cancer.
5. Conclusion In conclusion, our study revealed that XRCC1 Arg399Gln and T-77C polymorphisms may alter the risk of lung cancer in women nonsmokers in China. Moreover, because genetic polymorphisms often vary between ethnic groups, further studies are needed to clarify the association between XRCC1 polymorphisms and lung cancer in diverse ethnic women nonsmokers.
Conflict of interest None.
Acknowledgements This study was supported by grants no. 30471493 from National Nature Science Foundation of China, grant no. 00726 from China Medical Board. The authors are most grateful to Dr. Hugo De Vuyst (International Agency for Research on Cancer, Lyon) for revising the final manuscript.
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