Occupation as a risk factor of small cell lung cancer.

Small cell lung cancer (SCLC) comprises approximately 10% of all lung cancer cases. Tobacco is its main risk factor; however, occupation might play a role in this specific lung cancer subtype. The effect of occupation on SCLC risk has been hardly studied and therefore we aim to assess the role of occupation on the risk of SCLC. To do this, we designed a multicentric, hospital-based, case-control study. Cases consisted exclusively in SCLC patients and controls were recruited from patients having minor surgery at the participating hospitals. Face to face interviews emphasizing occupation and tobacco consumption were held and residential radon was also measured. Logistic regression models were adjusted with odds ratios with 95%CI as estimations of the effect. 423 cases and 905 controls were included. Smoking prevalence was higher in cases compared to controls. Those who worked in known-risk occupations for lung cancer showed an OR of 2.17 (95%CI 1.33; 3.52), with a similar risk when men were analysed separately. The results were adjusted by age, sex, smoking and indoor radon exposure. Those who worked in known-risk occupations and were moderate or heavy smokers had a SCLC risk of 12.19 (95%CI 5.68-26.38) compared with never or moderate smokers who had not worked in such occupations. Occupation is a relevant risk factor of SCLC, and it seems that its effect is boosted when tobacco smoking is present.

Residential Radon and Small Cell Lung Cancer. Final Results of the Small Cell Study.

INTRODUCTION: Residential radon is considered the second cause of lung cancer and the first in never smokers. Nevertheless, there is little information regarding the association between elevated radon levels and small cell lung cancer (SCLC). We aimed to assess the effect of residential radon exposure on the risk of SCLC in general population through a multicentric case-control study. METHODS: A multicentric hospital-based case-control study was designed including 9 hospitals from Spain and Portugal, mostly including radon-prone areas. Indoor radon was measured using Solid State Nuclear Track Detectors at the Galician Radon Laboratory. RESULTS: A total of 375 cases and 902 controls were included, with 24.5% of cases being women. The median number of years living in the measured dwelling was higher than 25 years for both cases and controls. There was a statistically significant association for those exposed to concentrations higher than the EPA action level of 148Bq/m3, with an Odds Ratio of 2.08 (95%CI: 1.03-4.39) compared to those exposed to concentrations lower than 50Bq/m3. When using a dose-response model with 100Bq/m3 as a reference, it can be observed a linear effect for small cell lung cancer risk. Smokers exposed to higher radon concentrations pose a much higher risk of SCLC compared to smokers exposed to lower indoor radon concentrations. CONCLUSIONS: Radon exposure seems to increase the risk of small cell lung cancer with a linear dose-response pattern. Tobacco consumption may also produce an important effect modification for radon exposure.

Radon, Tobacco Exposure and Non-Small Cell Lung Cancer Risk Related to BER and NER Genetic Polymorphisms.

INTRODUCTION: Tobacco consumption and radon exposure are considered the first and second most common causes of lung cancer, respectively. The aim of this study was to analyze both whether selected genetic polymorphisms in loci that are in DNA repair pathways, are related to non-small-cell lung cancer (NSCLC) and whether they may modulate the association between residential radon exposure and lung cancer in both smokers and never smokers. METHODS: A multicentre, hospital-based, case-control study with 826 cases and 1201 controls was designed in a radon-prone area. Genotyping was determined in whole blood and residential radon exposure was measured in participants' dwellings. RESULTS: Attending to tobacco exposure, the variant in the gene NBN (rs1805794) was associated with lung cancer in never smokers (OR 2.72; 95%1.44-5.2) and heavy smokers (OR 3.04; 95%CI 1.21-7.69). The polymorphism with the highest lung cancer association was OGG1 (rs125701), showing an OR of 8.04 (95%CI 1.64-58.29) for its homozygous variant genotype in heavy smokers. Attending to indoor radon exposure (>200Bq/m3), rs1452584, for its homozygous variant genotype, showed the highest association (OR 3.04 (95%CI 1.15-8.48). CONCLUSION: The genes analyzed seem to have no association with the fully adjusted model, but they might modulate lung cancer association when different categories of tobacco consumption are considered (i.e. heavy smokers). This association may similarly be elevated for those individuals having high indoor radon exposures, though at a minor extent.

Fruits and Vegetables and Lung Cancer Risk in Never Smokers. A Multicentric and Pooled Case-Control Study.

BACKGROUND: The etiology of lung cancer in never smokers is partly unknown. We aimed to assess the effect of fruits and vegetables consumption on lung cancer risk in never smokers. METHODS: We pooled five multicenter case-control studies performed in Northwestern Spain. Cases and controls were all never smokers. All lung cancer cases had anatomopathological confirmed diagnoses. We performed a multivariate logistic regression to analyze the effect of different types of fruits and vegetables consumption on lung cancer risk. RESULTS: A total of 438 cases and 781 controls were included. We observed that a consumption from one to six times per week shows a negative association with lung cancer risk for: kiwis (OR 0.67; 95%CI 0.46-0.95), oranges (OR 0.55; 95%CI 0.37-0.80), turnip tops (OR 0.48; 95%CI 0.34-0.66), "berza gallega" (OR 0.70; 95%CI 0.51-0.97) and broccoli (OR 0.55; 95%CI 0.35-0.83) compared to less than once a week consumption. On the other hand, we found an increased risk for lung cancer with a daily consumption of tomatoes, carrots and potatoes. CONCLUSIONS: Oranges, kiwis, turnip tops, berza gallega and broccoli may play a protective role on lung cancer development in never smokers while tomatoes, carrots and potatoes might have some association with this disease.

Residential radon and lung cancer characteristics at diagnosis.

PURPOSE: This study sought to ascertain whether there might be an association between radon concentrations and age, gender, histologic type, and tumor stage at diagnosis. MATERIALS AND METHODS: Lung cancer cases from different multicenter case-control studies were analyzed, and clinical data were retrieved from electronic health records and personal interviews. A radon device was placed in all dwellings of participants, and we then tested the existence of an association between residential radon and lung cancer characteristics at diagnosis. RESULTS: Of the total of 829 lung cancer cases included, 56.7% were smokers or ex-smokers. There was no association between indoor radon concentrations and age, gender, histologic type or tumor stage at diagnosis. Median indoor radon concentrations increased with age at diagnosis for men, but not for women. When analyzing participants exposed to more than 1000 Bq/m3, a predominance of small cell lung cancer and a higher presence of advanced stages (IIIB and IV) were observed. CONCLUSIONS: There seems to be no association between radon and age, gender, histologic type or tumor stage at diagnosis. Higher radon exposure is more frequent in the case of small-cell lung cancer.

Residential Radon and Small Cell Lung Cancer. Final Results of the Small Cell Study.

INTRODUCTION: Residential radon is considered the second cause of lung cancer and the first in never smokers. Nevertheless, there is little information regarding the association between elevated radon levels and small cell lung cancer (SCLC). We aimed to assess the effect of residential radon exposure on the risk of SCLC in general population through a multicentric case-control study. METHODS: A multicentric hospital-based case-control study was designed including 9 hospitals from Spain and Portugal, mostly including radon-prone areas. Indoor radon was measured using Solid State Nuclear Track Detectors at the Galician Radon Laboratory. RESULTS: A total of 375 cases and 902 controls were included, with 24.5% of cases being women. The median number of years living in the measured dwelling was higher than 25 years for both cases and controls. There was a statistically significant association for those exposed to concentrations higher than the EPA action level of 148Bq/m3, with an Odds Ratio of 2.08 (95%CI: 1.03-4.39) compared to those exposed to concentrations lower than 50Bq/m3. When using a dose-response model with 100Bq/m3 as a reference, it can be observed a linear effect for small cell lung cancer risk. Smokers exposed to higher radon concentrations pose a much higher risk of SCLC compared to smokers exposed to lower indoor radon concentrations. CONCLUSIONS: Radon exposure seems to increase the risk of small cell lung cancer with a linear dose-response pattern. Tobacco consumption may also produce an important effect modification for radon exposure.

Polymorphisms in the BER and NER pathways and their influence on survival and toxicity in never-smokers with lung cancer.

Polymorphisms in DNA repair pathways may play a relevant role in lung cancer survival in never-smokers. Furthermore, they could be implicated in the response to chemotherapy and toxicity of platinum agents. The aim of this study was to evaluate the influence of various genetic polymorphisms in the BER and NER DNA repair pathways on survival and toxicity in never-smoker LC patients. The study included never-smokers LC cases diagnosed from 2011 through 2019, belonging to the Lung Cancer Research In Never Smokers study. A total of 356 never-smokers cases participated (79% women; 83% adenocarcinoma and 65% stage IV). Survival at 3 and 5 years from diagnosis was not associated with genetic polymorphisms, except in the subgroup of patients who received radiotherapy or chemo-radiotherapy, and presented with ERCC1 rs3212986 polymorphism. There was greater toxicity in those presenting OGG1 rs1052133 (CG) and ERCC1 rs11615 polymorphisms among patients treated with radiotherapy or chemo-radiotherapy, respectively. In general, polymorphisms in the BER and NER pathways do not seem to play a relevant role in survival and response to treatment among never-smoker LC patients.

Lung cancer risk and residential radon exposure: A pooling of case-control studies in northwestern Spain.

BACKGROUND: Through a pooled case-control study design, we have assessed the relationship between residential radon exposure and lung cancer risk. Other objectives of the study were to evaluate the different risk estimates for the non-small cell lung cancer histological types and to assess the effect modification of the radon exposure on lung cancer risk by tobacco consumption. METHODS: We collected individual data from various case-control studies performed in northwest Spain that investigated residential radon and lung cancer. Cases had a confirmed anatomopathological diagnosis of primary lung cancer and controls were selected because they were undergoing ambulatory evaluation or surgical procedures that were unrelated to tobacco use. Residential radon was measured using alpha track detectors. Results were analyzed using logistic regression. RESULTS: 3704 participants were enrrolled, 1842 cases and 1862 controls. Data show that lung cancer risk increases with radon exposure, finding a significant association of radon exposure with lung cancer at radon exposures above 50 Bq/m3. The estimated adjusted OR for individuals exposed to concentrations >200 Bq/m3 was 2.06 (95% CI: 1.61-2.64) compared with those exposed to ≤50 Bq/m3. Within a smoking category, lung cancer risk increases markedly as radon concentration increases, reaching an OR of 29.3 (95% CI: 15.4-55.7) for heavy smokers exposed to more than 200 Bq/m.3 CONCLUSIONS: This study confirms that residential radon exposure is a risk factor for lung cancer well below action levels established by international organizations. As expected, there is also an effect modification between radon exposure and tobacco consumption.

Lung cancer survival in never-smokers and exposure to residential radon: Results of the LCRINS study.

We aimed to evaluate lung cancer survival in never-smokers, both overall and specifically by sex, exposure to residential-radon, age, histological type, and diagnostic stage. We included lung cancer cases diagnosed in a multicentre, hospital-based, case-control-study of never-smoker patients, diagnosed from January-2011 to March-2015 (Lung Cancer Research In Never Smokers study). 369 never-smokers (79% women; median age 71 years; 80% adenocarcinoma; 66% stage IV) were included. Median overall survival, and at one, 3 and 5 years of diagnosis was 18.3 months, 61%, 32% and 22%, respectively. Higher median survival rates were obtained for: younger age, adenocarcinoma, actionable mutations, and earlier-stage at diagnosis. Higher indoor radon showed a higher risk of death in multivariate analysis. Median lung cancer survival in never-smokers seems higher than that in ever-smokers. Patients with actionable mutations have a significantly higher survival. Higher indoor-radon exposure has a negative effect on survival.

Lung cancer risk and do-it-yourself activities. A neglected risk factor for lung cancer.

BACKGROUND: The aim of this study was to assess the relationship between do-it-yourself activities entailing the exposure to carcinogenic substances and the risk of lung cancer. METHODS: We pooled individual data from different case-control studies conducted in Northwestern Spain which investigated residential radon and lung cancer. Cases had an anatomopathologically confirmed primary lung cancer and controls were selected at the pre-surgery unit with uncomplicated surgeries. Both cases and controls were older than 30 years with no previous cancer history. All participants were interviewed face-to-face using a specific questionnaire. Painting, model building, furniture refinishing and woodworking or home carpentry were the do-it-yourself activities considered risky due to exposure to carcinogenic agents. RESULTS: We included 1528 cases and 1457 controls. Practicing do-it-yourself risk activities was more frequent among cases: 16.0% were exposed to carcinogenic exposures during leisure time, compared to 11.8% for controls. The overall adjusted OR for lung cancer risk among individuals who practiced do-it-yourself risk activities, was 1.77 (95% CI: 1.36-2.31); this was 2.17 (95% CI: 1.51-3.11) when the analysis was restricted to individuals who performed these activities for at least 10 years. These risks were greater when the analyses were carried out exclusively among never-smokers, with the respective ORs being 2.04 (95% CI: 1.38-3.01) and 3.10 (95% CI: 1.78-5.40). CONCLUSION: These results support the hypothesis that do-it-yourself activities involving exposure to certain carcinogens are associated with an increased risk of lung cancer, both in ever and never-smokers.

Residential radon, genetic polymorphisms in DNA damage and repair-related.

OBJECTIVES: To analyze the relationship of GSTT1, GSTM1, XRCC1 (rs25487), ERCC1 (rs11615, rs3212986), ERCC2 (rs13181), XRCC3 (rs861539), OGG1 (rs1052133), and Alpha-1-Antitrypsin mutations (AAT) with the risk of lung cancer in never-smokers, and ascertain if there is an effect modification between these polymorphisms and residential radon exposure. MATERIAL AND METHODS: We designed a multicenter hospital-based case-control study in a radon-prone area. 322 cases and 338 controls, all never-smokers, were included. They were selected using a frequency sampling based on sex and age distribution of the cases. Participants donated 3 ml. of whole blood used to determine genotype for polymorphisms. They placed a radon detector to measure residential radon exposure in their dwelling. RESULTS: The OR for deleted GSTM1 patients was 3.46 (95% CI = 1.52-7.89) at residential radon exposures above 200 Bq/m3. The ERCC1 rs3212986 polymorphism was the most associated with the risk of developing lung cancer, both for low and high radon exposures. The ERCC1 rs321986 GT and TT genotypes (at radon concentrations >200 Bq/m3) were more significantly associated with higher lung cancer risk (OR = 2.40, 95% CI = 1.29-4.45; OR = 4.45, 95% CI = 1.26-15.7, respectively). CONCLUSIONS: These findings support the hypothesis that certain polymorphisms in genes involved in DNA-repair and carriers of GSTM1 deletion have an increased risk of lung cancer in never-smokers exposed to residential radon.

Lung cancer and residential radon in never-smokers: A pooling study in the Northwest of Spain.

BACKGROUND: Using a pooled case-control study design, including only never-smokers, we have assessed the association of residential radon exposure with the subsequent occurrence of lung cancer. We also investigated whether residential radon poses a different risk specifically for adenocarcinoma. METHODS: We pooled individual data from different case-control studies conducted in recent years in Northwestern Spain which investigated residential radon and lung cancer. All participants were never-smokers. Cases had a confirmed biopsy of primary lung cancer. Hospital controls were selected at pre-surgery units, presenting for non-complex surgical procedures. They were interviewed using a standardized instrument. Residential radon was measured using alpha track detectors at the Galician Radon Laboratory at the University of Santiago de Compostela. RESULTS: A total of 1415 individuals, 523 cases and 892 controls were included. We observed an odds ratio of 1.73 (95%CI: 1.27-2.35) for individuals exposed to ≥ 200 Bq/m3 compared with those exposed to ≤100 Bq/m3. Lung cancer risk for adenocarcinoma was 1.52 (95%CI: 1.14-2.02) using the same categories for radon exposure. CONCLUSIONS: Residential radon is a clear risk factor for lung cancer in never-smokers. Our data suggest that radon exposure is associated with all histological types of lung cancer and also with adenocarcinoma, which is currently the most frequent histological type for this disease.

Chronic Obstructive Pulmonary Disease in Lung Cancer Patients: Prevalence, Underdiagnosis, and Clinical Characterization.

BACKGROUND: Lung cancer (LC) and chronic obstructive pulmonary disease (COPD) are associated with increased morbidity and mortality. The differential clinical and functional features among LC patients with or without COPD have not been defined. OBJECTIVES: The aims of this study were to examine the prevalence and underdiagnosis rate of COPD in LC patients and to compare the clinical and functional features of LC patients with and without COPD. METHODS: We designed a multicenter hospital-based study including all LC cases diagnosed from January 2014 to August 2016. We assessed epidemiological, clinical, radiological, functional, and histological variables in all cases. RESULTS: We recruited 602 patients with LC, most of them men (77.9%), with a median age of 67 ± 15 years. The COPD prevalence among LC patients was 51.5%, with a underdiagnosis rate of 71.6%. The LC+COPD patients were older and the proportion of men was higher compared with the LC-only patients. The LC+COPD patients had more pack-years, more squamous LC, a lower monoxide transfer coefficient (KCO), and higher Charlson index scores than patients with LC only. The median survival of LC-only patients was 37% longer than that of LC+COPD patients (22 vs. 16 months), but this difference was not statistically significant. CONCLUSIONS: Among LC patients, COPD is prevalent and underdiagnosed. Patients with LC+COPD more often have squamous LC, have greater comorbidities, and have a lower KCO. More effort should be made for an early diagnosis of COPD to select patients at higher risk of developing LC.

Alcohol consumption and lung cancer risk in never smokers: a pooled analysis of case-control studies.

Background: Lung cancer is the deadliest cancer in developed countries but the etiology of lung cancer risk in never smokers (LCRINS) is largely unknown. We aim to assess the effects of alcohol consumption, in its different forms, on LCRINS. Methods: We pooled six multi-center case-control studies developed in the northwest of Spain. Cases and controls groups were composed of never smokers. We selected incident cases with anatomopathologically confirmed lung cancer diagnoses. All participants were personally interviewed. We performed two groups of statistical models, applying unconditional logistic regression with generalized additive models. One considered the effect of alcohol type consumption and the other considered the quantity of each alcoholic beverage consumed. Results: A total of 438 cases and 863 controls were included. Median age was 71 and 66, years, respectively. Adenocarcinoma was the predominant histological type, comprising 66% of all cases. We found that any type of wine consumption posed an OR of 2.20 OR 95%CI 1.12-4.35), and spirits consumption had an OR of 1.90 (95%CI 1.13-3.23). Beer consumption had an OR of 1.33 (95%CI 0.82-2.14). These results were similar when women were analyzed separately, but for men there was no apparent risk for any alcoholic beverage. The dose-response analysis for each alcoholic beverage revealed no clear pattern. Conclusions: Wine and spirits consumption might increase the risk of LCRINSs, particularly in females. These results have to be taken with caution given the limitations of the present study.

Environmental tobacco smoke exposure and EGFR and ALK alterations in never smokers' lung cancer. Results from the LCRINS study.

Environmental tobacco smoke (ETS) exposure is a main risk factor of lung cancer in never smokers. Epidermal Growth Factor Receptor (EGFR) mutations and ALK translocations are more frequent in never smokers' lung cancer than in ever-smokers. We performed a multicenter case-control study to assess if ETS exposure is associated with the presence of EGFR mutations and its types and if ALK translocations were related with ETS exposure. All patients were never smokers and had confirmed lung cancer diagnosis. ETS exposure during childhood showed a negative association on the probability of EGRF mutation though not significant. Exposure during adulthood, at home or at workplace, did not show any association with EGFR mutation. The mutation type L858R seemed the most associated with a lower probability of EGFR alterations for ETS exposure at home in adult life. There is no apparent association between ETS exposure and ALK translocation. These results might suggest that ETS exposure during childhood or at home in adult life could influence the EGFR mutations profile in lung cancer in never smokers, reducing the probability of presenting EFGR mutation.

Small Cell Lung Cancer. Methodology and Preliminary Results of the SMALL CELL Study. / Cáncer de pulmón microcítico. Metodología y resultados preliminares del estudio SMALL CELL.

INTRODUCTION: Small cell lung cancer (SCLC) is the most aggressive histologic type of lung cancer, and accounts for approximately 10%-15% of all cases. Few studies have analyzed the effect of residential radon. Our aim is to determine the risk factors of SCLC. METHODS: We designed a multicenter, hospital-based case-control study with the participation of 11 hospitals in 4 autonomous communities. RESULTS: Results of the first 113 cases have been analyzed, 63 of which included residential radon measurements. Median age at diagnosis was 63 years; 11% of cases were younger than 50 years of age; 22% were women; 57% had extended disease; and 95% were smokers or former smokers. Median residential radon concentration was 128Bq/m3. Concentrations higher than 400Bq/m3 were found in 8% of cases. The only remarkable difference by gender was the percentage of never smokers, which was higher in women compared to men (P<.001). Radon concentration was higher in patients with stageIV disease (non-significant difference) and in individuals diagnosed at 63 years of age or older (P=.032). CONCLUSIONS: A high percentage of SCLC cases are diagnosed early and there is a predominance of disseminated disease at diagnosis. Residential radon seems to play an important role on the onset of this disease, with some cases having very high indoor radon concentrations.

Residential radon, EGFR mutations and ALK alterations in never-smoking lung cancer cases.

The aim of this study was to assess if residential radon exposure might cause EGFR mutations or ALK rearrangements in never-smokers.We designed a multicentre case-control study in a radon-prone area (Galicia, Spain); only lung cancer cases were included in the study. We obtained residential radon measurements and clinical information for all the participants. We compared the median values of residential radon between patients with EGFR mutations or ALK rearrangements versus those without them.323 patients were included. Median age was 70 years and 19.5% were males. 42 and 15% of patients were EGFR- and ALK-positive, respectively. The most frequent EGFR alterations were exon 19 deletions and exon 21 (L858R) single-point substitution mutations. ALK-positive patients were 10 years younger than ALK-negative patients. Residential radon levels were two-fold higher in patients with exon 19 deletions compared with patients with exon 21 (L858R) single-point substitution mutations (216 versus 118 Bq·m-3; p=0.057). There were no differences in residential radon levels by EGFR mutation status. ALK-positive patients (n=12) essentially had two-fold residential radon levels compared with ALK-negative patients (290 versus 164 Bq·m-3, respectively).Residential radon may have a role in the molecular signature of lung cancer in never-smokers, although more studies with larger sample sizes are needed to support this hypothesis.

Small cell lung cancer in never-smokers.

Our aim was to describe the characteristics of a case-series of never-smoker small cell lung cancer (SCLC) cases.Cases of SCLC were selected from a prospective, multicenter, hospital-based case-control study performed in Spain. Participants were never-smokers older than 30 years with an anatomo-pathological confirmation of primary lung cancer. We collected clinical and epidemiological variables according to the study's protocol.We included 19 SCLC cases, 18 females (94.7%), median age 75 years (interquartile range (IQR) 70-80 years). Median residential radon concentration was 195 Bq·m(-3) (IQR 130-229 Bq·m(-3)). 10 patients had limited disease and nine had extended disease. Median survival was 242 days (IQR 94-496 days); 1- and 2-year survival were 36.8% and 17.6%, respectively. Survival was much higher for individuals with limited disease than for those with extended disease (median 336 versus 235 days; 1-year survival 50% versus 22.2% and 2-year survival 27% versus 0%, respectively). Performance status at diagnosis was closely related to survival.SCLC is an infrequent, highly aggressive disease in never-smokers. Survival is poor, even for limited disease. Age at diagnosis in SCLC is higher than that observed for never-smokers with adenocarcinoma. Residential radon exposure is higher than the action levels recommended by the World Health Organization.

Alpha-1 Antitrypsin Deficiency and Lung Cancer Risk: A Case-Control Study in Never-Smokers.

BACKGROUND: Never-smokers comprise up to 25% of all lung cancer cases. They could have different molecular pathways for lung cancer induction compared with smokers. Alpha-1 antitrypsin (AAT) deficiency is a hereditary trait whose main characteristic is early onset of lung emphysema. Our aim is to know if AAT-deficient carriers have a higher risk of lung cancer in a study performed exclusively in never-smokers. METHODS: We designed a multicentre hospital-based case-control study, which included incident never-smoking lung cancer cases. Controls were never-smokers attending nonmajor surgery at the participating hospitals. Controls were frequency matched on age and gender with cases. We determined AAT variants (alleles S and Z) through polymerase chain reaction. RESULTS: Two hundred and twelve cases and 318 controls were included. PiSS individuals showed a lung cancer risk of 4.64 (95% confidence interval: 1.08-19.92) compared with those with normal genotype (PiMM). When the analysis was restricted to women, the risk for PiSS increased to 7.58 (95% confidence interval: 1.40-40.87). This risk for homozygous SS was even higher for individuals exposed to environmental tobacco smoke (greater than 20 years). The presence of other alleles did not show any effect on lung cancer risk. CONCLUSIONS: Never smoking SS homozygous individuals pose an increased risk of lung cancer. The risk is higher for individuals exposed to environmental tobacco smoke.