Heavy smoking and lung cancer: are women at higher risk? Result of the ICARE study

Background:

Whether women are more or equally susceptible to the carcinogenic effects of cigarette smoke on the lungs compared with men is a matter of controversy. Using a large French population-based case–control study, we compared the lung cancer risk associated with cigarette smoking by gender.

Methods:

The study included 2276 male and 650 female cases and 2780 male and 775 female controls. Lifetime smoking exposure was represented by the comprehensive smoking index (CSI), which combines the duration, intensity and time since cessation of smoking habits. The analysis was conducted among the ever smokers. All of the models were adjusted for age, department (a regional administrative unit), education and occupational exposures.

Results:

Overall, we found that the lung cancer risk was similar among men and women. However, we found that women had a two-fold greater risk associated with a one-unit increase in CSI than men of developing either small cell carcinoma (OR=15.9, 95% confidence interval (95% CI) 7.6, 33.3 and 6.6, 95% CI 5.1, 8.5, respectively; P<0.05) or squamous cell carcinoma (OR=13.1, 95% CI 6.3, 27.3 and 6.1, 95% CI 5.0, 7.3, respectively; P<0.05). The association was similar between men and women for adenocarcinoma.

Conclusion:

Our findings suggest that heavy smoking might confer to women a higher risk of lung cancer as compared with men.

Meta- and pooled analysis of GSTT1 and lung cancer: a HuGE-GSEC review

Lung cancer is the most common malignancy in the Western world, and the main risk factor is tobacco smoking. Polymorphisms in metabolic genes may modulate the risk associated with environmental factors. The glutathione S-transferase theta 1 gene (GSTT1) is a particularly attractive candidate for lung cancer susceptibility because of its involvement in the metabolism of polycyclic aromatic hydrocarbons found in tobacco smoke and of other chemicals, pesticides, and industrial solvents. The frequency of the GSTT1 null genotype is lower among Caucasians (10-20%) than among Asians (50-60%). The authors present a meta- and a pooled analysis of case-control, genotype-based studies that examined the association between GSTT1 and lung cancer (34 studies, 7,629 cases and 10,087 controls for the meta-analysis; 34 studies, 7,044 cases and 10,000 controls for the pooled analysis). No association was observed between GSTT1 deletion and lung cancer for Caucasians (odds ratio (OR) = 0.99, 95% confidence interval (CI): 0.87, 1.12); for Asians, a positive association was found (OR = 1.28, 95% CI: 1.10, 1.49). In the pooled analysis, the odds ratios were not significant for either Asians (OR = 0.97, 95% CI: 0.83, 1.13) or Caucasians (OR = 1.09, 95% CI: 0.99, 1.21). No significant interaction was observed between GSTT1 and smoking on lung cancer, whereas GSTT1 appeared to modulate occupational-related lung cancer.

Risk of fatal industrial accidents and death from other external causes among asphalt workers

The hypothesis that asphalt workers are at increased risk of mortality from industrial accidents and other external causes was tested. Mortality rates for external and violent causes of death in a cohort of asphalt industry employees from seven European countries and Israel were compared to that of the general population. There was no evidence that mortality from external causes was increased among long term employees in asphalt application and mixing. There was an increased risk for mortality due to external causes among short term workers. However, none of the fatal accidents among short term workers appear to have occurred during employment in the studied asphalt companies. Overall, no evidence was found supporting the hypothesis that asphalt workers are at increased risk of fatal industrial or road accidents. Mortality from other external causes did not increase in this population as a whole, but increased risks among short term workers deserve further attention.

A Bayesian partition model for case-control studies on highly polymorphic candidate genes

We present a new statistical model for the analysis of case-control or cohort studies examining a highly polymorphic candidate disease susceptibility gene. Many genotypes are possible for such a gene. Consequently, the average number of subjects having each genotype will be modest. If analyzed separately, the risks associated with most genotypes will be estimated imprecisely. Our Bayesian partition model clusters genotypes according to risk, only allowing partitions that satisfy a particular assumption about the joint effect of the two alleles making up a genotype. This assumption is genetically plausible, imposes structure on the set of genotype risks, and still leaves a highly flexible model. By Bayesian model averaging over partitions, the model becomes, in effect, a semiparametric model for genotype risk. It allows borrowing of strength, i.e., estimates of risk for one genotype are informed by the risk estimates of all the genotypes. We present the results of fitting the model to two datasets, one simulated and one genuine case-control study of the NAT1 gene and lung cancer, and compare it in a simulation study with a haplotype relative risk model. The partition model enables genotype risks to be estimated more accurately and the alleles to be ranked according to risk.

Metabolic gene polymorphism frequencies in control populations

Using the International Project on Genetic Susceptibility to Environmental Carcinogens (GSEC) database containing information on over 15,000 control (noncancer) subjects, the allele and genotype frequencies for many of the more commonly studied metabolic genes (CYP1A1, CYP2E1, CYP2D6, GSTM1, GSTT1, NAT2, GSTP, and EPHX) in the human population were determined. Major and significant differences in these frequencies were observed between Caucasians (n = 12,525), Asians (n = 2,136), and Africans and African Americans (n = 996), and some, but much less, heterogeneity was observed within Caucasian populations from different countries. No differences in allele frequencies were seen by age, sex, or type of controls (hospital patients versus population controls). No examples of linkage disequilibrium between the different loci were detected based on comparison of observed and expected frequencies for combinations of specific alleles.

Lack of interaction between asbestos exposure and glutathione S-transferase M1 and T1 genotypes in lung carcinogenesis

An interaction between occupational carcinogens and genetic susceptibility factors in determining individual lung cancer risk is biologically plausible, but the interpretation of available studies are limited by the small number of exposed subjects. We selected from the international database on Genetic Susceptibility and Environmental Carcinogens the studies of lung cancer that included information on metabolic polymorphisms and occupational exposures. Adequate data were available for asbestos exposure and GSTM1 (five studies) and GSTT1 (three studies) polymorphisms. For GSTM1, the pooled analysis included 651 cases and 983 controls. The odds ratio (OR) of lung cancer was 2.0 [95% confidence interval (CI) 1.4-2.7] for asbestos exposure and 1.1 (95% CI 0.9-1.4) for GSTM1-null genotype. The OR of interaction between asbestos and GSTM1 polymorphism was 1.1 (95% CI 0.6-2.1) based on 54 cases and 53 controls who were asbestos exposed and GSTM1 null. The case-only approach, which was based on 869 lung cancer cases and had an 80% power to detect an OR of interaction of 1.56, also provided lack of evidence of interaction. The analysis of possible interaction between GSTT1 polymorphism and asbestos exposure in relation to lung cancer was based on 619 cases. The prevalence OR of GSTT1-null genotype and asbestos exposure was 1.1 (95% CI 0.6-2.0). Our results do not support the hypothesis that the risk of lung cancer after asbestos exposure differs according to GSTM1 genotype. The low statistical power of the pooled analysis for GSTT1 genotypes hampered any firm conclusion. No adequate data were available to assess other interactions between occupational exposures and metabolic polymorphisms.

Polymorphisms of human aryl hydrocarbon receptor (AhR) gene in a French population: relationship with CYP1A1 inducibility and lung cancer

The Ah receptor (AhR) is a ligand-dependent transcription factor that positively regulates the expression of the CYP1A1 gene. We investigated the genetic polymorphisms of the AhR gene including the promoter, and examined the link between these polymorphisms, CYP1A1 inducibility and the lung cancer incidence. The AhR promoter region and the 11 exons of 30 subjects were screened. Among the three polymorphisms found, two [(2417)(A/G) ((157)G/A)] have never been described previously. The (1721)(G/A) and (2417)(A/G) are localized in exon 10 and lead to Arg(554)Lys and Met(786)Val substitutions, respectively. The other polymorphism was found in the 5'-untranslated region, resulting in the substitution of a G by an A at position 157 (157)(G/A). To evaluate the frequency of this allelic variant found, a DNA library of a case-control study of lung cancer (162 controls and 177 patients) was studied. There is no significant association between (1721)(G/A), (157)(G/A) and lung cancer: (1721)(G/A) and (157)(G/A) were detected at the same allele frequency of 0.086 and 0.25, respectively in both controls and patients. (2417)(A/G) was found in only one control of 100 (allele frequency 0.005). Statistical analysis did not show any relationship between both (1721)(G/A) and (157)(G/A) polymorphisms found and CYP1A1 inducibility. Considering the rareness of the (2417)(A/G) allelic variant we were not able to evaluate its association with inducibility. In conclusion, none of the polymorphisms were found to play a key role in the CYP1A1 inducibility or in the susceptibility to develop lung cancer.

Genetic polymorphisms of cytochrome P450 2A6 in a case-control study on lung cancer in a French population

Cytochrome P450 2A6 (CYP2A6) is involved in the C-oxidation of nicotine and in the metabolic activation of tobacco nitrosamines. Recent data have suggested that CYP2A6 genetic polymorphisms might play a role in tobacco dependence and consumption as well as in lung cancer risk. However, the previously published studies were based on a genotyping method that overestimated the frequencies of deficient alleles, leading to misclassification for the CYP2A6 genotype. In this study, we genotyped DNA from 244 lung cancer patients and from 250 control subjects for CYP2A6 (wild-type allele CYP2A6*1, and two deficient alleles: CYP2A6*2, and CYP2A6*4, the latter corresponding to a deletion of the gene) using a more specific procedure. In this Caucasian population, we found neither a relation between genetically impaired nicotine metabolism and cigarette consumption, nor any modification of lung cancer risk related to the presence of defective CYP2A6 alleles (odds ratio = 1.1, 95% confidence interval = 0.7-1.9).

Structural characterization of a new variant of the CYP2A6 gene (CYP2A6*1B) apparently diagnosed as heterozygotes of CYP2A6*1A and CYP2A6*4C

During the course of investigating the frequency of a CYP2A6 whole deletion-type polymorphism (CYP2A6*4C) in Japanese, an unexpectedly large population of heterozygotes for CYP2A6*4C and the wild-type (CYP2A6*1A) was found. Cloning of a cDNA encoding CYP2A6 from the liver of individuals judged as heterozygotes for CYP2A6*4C and the CYP2A6*1A was carried out to identify the causal allele(s) responsible for a possible overestimation. A clone isolated from the liver cDNA library possessed 58 bp sequences in the 3'-untranslated region, which was replaced with the corresponding region of the CYP2A7 gene. The same gene conversion existed in the genomic DNA, indicating that the replacement was not a cloning artifact. Based on the gene structure of the allele (CYP2A6*1B), this variant was thought to be one of the causal alleles responsible for overestimation of heterozygotes for CYP2A6*4C and CYP2A6* A. To investigate this further, we developed a genotyping method which could distinguish the CYP2A6*A, CYP2A6*1B and CYP2A6*4C alleles from each other. The results clearly showed that CYP2A6*1B was the sole allele responsible for the overestimation. We conclude that the new genotyping method allows determination of six genotypes of the CYP2A6 gene, simultaneously and precisely, in both Oriental and Caucasian populations.

Relation between inducibility of CYP1A1, GSTM1 and lung cancer in a French population

Smoking is the principal cause of lung cancer. However, not all smokers will develop this disease. Individual susceptibility to chemically induced cancer may be explained in part by genetic differences in the activation and detoxification of procarcinogens. The activation phase of polycyclic aromatic hydrocarbon (PAH) metabolism is governed by the enzyme CYP1A1, induced by PAH when it enters the body. The extent to which PAH induces CYP1A1 activity varies greatly from one subject to another. CYP1A1 inducibility has long been associated, although inconsistently, with an increased risk of lung cancer. In 1982, Kouri corroborated Kellerman's results with a new method for measuring inducibility, but few studies have reported using this method. The glutathione S-transferases (GSTs) are involved in the detoxification phase of PAH, and the allelic deletion of GSTM1 has been also associated with an increased risk of lung cancer. We conducted a case-control study to examine the risk of lung cancer related, separately and together, to CYP1A1 inducibility, GSTM1 polymorphism and cigarette smoking in a French population. The 611 subjects were 310 incident lung cancer cases and 301 hospital control subjects. We were able to constitute a DNA bank for 552 subjects (89.5%) and gather detailed information on smoking history for all of them. Inducibility could be measured for 195 cases and 183 control subjects. Results for GSTM1 polymorphism concern 247 cases and 254 control subjects. GSTM1 polymorphism and inducibility could both be assessed for 179 cases and 166 control subjects. The odds ratio related to inducibility was 1.7 [1.0-3.0] for medium and 3.1 (1.3-7.4) for hyper inducers. The association with GSTM1 was 1.6 (1.0-2.6). With a reference category of subjects who were both low inducers and GSTM1(+), we found an odds ratio for lung cancer of 8.1 (2-31) for the subjects with both risk factors [i.e. GSTM1(-) and hyper inducers]. Our data did not reveal evidence of interaction between smoking and inducibility. On the other hand, we found an interaction of 3.6 (0.6-21) between inducibility and GSTM1.

GSTM1, smoking and lung cancer: a case-control study

BACKGROUND

We conducted a case-control study to examine the risk of lung cancer in relation to GSTM1 polymorphism and cigarette smoking (primarily of black tobacco) in a French population.

METHODS

The 611 subjects were 301 incident lung cancer cases and 310 hospital controls. We were able to constitute a DNA bank for 547 subjects (89.5%) and gather detailed information on smoking history for all of them. Results presented here concern 247 cases and 254 controls.

RESULTS

Taking non- or light smokers as the reference category, we estimated odds ratios (OR) of 4.2 (95% CI: 2.6-6.7) and 5.2 (95% CI: 3.3-8.3) for the medium and heavy smokers respectively. On the other hand we estimated that the crude OR associating GSTM1 with lung cancer was 1.3 (95% CI: 0.9-1.8). Furthermore our data do not depart significantly from a multiplicative model of the combined effects of smoking and GSTM1 deficiency.

CONCLUSIONS

We conclude that smoking and the GSTM1 gene are each a risk factor for lung cancer, and that their combined effect does not differ significantly from that of a multiplicative model.

Cytochrome P450 CYP2D6 gene polymorphism and lung cancer susceptibility in Caucasians

Many studies have been performed in an attempt to establish a link between the polymorphism of the cytochrome P450 CYP2D6 gene and the incidence of lung cancer. Nevertheless, whether or not this genetic polymorphism has a role in the development of the disease remains unclear. Recently, new advances in our knowledge of the CYP2D6 gene and its locus (CYP2D) have been achieved. In particular, CYP2D6 was found to be highly polymorphic and multiple novel mutations and allelic variants of the gene have been identified. In addition, a number of CYP2D rearrangements, including those with amplification of the gene, have been demonstrated. Taking this new information into account, we have reconsidered the potential influence of CYP2D6 polymorphism in lung cancer susceptibility by performing a comparative analysis of the overall mutational spectrum of CYP2D6 and of the rearrangements of CYP2D in 249 patients with lung cancer and in 265 control individuals matched on age, sex, hospital and residence area. For this purpose, a strategy based on SSCP analysis of the entire coding sequence of CYP2D6 and on RFLP analysis of the gene locus was carried out in DNA samples from each individual. Forty mutations occurring in various combinations on 42 alleles of the gene and 82 different genotypes were identified. No significant difference in the distribution of the mutations, alleles or genotypes was observed between the two groups, except a particular genotype (CYP2D6*1A/*2), which was more common in the sub-group of moderate smokers (< 30 pack-years) suffering from small cell carcinoma (Odds Ratio (OR) 3.6, 95% CI 1.1-11.9). When the phenotype was predicted according to genotype, only a trend toward a higher frequency of ultrarapid metabolizers in patients was obtained. In spite of a complete analysis of the CYP2D6 gene and its locus, this case-control study provides elements against an influence of the CYP2D6 polymorphism on lung cancer susceptibility.

CYP2D6 genotype and lung cancer risk according to histologic type and tobacco exposure

Polymorphism for CYP2D6 was determined genetically as part of a hospital-based case-control study. The cases were males with a histologically confirmed lung cancer diagnosis, < 75 years old, and no previous cancer diagnosis. Male controls were matched for age, hospital and residence area. This study includes 301 cases and 310 controls. A DNA bank was established for 547 patients (89.5%), and genotypes for CYP2D6 were differentiated by the Heim and Meyer method for the DNA samples of 249 cases and 271 controls. Among the cases, the frequencies of homozygous for the wild-type (EM), heterozygous (HEM) and homozygous for the mutant alleles (PM) were 62%, 32% and 7%; among the controls: 57%, 37% and 6%. Using EM as the reference, and adjusting for age, hospital and residence, we estimated the odds ratios for the HEM group and the PM group at 0.8 (95% CI [0.5-1.2]) and 1.1 (95% CI [0.5-2.4]) respectively. The PM frequency among the cases of adenocarcinoma was twice as high as among the controls (OR = 1.8, 95% CI [0.7-4.9]). This result was not observed among squamous and small cell carcinoma (OR = 0.7, 95% CI [0.3-1.8]). Twelve different case-control studies on CYP2D6 and lung cancer have so far been performed; the ORs they estimate range from 0.1 to 2.0, with a median value of approximately 0.6. This result lends some support to the hypothesis that belonging to the PM group is associated with a slight protective effect against lung cancer, but does not take into account the possibility that results may vary according to histologic type. In this context, the suggestion of a positive relationship between CYP2D6 and adenocarcinoma seems to us to merit investigation.

Relationship between birthweight and occupational exposure to cytostatic drugs during or before pregnancy

The birthweight of babies whose mothers were exposed to cytostatic drugs during pregnancy was compared with that of infants whose mothers were not so exposed. The study was conducted in four French hospitals and covered 420 singleton live births to 466 women. One hundred and seven of the 420 births were exposed before or during pregnancy; 298 were not. Information about exposure was not available for the other 15. The mean birthweight of the babies of exposed mothers was 85 g lower than that of infants of unexposed mothers, but the difference was not statistically significant (95% CI -192.2-22.2 g). When gestational age and conventional risk factors were taken into account, the adjusted difference in the means of the birthweights was -56 (95% CI -155.1-43.1) g.

Retrospective evaluation of the exposure to polycyclic aromatic hydrocarbons: comparative assessments with a job exposure matrix and by experts in industrial hygiene

This work aimed at assessing the validity of job exposure matrix (JEM) for the retrospective evaluation of exposure to polycyclic aromatic hydrocarbons (PAH) within the framework of population-based case-control studies, taking the evaluation of industrial hygiene experts as reference. For this purpose, we used a case-control study for which the different levels of exposure were assessed by such experts after case by case evaluation of all job periods reported by the subjects. The JEM was applied to this set of data so that we had, according to job periods, the experts' evaluation on the one hand, and the JEM evaluation on the other. JEM sensitivity and specificity of the matrix vary widely from 0.13 to 0.96 and 0.58 to 0.99 respectively, depending on whether the experts chose a narrow or wide definition of exposure and on the cutoff point chosen to dichotomize the JEM. We also computed, according to the sensitivity and specificity of the JEM, the odds ratio (OR) and relative efficiency (RE) given by the JEM for several hypothetical OR and frequencies of exposure among the controls. These calculations were made for different definitions of exposure by the experts and different cutoff points for the JEM. The results show a bias in the JEM's evaluation of the OR. In addition, the RE varies widely from very low values to high values (0.05-0.45) depending on the experts' definition of exposure and the cutoff point chosen for the matrix. Note, however, that all these calculations were made taking the experts' evaluation as the reference.(ABSTRACT TRUNCATED AT 250 WORDS)

Risk of spontaneous abortion among nurses handling antineoplastic drugs

The purpose of the study was to evaluate the frequency of spontaneous abortion in two groups of women. One group consisted of women regularly involved in the preparation of cancer chemotherapy perfusions and therefore considered to be exposed to cytostatic agents; the other consisted of women not occupationally exposed to such agents. The study was carried out in four French hospitals. Four hundred and sixty-six women were involved; 534 pregnancies were described in which 139 were exposed and 357 were unexposed. The results showed that the frequency of spontaneous abortion was 26% for the exposed pregnancies and 15% in the unexposed ones (odds ratio 2.0). These results do not seem to be due either to the classic risk factors of spontaneous abortion (age, cigarette consumption during pregnancy, pregnancy order) (adjusted odds ratio 1.7) or to possible errors concerning the retrospective evaluation of prior gynecologic and obstetric history.

Comparison of relative risks obtained in ecological and individual studies: some methodological considerations

This paper is concerned with the problem of estimating relative risks from ecological correlation studies. In the first part, some of the biases encountered when analysing aggregated data are discussed and in particular attention is focused on the shape of the dose-response relationship obtained from aggregated and non-aggregated data, on the need for extrapolation and on the scale of aggregation. In the second part some empirical observations are made on these points by means of four examples concerning the relative risk between smoking and different pathologies. The estimates of relative risks derived from French geographical data and from case control or cohort studies are compared. The performance of ecological studies is discussed with respect to the strength of the risk factor considered, the geographical distribution of counfounding factors and the adjustment of different models.