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Journal of Cancer Research and Clinical Oncology logoLink to Journal of Cancer Research and Clinical Oncology
. 2007 Oct 19;134(6):645–652. doi: 10.1007/s00432-007-0328-4

Prognostic importance of DNA repair gene polymorphisms of XRCC1 Arg399Gln and XPD Lys751Gln in lung cancer patients from India

Leelakumari Sreeja 1, Volga S Syamala 1, Vani Syamala 1, Sreedharan Hariharan 1, Praveenkumar B Raveendran 1, R V Vijayalekshmi 1, Jayaprakash Madhavan 1,2, Ravindran Ankathil 1,✉
PMCID: PMC12160708  PMID: 17952468

Abstract

Purpose

Inter individual variation in lung cancer susceptibility may be modulated in part through genetic polymorphisms in the DNA repair genes, especially the genes involved in the Base Excision Repair (BER) and nucleotide excision repair (NER) pathway. Two of the genetic polymorphisms, XRCC1Arg399Gln and XPD Lys751Gln have been extensively studied in the association with lung cancer risk, although published studies have been inconclusive.

Methods

In order to verify the role of the common variant alleles in the XPD gene, we have genotyped 211 lung cancer patients and 211 healthy controls using PCR-RFLP assays in a hospital based, case-control study in an Indian population. Logistic regression models were fit to examine the relationship between the log odds of lung cancer and each covariate. Overall Survival in relation to various genotypes and clinicopathological factors were analyzed using Kaplan Meier estimates and hazard ratios were calculated using Cox Regression analysis.

Results

The carriers of XRCC1 399 AA genotypes were at higher risk of lung cancer (OR = 2.1, 95% CI:1.224–3.669, P = 0.007) than carriers of GG genotype. Subjects carrying 751 AC genotype were at an increased risk of carcinoma of the lung (OR = 1.8; 95% CI:1.233–2.807, P =  0.003) than subjects with AA genotypes. Compared to the XRCC1 399 GG/ XPD 751 AA reference genotype, the combined variants, XRCC1 399 GG/ XPD 751 AC+CC (OR = 1.9, 95% CI: 1.037–3.481), P = 0.03), XRCC1 399 GA+AA/ XPD 751 AA (OR = 1.7, 95% CI: 1.020–2.833, P = 0.04), XRCC1 399 GA+AA/XPD 751 AC+CC (OR = 2.7, 95% CI: 1.582–4.864, P = 0.01), had significantly higher odds ratios. Increasing numbers of either XPD or XRCC1 variant alleles were associated with shorter overall survival, the risk being significant for the XRCC1 gene polymorphism (P = 0.01 by log-rank test). The hazard of dying was significant for the XRCC1 399 AA genotype (HR = 3.04, 95%CI: 1.393–6.670, P = 0.005). Higher tumour stage also came out as significant predictors of patient death.

Conclusions

These findings suggest that genetic polymorphisms in the DNA repair genes may modulate overall lung cancer susceptibility and that pathological stage and XRCC1 Arg399Gln independently predicted overall survival among Indian lung cancer patients.

Keywords: DNA repair, XRCC1, XPD, Susceptibility, Combination genotypes, Stage, Survival

Introduction

DNA repair genes play a major role in maintaining genomic stability through different pathways that are mediated by base excision and nucleotide excision genes. Polymorphisms in DNA repair genes may be associated with differences in the repair efficiency of DNA damage and may influence an individual’s risk of lung cancer. It may result in subtle structural alteration of the repair enzymes and modulation of cancer susceptibility (Benhamou and Sarasin 2000). The genes belonging to Base excision repair (BER) and nucleotide excision repair (NER) pathway, such as X-ray Repair Cross Complementing Group 1 (XRCC1) and XP Complementation group D (Xeroderma Pigmentosum group D, XPD) have been extensively studied in the association with lung cancer. The XRCC1 gene product plays an important role in the BER pathway by acting as a scaffold for other DNA repair proteins, such as DNA polymerase β (Kubota et al. 1996) and DNA ligase III (Caldecott 2003). Genetic polymorphisms of the XRCC1 gene have been identified at codon 194 (C > T substitution at position 26304, exon 6, Arg to Trp), codon 280 (G > A substitution at position 27466, exon 9, Arg to His) and 399 (G > A substitution at position 28152, exon 10, Arg to Gln). The NER pathway repairs a wide variety of DNA damage, including cross-links, oxidative damage and bulky adducts (such as polycyclic aromatic hydrocarbon-DNA adducts). The XPD (XP Complementation group D) gene encodes a helicase, a major DNA repair protein, which is involved in transcription-coupled NER and in the removal of a variety of structurally unrelated DNA lesions (Lehmann 2001) including those induced by tobacco carcinogens (Tang et al. 2002; Leadon and Cooper 1993). Several non-synonymous single nucleotide polymorphisms (SNPs) have been described in the XPD gene, including those at codon 312 (G > A substitution at position 23591, exon 10, Asp > Asn) and codon 751 (A > C substitution at position 35931, exon 23, Lys > Gln). Within this pathway, plausible candidate susceptibility gene is the common XPD codon 751 polymorphism (Shen et al. 1998). The normal functioning XPD protein plays an essential role in NER and participates in the unwinding of DNA at the site of a deleterious DNA lesion (Sung et al. 1993; Hoeijmakers et al. 1996). The XRCC1 Arg399Gln polymorphism is located in the area coding for a PARP binding site. PARP is a zinc-finger containing enzyme that detects DNA strand breaks (Shall and de Murcia 2000). Carriers of the XRCC1 399 Gln variant allele have been shown to have higher levels of DNA adducts (Lunn et al. 1999) and to be at greater risk for ionizing radiation sensitivity (Hu et al. 2001) and tobacco-related DNA damage (Duell et al. 2000; Abdel-Rahman and El Zein 2000; Lei et al. 2002). Moreover, several studies showed that the XPD codon 751 polymorphism is associated with lung cancer (Butkiewicz et al. 2001; Spitz et al. 2001). This polymorphism appears to be connected with smoking status and may increase cancer risk among non-smokers (Zhou et al. 2002a). Although the functional significance of these polymorphisms has not yet been elucidated, it is possible that they may be responsible, in part, for the inter individual DNA damage repair variations in the general population and for a low DNA repair capacity phenotype characteristic of cancer patients (Lunn et al. 2000).To test this hypothesis, we performed a hospital based case-control study using a polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) assay to genotype two DNA repair genes XRCC1 Arg399Gln and XPD Lys751Gln polymorphisms in a case-control study in an Indian population, in relation to lung cancer susceptibility and overall survival.

DNA extraction and genotyping

Blood samples of all study subjects were collected in 5 ml ACD tubes and stored at −80°C until use. Genomic DNA was isolated using Phenol–Chloroform extraction method. Genotypic analysis of the XRCC1 399 G > A polymorphism was determined by the PCR-RFLP method, as described in detail earlier (Lunn et al. 2000). Briefly, PCR primers for the XRCC1 codon 399 (forward 5′-TTGTGCTTTCTCTGTGTCCA-3′ and reverse 5′-TCCTCCAGCCTTTTCTGATA-3′) were used to generate a 615-bp product containing the polymorphic sites. The PCR reactions were carried out in a 20-μl volume of 20 pmol of each primer, 0.2 mM each dNTP and 1× buffer and 1 U of Taq polymerase, with a denaturation of 94°C for 5 min, followed by 30 cycles of 30 s at 61°C and 45 s at 72°C and finally 7 min at 72°C. Following amplification, PCR products were digested using 10 U of restriction enzyme Msp I (New England BioLabs, Beverly, MA, USA) for 16 h at 37°C, and electrophoresed on a 3% agarose gel. The allele types were determined as follows: two fragments of 221 and 374 bp for the GG genotype, three fragments of 615, 374 and 221 bp for the GA genotype and a single 615 bp fragment for the AA genotype. The XPD 751 A > C polymorphism was also determined by PCR-RFLP method using specific primers (forward, 5′-GCCCGCTCTGGATTATACG-3′ and reverse, 5′-CTATCATCTCCTGGCCCCC-3′ as described (Tomescu et al. 2001). PCR reaction was performed in a 20-μl volume containing 1.5 mM MgCl2, 0.2 mM dNTP, 3% dimethyl sulfoxide, 0.2 μM primers, 100 ng template DNA and 1.5 U Taq polymerase in 1× PCR buffer, 50 mM KCl and 0.1% Triton X-100. Initial denaturation at 94°C for 3 min was followed by 38 cycles of 45 s at 94°C, 45 s at 60°C and 60 s at 72°C, and then a final extension step of 7 min at 72°C. Following PCR, 20 μl of PCR product was subjected to restriction digestion using 10 U of Pst I restriction enzyme (New England BioLabs, USA). The digested products were resolved on 3.0% agarose gel and stained with 0.5 μg/ml ethidium bromide. The restriction products of the XPD codon 751 AA, AC and CC genotypes had band sizes of 234/110, 234/171/110/63 and 110/63 bp, respectively. For quality control, a random 5% of the samples were repeated and all the inconclusive samples were reanalysed.

Statistical methods

The odds ratio (OR) and their 95% confidence intervals (CI) for the genotypes were calculated by unconditional logistic regression analysis, after adjusting for possible confounding factors such as age, gender and smoking status, to estimate the strength of the association between the genotypes and lung cancer risk. The genotypes were categorized into three groups (major allele homozygous, heterozygous and homozygous variant keeping the major allele as the reference group). Probability value at the <0.05 level of significance was calculated. In some cases, we combined the heterozygous genotype with the homozygous rare genotype for increasing sample size for the particular category. For the analysis of the combination of XPD and XRCC1 polymorphisms, individuals were placed into categories indicating the number of variant alleles present from both polymorphisms. Effect of genetic polymorphisms on the survival was also estimated using the method of Kaplan–Meier survival and assessed using the log rank test. For overall survival analysis, time from diagnosis to death or last follow-up was calculated. Patients who were not deceased were censored at the last date they were known to be alive based on the date of last contact. Cox proportional hazards models were used to evaluate the independent effect of genetic polymorphisms on the survival after adjusting for other covariates.

Results

Table 1 summarizes the distribution of demographic characteristics for this population. The mean age was 57.82 ± 11.74 for the cases and 56.21 ± 10.36 in controls, respectively. Cases included 184 (87.2%) males as well as 27 females (12.8%). Smokers were overrepresented in cases compared to controls (67.8% vs. 56.4%). The control group comprised of 182 males (86.3%) and 29 females (13.7%). Regarding the histology, Adenocarcinoma, squamous cell carcinoma, large cell carcinoma represented 49.3, 28.4 and 3.3% of the total 171 NSCLC patients, respectively. Also 9.5% were of SCLC and 20% were having other cellular types. Patients were grouped into two, stratified by stage. Stage I and II were combined and this group comprised of 45.5% patients. Likewise stage III and IV were grouped which included 40.3% patients. Also, 19.4% patients had metastasis. When the whole study group was considered, there was no difference in allele frequencies among cases and controls. The distribution of both the studied genotypes in the cases and control group was in the Hardy–Weinberg equilibrium (P > 0.05). Regarding the distribution of XRCC1 Arg399Gln genotypes in the study population, in cases 37% were GG, 40.8% GA and 22.3% GG when compared to 48.3, 37.9 and 13.7% in controls. The distribution of genotypes for XPD Lys751Gln polymorphism were 51.7% 751 AA, 42.2% AC and 6.2% CC respectively. Significantly higher odds ratios were obtained for XRCC1 399 AA genotype (OR = 2.1, 95% CI = 1.224–3.669, P = 0.007) as well as XPD 751AC genotype with an OR of 1.86 (95% CI = 1.233–2.807, P = 0.003) compared to their normal counterparts (Table 2). We also looked for the combined effect of these genes in lung cancer susceptibility. Compared to the XRCC1 399 GG/XPD 751 AA genotype which being the reference genotype, the other combined variants namely, XRCC1 399 GG/XPD 751 AC + CC (OR = 1.9, 95% CI = 1.037–3.481, P = 0.03), XRCC1 399 GA + AA/XPD 751 AA (OR = 1.7, 95% CI = 1.020–2.833, P = 0.04), XRCC1 399 GA + AA/XPD 751 AC + CC (OR = 2.7, 95% CI = 1.582–4.864, P = 0.01), had significantly higher odds ratios (Table 2). Clinical characteristics of the patients were compared across the XRCC1 399 and XPD 751 genotypes. There were no significant differences in the genotype distributions by clinicopathological features of lung cancer like stage, histology or metastasis (Data not shown). The associations of XRCC1 and XPD genotypes either singly or in combinations as well as clinicopathological features in lung cancer patients with survival were also tested. Data of 170 patients were available for the survival analysis, of which there were 66 deaths (Table 3). The median survival of the patients was 10 months. For patients possessing XRCC1 GG genotype, the median survival was 31months (95% CI = 17–45). Also, those with XRCC1 399 GA genotype had a median survival of 21 months (95% CI = 17.16–24.84) and XRCC1 399 AA genotype had 14 months (95% CI = 7.98–16.02). Hence the patients possessing XRCC1 399 AA genotype had poorer prognosis (P = 0.01 by log rank test) (Fig. 1). Patients with XPD 751 AA genotype had a median survival of 23 months (95% CI = 19.34–26.66). Patients with the XPD 751 AC and CC genotypes had a median survival of 20 (95% CI = 15.19–24.81) and 14 months (95% CI = 2.77–25.23), respectively (log rank P = 0.19). When both SNPs of XRCC1 and XPD were analysed in combination, carriers of XRCC1 399 GA + AA/XPD 751 AA (Median Survival-31 months), XRCC1 399 GA + AA/XPD 751 AA (Median Survival-23 months) and XRCC1 399 GA + AA/XPD 751 AC + CC (Median Survival-18 months) genotypes were associated with reduced overall survival (log rank P-value = 0.08) but was not significant. We next investigated the association of clinicopathological features of lung cancer with survival. We included histology, tumour stage and metastasis. But survival differences in this study were most apparent in individuals with higher stage disease who had median survival of 14 months compared to 31 months in patients with stage I and II (log rank P-value = 0.002) (Fig. 2) and those who had metastasis who had a median survival of 15 months compared to non metastatic group (log rank P-value = 0.02). To find out which of the genotypes and clinical factors were independent prognostic factors influencing prognosis, effects of survival were assessed using cox proportional hazard model. In the multivariate analysis, the Hazard Ratio (with the XRCC1 399 GG group being the reference) for XRCC1 399 GA was 1.8 (P = 0.07) compared to 3.0 in the AA group (P = 0.005), the difference being significant. On the contrary, the relative risk of dying (with the XPD 751 AA group being the reference) was 1.3 for those with the AC genotype (P = 0.29) and 2.45 for the CC group (P = 0.06), but statistically not significant. Regarding the clinical factors, higher tumour stage came out to be significant (HR = 2.1, P = 0.02).

Table 1.

Demographic characteristics of patients and controls

Variables Cases (N=211) Controls (N=211) OR (95% CI) P-value
Age
Mean age 57.82 ± 11.74 56.21 ± 10.36 1.01 (0.996–1.031) 0.138
≤50 years 53 (49.5%) 54 (50.5%)
≥50 years 158 (50.2%) 157(49.8%) 1.02 (0.661–1.590) 0.991
Gender
Male (%) 182 (86.3%) 184 (87.2%) 1.08 (0.619–1.906) 0.774
Female (%) 29 (13.7%) 27 (12.8%) 0.9 (0.525–1.617) 0.774
Smoking
Non-smokers 68(32.2%) 92(43.6%)
Smokers 143 (67.8%) 119 (56.4%) 1.6 (1.117–2.473) 0.01
Positive family history of cancer
No 179 (84.8%) 189 (89.6%)
Yes 32 (15.2%) 22 (10.4%) 1.5 (0.860–2.743) 0.147
Histology
NSCLC 171 (81%)
SCLC 20 (9.5%) NA
Unclassified 20 (9.5%)
Stage
Stage I and II 96 (45.5%)
Stage III and IV 85 (40.3%) NA
Stage unknown 30 (14.21%)
Metastasis
No 170(80.6%)
Yes 41 (19.4%) NA
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Table 2.

Association between XRCC1 Arg399Gln and XPD Lys751Gln genotypes either singly or in combinations to development of lung cancer

Cases/control OR (95% CI)a P-value
Genotype
XRCC1 399 GG 78/102 Reference
XRCC1 399 GA 86/80 1.4 (0.920–2.148) 0.11
XRCC1 399 AA 47/29 2.1 (1.224–3.669) 0.007
XPD 751 AA 109/139 Reference
XPD 751 AC 89/61 1.8 (1.233–2.807) 0.003
XPD 751 CC 13/11 1.5 (0.650–3.495) 0.33
Genotype combinations
XRCC1 399 GG/XPD 751 AA 40/68 Reference
XRCC1 399 GG/XPD 751 AC + CC 38/34 1.9 (1.037–3.481) 0.03
XRCC1 399 GA + AA/XPD 751 AA 71/71 1.7 (1.020–2.833) 0.04
XRCC1 399 GA + AA/XPD 751 AC + CC 62/38 2.7 (1.582–4.864) 0.01
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aOdds ratio adjusted for age, gender and smoking

Table 3.

XRCC1 399 and XPD 751 genotypes and clinical features in relation to overall survival in patients with lung cancer polymorphisms and clinicopathological factors with respect to overall survival

Parameter Events/censored Median survival Log rank P-value Hazard ratio (95% CI) P-value
XRCC1 399 GG 16/47 31 Reference
XRCC1 399 GA 31/40 21 0.01 1.87 (0.941–3.755) 0.07
XRCC1 399 AA 19/17 12 3.04 (1.393–6.670) 0.005
XPD 751 AA 29/60 23 Reference
XPD751 AC 30/40 20 0.19 1.34 (0.767–2.368) 0.29
XPD 751 CC 7/4 14 2.45 (0.957–6.302) 0.06
Stage I and II 24/49 31 0.002 Reference
Stage III and IV 37/37 14 2.1 (1.089–4.403) 0.02
No metastasis 45/86 31 1
Metastasis 21/18 15 0.02 1.08 (0.556–2.127) 0.80
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Fig. 1.

Fig. 1

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Kaplan Meier Survival Curve showing association of XRCC1 Arg399Gln Genotype on Lung Cancer Overall Survival

Fig. 2.

Fig. 2

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Kaplan Meier Survival Curve showing association of Stage on Lung Cancer Overall Survival

Discussion

Recent lung cancer studies have focused on identifying the effects of SNPs in candidate genes, among which DNA repair genes are increasingly being studied. In our study, we assessed two common polymorphisms of the XRCC1 and XPD genes that may influence DNA repair capacity and their association with lung cancer risk and overall survival. The polymorphisms chosen for this study also have been shown to have functional significance and may be responsible, in part, in the inter individual DNA damage repair variations in the general population and for a low DNA repair capacity phenotype characteristic of cancer patients (Helzlsouer et al. 1996; Wei and Spitz 1997).

In the present study, significantly higher odds ratios were noted for XRCC1 399 AA genotype (P = 0.007) compared to their normal counterparts. Carriers of the XRCC1 399 AA variant have been shown to have higher levels of DNA adducts (Lunn et al. 1999) and to be at greater risk for ionizing radiation sensitivity (Hu et al. 2001) and tobacco-related DNA damage (Duell et al. 2000; Abdel-Rahman and El Zein 2000; Lei et al. 2002). The variant genotypes of XRCC1 399 GA and AA were more frequent in patients (Zienolddiny et al. 2006; Chacko et al. 2005).The XRCC1 399 AA variant genotype and risk for lung cancer has been reported previously by (Divine et al. 2001) who reported an association between the this variant and elevated risk for lung adenocarcinoma (OR = 2.5, 95% CI = 1.1–5.8) and another hospital based study (Park et al. 2002) found a further increased risk among squamous cell cases among Koreans (OR = 3.3, 95% CI = 1.2–9.2). However, in another study (Hu et al. 2005) no significant association for the XRCC1 exonic variant 399 and lung cancer risk was obtained. Two studies in Chinese populations also found no significant association between XRCC1 G399A polymorphism and lung cancer (Ratnasinghe et al. 2001; Chen et al. 2002). In Caucasian populations, some studies reported that the XRCC1 399 AA genotype significantly associated with lung cancer risk (Divine et al. 2001; Zhou et al. 2003b). These findings provide evidence that this specific polymorphism of the XRCC1 gene is associated with reduced DNA repair efficiency. The G399A polymorphism occurs in a region of the XRCC1 gene that contains biologically important domains (the PARP binding and the BRCT domain), and these domains have homology with other DNA repair-related genes (Masson et al. 1998).The protein encoded by XPD is involved in transcription-coupled NER and is an integral member of the basal transcription factor TFIIH complex (which is necessary for normal transcription initiation NER. The XPD 751 CC variant gene leads to conformational change in the coded protein at the domain of interaction between the XPD protein and its helicase activator, p44 protein, inside the TFIIH complex (Coin et al. 1998). Significantly risk modulating effect was noticed for XPD 751 AC genotype with an odds ratio of 1.8 (95% CI = 1.233–2.807, P = 0.003) compared to normal genotype in the present study. The A751C variant of XPD has been associated with increased risk of lung cancer in several other studies (Spitz et al. 2003; Hou et al. 2002; Zhou et al. 2002b; Ramachandran et al. 2006). The carriers of XPD 751 AC genotype were at 2.7-fold (95% CI = 1.12–6.93) higher risk of lung cancer than carriers of the AA genotype in one study (Yin et al. 2006) in northeastern Chinese population. In another study (Xing et al. 2002) compared with those having the 751 AA genotype, subjects carrying at least one variant were at a borderline increased risk of SCC of the lung (OR = 1.5; 95% CI = 0.94–2.46). In Norwegian lung cancer population, there was a significant association of XPD variants in modulating NSCLC risk (Zienolddiny et al. 2006). So also, A > C transversions, however, were marginally increased among patients with at least one XPD variant allele compared with patients who were wild-type homozygotes (Hou et al. 2003). These studies are all consistent with the reports indicating that heterozygosity is considered to carry the risk. However, contrasting results also exist as in one study (De Ruyck et al. 2007).

From a genetic perspective, in most multifactorial diseases, single polymorphisms in single genes are unlikely to alter the expression or function of specific proteins to the extent of producing a pathological phenotype. It is more likely that the combined effect of different SNPs in a gene produce a change in expression or protein function. Since a combination of XRCC1 as well as XPD genes could be more important than single SNPs, we looked for the effect of combined genotypes with regard to lung cancer risk. Compared to the XRCC1 399 GG/XPD 751 AA genotype which being the reference genotype, the other combined variants namely, XRCC1 399 GG/XPD 751 AC + CC (P = 0.03), XRCC1 399 GA + AA/XPD 751 AA (P = 0.04), XRCC1 399 GA + AA/XPD 751 AC+CC (P = 0.01), had significantly higher odds ratios. Another study (Zhou et al. 2003a) found that the risk of lung cancer amongst non-smokers increased progressively with the increase in the number of high-risk alleles of XRCC1 and XPD genes. Another study (Gao et al. 2006) reported in patients with the XRCC1 399 AA genotype, which results in a lower BER capacity were more likely to have p53 mutations, compared with patients with GG genotype. In addition, the p53 mutation frequency increased with an increasing number of combined genotypes associated with a lower DNA repair capacity XPD 751, and XRCC1 399. The XRCC1 codon 399 AA genotype was also associated with adenine to guanine p53 mutations in non-small cell lung cancer in one study (Casse et al. 2003). Regarding distributions of XRCC1 399 and XPD 751 genotypes and clinical characteristics of lung cancer patients, even though higher odds ratios were obtained there were no significant associations with histopathologic variables like tumour histology, metastasis or tumour stage. Because of XRCC1 and XPD are all involved in the DNA repair pathway; we explored the single/combined genotypes as well as clinicopathological features of lung cancer patients on overall survival of the patients with lung carcinoma. Data of 170 patients were available for the survival study, of which there were 66 deaths. Median Survival of the patients was 10 months. For patients possessing XRCC1 399 GG, XRCC1 GA and XRCC1 AA genotypes, the median survival was 31, 21 and 14 months, respectively. In the multivariate Cox model, XRCC1 399 genotypes remained an independent prognostic factor. The Hazard Ratio (with the XRCC1 Arg/Arg group being the reference) for XRCC1 GA was 1.8 (P = 0.07) compared to 3.04 in the AA group (P = 0.005), the difference being significant. Patients with XPD AA genotype had a median survival of 23 months, while AC and CC genotypes had a median survival of 20 and 14 months, respectively (log rank P-value = 0.19). On the contrary, the relative risk of dying with the XPD AA (reference) was 1.3, for those with the AC genotype (P = 0.29) and 2.4 for the CC group (P = 0.06), but statistically not significant. We could observe that the patients carrying none of the adverse genotypes (XRCC1 399 GG, XPD 751 AA and XRCC1 399 GG/XPD 751 AA) had much better survival than those carrying variant alleles. We could observe that the XRCC1 399 AA variant genotype was associated with a significantly decreased overall survival. In the BER genes, the variant alleles of XRCC1 399 were significantly associated and poor survival (HR = 1.9; 95% CI = 1.00–3.72) (Wu et al. 2006). Another study (Smith et al. 2007) reported that carriers of the glutamine-encoding allele at codon 751 of the XPD DNA repair gene were significantly more likely to have a karyotype associated with a less favourable prognosis. Another study (Gurubhagavatula et al. 2004) demonstrated that the XPD and XRCC1 variant genotypes, both alone and in combination, are associated with decreased overall survival in their patient population. However, polymorphism of codons 751 in the XPD gene did not affect patient survival in one study (Ryu et al. 2004). These observations demonstrated for the first time the effect of polymorphisms of NER and BER genes on lung cancer patient survival in Indian lung cancer patients.

Many individual clinical features of the patient may come into play. The stage of disease at the time of diagnosis not only plays a key role in the selected treatment but also has a direct impact on the survival rate. In our study, higher tumour stage had a significant effect on the survival which is in accordance with one study (Ahrendt et al. 2003). Multivariate analysis showed that higher stage (Stage II and III) was overall an independent prognostic factor with a twofold increased risk of death. It may be possible that those individuals with higher stage disease already have too many genetic alterations during their tumour growth which reduces their survival period. No significant association with tumour histology was observed in our study. Approximately 60% of SCLC and 30–40% of NSCLC patients present with higher stage metastatic disease. Although lung cancer can metastasize to virtually any organ site, the most common sites that are clinically apparent are the central nervous system, bones, liver and adrenal glands. Those metastatic patients too had significantly shorter survival probabilities (log rank P-value = 0.02) when compared to patients who had no metastasis but in the multivariate cox regression model after adjusting for other covariates, the hazard ratio was not significant. Hence the results showed that pathologic stage also plays a role in influencing the survival for patients with lung cancer.

In brief, to our knowledge, this is the first report of XRCC1 and XPD polymorphisms in relation to lung cancer overall survival in Indian population. Our results suggests that XRCC1 399 AA and XPD 751GA genotypes might be risk genotypes for lung cancer. In our patients, presence of XRCC1 399 AA genotype and higher tumour stage were independent prognostic factors affecting patient survival. The limitations of our study are our sample size, due to that our ability to precisely measure the magnitude of the effect modification or interaction of the genes is limited. Because DNA repair is a complex process with overlapping substrate specificity, it takes many proteins of various DNA repair pathways acting in concert to maintain cell viability and genome integrity and larger studies with biological characterization of the variant in diverse ethnic populations are needed to validate our findings.

Acknowledgements

We wish to thank all the participants for their contribution. We also thank the support provided by the staff members of various clinical Departments of Regional Cancer Centre, Trivandrum. This work was supported by the grants from Department of Science & Technology, Govt. of India and Indian Council of Medical Research, Govt. of India.

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