Risk modification by CYP1A1 and GSTM1 polymorphisms in the association of environmental tobacco smoke and lung cancer: a case-control study in Japanese nonsmoking women

Lung cancer in patients who have never smoked - an emerging disease

Lung cancer is the most common cause of cancer-related deaths globally. Although smoking-related lung cancers continue to account for the majority of diagnoses, smoking rates have been decreasing for several decades. Lung cancer in individuals who have never smoked (LCINS) is estimated to be the fifth most common cause of cancer-related deaths worldwide in 2023, preferentially occurring in women and Asian populations. As smoking rates continue to decline, understanding the aetiology and features of this disease, which necessitate unique diagnostic and treatment paradigms, will be imperative. New data have provided important insights into the molecular and genomic characteristics of LCINS, which are distinct from those of smoking-associated lung cancers and directly affect treatment decisions and outcomes. Herein, we review the emerging data regarding the aetiology and features of LCINS, particularly the genetic and environmental underpinnings of this disease as well as their implications for treatment. In addition, we outline the unique diagnostic and therapeutic paradigms of LCINS and discuss future directions in identifying individuals at high risk of this disease for potential screening efforts.

Association between polymorphisms in the CYP1A1, CYP2E1 and GSTM1 genes, and smoking, alcohol and upper digestive tract carcinomas in a high-incidence area of northern China

Metabolic gene variants, smoking, and alcohol consumption are important upper digestive tract cancer (UDTC) risk factors. However, the gene-gene and gene-environment interactions remain unclear. A case-control study in a high incidence area for upper digestive tract cancer was conducted in China. DNA was extracted from buffy coat samples for PCR or PCR-restriction fragment length polymorphism. Smoking and alcohol drinking status was determined by questionnaires. Odds ratios (ORs) and 95% confidence intervals (CIs) were used to assess the associations. After adjusting for confounding factors, smoking increased esophageal cancer (EC), gastric cardia cancer (GCC) and gastric antral carcinoma (GAC) risk by 3.594, 4.658, and 3.999-fold, respectively. Alcohol consumption increased EC, GCC and GAC risk by 1.953, 2.442 and 1.765-fold, respectively. The cytochrome P4501A1 (CYP1A1) rs4646903 T>C polymorphism increased GCC risk, the cytochrome P4502E1 (CYP2E1) rs2031920 C>T polymorphism increased EC risk, while the GSTM1 null genotype decreased EC risk. An association existed between the following: CYP1A1 rs4646903 and smoking in EC, GCC and GAC; CYP1A1 rs4646903 and alcohol consumption in EC and GCC; CYP2E1 rs2031920 and smoking in EC, GCC and GAC and CYP2E1 rs2031920 and alcohol consumption in EC and GCC. No association was observed between CYP1A1 and CYP2E1. The glutathione S-transferase mu 1 (GSTM1) null genotype decreased EC risk (OR=0.510). Smoking/drinking are upper digestive tract cancer risk factors. The CYP1A1 rs4646903 and CYP2E1 rs2031920 polymorphisms were risk factors of GCC or EC, and the GSTM1 null genotype may serve a protective role against EC. The results of the present study indicated that gene-environment interactions increase the risk of UDTC.

Meta-Analysis and Systematic Review in Environmental Tobacco Smoke Risk of Female Lung Cancer by Research Type

More than 50% of women worldwide are exposed to Environmental Tobacco Smoke (ETS). The impact of ETS on lung cancer remains unclear. Cohort studies since the late 1990s have provided new evidence of female lung cancer risk due to ETS. The objective of this meta-analysis and systematic review was to analyze the association of ETS with female lung cancer risk from 1997 to 2017, organised based on research design. According to our applied inclusion and exclusion criteria, 41 published studies were included. The relative risk (RR) from the cohort studies or odds ratio (OR) from case-control studies were extracted to calculate the pooled risks based on the type of study. The summary risks of ETS were further explored with the modulators of ETS exposure sources and doses. The pooled risks of lung cancer in non-smoking women exposed to ETS were 1.35 (95% CI: 1.17⁻1.56), 1.17 (95% CI: 0.94⁻1.44), and 1.33 (95% CI: 1.17⁻1.51) for case-control studies, cohort studies, and both types of studies, respectively. The summary RR estimate of the cohort studies was not statistically significant, but the RR increased with increasing doses of ETS exposure (p trend < 0.05). Based on the results of this study, ETS might be an important risk factor of female lung cancer in non-smokers.

The Interaction of Smoking with Gene Polymorphisms on Four Digestive Cancers: A Systematic Review and Meta-Analysis

The main purpose of this study was to perform a meta-analysis to assess the interaction between smoking and nine genes (GSTM1, GSTT1, GSTP1, CYP1A1, NAT2, SULT1A1, hOGG1, XRCC1 and p53) on colorectal cancer, gastric cancer, liver cancer and oesophageal cancer. Published articles from the PubMed, ISI and EMBASE databases were retrieved. A total of 67 case-control studies or nested case-control studies were identified for the analysis. The pooled jodds ratio (OR) with 95% confidence interval (CI) was calculated using the random effect model. The overall study showed that the GSTM1 polymorphism was associated with the risk of the four digestive cancers among Asian population (OR 1.284, 95% CI: 1.122-1.470, p: 0). Subgroup analyses by cancer site showed that GSTM1 null genotype increased the gastric cancer risk in total population (OR 1.335, 95% CI: 1.145-1.556, p: 0). However, the association of GSTM1 null genotype with the oesophageal cancer risk was found in smokers (OR 1.382, 95% CI: 1.009-1.894, p:0.044), but not in non-smokers (OR 1.250, 95% CI: 0.826-1.891, p:0.290). Moreover, smokers with the CYP1A1 IIe462Val polymorphism were at an increased cancer risk in Asian population (OR=1.585, 95% CI 1.029-2.442, p: 0.037). None of the other gene-smoking interactions was observed in the above cancers. This meta-analysis reveals two potential gene-smoking interactions, one is between smoking and GSTM1 on oesophageal cancer, and the other is between smoking and CYP1A1 IIe462Val on the four cancers in Asian population. Future studies need to be conducted to verify the conclusions.

Synergistic Association of CYP1A1 Polymorphisms with Increased Susceptibility to Squamous Cell Lung Cancer in North Indian Smokers

Objectives

Studies in different populations have shown that polymorphisms within the CYP1A1 gene play an important role in determining individual susceptibility to lung cancer. However, the data obtained so far have been contradictory within the same or different populations. Few studies have focused on the synergistic effect of CYP1A1 polymorphisms on the susceptibility to lung cancer overall and to different histological subtypes along with the impact of smoking.

Methods

A total of 704 individuals (353 lung cancer patients and 351 controls) were evaluated for CYP1A1 polymorphisms. CYP1A1 genotyping was done by means of PCR-RFLP.

Results

A CYP1A1 mutant genotype was found to be significantly associated with lung cancer (OR = 3.15; 95% CI = 1.75-5.71; p = 0.0001) and this risk was 4-fold higher in case of squamous cell carcinoma (SCC). The CYP1A1 m2 allelic variant was found to be strongly associated with the risk of SCC and adenocarcinoma. The combined “at risk” genotypes of the CYP1A1 m1 and m2 allelic variants were associated with lung cancer risk and this risk was higher in case of SCC (OR = 2.0; 95% CI = 1.97-3.81; p = 0.028). Furthermore, the lung cancer risk was associated with smoking, especially in heavy smokers carrying CYP1A1 variant genotypes. We also observed that heavy smokers with the mutant m1 genotype were at increased risk of SCC (OR = 5.4; 95% CI = 2.4-11.9; p<0.0001). Furthermore, when stratified for smoking dose and histology, the effect was compounded in heavy smokers and SCC (OR = 7.5; 95% CI = 1.8-30.9; p = 0.004).

Conclusions

Polymorphism in the CYP1A1 gene is an important risk modifier for lung cancer.

Secondhand smoke exposure and risk of lung cancer in Japan: a systematic review and meta-analysis of epidemiologic studies

OBJECTIVE

Systematic evaluation of the association between secondhand smoke exposure and lung cancer in Japan has yet to be conducted. Here, we performed a systematic review and meta-analysis of the relationship between secondhand smoke and lung cancer in Japanese non-smokers.

METHODS

Relevant studies were collected from the MEDLINE and Ichushi Web databases using a combination of search terms and Medical Subject Headings. Eligible studies were identified, and relative risks or odds ratios were extracted to calculate pooled risk estimates. This procedure was performed independently by at least two authors. Stratified analyses were carried out according to study design, publication year, and whether or not potential confounding variables were accounted for. The presence of publication bias was assessed via funnel plots.

RESULTS

We identified four cohort studies and five case-control studies. Quantitative synthesis was conducted only for secondhand smoke exposure in the home during adulthood. Of the 12 populations included in meta-analysis, positive secondhand smoke exposure-lung cancer associations were observed in 11, whereas an inverse association was found in the remaining 1. The pooled relative risk of lung cancer associated with secondhand smoke exposure was 1.28 (95% confidence interval: 1.10-1.48). We found no evidence of publication bias, and a significant association remained even when potentially missing studies were included (pooled relative risk: 1.26; 95% confidence interval: 1.09-1.46). The results were stable across different subgroup analyses, including by study design, publication year, and when adjusting for confounding variables.

CONCLUSIONS

Secondhand smoke exposure in the home during adulthood results in a statistically significant increase in the risk of lung cancer.

Meta-analysis of GSTM1 null genotype and lung cancer risk in Asians

BACKGROUND

Several molecular epidemiological studies have been conducted to examine the association between glutathione S-transferase M 1 (GSTM1) null genotype and lung cancer in Asians; however, the conclusions remained controversial. We therefore performed an extensive meta-analysis on 31 published case-control studies with a total of 5347 lung cancer cases and 6072 controls.

MATERIAL/METHODS

PubMed and EMBASE were searched to identify case-control studies investigating the associations of GSTM1 null genotype with risk of lung cancer in Asians. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the strength of association between lung cancer risk and polymorphism of GSTM1.

RESULTS

GSTM1 null genotype was significantly associated with lung cancer risk (OR=1.43; 95% CI, 1.30-1.58). This result remained statistically significant when the adjusted ORs were combined (OR=1.38; 95% CI, 1.23-1.54). In the subgroup analysis by sex, there were significant associations in women and men. When stratifying for histology, this genotype showed increased adenocarcinoma risk and squamous cell carcinoma risk. In the subgroup analysis stratified by smoking status, lung cancer risk was increased in both smokers and non-smokers.

CONCLUSIONS

This study suggests that GSTM1 null genotype is a risk factor for lung cancer in Asians.

Genetic polymorphism of glutathione S-transferase P1 (GSTP1) in Delhi population and comparison with other global populations

Glutathione S-transferases (GSTs) belong to a super family of phase II detoxification enzymes, which play an important role in protecting cells from damage caused by endogenous and exogenous compounds by conjugating reactive intermediates with glutathione to produce less reactive water-soluble compounds. In the present study, we determined the frequencies of two polymorphisms in exon 5 and exon 6 of GSTP1 gene in 500 normal individuals from Delhi. GSTP1 polymorphism was analysed by PCR-RFLP using amplification refractory mutation system (ARMS) assay. Two polymorphic sites in GSTP1 (Ile105 → Val105; Ala114 → Val114) have been analysed simultaneously, which results in four alleles: GSTP1*A (wild-type Ile105; Ala114), GSTP1*B (Val105; Ala114), GSTP1*C (Val105; Val114) and GSTP1*D (Ile105; Val114). The GSTP1 allele frequency in Delhi population was 0.663, 0.248, 0.069, and 0.020 for GSTP1*A, GSTP1*B, GSTP1*C, and GSTP1*D respectively. The frequency of Ile105 and Val105 allele was 0.683 and 0.317 respectively and it was calculated for the purpose of comparison with published data where all the four alleles were not analysed. GSTP1 alleles from Delhi population were compared with reported frequencies from all over India, and from other ethnic groups worldwide. This study would provide a basic database for future genetic studies.

Reduced expression of DENND2D through promoter hypermethylation is an adverse prognostic factor in squamous cell carcinoma of the esophagus

Esophageal cancer ranks sixth in cancer mortality worldwide and patients with esophageal squamous cell carcinoma (ESCC) have a poor prognosis with a 5-year survival rate of less than 10%. Elucidation of the mechanisms of carcinogenesis and tumor progression in esophageal cancer is urgently required to develop targets for therapy and prognostic biomarkers. In the present study, the expression and regulatory mechanism of the differentially expressed in normal and neoplastic cells domain containing 2D (DENND2D), which is a regulator of Rab GTPases, were investigated to explore its potential as a tumor suppressor gene for ESCC. The level of DENND2D mRNA expression in ESCC cell lines and surgical specimens was determined using a quantitative real-time reverse transcription-polymerase chain reaction assay, and the relationship between the expression levels of DENND2D mRNA and clinicopathological factors was evaluated. The expression and distribution of DENND2D were determined using immunohistochemistry. DNA methylation analysis was performed to determine the regulatory mechanism of DENND2D expression in ESCC. The level of DENND2D mRNA expression was reduced in 8/9 ESCC cell lines and in 59/65 surgical specimens, and the mean expression levels were significantly lower in cancerous tissues compared to corresponding normal tissues (p<0.001). The expression pattern of DENND2D protein and mRNA was consistent. Downregulation of DENND2D mRNA in ESCC tissues was identified as an independent prognostic factor in multivariate analysis (hazard ratio, 2.194; p=0.039). The DENND2D promoter was methylated in 5/9 ESCC cell lines, and DNA demethylation reactivated DENND2D mRNA expression. Hypermethylation of DENND2D was frequently detected in ESCC tissues (64.6%) and was significantly associated with downregulation of DENND2D mRNA expression (P=0.008). Taken together, our data suggest that DENND2D is a candidate tumor suppressor gene that was inactivated by promoter hypermethylation in patients with ESCC and may serve as a novel biomarker of ESCC.

Genetic polymorphisms of GSTM1 and GSTT1 genes in Delhi and comparison with other Indian and global populations

The glutathione S-transferases (GSTs) are involved in the metabolism of many xenobiotics, including an array of environmental carcinogens, pollutants, and drugs. Genetic polymorphisms in these genes may lead to inter- individual variation in susceptibility to various diseases. In the present study, GSTM1 and GSTT1 polymorphisms were analysed using a multiplex polymerase chain reaction in 500 normal individuals from Delhi. The frequency of individuals with GSTM1 and GSTT1 null genotypes were 168 (33.6%) and 62 (12.4%) respectively, and 54 (10.8%) were having homozygous null genotype for both the genes GSTM1 and GSTT1 simultaneously. The studied population was compared with reported frequencies from other neighbouring state populations, as well as with those from other ethnic groups; Europeans, Blacks, and Asians. The prevalence of homozygous null GSTM1 genotype is significantly higher in Caucasians and Asians as compared to Indian population. The frequency of GSTT1 homozygous null genotypes is also significantly higher in blacks and Asians. We believe that due to large number of individuals in this study, our results are reliable estimates of the frequencies of the GSTM1, GSTT1 in Delhi. It would provide a basic database for future clinical and genetic studies pertaining to susceptibility and inconsistency in the response and/or toxicity to drugs known to be the substrates for GSTs.

GSTM1 and GSTT1 polymorphism and susceptibility to esophageal cancer in high- and low-risk regions of India

Glutathione transferases, a super family of dimeric phase II metabolic enzymes play a vital role in biotransformation of many substances. This study evaluates the influence of genetic polymorphism of GSTM1 and GSTT1 gene loci on esophageal cancer risk in Assam and Delhi from India. DNA from blood samples of esophageal cancer cases (203,112) and controls (286,150) from Assam and Delhi, respectively, were extracted. GSTM1 and GSTT1 polymorphisms were analyzed by multiplex PCR procedure. Differences in proportions were tested using Pearson's chi-square test with odds ratio (OR) and 95 % confidence interval (CI). Risk of esophageal cancer was approximately twice in individuals having homozygous GSTM1 (OR-2.1, 95 % CI, 1.44-3.13) and GSTT1 null genotypes (OR-1.7,95 % CI, 0.99-2.77) in Assam, and around three times in GSTT1 null genotype (OR-2.9, 95 % CI, 1.56-5.27) in Delhi population. GSTM1 null genotype seems to play a protective role (OR-0.7, 95 % CI, 0.39-1.27) in Delhi. A significant association of GSTM1 null genotype with esophageal cancer was observed in a younger age group in Assam (OR-2.7, 95 % CI, 1.48-5.01), and in Delhi population association was observed in smokers with GSTT1 null genotype (OR-2.5, 95 % CI, 1.04-6.07), and alcoholics having GSTM1 null genotype (OR-2.6, 95 % CI, 0.99-6.77). Significant association of GSTM1 null genotype in Assam was observed between cancer cases and controls in fermented betel nut chewers only (OR-2.8, 95 % CI, 1.19-6.72), whereas, smoking and alcohol failed to show any correlation with GSTM1/GSTT1 genotypes. Cancer development is not only due to exogenous or endogenous carcinogens but depends on their interaction with genes that are involved in the detoxification of these carcinogens.

Lung cancer in never smokers

Lung cancer in never smokers (LCINS) is the seventh leading cause of death among solid tumors. The main risk factor for lung cancer is smoking; however, approximately 15% of lung cancer patients have never smoked. LCINS is more frequent in women, irrespective of geographical location, nevertheless, the highest incidence has been found in South-East Asia. The histological incidence of adenocarcinoma is higher in the group of never smokers than squamous cell carcinoma. There is a familial clustering of lung cancer that is more pronounced in never smokers, where the family history was associated with an increased risk. Genome-wide association studies identified certain chromosomal aberrations in LCINS. Furthermore, the oncogenic mutation pattern is distinct in nonsmoking patients: activating mutations of EGFR or anaplastic lymphoma kinase are more frequent. The etiology of LCINS includes several environmental factors as well, such as environmental tobacco smoke, viral and hormonal factors, a variety of pulmonary diseases and certain occupational exposures. It is now established that EGFR-tyrosine kinase inhibitor treatment (erlotinib and geftinib) in lung cancer is more effective in LCINS, owing to the higher incidence of EGFR mutation in nonsmokers. Despite the growing body of information on LCINS in recent years there is a need to further investigate the pathogenesis of this particular lung cancer. Future studies on LCINS should try to tackle the issues of prevention, early diagnosis and the exploration of novel therapeutic targets to combat lung cancer disease.

CYP1A1 MspI and exon7 gene polymorphisms and lung cancer risk: an updated meta-analysis and review

BACKGROUND

Many studies have examined the association between the CYP1A1 MspI and exon 7 gene polymorphisms and lung cancer risk in various populations, but their results have been inconsistent.

METHODS

To assess this relationship more precisely, a meta-analysis and review were performed. The PubMed, Embase, Web of Science, and CNKI database was searched for case-control studies published up to June 2010. Data were extracted and pooled odds ratios (OR) with 95% confidence intervals (CI) were calculated.

RESULTS

Ultimately, 64 studies, comprising 18,397 subjects from 49 case-control studies of the MspI genotype and 18,518 patients from 40 case-control studies of the exon 7 genotype, were included. A significantly elevated lung cancer risk was associated with 2 MspI genotype variants (for type C vs. Type A: OR = 1.26, 95% CI = 1.12-1.42; for types B and C combined vs. Type A: OR = 1.20, 95% CI = 1.13-1.28) in overall population. In the stratified analysis, a significant association was found in Asians, Caucasians, lung SCC, lung AC and Male population, not in mixed population, lung SCLC and female population. However, inconsistent results were observed for CYP1A1 exon7 in our meta-analysis, two variants of the exon 7 polymorphism were associated with a significantly higher risk for lung cancer (for Val/Val vs. Ile/Ile: OR = 1.24, 95% CI = 1.09-1.42; for (Ile/Val +Val/Val) vs. Ile/Ile: OR = 1.15, 95% CI = 1.07-1.24) in overall population. In the stratified analysis, a significant assocation was found in Asians, Caucasians, lung SCC and Female population, not in mixed population, lung AD, lung SCLC and Male population. Additionally, a significant association was found in smoker population and not found in non-smoker populations for CYP1A1 MspI and exon7 gene.

CONCLUSIONS

This meta-analysis suggests that the MspI and exon 7 polymorphisms of CYP1A1 correlate with increased lung cancer susceptibility and there is an interaction between two genotypes of CYP1A1 polymorphism and smoking, but these associations vary in different ethnic populations, histological types of lung cancer and gender of case and control population.

Polymorphisms of Metabolizing Enzymes and Susceptibility to Ethmoid Intestinal-type Adenocarcinoma in Professionally Exposed Patients

Intestinal-type adenocarcinoma (ITAC) of ethmoid is a rare tumor associated with occupational exposure to wood and leather dusts. Polymorphisms in xenobiotic metabolizing enzymes play an important role in gene-environment interactions and may contribute to a high degree of variance in individual susceptibility to cancer risk. The aim of this study was to investigate by polymerase chain reaction the role of polymorphisms at CYP1A1 and GSTM1 genes in 30 ethmoid ITAC patients and 79 healthy donors. The distribution of Thr/Asn genotype at CYP1A1 codon 461 was significantly overrepresented among the patients (23.3%; P = .0422), whereas the Ile/Val genotype at CYP1A1 codon 462 was not significantly different between cases and controls (P = .76). The GSTM1 null genotype was not significantly different between cases and control (P = 1), but we observed that the combined codon 461 Thr/Asn and GSTM1 null genotype was overrepresented in the patient group (P = .0019). The results reveal that patients with CYP1A1 codon 461 polymorphism may be at high genetic risk of ITAC and that the risk increases in the presence of combined polymorphism of CYP1A1 and GSTM1 null genotype. This strongly suggests that CYP1A1 codon 461 and GSTM1 null genotype may be useful in selecting exposed individuals at risk for ethmoid ITAC.

Lung cancer in never smokers

Lung cancer in never smokers (LCINS) has lately been recognized as a unique disease based on rapidly gained knowledge from genomic changes to treatment responses. The focus of this article is on current knowledge and challenges with regard to LCINS expanded from recent reviews highlighting five areas: (1) distribution of LCINS by temporal trends, geographic regions, and populations; (2) three well-recognized environmental risk factors; (3) other plausible environmental risk factors; (4) prior chronic lung diseases and infectious diseases as risk factors; and (5) lifestyles as risk or protective factors. This article will also bring attention to recently published literature in two pioneering areas: (1) histological characteristics, clinical features with emerging new effective therapies, and social and psychological stigma; and (2) searching for susceptibility genes using integrated genomic approaches.

Assessment of cumulative evidence for the association between glutathione S-transferase polymorphisms and lung cancer: application of the Venice interim guidelines

OBJECTIVE

There is an overwhelming abundance of genetic association studies available in the literature, which can often be collectively difficult to interpret. To address this issue, the Venice interim guidelines were established for determining the credibility of the cumulative evidence. The objective of this report is to evaluate the literature on the association of common glutathione S-transferase (GST) variants (GSTM1 null, GSTT1 null and GSTP1 Ile105Val polymorphism) and lung cancer, and to assess the credibility of the associations using the newly proposed cumulative evidence guidelines.

METHODS

Information from the literature was enriched with an updated meta-analysis and a pooled analysis using data from the Genetic Susceptibility to Environmental Carcinogens database.

RESULTS

There was a significant association between GSTM1 null and lung cancer for the meta-analysis (meta odds ratio=1.17, 95% confidence interval: 1.10-1.25) and pooled analysis (adjusted odds ratio=1.10, 95% confidence interval: 1.04-1.16), although substantial heterogeneity was present. No overall association between lung cancer and GSTT1 null or GSTP1 Ile105Val was found. When the Venice criteria was applied, cumulative evidence for all associations were considered 'weak', with the exception of East Asian carriers of the G allele of GSTP1 Ile105Val, which was graded as 'moderate' evidence.

CONCLUSION

Despite the large amounts of studies, and several statistically significant summary estimates produced by meta-analyses, the application of the Venice criteria suggests extensive heterogeneity and susceptibility to bias for the studies on association of common genetic polymorphisms, such as with GST variants and lung cancer.

Lung cancer in never smokers: molecular profiles and therapeutic implications

The majority of lung cancers are caused by long term exposure to the several classes of carcinogens present in tobacco smoke. Although a significant fraction of lung cancers in never smokers may also be attributable to tobacco, many such cancers arise in the absence of detectable tobacco exposure, and may follow a very different cellular and molecular pathway of malignant transformation. Recent studies summarized here suggest that lung cancers arising in never smokers have a distinct natural history, profile of oncogenic mutations, and response to targeted therapy. The majority of molecular analyses of lung cancer have focused on genetic profiling of pathways responsible for metabolism of primary tobacco carcinogens. Limited research has been conducted evaluating familial aggregation and genetic linkage of lung cancer, particularly among never smokers in whom such associations might be expected to be strongest. Data emerging over the past several years show that lung cancers in never smokers are much more likely to carry activating mutations of the epidermal growth factor receptor (EGFR), a key oncogenic factor and direct therapeutic target of several newer anticancer drugs. EGFR mutant lung cancers may represent a distinct class of lung cancers, enriched in the never-smoking population, and less clearly linked to direct tobacco carcinogenesis. These insights followed initial testing and demonstration of efficacy of EGFR-targeted drugs. Focused analysis of molecular carcinogenesis in lung cancers in never smokers is needed, and may provide additional biologic insight with therapeutic implications for lung cancers in both ever smokers and never smokers.

Glutathione S-transferase M1 (GSTM1) polymorphisms and lung cancer: a literature-based systematic HuGE review and meta-analysis

Multiple genes have been studied for potential associations with lung cancer. The gene most frequently associated with increased risk has been glutathione S-transferase M1 (GSTM1). The glutathione S-transferase enzyme family is known to catalyze detoxification of electrophilic compounds, including carcinogens, therapeutic drugs, environmental toxins, and products of oxidative stress. In this review, the authors summarize the available evidence associating lung cancer with the GSTM1 gene. They describe results from an updated meta-analysis of 98 published genetic association studies investigating the relation between the GSTM1 null variant and lung cancer risk including 19,638 lung cancer cases and 25,266 controls (counting cases and controls in each study only once). All studies considered, the GSTM1 null variant was associated with an increased risk of lung cancer (odds ratio (OR) = 1.22, 95% confidence interval (CI): 1.14, 1.30), but no increase in risk was seen (OR = 1.01, 95% CI: 0.91, 1.12) when only the five largest studies (>500 cases each) were considered. Furthermore, while GSTM1 null status conferred a significantly increased risk of lung cancer to East Asians (OR = 1.38, 95% CI: 1.24, 1.55), such a genotype did not confer increased risk to Caucasians. More data regarding the predictive value of GSTM1 genetic testing are needed before population-based testing may be reasonably considered.

Lung cancer susceptibility: are we on our way to identifying a high-risk group?

Many studies have investigated lung cancer susceptibility based on the presence of low-penetrance, high-frequency single nucleotide polymorphisms. Identifying such susceptibility polymorphisms may lead to the development of tests that allow a more focused follow-up of a high-risk group. Genetic polymorphisms of xenobiotic metabolism, DNA repair, cell-cycle control, immunity, addiction and nutritional status have been described as promising candidates. Genetic polymorphisms in both metabolic activation (Phase I) and detoxification (Phase II) enzymes influence DNA damage. The DNA repair system is a critical cellular response that counteracts the carcinogenic effects of DNA. Thus, genetically determined susceptibility to carcinogens depends on the balance between metabolic and DNA repair enzymes. This review evaluates whether or not a specific polymorphism or a combination of such polymorphisms can effectively predict high-risk groups.

Meta-analysis of studies of passive smoking and lung cancer: effects of study type and continent

BACKGROUND

To calculate a pooled estimate of relative risk (RR) of lung cancer associated with exposure to passive smoking in never smoking women exposed to smoking spouses. This study is an updated meta-analysis that also assesses the differences between estimated risks according to continent and study type using meta-regression.

METHODS

From a total of 101 primary studies, 55 studies are included in this meta-analysis, of which, 7 are cohort studies, 25 population-based case-control and 23 non-population-based case-control studies. Twenty previously published meta-analyses are also reviewed. Fixed and random effect models and meta-regression are used to obtain pooled estimates of RR and P-value functions are used to demonstrate consistency of results.

RESULTS

The pooled RR for never-smoking women exposed to passive smoking from spouses is 1.27 (95% CI 1.17-1.37). The RR for North America is 1.15 (95% CI 1.03-1.28), Asia, 1.31 (95% CI 1.16-1.48) and Europe, 1.31 (1.24-1.52). Sequential cumulative meta-analysis shows no trend. There is no strong evidence of publication bias.

CONCLUSIONS

The abundance of evidence, consistency of finding across continent and study type, dose-response relationship and biological plausibility, overwhelmingly support the existence of a causal relationship between passive smoking and lung cancer.

Polymorphism of selected enzymes involved in detoxification and biotransformation in relation to lung cancer

Available data indicate that there are significant differences in individual susceptibility to lung cancer within the human population. It is believed to be underlie by inherited genetic predispositions related to the genetic polymorphism of several enzymes involved in the detoxification and xenobiotic metabolism. In this review, we collect and discuss the evidence reported up to date on the association between lung cancer and genetic polymorphism of cytochromes P450, N-acetyltransferase, glutathione S-transferases, microsomal epoxide hydrolase, NAD(P)H:quinone oxidoreductase, myeloperoxidase and glutathione peroxidase. All these genes might appear to be candidates for lung cancer susceptibility genes, nevertheless, the present state of the art still offers only a limited explanation of the link between such polymorphisms and increased risk of lung cancer.

Factores etiológicos del cáncer de pulmón: fumador activo, fumador pasivo, carcinógenos medioambientales y factores genéticos

Every year, in Spain 18,000 new cases of lung cancer (LC) are diagnosed. Approximately, 80-90% LC in men and women are directly attributable to tobacco abuse. Cigarette smoke contains over 300 chemicals, 40 of which are known to be potent carcinogens. In the last decade, as in Spain, prevalence of smoking in women has generally increased in the European Union. LC risk can be substantially reduced after smoking cessation, yet never reaches baseline. On the other hand, environmental tobacco smoke exposure (passive smoking) in nonsmokers appears to have a significantly increased risk of LC. An updated of etiology factors of LC, risk related to duration as well as intensity of smoking, relationship between environmental tobacco smoke exposure and LC risk, genetic predisposition and a variety of occupational and environmental exposures implicated as potential risk factors for the development of LC will be reviewed here.

Lung Cancer in Never Smokers: A Review

Lung cancer is the leading cause of cancer-related death in the United States. Although tobacco smoking accounts for the majority of lung cancer, approximately 10% of patients with lung cancer in the United States are lifelong never smokers. Lung cancer in the never smokers (LCINS) affects women disproportionately more often than men. Only limited data are available on the etiopathogenesis, molecular abnormalities, and prognosis of LCINS. Several etiologic factors have been proposed for the development of LCINS, including exposure to radon, cooking fumes, asbestos, heavy metals, and environmental tobacco smoke, human papillomavirus infection, and inherited genetic susceptibility. However, the relative significance of these individual factors among different ethnic populations in the development of LCINS has not been well-characterized. Adenocarcinoma is the predominant histologic subtype reported with LCINS. Striking differences in response rates and outcomes are seen when patients with advanced non–small-cell lung cancer (NSCLC) who are lifelong never smokers are treated with epidermal growth factor receptor tyrosine kinase (EGFR-TK) inhibitors such as gefitinib or erlotinib compared with the outcomes with these agents in patients with tobacco-associated lung cancer. Interestingly, the activating mutations in the EGFR-TK inhibitors have been reported significantly more frequently in LCINS than in patients with tobacco-related NSCLC. This review will summarize available data on the epidemiology, risk factors, molecular genetics, management options, and outcomes of LCINS.

Radon, secondhand smoke, glutathione-S-transferase M1 and lung cancer among women

Tobacco smoke and ionizing radiation induce oxidative stress by transmitting or generating reactive oxygen species (ROS). We hypothesized that glutathione-S-transferase M1 (GSTM1) null homozygotes would have decreased ability to neutralize ROS that might increase their susceptibility to lung cancer. A case-only design was used with lung cancer cases pooled from 3 previously completed case-control studies using archival tissue samples from 270 lung cancer cases to genotype GSTM1. Radon concentrations were measured with long-term alpha-track radon detectors. Secondhand smoke (SHS) was measured with questionnaires and interviews. Unconditional logistic regression was used to calculate the interaction odds ratios (OR) and 95% confidence intervals (95% CI). Radon concentrations >121 Bq m(-3) were associated with a >3-fold interaction OR (OR = 3.41; 95% CI = 1.10, 10.61) for GSTM1 null homozygotes compared to GSTM1 carriers; the linear trend was significant (p trend = 0.03). The SHS and GSTM1 interaction OR was also elevated (OR = 2.28; 95% CI = 1.15-4.51) among never-smokers. This may be the first study to provide evidence of a GSTM1 and radon interaction in risk of lung cancer. Additionally, these findings support the hypothesis that radon and SHS promote neoplasia through shared elements of a common pathway.

Dose effects in gene environment interaction: an enzyme kinetics based approach

There have been many observations of different forms of the effect of dose in toxicological and pharmacological research into gene environment interactions. In one form, the effect of genetic variation is seen to be more potent at lower doses, while in the other, the genetic variant has a stronger effect at higher doses of exposure. The application of principles of classical enzyme kinetics to this problem has led to a hypothesis that for any gain of function polymorphism, a low exposure gene (LEG) or low dose effect will always be observed, while for any loss of function polymorphism, the high exposure gene (HEG) effect will always be seen. Furthermore the dose effect is found to be independent of any effects on Vmax, but is related to effects on Km of the gene product. The hypothesis is derived from the Michaelis-Menten equation, and if supported by experimental evidence, could lead to important implications for drug dosage and toxicological risk analysis in the context of individual differences in genetic profiles.

Five glutathione s-transferase gene variants in 23,452 cases of lung cancer and 30,397 controls: meta-analysis of 130 studies

BACKGROUND

Glutathione S-transferases (GSTs) are known to abolish or reduce the activities of intracellular enzymes that help detoxify environmental carcinogens, such as those found in tobacco smoke. It has been suggested that polymorphisms in the GST genes are risk factors for lung cancer, but a large number of studies have reported apparently conflicting results.

METHODS AND FINDINGS

Literature-based meta-analysis was supplemented by tabular data from investigators of all relevant studies of five GST polymorphisms (GSTM1 null, GSTT1 null, I105V, and A114V polymorphisms in the GSTP1 genes, and GSTM3 intron 6 polymorphism) available before August, 2005, with investigation of potential sources of heterogeneity. Included in the present meta-analysis were 130 studies, involving a total of 23,452 lung cancer cases and 30,397 controls. In a combined analysis, the relative risks for lung cancer of the GSTM1 null and GSTT1 null polymorphisms were 1.18 (95% confidence interval [CI]: 1.14-1.23) and 1.09 (95% CI: 1.02-1.16), respectively, but in the larger studies they were only 1.04 (95% CI: 0.95-1.14) and 0.99 (95% CI: 0.86-1.11), respectively. In addition to size of study, ethnic background was a significant source of heterogeneity among studies of the GSTM1 null genotype, with possibly weaker associations in studies of individuals of European continental ancestry. Combined analyses of studies of the 105V, 114V, and GSTM3*B variants showed no significant overall associations with lung cancer, yielding per-allele relative risks of 1.04 (95% CI: 0.99-1.09), 1.15 (95% CI: 0.95-1.39), and 1.05 (95% CI: 0.89-1.23), respectively.

CONCLUSIONS

The risk of lung cancer is not strongly associated with the I105V and A114V polymorphisms in the GSTP1 gene or with GSTM3 intron 6 polymorphism. Given the non-significant associations in the larger studies, the relevance of the weakly positive overall associations with the GSTM1 null and the GSTT1 null polymorphisms is uncertain. As lung cancer has important environmental causes, understanding any genetic contribution to it in general populations will require the conduct of particularly large and comprehensive studies.

Metabolic gene polymorphisms and lung cancer risk in non-smokers. An update of the GSEC study

BACKGROUND

Since genetic factors may play an important role in lung cancer development at low dose carcinogen exposure, non-smokers are a good model to study genetic susceptibility and its interaction with environmental factors.

MATERIALS AND METHODS

We evaluated the role of the metabolic gene polymorphisms CYP1A1MspI, CYP1A1Ile462Val, GSTM1, and GSTT1 in non-smoker lung cancer patients from the International Collaborative Study on Genetic Susceptibility to Environmental Carcinogens (GSEC). Non-smokers (defined as subjects who never smoked on a regular basis) were selected from the GSEC database. We pooled the raw data from 21 case-control studies for a total of 2764 Caucasians (555 cases and 2209 controls) and 383 Asians (113 cases and 270 controls). Tests of heterogeneity and of inclusion bias were performed.

RESULTS

A significant association between lung cancer and CYP1A1Ile462Val polymorphism was observed in Caucasians (adjusted OR=2.04, 95% CI 1.17-3.54). GSTT1 deletion seems to be a risk factor for lung cancer in Caucasian non smokers only when the analysis was restricted to studies including healthy controls (adjusted OR=1.66, 95% CI 1.12-2.46). A protective effect on lung cancer was observed with the combination of CYP1A1 wild type, GSTM1 null, and GSTT1 non-null genotypes. None of the analysed polymorphisms were associated with lung cancer in Asian non-smokers.

DISCUSSION

Our analysis confirms previous findings that CYP1A1Ile462Val polymorphism may play a role in lung carcinogenesis in Caucasian non-smokers.

Lung cancer in Asian women-the environment and genes*

The mortality rate of lung cancer in Asian women has increased significantly in the past few decades. Environmental factors include tobacco smoke (active and environmental), other indoor pollutions (cooking oil vapours, coal burning, fungus spores), diet, and infections. Active tobacco smoking is not the major factor. The relative risk of lung cancer among non-smoking women ever exposed to environmental smoke from their husbands was 1.20 from a meta-analysis. Cooking oil vapours associated with high temperature wok cooking and indoor coal burning for heating and cooking in unvented homes, particularly in rural areas, are risk factors for Chinese women. Chronic benign respiratory diseases due to the fungus Microsporum canis probably accounts for the high incidence of lung cancer in northern Thai women at Sarapee. Diets rich in fruits, leafy green vegetables, and vitamin A are protective, while cured meat (Chinese sausage, pressed duck and cured pork), deep-fried cooking, and chili increased the risk. Tuberculosis is associated with lung cancer. Also, a Taiwanese study showed that the odds ratio of papillomavirus (HPV) 16/18 infection in non-smoking female lung cancer patients was 10.1, strongly suggesting a causative role. Genetic factors have also been studied in Chinese women, including human leucocyte antigens, K-ras oncogene activation, p53 mutation, polymorphisms of phase I activating enzymes (cytochrome P450, N-acetyltransferase slow acetylator status), and phase II detoxifying enzymes (glutathione-S-transferases, N-acetyltransferase rapid acetylator status). New molecular screening technology would facilitate identification of molecular targets for future studies. The interaction between environmental and genetic factors should also be further elucidated.

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.

CYP1A1 polymorphisms and risk of lung cancer in non-smoking Chinese women: influence of environmental tobacco smoke exposure and GSTM1/T1 genetic variation

OBJECTIVE

We examined whether polymorphisms of CYP1A1, which plays a role in the metabolic activation of polycyclic aromatic hydrocarbons (PAHs), confer an increased risk of lung cancer in lifetime non-smoking Chinese women.

METHODS

A total of 126 incident lung cancer cases, of which 87.7 were pathologically confirmed, and 162 age-matched hospital controls were included. CYP1A1 MspI and Ile(462)Val polymorphisms were genotyped and tested for association with this disease.

RESULTS

An elevated risk of lung cancer was observed among individuals with the MspI CC (OR=1.7, 95 CI=0.9-3.3) and Ile(462)Val ValVal genotypes (OR=2.8, 95 CI=1.1-7.6). After stratifying by environmental tobacco smoke (ETS) exposure, the risk of lung cancer associated with both polymorphisms was higher among individuals with lower exposure to ETS, compared with those who reported at least weekly exposure. Individuals with the MspI CC genotype showed a two-fold higher risk of lung cancer if they were also null for either GSTM1 or T1 (OR=2.3, 95CI=1.0-5.0 and OR=2.7, 95 CI=1.1-6.9, respectively, compared to other genotype combinations combined).

CONCLUSIONS

CYP1A1 is a susceptibility gene for lung cancer among non-smoking Asian women and this association can be influenced by ETS exposure and genetic variation at GST genes.

Environmental tobacco smoke and risk of respiratory cancer and chronic obstructive pulmonary disease in former smokers and never smokers in the EPIC prospective study

OBJECTIVES

To investigate the association between environmental tobacco smoke, plasma cotinine concentration, and respiratory cancer or death.

DESIGN

Nested case-control study within the European prospective investigation into cancer and nutrition (EPIC).

PARTICIPANTS

303,020 people from the EPIC cohort (total 500,000) who had never smoked or who had stopped smoking for at least 10 years, 123,479 of whom provided information on exposure to environmental tobacco smoke. Cases were people who developed respiratory cancers or died from respiratory conditions. Controls were matched for sex, age (plus or minus 5 years), smoking status, country of recruitment, and time elapsed since recruitment.

MAIN OUTCOME MEASURES

Newly diagnosed cancer of lung, pharynx, and larynx; deaths from chronic obstructive pulmonary disease or emphysema. Plasma cotinine concentration was measured in 1574 people.

RESULTS

Over seven years of follow up, 97 people had newly diagnosed lung cancer, 20 had upper respiratory cancers (pharynx, larynx), and 14 died from chronic obstructive pulmonary disease or emphysema. In the whole cohort exposure to environmental tobacco smoke was associated with increased risks (hazard ratio 1.30, 95% confidence interval 0.87 to 1.95, for all respiratory diseases; 1.34, 0.85 to 2.13, for lung cancer alone). Higher results were found in the nested case-control study (odds ratio 1.70, 1.02 to 2.82, for respiratory diseases; 1.76, 0.96 to 3.23, for lung cancer alone). Odds ratios were consistently higher in former smokers than in those who had never smoked; the association was limited to exposure related to work. Cotinine concentration was clearly associated with self reported exposure (3.30, 2.07 to 5.23, for detectable/non-detectable cotinine), but it was not associated with the risk of respiratory diseases or lung cancer. Frequent exposure to environmental tobacco smoke during childhood was associated with lung cancer in adulthood (hazard ratio 3.63, 1.19 to 11.11, for daily exposure for many hours).

CONCLUSIONS

This large prospective study, in which the smoking status was supported by cotinine measurements, confirms that environmental tobacco smoke is a risk factor for lung cancer and other respiratory diseases, particularly in ex-smokers.

Genotoxicity of environmental tobacco smoke: a review

Environmental tobacco smoke (ETS), or second-hand smoke, is a widespread contaminant of indoor air in environments where smoking is not prohibited. It is a significant source of exposure to a large number of substances known to be hazardous to human health. Numerous expert panels have concluded that there is sufficient evidence to classify involuntary smoking (or passive smoking) as carcinogenic to humans. According to the recent evaluation by the International Agency for Research on Cancer, involuntary smoking causes lung cancer in never-smokers with an excess risk in the order of 20% for women and 30% for men. The present paper reviews studies on genotoxicity and related endpoints carried out on ETS since the mid-1980s. The evidence from in vitro studies demonstrates induction of DNA strand breaks, formation of DNA adducts, mutagenicity in bacterial assays and cytogenetic effects. In vivo experiments in rodents have shown that exposure to tobacco smoke, whole-body exposure to mainstream smoke (MS), sidestream smoke (SS), or their mixture, causes DNA single strand breaks, aromatic adducts and oxidative damage to DNA, chromosome aberrations and micronuclei. Genotoxicity of transplacental exposure to ETS has also been reported. Review of human biomarker studies conducted among non-smokers with involuntary exposure to tobacco smoke indicates presence of DNA adducts, urinary metabolites of carcinogens, urinary mutagenicity, SCEs and hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene mutations (in newborns exposed through involuntary smoking of the mother). Studies on human lung cancer from smokers and never-smokers involuntarily exposed to tobacco smoke suggest occurrence of similar kinds of genetic alterations in both groups. In conclusion, these overwhelming data are compatible with the current knowledge on the mechanisms of carcinogenesis of tobacco-related cancers, occurring not only in smokers but with a high biological plausibility also in involuntary smokers.

Ah receptor, CYP1A1, CYP1A2 and CYP1B1 gene polymorphisms are not involved in the risk of recurrent pregnancy loss

The etiology of recurrent pregnancy loss (RPL) remains unclear, but it may be related to a possible genetic predisposition together with involvement of environmental factors. We examined the relation between RPL and polymorphisms in four genes, human aryl hydrocarbon (Ah) receptor, cytochrome P450 (CYP) 1A1, CYP1A2 and CYP1B1, which are involved in the metabolism of a wide range of environmental toxins and carcinogens. All cases and controls were women resident in Sapporo, Japan and the surrounding area. The Ah receptor, CYP1A1, CYP1A2 and CYP1B1 genotypes were assessed in 113 Japanese women with recurrent pregnancy loss (RPL) and 203 ethnically matched women experiencing at least one live birth and no spontaneous abortion (control). No significant differences in Ah receptor, CYP1A1, CYP1A2 and CYP1B1 genotype frequencies were found between the women with RPL and the controls [Ah receptor: Arg/Arg (reference); Arg/Lys and Lys/Lys, odds ratio (OR)=0.67; 95% confidence interval (CI)=0.40-1.11, CYP1A1: m1m1 (reference); m1m2 and m2m2, OR = 0.86; 95% CI = 0.53-1.40, CYP1A2: C/C and C/A (reference); A/A, OR = 1.16; 95% CI = 0.71-1.88, CYP1B1: Leu/Leu (reference); Leu/Val and Val/Val, OR = 1.18; 95% CI = 0.68-2.02]. The present study suggests that the Ah receptor, CYP1A1, CYP1A2 and CYP1B1 gene polymorphisms are not major genetic regulators in RPL.