Gender difference in DNA adduct levels among nonsmoking lung cancer patients

Environmental exposure and HPV infection may act synergistically to induce lung tumorigenesis in nonsmokers

Most studies of lung tumorigenesis have focused on smokers rather than nonsmokers. In this study, we used human papillomavirus (HPV)-positive and HPV-negative lung cancer cells to test the hypothesis that HPV infection synergistically increases DNA damage induced by exposure to the carcinogen benzo[a]pyrene (B[a]P), and contributes to lung tumorigenesis in nonsmokers. DNA adduct levels induced by B[a]P in HPV-positive cells were significantly higher than in HPV-negative cells. The DNA adduct formation was dependent on HPV E6 oncoprotein expression. Gene and protein expression of two DNA repair genes, XRCC3 and XRCC5, were lower in B[a]P-treated E6-positive cells than in E6-negative lung cancer cells. The reduced expression was also detected immunohistochemically and was caused by increased promoter hypermethylation. Moreover, mutations of p53 and epidermal growth factor receptor (EGFR) genes in lung cancer patients were associated with XRCC5 inactivation. In sum, our study indicates that HPV E6-induced promoter hypermethylation of the XRCC3 and XRCC5 DNA repair genes and the resultant decrease in their expression increases B[a]P-induced DNA adducts and contributes to lung tumorigenesis in nonsmokers.

The association of GSTM1 deletion polymorphism with lung cancer risk in Chinese population: evidence from an updated meta-analysis

Previous studies have reported the association of glutathione S-transferase M1 (GSTM1) deletion polymorphism with genetic susceptibility of lung cancer in Chinese population. However, the results remained controversial. The aim of this study was to clarify the association of GSTM1 deletion polymorphism with lung cancer risk in Chinese population. Systematic searches were performed through the search engines of Medline/Pubmed, Web of Science, EMBASE, CNKI and Wanfang Medical Online. The pooled effects were calculated by STATA 10.0 software package and Review Manager 5.0.24. Overall, we observed an association of GSTM1 deletion polymorphism with increased lung cancer risk in Chinese population (odds ratio (OR) = 1.46, 95% confidence interval (95%CI): 1.32-1.66 for null genotype vs. present genotype) based on 53 studies including 7,833 cases and 10,353 controls. We also observed an increased risk of GSTM1 null genotype for lung cancer in stratified analyses by source of control, smoking status and histological type. The findings suggest that GSTM1 deletion polymorphism may contribute to lung cancer risk in Chinese population. Further, well-designed studies with larger sample sizes are required to verify the results.

The associations between two vital GSTs genetic polymorphisms and lung cancer risk in the Chinese population: evidence from 71 studies

BACKGROUND

The genetic polymorphisms of glutathione S-transferase (GSTs) have been suspected to be related to the development of lung cancer while the current results are conflicting, especially in the Chinese population.

METHODS

Data on genetic polymorphisms of glutathione S-transferase Mu 1 (GSTM1) from 68 studies, glutathione S-transferase theta 1 (GSTT1) from 17 studies and GSTM1-GSTT1 from 8 studies in the Chinese population were reanalyzed on their association with lung cancer risk. Odds ratios (OR) were pooled using forest plots. 9 subgroups were all or partly performed in the subgroup analyses. The Galbraith plot was used to identify the heterogeneous records. Potential publication biases were detected by Begg's and Egger's tests.

RESULTS

71 eligible studies were identified after screening of 1608 articles. The increased association between two vital GSTs genetic polymorphisms and lung cancer risk was detected by random-effects model based on a comparable heterogeneity. Subgroup analysis showed a significant relationship between squamous carcinoma (SC), adenocarcinoma (AC) or small cell lung carcinoma (SCLC) and GSTM1 null genotype, as well as SC or AC and GSTT1 null genotype. Additionally, smokers with GSTM1 null genotype had a higher lung cancer risk than non-smokers. Our cumulative meta-analysis demonstrated a stable and reliable result of the relationship between GSTM1 null genotype and lung cancer risk. After the possible heterogeneous articles were omitted, the adjusted risk of GSTs and lung cancer susceptibility increased (fixed-effects model: ORGSTM1 = 1.23, 95% CI: 1.19 to 1.27, P<0.001; ORGSTT1 = 1.18, 95% CI: 1.10 to 1.26, P<0.001; ORGSTM1-GSTT1 = 1.33, 95% CI: 1.10 to 1.61, P = 0.004).

CONCLUSIONS

An increased risk of lung cancer with GSTM1 and GSTT1 null genotype, especially with dual null genotype, was found in the Chinese population. In addition, special histopathological classification of lung cancers and a wide range of gene-environment and gene-gene interaction analysis should be taken into consideration in future studies.

Women are more susceptible than men to oxidative stress and chromosome damage caused by polycyclic aromatic hydrocarbons exposure

Exposure to environmental polycyclic aromatic hydrocarbons (PAHs) has been associated with increased risk of cancer, but evidence for gender differences in this association is limited. The aim of this study was to examine the gender differences in PAHs caused early genotoxic effects such as oxidative stress and chromosome damage, which are potential carcinogenic etiology of PAHs. A total of 478 nonsmoking workers (272 men and 206 women) from a coke oven plant were recruited. We determined 16 environmental PAHs in their workplaces, and measured concentrations of 12 urinary PAH metabolites (OH-PAHs), plasma benzo[a]pyrene-r-7,t-8,t-9,c-10-tetrahydotetrol-albumin (BPDE-Alb) adducts, urinary 8-hydroxydeoxyguanosine (8-OHdG) and 8-iso-prostaglandin-F2α (8-iso-PGF2α), and micronucleus frequencies in lymphocytes in all subjects. It showed that, women working at the office, adjacent to the coke oven, and on the bottom or side of the coke oven displayed significantly higher levels of urinary 8-OHdG and 8-iso-PGF2α, and lymphocytic micronucleus frequencies compared with men working at above areas, respectively (all P < 0.05). These gender differences remain significant after adjusted for potential confounders and urinary ΣOH-PAHs or plasma BPDE-Alb adducts. A significant interaction existed between gender and BPDE-Alb adducts on increasing micronucleus frequencies (Pinteraction  < 0.001). We further stratified all workers by the tertiles of urinary ΣOH-PAHs or plasma BPDE-Alb adducts, and the above gender differences were more evident in the median- and high-exposure groups (all P < 0.05). In conclusion, women were more susceptible than men to oxidative stress and chromosome damage induced by PAHs, which may add potential evidence underlying gender differences in PAH exposure-related lung cacinogenesis.

Rad51C: a novel suppressor gene modulates the risk of head and neck cancer

We conducted a case-control study to investigate the possible association between the head and neck cancer (HNC) and genetic variability of Rad51C tumor suppressor gene. Eight polymorphic sites spanning over non-coding regions of Rad51C promoter, exon 1 and intron 1 were genotyped in 81 HNC cases and 156 healthy controls using the real-time PCR technique. One investigated site turned out to be not polymorphic, while among the remaining seven sites a significant HNC risk-increasing effect was found for rs16943176 (c.-118G>A), rs12946397 (c.-26C>T) and rs17222691 (c.145+947C>T) on both allelic (OR=1.8; p<0.05) and genotypic (OR=2.0; p<0.05) level. Furthermore, our data seem to provide marginal evidence, that this effect might possibly be confined to women only (OR=2.8; p=0.05 for allelic and OR=3.7; p=0.05 for genotypic comparisons). These SNPs were found to co-segregate together forming two distinct, HNC risk-modulating haplotypes. The genetic variability of Rad51C might thus be of relevance with respect to HNC risk.

DDX3 loss by p53 inactivation promotes tumor malignancy via the MDM2/Slug/E-cadherin pathway and poor patient outcome in non-small-cell lung cancer

P53 inactivation by p53 mutation and E6 oncoprotein has a crucial role in human carcinogenesis. DDX3 has been shown to be a target of p53. In this study, we hypothesized that DDX3 loss by p53 inactivation may promote tumor malignancy and poor patients' outcome. Mechanically, DDX3 loss by p53 knockdown and E6 overexpression was observed in A549 lung cancer cells. Conversely, DDX3 expression was markedly elevated by wild-type (WT) p53 ectopic expression in p53-null H1299 cells, E6-knockdown TL-1 lung cancer and SiHa cervical cancer cells. Interestingly, DDX3 loss promotes soft-agar growth and invasive capability; however, both capabilities were suppressed by DDX3 overexpression. We next expected that DDX3 loss might result in Slug-suppressed E-cadherin expression via decreased MDM2-mediated Slug degradation. As expected, MDM2 transcription is suppressed by DDX3 loss via decreased SP1 binding activity to the MDM2 promoter. Consequently, Slug expression was elevated by the reduction of MDM2 because of DDX3 loss, and E-cadherin expression was suppressed by Slug. Consistent observations in the correlation of DDX3 loss with MDM2, Slug and E-cadherin were seen in lung tumors from lung cancer patients. In addition, patients with low-DDX3 tumors had poorer survival and relapse than patients with high-DDX3 tumors. In conclusion, we suggest that DDX3 loss by p53 inactivation via MDM2/Slug/E-cadherin pathway promotes tumor malignancy and poor patient outcome.

Lung cancer in women

Recent biological advances in tumor research provide clear evidence that lung cancer in females is different from that in males. These differences appear to have a direct impact on the clinical presentation, histology, and outcomes of lung cancer. Women are more likely to present with lung adenocarcinoma, tend to receive a diagnosis at an earlier age, and are more likely to be diagnosed with localized disease. Women may also be more predisposed to molecular aberrations resulting from the carcinogenic effects of tobacco, but do not appear to be more susceptible than men to developing lung cancer. The gender differences found in female lung cancer make it mandatory that gender stratification is used in clinical trials in order to improve the survival rates of patients with lung cancer.

EGFR exon 19 in-frame deletion and polymorphisms of DNA repair genes in never-smoking female lung adenocarcinoma patients

We explored potential associations between genetic polymorphisms in genes related to DNA repair and detoxification metabolism and epidermal growth factor receptor (EGFR) mutations in a cohort of 410 never-smoking patients with lung adenocarcinoma. Multivariate-adjusted odds ratios (aORs) and corresponding 95% confidence intervals (CI) of EGFR mutation status in association with the genotypes of DNA repair and detoxification metabolism genes were evaluated using logistic regression analysis. We found an association between in-frame deletion in EGFR exon 19 and a single nucleotide polymorphism (SNP) rs1800566C/T located in NQO1 (aOR, 2.2 with 95% CI, 1.0-4.8) in female never-smokers. The SNP rs744154C/G in ERCC4 was also associated with the EGFR exon 19 in-frame deletion both in never-smokers (aOR, 1.7 with 95% CI, 1.0-3.0) and female never-smokers (aOR, 1.9 with 95% CI, 1.0-3.6). Although the association was marginally significant in multivariate logistic regression analysis, the A/A genotype of rs1047840 in EXO1 was associated with a 7.6-fold increase in the occurrence of the EGFR exon 19 in-frame deletion in female never-smokers. Moreover, risk alleles in NQO1, ERCC4 and EXO1 were associated with an increasing aOR of the EGFR exon 19 in-frame deletion both in never-smokers (p = 0.007 for trend) and female never-smokers (p = 0.002 for trend). Our findings suggest that the in-frame deletion in EGFR exon 19 is associated with polymorphisms in DNA repair and detoxification metabolism genes in never-smoking lung adenocarcinoma patients, especially in females.

Development and validation of a direct sandwich chemiluminescence immunoassay for measuring DNA adducts of benzo[a]pyrene and other polycyclic aromatic hydrocarbons

We have developed and validated a sandwich chemiluminescence immunoassay (SCIA) which measures polycyclic aromatic hydrocarbon (PAH)-DNA adducts combining high throughput and adequate sensitivity, appropriate for evaluation of adduct levels in human population studies. Fragmented DNA is incubated with rabbit antiserum elicited against DNA modified with r7,t8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) and subsequently trapped by goat anti-rabbit IgG bound to a solid surface. Anti-single-stranded (ss) DNA antibodies binds in a quantity proportional to the adduct levels and is detected by chemiluminescence. The BPDE-DNA SCIA has a limit of detection of 3 adducts per 10(9) nucleotides with 5 μg DNA per well. We have validated the BPDE-DNA SCIA using DNA modified in vitro, DNA from benzo[a]pyrene (BP)-exposed cultured cells and mice. The levels of adduct measured by SCIA were lower (30-60%) than levels of bulky DNA adducts measured in the same samples by (32)P-postlabelling. The BPDE-DNA SCIA also detected adducts produced in vivo by PAHs other than BP. When blood DNA samples from maternal/infant pairs were assayed by BPDE-DNA SCIA, the adduct levels obtained were significantly correlated. However, there was no correlation between (32)P-postlabelling and SCIA values for the same samples. The SCIA can be extended to any DNA adduct and is expected to provide, when fully automated, a valuable high-throughput approach in large-scale population studies.

Lung cancer in women: the differences in epidemiology, biology and treatment outcomes

Although the prevalence of lung cancer in men has been decreasing, it has been increasing in women. Without a doubt, lung cancer is a major health problem for women in the USA, not only owing to its high incidence rate but, more alarming, the high mortality rate. Lung cancer kills more women each year than breast, ovarian and uterine cancers combined. One of the most important risk factors for the development of lung cancer in both men and women is cigarette smoking. Unfortunately, the prevalence of smoking among women has increased significantly since 1980, which is a major concern as epidemiologic data suggest that women may be more susceptible to developing lung cancer than men. Many will argue, however, that after adjusting for tobacco exposure, some studies have failed to show that women are at a higher risk for developing lung cancer. Indeed, the increased risk of lung cancer in women remains controversial. There is, however, little controversy to the fact that the biology of lung cancer differs between the sexes. This paper summarizes the explanations for the sex differences in lung cancer, including differences in molecular abnormalities, growth factor receptors, hormonal influences, differences in cytochrome P-450 enzymes and DNA repair capacity, as well as variations in treatment outcomes.

Influence of polymorphisms in MTHFR 677 C→T, TYMS 3R→2R and MTR 2756 A→G on NSCLC risk and response to platinum-based chemotherapy in advanced NSCLC

AIMS

Genetic factors may contribute to individual differences in cancer susceptibility, drug efficacy and toxicity. This study was designed to investigate the effects of the polymorphisms of methylenetetrahydrofolate reductase 677 C→T (MTHFR 677 C→T), thymidylate synthase (TYMS 3R→2R),and methionine synthase 2756 A→G (MTR 2756 A→G) on the risk of lung cancer and response to platinum-based chemotherapy in advanced non-small-cell lung cancer (NSCLC).

MATERIALS & METHODS

We conducted a case-control study involving 438 NSCLC cases (including 101 follow-up cases) and 641 healthy controls in North China.

RESULTS & CONCLUSION

Using a genetic model analysis, the polymorphism MTHFR 677 C→T showed a significantly increased risk for NSCLC in women but not in men, which was observed in the codominant model (CT vs CC adjusted odds ratio [OR] = 2.46; 95% confidence interval [CI]: 1.37-4.42; p = 0.003; TT vs CC adjusted OR: 2.04; 95% CI: 1.09-3.81; p = 0.03) and the dominant model (CT + TT vs CC adjusted OR: 2.30; 95% CI: 1.31-4.05; p = 0.004). In addition, we found that patients with the MTHFR 677 TT genotype showed a better response to platinum-based chemotherapy in the recessive model (TT vs CT + CC adjusted OR: 0.24; 95% CI: 0.09-0.68; p = 0.007), the generalized OR was 0.44 (0.22-0.88; p = 0.04). There were no significant associations of the polymorphisms of TYMS 3R→2R or MTR 2756 A→G with the risk of NSCLC or response to platinum-based chemotherapy in advanced NSCLC in any genetic model. Our results suggest that genetic polymorphisms of MTHFR 677 C→T may contribute to NSCLC development in Chinese women and could also influence treatment response for advanced NSCLC patients with platinum-based chemotherapy. Further studies with larger sample sizes are required to validate this association.

Gender is a risk factor for lung cancer

Results of epidemiological studies suggest that, after one controls for the number of cigarettes smoked, women have a three times higher risk of getting lung cancer than men. Although the mechanism(s) explaining this gender-dependent difference in lung cancer risk is not known, it is thought that endocrine factors may play an important role. Normal human bronchial epithelial cells contain estrogen receptors and synthesize 17β-estradiol (E(2)) and estrone (E(1)), which can undergo further metabolism into the catechol estrogens, 4-hydroxyestradiol (4-OHE(2)) and 4-hydroxyestrone (4-OHE(1)), respectively. Catechol estrogens are formed from E(2) by the actions of cytochrome p450 1B1 (CYP1B1). CYP1B1 is present in normal human bronchial epithelial) cells, and its activity is increased by cigarette smoking. Both 4-OHE(1) and 4-OHE(2) are mutagenic and carcinogenic and may exert their biological effects by inducing DNA adducts in cancer-related genes, including the tumor suppressor gene p53 and the proto-oncogene K-ras. Women with lung cancer have a different p53 mutational spectrum and a higher frequency of K-ras mutations than do men with lung cancer. Both clinical and basic research studies support the hypothesis that E(2) and cigarette smoking are cofactors in lung carcinogenesis in women. More specifically, cigarette smoke stimulates metabolism of E(2) into the genotoxic metabolites, 4-OHE(1) and 4-OHE(2,) which interact with DNA in cancer-related genes, including the tumor suppressor gene, p53, and the proto-oncogene K-ras, two genes frequently mutated in patients with lung cancer. E(2) may stimulate cellular proliferation and enhance tumor growth.

Gender-related disparities in non-small cell lung cancer

Epidemiological studies clearly outline some disparities in cancer onset, progression as well as prognosis and therapeutic response between sexes. In particular, in lung cancer, the leading cause of cancer death, at least in Western countries, a gender disparity appears now to emerge, especially for non-small cell lung cancer (NSCLC). Such a disparity is apparently due to a variety of mechanisms, ranging from genetic and epigenetic differences to gender-specific lifestyle as well as to behavioral causes and, clearly, to sex hormones activity. Here we briefly recapitulate gender differences in terms of risk factors, histopathological features and pathogenetic mechanisms in NSCLC, and hypothesize that a gender-oriented pharmacology could beneficially impact on innovative therapeutic strategies.

Haplotypes of estrogen receptor-beta and risk of non-small cell lung cancer in women

Epidemiologic and biologic evidence suggests that lung cancer has different clinical and biological characteristics in women, and that estrogen may contribute to the pathogenesis of non-small cell lung cancer (NSCLC). We investigated whether germline variation in the estrogen receptor-beta gene (ESR2) is associated with lung cancer risk among 1021 female cases and 826 female controls enrolled in the Lung Cancer Susceptibility Study at the Massachusetts General Hospital from 1992 to 2004. Four haplotype-tagging polymorphisms (htSNPs) (rs3020450, rs1256031, rs1256049, rs4986938) captured the common genetic variation across the ESR2 locus from a set of markers culled from healthy controls from a public database and sequencing the coding regions of 95 breast cancer cases. Using the expectation-maximization algorithm, five common haplotypes were resolved (CCGC (43%), TCAT (287%), TCAC (11%), CCAC (9%) and CCAT (6%)). Multivariate logistic regression was used to estimate adjusted odds ratios (OR) and their 95% confidence intervals (95% CI) for individual htSNPs and haplotype scores. Neither the four individual htSNPs nor their resolved haplotypes were associated with lung cancer risk in the entire population, nor in strata defined by parity (yes versus no), age (<50 years versus ≥ 50 years) or smoking history (current-, former-, never-smokers). Our findings indicate that ESR2 is not associated with risk of lung cancer in women.

The association between methylene-tetrahydrofolate reductase gene polymorphism and lung cancer risk

This study aimed to determine the relation between methylene-tetrahydrofolate reductase (MTHFR) gene polymorphism and lung cancer risk and the frequency of this polymorphism. The study involved 64 lung cancer patients (the study group) with definitive diagnosis and 61 noncancerous subjects (the control group). MTHFR C677T and A1298C mutation analysis was made using DNA isolated from peripheric blood and multiplex PCR and reverse hybridization strip test. Eighty-four percent of the patients were male. The age, gender, and history of alcohol use of the patients and control group were statistically similar. While MTHFR 677T and 677C allele frequency was 0.33 and 0.67 in the patients respectively, it was 0.29 and 0.71 in the control group. The frequencies of MTHFR 1298C and 1298A were 0.33 and 0.67 in the patients, and it was 0.31 and 0.69 in the control group respectively. When MTHFR 677TT and 677CT genotypes were compared with 677CC genotype, lung cancer risk was 2.4 times higher in the 677TT genotype. When MTHFR 1298AC and 1298CC genotypes were compared with 1298AA genotype, lung cancer risk was 1.5 times higher in 1298CC genotype. According to the results, allele frequency of homozygote T and C was high in lung cancer patients. It was 3.05 and 1.29 times higher in smokers than in non-smokers, and 3.05 and 1.64 times higher in males than in females; 3.0 and 2.44 times higher in those with non-small cell lung cancer than in those with small-cell lung cancer.

Parity and risk of lung cancer in women

Patterns of lung cancer incidence suggest that gender-associated factors may influence lung cancer risk. Given the association of parity with risk of some women's cancers, the authors hypothesized that childbearing history may also be associated with lung cancer. Women enrolled in the Lung Cancer Susceptibility Study at Massachusetts General Hospital (Boston, Massachusetts) between 1992 and 2004 (1,004 cases, 848 controls) were available for analysis of the association between parity and lung cancer risk. Multivariate logistic regression was used to estimate adjusted odds ratios and 95% confidence intervals. After results were controlled for age and smoking history, women with at least 1 child had 0.71 times the odds of lung cancer as women without children (odds ratio = 0.71, 95% confidence interval: 0.52, 0.97). A significant linear trend was found: Lung cancer risk decreased with increasing numbers of children (P < 0.001). This inverse association was stronger in never smokers (P = 0.12) and was limited to women over age 50 years at diagnosis (P = 0.17). Age at first birth was not associated with risk. The authors observed a protective association between childbearing and lung cancer, adding to existing evidence that reproductive factors may moderate lung cancer risk in women.

Association between estrogen receptor-beta expression and epidermal growth factor receptor mutation in the postoperative prognosis of adenocarcinoma of the lung

PURPOSE

Adenocarcinoma of the lung unrelated to a smoking habit occurs more frequently in women than men, thus suggesting an association between female hormones and development of these tumors. The aim of this study was to elucidate the correlation between expression of estrogen receptor (ER) and clinicopathologic factors, including a mutation in the tyrosine kinase domain of epidermal growth factor receptor (EGFR), and prognosis in adenocarcinoma of the lung.

PATIENTS AND METHODS

This study evaluated 447 resected primary lung adenocarcinoma specimens. The expression of ERalpha and ERbeta was evaluated with an immunohistochemical method. The EGFR mutation was evaluated with polymerase chain reaction.

RESULTS

A strong cytoplasmic expression of ERalpha and nuclear expression of ERbeta were detected in 49.4% and 48.5% of all patients, respectively. A strong nuclear expression of ERbeta was independently associated with the EGFR mutations (odds ratio = 2.947; 95% CI, 1.97 to 4.57; P < .001) and good differentiation (odds ratio = 1.84; 95% CI, 1.21 to 2.80; P = .004) and was correlated with an increasing disease-free survival in patients with EGFR mutations (hazard ratio = 2.18; 95% CI, 1.18 to 4.06; P = .014). However, no prognostic significance was identified in patients without EGFR mutations. No clinicopathologic and/or prognostic significance of a strong expression of cytoplasmic ERalpha was found.

CONCLUSION

A strong nuclear expression of ERbeta correlates with EGFR mutations, and its favorable prognostic significance was influenced by the EGFR mutations in adenocarcinoma of the lung.

Molecular epidemiology to better predict lung cancer risk

Although it is clear that smoking causes lung cancer, it is not known why some smokers develop the disease while others do not. Little is also known regarding risk factors for lung cancer among never-smokers, particularly women, or why women with lung cancer are more likely to have a family history of cancer, to be diagnosed at a young age, or to have adenocarcinoma. The application of molecular epidemiology to the study of lung cancer risk might facilitate elucidation of these questions. In this review, the molecular epidemiology of lung cancer is discussed, with an emphasis on studies of genetic variability in metabolic pathways as a means for determining susceptibility. Work that has assessed intermediate markers of risk, such as DNA adducts, is also presented, as are studies of tumor tissue alterations, such as mutations and DNA methylation, in relation to risk of lung cancer. Finally, approaches to evaluating factors that might explain the differing epidemiology of lung cancer between men and women are also presented. It is likely that, by incorporating biomarkers of susceptibility, exposure, and effect, molecular epidemiologic approaches might better define factors that explain some of the variability in lung cancer risk.

Women and lung cancer

OBJECTIVES

There is expanding evidence that lung cancer has a multitude of sex differences. This article will review these differences and discuss nursing implications for women with lung cancer.

DATA SOURCES

Research and journal articles.

CONCLUSION

Understanding the sex differences of lung cancer is essential for individualizing care for women with lung cancer.

IMPLICATIONS FOR NURSING PRACTICE

Nurses play an integral role throughout the trajectory of illness for women with lung cancer. Understanding the sex differences will help nurses to individualize the care for this population to meet their specific needs.

The Impact of Sex and Smoking Status on the Mutational Spectrum of Epidermal Growth Factor Receptor Gene in Non–small Cell Lung Cancer

PURPOSE

Mutation of epidermal growth factor receptor (EGFR) gene has been reported to be present in non-small cell lung cancer (NSCLC) and significantly associated with female sex and never-smoking status. In this study, we extensively investigated the impact of sex and smoking on the EGFR mutation.

EXPERIMENTAL DESIGN

We examined EGFR exons 18 to 21 status in 1,467 NSCLC patients by direct sequencing to study the impact of sex and smoking status on the EGFR mutational spectrum.

RESULTS

Among 1,467 patients, 197 mutations were found at exon 19, 176 at exon 21, 21 at exon 18, and 24 at exon 20. To examine the independent effect of sex and smoking, the mutational status of each exon was compared between smokers and never smokers in each sex and between males and females stratified by smoking status. In females, exon 19 (P = 0.001) and exon 21 (P < 0.001) mutations were significantly less frequent in ever smokers compared with never smokers. In males, exon 19 (P < 0.001), exon 21 (P < 0.001), and exon 18 (P = 0.003) mutations were significantly less frequent in ever smokers compared with never smokers. In analysis stratified by smoking, there was no difference in sex among never smokers. However, exon 19 mutations were significantly less frequent in males compared with females among ever smokers (P = 0.003). In addition, the interactive effect of male sex and ever smoking status significantly decreased the frequency of exon 19 mutations (P = 0.047) when female never smoker was set as a reference.

CONCLUSION

Both sex and smoking status could influence the EGFR mutational spectrum. Our findings suggest that individual EGFR exons may have differing susceptibilities for mutagenesis.

DNA damage, a biomarker of carcinogenesis: its measurement and modulation by diet and environment

Free radicals and other reactive oxygen or nitrogen species are constantly generated in vivo and can cause oxidative damage to DNA. This damage has been implicated to be important in many diseases, including cancer. The assessment of damage in various biological matrices, such as tissues, cells, and urine, is vital to understanding this role and subsequently devising intervention strategies. During the last 20 years, many analytical techniques have been developed to monitor oxidative DNA base damage. High-performance liquid chromatography-electrochemical detection and gas chromatography-mass spectrometry are the two pioneering contributions to the field. Currently, the arsenal of methods available include the promising high-performance liquid chromatography-tandem mass spectrometry technique, capillary electrophoresis, 32P-postlabeling, antibody-base immunoassays, and assays involving the use of DNA repair glycosylases such as the comet assay. The objective of this review is to discuss the biological significance of oxidative DNA damage, evaluate the effectiveness of several techniques for measurement of oxidative DNA damage in various biological samples and review current research on factors (dietary and non-dietary) that influence DNA oxidative damage using these techniques.

Clinicopathologic characteristics of the EGFR gene mutation in non-small cell lung cancer

BACKGROUND

The authors sought to define clinicopathologic features associated with mutations of the epidermal growth factor receptor (EGFR) gene in non-small cell lung cancer (NSCLC).

METHODS

The authors evaluated surgically resected NSCLC tumors for EGFR (exons 18-21) and KRAS (codons 12-13) mutations and immunohistochemistry (EGFR, phosphorylated-EGFR, and HER2/Neu), and correlated results with clinical outcome and patient and disease features. After their analysis on 159 patients was completed, they selected a second cohort of Asian patients (n = 22) and compared EGFR mutation results to place of birth and immigration to the United States.

RESULTS

Of 159 patients, 14 had EGFR mutations and 18 had KRAS mutations. EGFR mutations were associated with adenocarcinoma (p = 0.002), female gender (p = 0.02), never-smoking (p < 0.0001), Asian ethnicity (p = 0.005), air bronchograms (p = 0.004), and multiple wedge resections (p = 0.03). Although statistical significance was not reached, a higher incidence of synchronous primary cancers (36% versus 17%; p = 0.09) and a smaller median tumor size (11.8 cm versus 24.0 cm; p = 0.24) were seen. There was no difference in disease-free survival; however, median overall survival in patients with EGFR mutations was shorter (3.49 versus 4.29 years; p = 0.85). EGFR mutation did not correlate with immunohistochemistry. In the second cohort of 22 Asian patients, 12 (55%) had the mutation. Of interest, there was no geographic difference in incidence of EGFR mutation. Asian women with the EGFR mutation developed adenocarcinoma at an earlier age than other lung cancer patients.

CONCLUSION

There is a distinct clinical profile for NSCLC patients with the EGFR mutation. However, this mutation does not alter disease-free survival and is likely attributable to an inherited susceptibility instead of an environmental effect.

The growing burden of chronic obstructive pulmonary disease and lung cancer in women: examining sex differences in cigarette smoke metabolism

Smoking-related lung diseases such as chronic obstructive pulmonary disease (COPD) and lung cancer are growing epidemics in women in the United States and elsewhere. Although some of this disturbing trend in women can be attributed to changing smoking habits, there is emerging evidence that women may be biologically more susceptible to the harmful effects of cigarette smoke than are men. Estrogen and related compounds may up-regulate the expression of cytochrome P450 (CYP) enzymes in lungs and liver, which are involved in the metabolism of various constituents of cigarette smoke. Although metabolism of foreign substances is usually beneficial in eliminating potential toxins from the body, in some instances the metabolic process can transform harmless substances into toxic chemicals through a process called metabolic bioactivation. One important xenobiotic substrate for CYP enzymes in cigarette smoke is polycyclic aromatic hydrocarbon, which in its native form is relatively harmless in small doses but upon bioactivation by CYP enzymes, can become very toxic substances for the lungs. In this article, we explore CYP and other related pathways as potential mechanisms and targets of future research and novel discoveries to curb the growing epidemic of COPD and lung cancer in women.

Reduced XPC messenger RNA level may predict a poor outcome of patients with nonsmall cell lung cancer

BACKGROUND

Homologous deletion of the xeroderma pigmentosum complementary group C (XPC) repair gene frequently causes lung adenocarcinoma in mice, suggesting that an XPC defect may play a critical role in lung tumorigenesis. The current study attempted to determine whether reduced XPC mRNA levels predict the clinical outcome of lung cancer patients.

METHODS

XPC, p27(kip) (cdk inhibitory protein), and S-phase kinase-associated protein (skp2) levels were evaluated by Western blot analysis in a series of lung cancer cell lines with different invasive abilities. Migration and invasive abilities were measured using a modified Boyden chamber without and with Matrigel, respectively. To test whether XPC affects cell invasive ability, XPC gene protein expression was reduced in low invasive cells by RNA interference (RNAi) and assayed with Boyden chamber. XPC mRNA levels in 126 nonsmall cell lung cancers (NSCLCs) were examined by real-time-reverse-transcriptase polymerase chain reaction (RT-PCR). The prognostic value of XPC mRNA expression was statistically analyzed by the Kaplan-Meier method and Cox proportional hazards regression.

RESULTS

The expression of XPC was reduced with increasing invasive potential in CL1-series lung cancer cell lines. When the XPC level was reduced by RNAi, cell migration and invasiveness increased markedly; the increased invasiveness may be caused by decreased expression of p27(kip) and increased expression of skp2 and E2F transcription factor 1. To determine whether reduced XPC expression was correlated with tumor aggressiveness and poor patient survival, XPC mRNA levels were evaluated by real-time RT-PCR. Kaplan-Meier analysis demonstrated that the median survival of patients with lower XPC mRNA levels was shorter compared with patients with higher XPC mRNA levels (P = .0440). Cox regression analysis further indicated that XPC mRNA level may act as an independent prognostic factor for NSCLC patients (P = .014).

CONCLUSIONS

The results of the current study suggest that reduced XPC mRNA level may constitute an independent prognostic factor for NSCLC patients.

A possible role for dihydrodiol dehydrogenase in the formation of benzo[a]pyrene-DNA adducts in lung cancer cells and tumor tissues

Epidemiological studies indicate that there is a gender difference in the susceptibility to tobacco and environmental carcinogens, and this gender difference is suspected to result in a higher risk for lung cancer among women. However, the molecular mechanisms underlying this sexual dimorphism remain unclear. In the present study, we have evaluated the roles of CYP1A1 and dihydrodiol dehydrogenase (DDH) in the formation of benzo[a]pyrene (BaP) DNA adducts in various lung cancer cell lines. Among six lung cancer cell lines tested, higher adduct levels were observed in CL-3 and CL1-1 cells, which had relatively high expression of both CYP1A1 and DDH isoform 1 (DHH1). To determine whether a reduction in DDH expression changed the adduct levels, an siRNA was used to knock down DDH1 expression in CL-3 cells. The BaP adduct levels in siDDH-CL-3 cells increased 1.4-2.2-fold relative to that of the parental CL-3 cells. We also examined BaP-like DNA adducts, and CYP1A1 and DDH1 expression by immunohistochemistry in 120 lung tumors. Detection of DNA adducts correlated with CYP1A1-positive tumors (P = 0.023), but not with DDH1-positive tumors. In addition, 28 of 33 tumors (85%) that were CYP1A1-positive and DDH1-negative contained detectable levels of DNA adducts, a proportion that was higher than for tumors from the other three categories of CYP1A1 and DDH1 expression (P = 0.012). Finally, a greater proportion of adduct-positive tumors from females were CYP1A1-positive/DDH1-negative (45.3%) than were tumors from males (27.3%). These results suggest that the reduction of DDH expression in lung tumors may contribute to an increase in DNA adduct levels, which may be partly responsible for the higher susceptibility of female lung cancer patients to DNA damage.

Head and neck cancer cell lines exhibit differential mitochondrial repair deficiency in response to 4NQO

Constituents of tobacco can cause DNA adduct formation and are implicated in head and neck squamous cell cancer (HNSC) development. We investigated the capacity of HNSC cell lines to repair mitochondrial DNA (mtDNA) damage induced by a DNA adduct-forming agent. HNSC cell lines underwent 4-nitroquinoline 1-oxide (4NQO) exposure with subsequent rescue with normal media. Real-time quantitative PCR for nuclear DNA (nDNA) and mtDNA was performed. mtDNA to nDNA ratios were calculated and standardized to mock-treated cells to assess mtDNA repair ability. Two of three tested cancer cell lines exposed to 4NQO exhibited consistent decreases in mtDNA/nDNA ratios throughout the different repair timepoints. At 24 h mtDNA/nDNA ratios of JHU-O19 and JHU-O22 decreased to 63% and 60% of controls, respectively. Conversely, a control keratinocyte cell line exhibited overall increases in mtDNA/nDNA ratios compared to baseline suggesting intact DNA repair mechanisms. By using a DNA adduct formation and repair model featuring 4NQO and HNSC cell lines, we have implicated faulty mtDNA repair as having a potential role in HNSC.

Gender difference in estrogen receptor alpha promoter hypermethylation and its prognostic value in non-small cell lung cancer

It has been documented that estrogen receptor (ER) transcription silencing due to hypermethylation is linked to the tumor progression of breast, uterine and prostate cancers. Additionally, ER hypermethylation in lung tumors has been associated with the exposure of specific carcinogens in animal study. The role of hypermethylation-induced ER transcription silencing in lung tumor progression and its prognostic value for non-small cell lung cancer (NSCLC) patients remained unclear. In our study, ER hypermethylation of 123 lung tumors and adjacent normal parts were examined by methylation-specific PCR (MSP). Estrogen receptor mRNA expression in lung tumors was determined by RT-PCR. Our data indicated that ER hypermethylation was only detected in lung tumors, but not in adjacent normal lung tissues. This suggests that ER hypermethylation may be associated with lung tumorigenesis. Among the clinical parameters studied, only gender factor was correlated with ER hypermethylation with a higher frequency of ER hypermethylation being in male patients than in female patients (58 vs. 34%, p = 0.01). After being stratified by gender and cigarette smoking status, a similarly high prevalence of ER hypermethylation was found in male smoking and nonsmoking patients (60 vs. 61%) as compared to that of female nonsmoking patients (34%). To investigate if 17-beta estradiol (E2) was responsible for such gender difference in ER hypermethylation, a lung cancer A549 cell with ER hypermethylation and without ER mRNA expression was treated with E2 of various concentrations for defined time intervals to show that an E2 treatment could restore the expression of ER mRNA and eliminate ER hypermethylation. Western blot data also showed that acetylated histone 3 and histone 4 of chromatin were increased significantly by E2 treatment. Thus, E2 can make ER mRNA re-expression by eliminating ER hypermethylation. To elucidate the prognostic value of ER hypermethylation, Kaplan-Meier analysis was carried out to show that patients with ER hypermethylation had a poorer prognosis than those without ER hypermethylation. Such prognostic prediction, however, applied only to male (p = 0.0044) patients. Cox regression analysis further showed the feasibility of ER hypermethylation as an independent prognostic factor of NSCLC (p = 0.007). It is possible that antiestrogens may have different therapeutic values for male and female lung cancer patients.

Sex differences in risk of lung cancer associated with methylene-tetrahydrofolate reductase polymorphisms

Methylenetetrahydrofolate reductase (MTHFR) catalyzes the metabolism of folate and nucleotides needed for DNA synthesis and repair. Variations in MTHFR functions likely play roles in the etiology of lung cancer. The MTHFR gene has three nonsynonymous single nucleotide polymorphisms (i.e., C677T, A1298C, and G1793A) that have a minor allele frequency of >5%. We investigated the associations between the frequencies of MTHFR variant genotypes and risk of lung cancer in a hospital-based case-control study of 1,051 lung cancer patients and 1,141 cancer-free controls in a non-Hispanic White population. We found that compared with the MTHFR 1298AA genotype, the 1298CC genotype was associated with a significantly increased risk of lung cancer in women [(odds ratio (OR), 2.09; 95% confidence interval (95% CI), 1.32-3.29)] but not in men (OR, 0.95; 95% CI, 0.62-1.45). The MTHFR 677TT genotype was associated with a significantly decreased risk of lung cancer in women (OR, 0.60; 95% CI, 0.40-0.92) but not in men. No association was found between the MTHFR G1793A polymorphism and risk of lung cancer. Further analysis suggested evidence of gene-dietary interactions between the MTHFR C677T polymorphism and dietary intake of vitamin B6, vitamin B12, and methionine in women and evidence of gene-environment interactions between the MTHFR C677T and A1298C polymorphisms and tobacco smoking in men. In conclusion, the polymorphisms of MTHFR may contribute to the risk of lung cancer in non-Hispanic Whites and modify the risk associated with the dietary and environmental exposure in a sex-specific manner.

Gender differences in genetic damage induced by the tobacco-specific nitrosamine NNK and the influence of the Thr241Met polymorphism in the XRCC3 gene

The rapid increase in adenocarcinoma of the lung and mortality amongst women strongly suggests that gender differences exist in sensitivity to certain tobacco carcinogens. In the current study, we performed the mutagen-sensitivity assay, with the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), to test the hypothesis that women are more sensitive to the genotoxic effects of NNK than men. Chromosome aberration (CA) frequencies in peripheral blood lymphocytes (PBLs) from 99 patients were evaluated before and after in vitro exposure to NNK. Because the Thr241Met polymorphism in the DNA-repair gene XRCC3 is associated with increased risk of tobacco-related cancers, especially among women, we also tested the hypothesis that individuals who inherit the homozygous variant 241Met allele are more sensitive to the genotoxic effects of NNK. CA frequency was significantly higher 1 hr after NNK treatment in women, compared with men (P = 0.02). When smoking and gender were considered together, a significant interaction was observed. PBLs from female smokers had significantly higher frequencies of NNK-induced CA, compared with female nonsmokers 1 hr after treatment (P = 0.02). We observed no overall effect of the Thr241Met polymorphism on NNK-induced CA in men, women, smokers, or nonsmokers. Overall, our data indicate that women are more sensitive to the genotoxic effects of NNK than men. Because in past years smoking among women has increased, and in view of the close correlation between NNK exposure and adenocarcinoma of the lung, our data provide a plausible explanation for the recent increase in the incidence of this cancer among women.

Lung cancer in women

Lung cancer is the leading cause of cancer death in the United States and is responsible for 20,000 more deaths yearly in US women than breast cancer. Cigarette smoking is the major cause of lung cancer, and unfortunately, approximately 22 million US women smoke. Mounting evidence suggests that there are significant differences in lung cancer between the sexes. There is a difference in the histologic distribution of lung cancer, with glandular differentiation being more common in women. Genetic variation may account for differences in susceptibility, and hormonal and biologic factors may play a role in carcinogenesis. Lung cancer patients have few therapeutic options. A more thorough understanding of the heterogeneity of lung cancer across populations may lead to innovations in treatment and prevention strategies.

Cytochrome P-450 1A1 gene polymorphisms and risk of breast cancer: a HuGE review

Cytochrome P-450 (CYP) 1A1 plays a key role in phase I metabolism of polycyclic aromatic hydrocarbons and in estrogen metabolism. It is expressed predominantly in extrahepatic tissues, including the breast. Four CYP1A1 gene polymorphisms (3801T --> C, Ile462Val, 3205T --> C, and Thr461Asp) have been studied in relation to breast cancer. The 3801C variant is more common than the Val variant. Both variants occur more frequently in Asians than in White populations. The 3205T --> C polymorphism has been observed in African Americans only. Little data are available on the geographic/ethnic distribution of the Thr461Asp polymorphism. The functional significance of the polymorphisms is unclear. In 17 studies, no consistent association between breast cancer and CYP1A1 genotype was found. Meta-analysis found no significant risk for the genotypes 1) 3801C/C (relative risk (RR) = 0.97, 95% confidence interval (CI): 0.52, 1.80) or 3801T/C (RR = 0.91, 95% CI: 0.70, 1.19) versus 3801T/T, 2) Val/Val (RR = 1.04, 95% CI: 0.63, 1.74) or Ile/Val (RR = 0.92, 95% CI: 0.76, 1.10) versus Ile/Ile, or 3) Asp/Asp (RR = 0.95, 95% CI: 0.20, 4.49) or Thr/Asp (RR = 1.12, 95% CI: 0.87, 1.43) versus Thr/Thr. Future studies should explore possible interactions between CYP1A1 and sources of polycyclic aromatic hydrocarbons, markers of estrogen exposure, other lifestyle factors influencing hormonal levels, and other genes involved in polycyclic aromatic hydrocarbon metabolism or hormonal biosynthesis.

Gender and lung cancer

Although lung cancer is the leading cause of cancer death among men and women in the United States, female smokers appear to be at increased risk. After controlling for the number of cigarettes smoked, female sex imparts a significant, independent risk for most histologic types of lung cancer. Cigarette smoking, genetics, and endocrine factors may interact to contribute to the disparity in lung cancer risk between the sexes. Estrogens have direct and indirect actions in the lung, and estrogen has been implicated in lung carcinogenesis in female smokers. This review of the literature will focus on endocrine factors and tobacco carcinogens as risk factors for lung cancer in women.

Protection by quercetin against cooking oil fumes-induced DNA damage in human lung adenocarcinoma CL-3 cells: role of COX-2

Epidemiological studies have shown that the incidence of lung cancer was associated with exposure to cooking oil fumes (COF) in nonsmoking Taiwanese women. We suspect that quercetin may be a potent inhibitor for reduction of COF-induced DNA damage and prevention of lung cancer development. Comet assay was used to evaluate the DNA damage induced by a relatively low dose of COF (100 g/ml) in human lung adenocarcinoma CL-3 cells. To understand whether quercetin has the most potent protective effect on COF-induced DNA damage, the 50% inhibition concentration of quercetin for COF-induced DNA damage (IC50) was compared with IC50 values of alpha-naphthoflavone(alpha-NF), NS-398, and NaN3 (specific inhibitors) or scavengers of cytochrome P-450 1A1, cyclooxygenase-2 (COX-2),and reactive oxygen species. The IC50 of quercetin was only 1/2, 1/3, and 1/35 of IC50 values of alpha-NF, NS-398, and NaN3,respectively. Clearly, quercetin was the most effective inhibitor of COF-induced DNA damage, followed sequentially by kappa-NF, NS-398, and NaN3. To further elucidate whether inhibition of COF-induced DNA damage of quercetin is mediated through the inhibition of COX-2 gene expression by altering the nuclear factor-kappaB pathway, COX-2 mRNA and its protein expressions induced by COF were evaluated by reverse transcription-polymerase chain reaction and Western blot, respectively. Our data showed that COX-2 mRNA and protein levels were significantly repressed by addition of quercetin in a dose-dependent manner. Gel retardation assay showed that nuclear factor-kappaB DNA binding activity induced by COF was significantly inhibited by quercetin. From our previous and present studies, it is revealed that coexpression of COX-2 and cytochrome P-450 1A1 caused by COF may contribute to genomic instability in lung cancer development. Thus quercetin may act as a potent chemopreventive agent of lung cancer for nonsmoking Taiwanese women.

Environmental exposure and lung cancer among nonsmokers: an example of Taiwanese female lung cancer

Lung cancer is the leading cause of cancer death worldwide and in Taiwan. Cigarette smoking is considered to be the most important risk factor, since about 90% of lung cancer can be related to cigarette smoking. Despite the recent decrease of cigarette smoking, lung cancer is still the leading cause of cancer death in the United States. In Taiwan, only around 50% of lung cancer incidence could be associated with cigarette smoking, particularly less than 10% of Taiwanese women are smokers. Thus, the aetiology of lung cancer for nonsmokers remains unknown. DNA damages including bulky and oxidative damage may be related with mutation of tumor suppressor genes, such as p53 gene. The high DNA adduct levels in female may be associated with frequent exposure to indoor cooking oil fumes (COF) and outdoor heavy air pollution. Oxidative stress induced by COF was also discussed. Different p53 mutation spectra and mutation frequency between genders reflected that different environmental factors may be involved in nonsmoking male and female lung cancer development. Most importantly, our recent report has demonstrated that human papillomavirus (HPV) infection was associated with nonsmoking female lung cancer. Based on our studies with Taiwanese nonsmoking lung cancer as the model, the possible aetiological factors of lung cancer incidence in Taiwanese nonsmokers were elucidated.

Chromosomal aberrations of primary lung adenocarcinomas in nonsmokers

BACKGROUND

Lung carcinoma is a common malignancy, and tobacco carcinogenesis is the major cause. Studies on individual genes or loci have suggested, that in tumors from nonsmokers, different genetic alterations are present compared with tumors from smokers. It is possible that distinct genetic pathways may be involved. However, the targets remain largely unknown; and, to the authors' knowledge, molecular cytogenetics studies on lung carcinomas from nonsmokers have not been reported.

METHODS

Comparative genomic hybridization (CGH) analysis was performed on primary lung adenocarcinoma samples from 32 patients who never smoked to identify loci of frequent aberrations.

RESULTS

Different extents of aberration were found in 31 of the 32 samples studied. The most frequently altered locus was gain of 16p (59% of samples) followed by gain of 20q (44% of samples), with the minimal overlapping regions at 16p13.1-p13.2 and 20q13.2, respectively. Other over-represented loci with > 30% frequency were observed at 5p (34% of samples), 7p (41% of samples), 8q (31% of samples), 17q (34% of samples), and 19q (34% of samples); and high-level DNA amplifications were detected at 1q, 7p, 12q, 19q, and 20q. DNA under-representation was observed less commonly and included 8p (28% of samples), 9p (22% of samples), 13q (28% of samples), and 18q (38% of samples).

CONCLUSIONS

The current study identified targets of frequent genetic aberration in primary adenocarcinomas from nonsmokers. Compared with reported CGH findings in the literature, the current findings suggest that DNA gain at 16p is the distinct aberration involved in these tumors. Other frequently altered loci involve commonly reported oncogenic and tumor suppressor loci, suggesting an overlap with the genetic pathways of tobacco-induced lung carcinogenesis.

The TP53 gene, tobacco exposure, and lung cancer

Of the various genetic alterations in lung cancer, the abnormalities of the TP53 gene (p53) are among the most frequent and important events. Because of its importance, many aspects of TP53 have been studied, including preneoplastic lesions and TP53as a marker for early detection and prognosis and as a therapeutic option. We summarize recent knowledge of TP53 in lung cancer with a special emphasis on the relationship between smoking exposure (e.g, cigarette, etc.) and specific mutational pattern of TP53by analyzing the latest version of the International Agency for Research on Cancer (IARC) database on TP53 mutations in human cancer. Our analysis confirmed several other studies showing significant differences in the frequencies of G:C to T:A transversions between ever-smokers and never-smokers. Furthermore, when comparing the mutational spectrum by gender, important differences were noted between male and female never-smokers. We concluded that the previously noted G:C to T:A transversions were mainly due to female smokers having a high frequency of these changes compared to female never-smokers. There was no relationship between adenocarcinomas and squamous cell carcinomas independent of gender. We also examined the seven codons which have been previously identified as hot spots, that is, the sites of frequent G:C to T:A transversions in smoking-related lung cancers. However, there was no specific codon which was strongly related to smoke exposure despite a moderate relationship. We considered the term "warmspot" may be more appropriate. While mutations of TP53 are frequent in lung cancers, further investigation is necessary to understand their role for lung carcinogenesis, especially as they relate to gender differences, and to translate our laboratory knowledge to clinical applications.

DNA adduct burden and tobacco carcinogenesis

DNA adducts associated with tobacco smoking could provide a marker of biologically effective dose of tobacco carcinogens and improve individual cancer risk prediction. A significant number of clinical and epidemiologic studies have reported associations of increased DNA adduct levels with the occurrence of the prevalent tobacco related cancers including cancer of the lung, head and neck, and bladder. The inducibility of DNA adducts following in vitro treatments using blood lymphocytes also appears to be a risk factor in the development of lung and head and neck cancer. Corroborative evidence pointing to the importance of DNA adducts in tobacco carcinogenesis include numerous studies showing associations of tobacco smoke exposure with the induction of DNA adducts in humans in vivo. Further effort is necessary, however, to more fully characterize the dose-response relationship between smoking and DNA adducts in exposed target and surrogate tissues. The relationship between gene polymorphisms thought to modify tobacco-related cancer risk and DNA adduct levels is complex. Results of some DNA adduct studies (both in vitro and in vivo) appear inconsistent with the epidemiologic findings. This is evident for polymorphisms involving both carcinogen metabolism (e.g. GSTP1) and DNA repair (e.g. XRCC1). Molecular studies of human tumors suggest associations of p53 mutation with DNA adducts and have revealed correlations of DNA adduct levels with somatic alterations (e.g. 3p21 LOH) that are thought to occur at the very earliest stages of tobacco carcinogenesis. More research is needed to assess the relationship between endogenous sources of DNA adducts and tobacco smoke exposure and the relative oncogenic effects of chemically stable versus unstable DNA adducts. Many potentially fruitful new avenues of cancer research are emerging that integrate DNA adduct analyses with assessments of smoking, genetics, diet and ambient air quality. These investigations aim to understand the multifactorial nature of interindividual variability in response to tobacco carcinogens. As these trends continue a variety of innovative study designs and approaches will become important in human populations.