Differential effects of smoking on lung cancer mortality before and after household stove improvement in Xuanwei, China

Ellie A, Dong H, Ahmad UM. Health Effects of Exposure to Indoor Semi-Volatile Organic Compounds in Chinese Building Environment: A Systematic Review

People spend a considerable portion of their lives indoors; thus, the quality of the indoor environment is crucial. Semi-volatile organic compounds (SVOCs) are among the primary indoor pollutants responsible for various health risks. This paper systematically reviews the impact of SVOC exposure on human health in Chinese built environments. Based on a set of criteria, we judged 12 publications as providing sufficient information on both SVOC exposure and health effects to inform the relationship. Out of six studies on polycyclic aromatic hydrocarbons (PAHs), three observed a positive association between PAH exposure and lung cancer. Out of six studies of phthalate exposure, two studies reported a significant positive association between DEP and DiBP and asthma, between DEP and DEHP and dry cough among children, and between DBP and rhinitis among younger adults. The results of this review suggest that there might be a link between phthalate exposure and asthma and allergies, as well as a link between PAH exposure and lung cancer. However, due to the limited number of studies conducted, more evidence is necessary to definitively guide the establishment of standards for SVOC control in China.

Sub-multiplicative interaction between polygenic risk score and household coal use in relation to lung adenocarcinoma among never-smoking women in Asia

We previously identified 10 lung adenocarcinoma susceptibility loci in a genome-wide association study (GWAS) conducted in the Female Lung Cancer Consortium in Asia (FLCCA), the largest genomic study of lung cancer among never-smoking women to date. Furthermore, household coal use for cooking and heating has been linked to lung cancer in Asia, especially in Xuanwei, China. We investigated the potential interaction between genetic susceptibility and coal use in FLCCA. We analyzed GWAS-data from Taiwan, Shanghai, and Shenyang (1472 cases; 1497 controls), as well as a separate study conducted in Xuanwei (152 cases; 522 controls) for additional analyses. We summarized genetic susceptibility using a polygenic risk score (PRS), which was the weighted sum of the risk-alleles from the 10 previously identified loci. We estimated associations between a PRS, coal use (ever/never), and lung adenocarcinoma with multivariable logistic regression models, and evaluated potential gene-environment interactions using likelihood ratio tests. There was a strong association between continuous PRS and lung adenocarcinoma among never coal users (Odds Ratio (OR) = 1.69 (95% Confidence Interval (CI) = 1.53, 1.87), p=1 × 10-26). This effect was attenuated among ever coal users (OR = 1.24 (95% CI: 1.03, 1.50), p = 0.02, p-interaction = 6 × 10-3). We observed similar attenuation among coal users from Xuanwei. Our study provides evidence that genetic susceptibility to lung adenocarcinoma among never-smoking Asian women is weaker among coal users. These results suggest that lung cancer pathogenesis may differ, at least partially, depending on exposure to coal combustion products. Notably, these novel findings are among the few instances of sub-multiplicative gene-environment interactions in the cancer literature.

Analysis of the associations of indoor air pollution and tobacco use with morbidity of lung cancer in Xuanwei, China

BACKGROUND

Indoor air pollution emitted by smoky coal combustion in unventilated fire pits used to cause high lung cancer mortality in Xuanwei. Stove improvements were implemented from the 1970s to the 1980s. However, the present lung cancer mortality rate in Xuanwei shows almost no significant declining trend. Tobacco use is another established risk factor for lung cancer. Smoking prevalence and secondhand smoke (SHS) exposure rate are both high in Xuanwei. Therefore, in this study we evaluated the relationship among indoor air pollution over 30 years ago, tobacco use, and lung cancer risk, to further explore the competitive effects of these two risk factors.

METHODS

A case-control study design was used. We constructed an unconditional logistic regression model to evaluate the relationship among indoor air pollution, tobacco use, and lung cancer risk, adjusting the covariates and with an interactive term between the two key variables. We further quantitatively assessed the maximum decrease in the indoor air pollution effect when facing competition from tobacco use via a sensitivity analysis. First, the effect of indoor air pollution on lung cancer without considering tobacco use was estimated. Then, we calculated a "bias factor" and divided the effect estimation by this factor.

RESULTS

We found a strong delayed effect of indoor air pollution over 30 years ago in each subgroup with different tobacco use history. The effects of tobacco use were relatively small, but in areas without smoky coal combustion and indoor air pollution over 30 years prior, the lung cancer risk caused by tobacco use became much stronger and statistically significant. Moreover, we assessed that the effects of tobacco use on lung cancer could reduce a maximum of 18%-30% of the effects of indoor air pollution, but did not influence their statistical significance; the competitive effect from ever smoking was stronger than that from SHS exposure.

CONCLUSIONS

At present in Xuanwei, delayed effect of the indoor air pollution over 30 years ago remains the major risk factor for lung cancer. Concomitantly, the adverse effect of tobacco use on lung cancer is becoming more apparent; local governments should start considering public health activities for smoking cessation promotion and SHS exposure prevention.

Size-segregated emission factors and health risks of PAHs from residential coal flaming/smoldering combustion

Residential coal combustion is one of the main sources of ambient polycyclic aromatic hydrocarbons (PAHs). Updating its emission estimation is limited by the shortages of emission factors, especially for them in different particle sizes and from different combustion conditions. PAH emission factors (EFs) for nine size-segregated particle segments emitted from smoldering and flaming combustion of residential coals (four kinds of raw coals (RCs) and three kinds of honeycomb coal briquettes (HCBs)) were obtained in China, using a dilution sampling system. EFs of PAHs for the flaming and smoldering of HCB ranged from 1.32 to 2.04 mg kg^-1 and 0.35 to 5.36 mg kg^-1, respectively. The EFs of PAHs for RC flaming combustion varied from 0.50 to 218.96 mg kg^-1. About 53.5-96.4% and 47.4-90.9% of PAHs concentrated in PM_2.1 and PM_1.1, respectively. Different fuel types and combustion conditions strongly affected the PAH EFs. The PAH EF for the RC was 0.3 times that for HCB in Guizhou, which implied that PAH EFs for RC combustion were not always higher than those from HCB burning. For different combustion conditions, the PAH EFs from flaming were more than 2.5 times higher than those from smoldering for HCB except in the Anhui region. Results indicated that current PAH EFs may not be universal, which may bias the establishment of control policies for toxic pollutants emitted from domestic coal burning. On average, 73.2 ± 15.5% of total PAH potential toxicity risks were concentrated in submicron particles. More size-segregated PAH EFs for residential coal combustion should be investigated considering combustion conditions with a uniform sampling method in China.

Bituminous coal combustion and Xuan Wei Lung cancer: a review of the epidemiology, intervention, carcinogens, and carcinogenesis

Indoor air pollution from bituminous coal combustion has been linked to the extremely high lung cancer rates of nonsmoking women in Xuan Wei County, Yunnan Province, China. Venting the smoke outdoors by installing chimneys was found to be effective at reducing the lung cancer risk in a cohort study of 21,232 farmers in central Xuan Wei. However, the lung cancer mortality rates in all 1.2 million residents of Xuan Wei have been increasing dramatically over the last four decades. It was higher than that in Yunnan Province and China overall, with significant heterogeneities in the geographic patterns of Xuan Wei. Intervention measures targeting certain types of coal or certain carcinogenic components in coal smoke need to be explored. To inform targeted intervention policies, it is essential to pinpoint the specific substance (particulate matter, organic extract, PAHs, free radicals, crystalline silica, and inorganic matter) that might account for the carcinogenicity of bituminous coal smoke. Exploring the underlying carcinogenesis mechanisms would also contribute to the intervention and control of the lung cancer epidemic in Xuan Wei, China. Here we review the suspected carcinogens and carcinogenesis mechanisms and discuss future research directions towards a better understanding of the etiology of lung cancer in Xuan Wei, China.

Effectiveness of interventions to reduce household air pollution and/or improve health in homes using solid fuel in low-and-middle income countries: A systematic review and meta-analysis

BACKGROUND

Cookstove intervention programs have been increasing over the past two (2) decades in Low and Middle Income Countries (LMICs) across the globe. However, there remains uncertainty regarding the effects of these interventions on household air pollution concentrations, personal exposure concentrations and health outcomes.

OBJECTIVES

The primary objective was to determine if household air pollution (HAP) interventions were associated with improved indoor air quality (IAQ) in households in LMICs. Given the potential impact of HAP interventions on health, a secondary objective was to evaluate the effectiveness of HAP interventions to improve health in populations receiving these interventions.

DATA SOURCES

OVID Medline, Ovid Embase, SCOPUS and PubMED were searched from their inception until December 2015 with no restrictions on study design. The WHO Global database of household air pollution measurements and Members' archives were also reviewed together with the reference lists of identified reviews and relevant articles.

STUDY ELIGIBILITY CRITERIA, PARTICIPANTS AND INTERVENTION

We considered randomized controlled trials, or non-randomized control trials, or before-and-after studies; original studies; studies conducted in a LMIC (based on the United Nations Human Development Report released in March 2013 (World Bank, 2013); interventions that were explicitly aimed at improving IAQ and/or health from solid fuel use; studies published in a peer-reviewed journal or student theses or reports; studies that reported on outcomes which was indicative of IAQ or/and health. There was no restriction on the type of comparator (e.g. household receiving plancha vs. household using traditional cookstove) used in the intervention study.

STUDY APPRAISAL AND SYNTHESIS METHODS

Five review authors independently used pre-designed data collection forms to extract information from the original studies and assessed risk of bias using the Effective Public Health Practice Project (EPHPP). We computed standardized weighted mean difference (SMD) using random-effects models. Heterogeneity was computed using the Q and I2-statistics. We examined the influence of various characteristics on the study-specific effect estimates by stratifying the analysis by population type, study design, intervention type, and duration of exposure monitoring. The trim and fill method was used to assess the potential impact of missing studies.

RESULTS

Fifty-five studies met our a priori inclusion criteria and were included in the systematic review. Fifteen studies provided 43 effect estimates for our meta-analysis. The largest improvement in HAP was observed for average particulate matter (PM) (SMD=1.57) concentrations in household kitchens (1.03), followed by daily personal average concentrations of PM (1.18), and carbon monoxide (CO) concentrations in kitchens. With respect to personal PM, significant improvement was observed in studies of children (1.26) and studies monitoring PM for ≥24h (1.32). This observation was also noted in terms of studies of kitchen concentrations of CO. A significant improvement was also observed for kitchen levels of PM in both adult populations (1.56) and in RCT/cohort designs (1.59) involving replacing cookstoves without chimneys. Our findings on health outcomes were inconclusive.

LIMITATIONS, CONCLUSIONS AND IMPLICATIONS OF KEY FINDINGS

We observed high statistical between study variability in the study-specific estimate. Thus, care should be taken in concluding that HAP interventions - as currently designed and implemented - support reductions in the average kitchen and personal levels of PM and CO. Further, there is limited evidence that current stand-alone HAP interventions yield any health benefits. Post-intervention levels of pollutants were generally still greatly in excess of the relevant WHO guideline and thus a need to promote cleaner fuels in LMICs to reduce HAP levels below the WHO guidelines.

SYSTEMATIC REVIEW REGISTRATION NUMBER

The review has been registered with PROSPERO (registration number CRD42014009768).

Outdoor, indoor, and personal black carbon exposure from cookstoves burning solid fuels

Black carbon (BC) emissions from solid fuel combustion are associated with increased morbidity and mortality and are important drivers of climate change. We studied BC measurements, approximated by particulate matter (PM2.5 ) absorbance, in rural Yunnan province, China, whose residents use a variety of solid fuels for cooking and heating including bituminous and anthracite coal, and wood. Measurements were taken over two consecutive 24-h periods from 163 households in 30 villages. PM2.5 absorbance (PMabs ) was measured using an EEL 043 Smoke Stain Reflectometer. PMabs measurements were higher in wood burning households (16.3 × 10(-5) /m) than bituminous and anthracite coal households (12 and 5.1 × 10(-5) /m, respectively). Among bituminous coal users, measurements varied by a factor of two depending on the coal source. Portable stoves (which are lit outdoors and brought indoors for use) were associated with reduced PMabs levels, but no other impact of stove design was observed. Outdoor measurements were positively correlated with and approximately half the level of indoor measurements (r = 0.49, P < 0.01). Measurements of BC (as approximated by PMabs ) in this population are modulated by fuel type and source. This provides valuable insight into potential morbidity, mortality, and climate change contributions of domestic usage of solid fuels.

Cooking Coal Use and All-Cause and Cause-Specific Mortality in a Prospective Cohort Study of Women in Shanghai, China

BACKGROUND

Nearly 4.3 million deaths worldwide were attributable to exposure to household air pollution in 2012. However, household coal use remains widespread.

OBJECTIVES

We investigated the association of cooking coal and all-cause and cause-specific mortality in a prospective cohort of primarily never-smoking women in Shanghai, China.

METHODS

A cohort of 74,941 women were followed from 1996 through 2009 with annual linkage to the Shanghai vital statistics database. Cause-specific mortality was identified through 2009. Use of household coal for cooking was assessed through a residential history questionnaire. Cox proportional hazards models estimated the risk of mortality associated with household coal use.

RESULTS

In this cohort, 63% of the women ever used coal (n = 46,287). Compared with never coal use, ever use of coal was associated with mortality from all causes [hazard ratio (HR) = 1.12; 95% confidence interval (CI): 1.05, 1.21], cancer (HR = 1.14; 95% CI: 1.03, 1.27), and ischemic heart disease (overall HR = 1.61; 95% CI: 1.14, 2.27; HR for myocardial infarction specifically = 1.80; 95% CI: 1.16, 2.79). The risk of cardiovascular mortality increased with increasing duration of coal use, compared with the risk in never users. The association between coal use and ischemic heart disease mortality diminished with increasing years since cessation of coal use.

CONCLUSIONS

Evidence from this study suggests that past use of coal among women in Shanghai is associated with excess all-cause mortality, and from cardiovascular diseases in particular. The decreasing association with cardiovascular mortality as the time since last use of coal increased emphasizes the importance of reducing use of household coal where use is still widespread.

CITATION

Kim C, Seow WJ, Shu XO, Bassig BA, Rothman N, Chen BE, Xiang YB, Hosgood HD III, Ji BT, Hu W, Wen C, Chow WH, Cai Q, Yang G, Gao YT, Zheng W, Lan Q. 2016. Cooking coal use and all-cause and cause-specific mortality in a prospective cohort study of women in Shanghai, China. Environ Health Perspect 124:1384-1389; http://dx.doi.org/10.1289/EHP236.

Decomposing contribution of age and non-age factors to rapid growth of lung cancer in Xuanwei over past 30 years

BACKGROUND

From 1973 to 2005, the lung cancer mortality in Xuanwei had increased constantly. Effect analysis of age and non-age factors on lung cancer is important for local policy-making.

METHODS

Demographic and death data was collected and used. Factors of lung cancer were classified into age and non-age factors. The contribution of the two factors to lung cancer was evaluated by method of decomposing the differences of mortality rate.

RESULTS

For males, the non-age factors were the major contributor to growth of lung cancer mortality, and 78.46% of all growth was attributed to non-age factors. For females, the non-age factors were the absolute contributor to growth of lung cancer in 1973-1992. From 1992 to 2005, the contribution proportion had reduced to 75.39%.

CONCLUSIONS

Aging was one of risk factors for lung cancer in Xuanwei, but not the main factor. It was supposed that multiple environmental risk factors were related with high growth of lung cancer in Xuanwei. Policy-making should focus on the non-age factors.

Chinese water-pipe smoking and the risk of COPD

BACKGROUND

Studies show that the incidence of COPD has remained high in southwest China despite the 1976 National Stove Improvement Program for indoor air quality. Chinese water-pipe tobacco smoking (commonly referred to as water-pipe smoking), which is thought to be less harmful under the assumption that no charcoal is used and water filters tobacco smoke, is popular in China. We investigated whether Chinese water-pipe use and exposure are associated with the risk of COPD.

METHODS

This multicenter, cross-sectional study enrolled 1,238 individuals from 10 towns in the Fuyuan area, Yunnan Province, China. A matched design was used to estimate the impact of active and passive exposure to Chinese water-pipe smoking on COPD risk; multivariate analyses adjusted for other risk factors. We also collected the water from Chinese water pipes to assess the mutagenicity of its major components and simulated Chinese water-pipe smoke exposure fine particulate 2.5 (PM2.5) by using the High Volume Air Sampler and individuals' sera to search for the potential protein biomarkers of COPD.

RESULTS

The increased risk of COPD was profound for Chinese water-pipe smokers (adjusted OR, 10.61; 95% CI, 6.89-16.34), Chinese water-pipe passive smokers (adjusted OR, 5.50; 95% CI, 3.61-8.38), cigarette smokers (adjusted OR, 3.18; 95% CI, 2.06-4.91), and cigarette passive smokers (adjusted OR, 2.52; 95% CI, 1.62-3.91) compared with never-smoking control subjects. Chinese water-pipe use aggravates lungs with more PM2.5 compared with cigarettes. ChemR23 and tissue inhibitor of metalloproteinase-1 may be potential protein biomarkers of COPD.

CONCLUSIONS

Chinese water-pipe smoking significantly increases the risk of COPD, including the risk to women who are exposed to the water-pipe smoke.

TRIAL REGISTRY

Chinese Clinical Trial Registry; No.: ChiCTR-CCH-12002235; URL: www.chictr.org/cn/

Household air pollution and lung cancer in China: a review of studies in Xuanwei

Over half of the world's population is exposed to household air pollution from the burning of solid fuels at home. Household air pollution from solid fuel use is a leading risk factor for global disease and remains a major public health problem, especially in low- and mid-income countries. This is a particularly serious problem in China, where many people in rural areas still use coal for household heating and cooking. This review focuses on several decades of research carried out in Xuanwei County, Yunnan Province, where household coal use is a major source of household air pollution and where studies have linked household air pollution exposure to high rates of lung cancer. We conducted a series of case-control and cohort studies in Xuanwei to characterize the lung cancer risk in this population and the factors associated with it. We found lung cancer risk to vary substantially between different coal types, with a higher risk associated with smoky (i.e., bituminous) coal use compared to smokeless (i.e., anthracite) coal use. The installation of a chimney in homes resulted in a substantial reduction in lung cancer incidence and mortality. Overall, our research underscores the need among existing coal users to improve ventilation, use the least toxic fuel, and eventually move toward the use of cleaner fuels, such as gas and electricity.

Smoky coal, tobacco smoking, and lung cancer risk in Xuanwei, China

OBJECTIVES

Lung cancer rates in Xuanwei are the highest in China. In-home use of smoky coal has been associated with lung cancer risk, and the association of smoking and lung cancer risk strengthened after stove improvement. Here, we explored the differential association of tobacco use and lung cancer risk by the intensity, duration, and type of coal used.

MATERIALS AND METHODS

We conducted a population-based case-control study of 260 male lung cancer cases and 260 age-matched male controls. Odds ratios (OR) and 95% confidence interval (CI) for tobacco use was calculated by conditional logistic regression.

RESULTS

Use of smoky coal was significantly associated with an increased risk of lung cancer, and tobacco use was weakly and non-significantly associated with lung cancer risk. When the association was assessed by coal use, the cigarette-lung cancer risk association was null in hazardous coal users and elevated in less hazardous smoky coal users and non-smoky coal users. The risk of lung cancer per cigarette per day decreased as annual use of coal increased (>0-3 tons: OR: 1.09; 95% CI: 1.03-1.17; >3 tons: OR: 0.99; 95% CI: 0.95-1.03). Among more hazardous coal users, attenuation occurred at even low levels of usage (>0-3 tons: OR: 1.02; 95% CI: 0.91-1.14; >3 tons: OR: 0.94; 95% CI: 0.97-1.03).

CONCLUSION

We found evidence that smoky coal attenuated the tobacco and lung cancer risk association in males that lived in Xuanwei, particularly among users of hazardous coal where even low levels of smoky coal attenuated the association. Our results suggest that the adverse effects of tobacco may become more apparent as China's population continues to switch to cleaner fuels for the home, underscoring the urgent need for smoking cessation in China and elsewhere.

Indoor fuel exposure and the lung in both developing and developed countries: an update

Almost 3 billion people worldwide burn solid fuels indoors. Despite the large population at risk worldwide, the effect of exposure to indoor solid fuel smoke has not been adequately studied. Indoor air pollution from solid fuel use is strongly associated with chronic obstructive pulmonary disease, acute respiratory tract infections, and lung cancer, and weakly associated with asthma, tuberculosis, and interstitial lung disease. Tobacco use further potentiates the development of respiratory disease among subjects exposed to solid fuel smoke. There is a need to perform additional interventional studies in this field.

Research opportunities for cancer associated with indoor air pollution from solid-fuel combustion

BACKGROUND

Indoor air pollution (IAP) derived largely from the use of solid fuels for cooking and heating affects about 3 billion people worldwide, resulting in substantial adverse health outcomes, including cancer. Women and children from developing countries are the most exposed populations. A workshop was held in Arlington, Virginia, 9-11 May 2011, to better understand women's and children's potential health effects from IAP in developing countries. Workshop participants included international scientists, manufacturers, policy and regulatory officials, community leaders, and advocates who held extensive discussions to help identify future research needs.

OBJECTIVES

Our objective was to identify research opportunities regarding IAP and cancer, including research questions that could be incorporated into studies of interventions to reduce IAP exposure. In this commentary, we describe the state of the science in understanding IAP and its associations with cancer and suggest research opportunities for improving our understanding of the issues.

DISCUSSION

Opportunities for research on IAP and cancer include studies of the effect of IAP on cancers other than lung cancer; studies of genetic factors that modify susceptibility; studies to determine whether the effects of IAP are mediated via germline, somatic, and/or epigenetic changes; and studies of the effects of IAP exposure via dermal and/or oral routes.

CONCLUSIONS

IAP from indoor coal use increases the risk of lung cancer. Installing chimneys can reduce risk, and some genotypes, including GSTM1-null, can increase risk. Additional research is needed regarding the effects of IAP on other cancers and the effects of different types of solid fuels, oral and dermal routes of IAP exposure, genetic and epigenetic mechanisms, and genetic susceptibility.

Risk of lung cancer associated with domestic use of coal in Xuanwei, China: retrospective cohort study

OBJECTIVE

To estimate the risk of lung cancer associated with the use of different types of coal for household cooking and heating.

SETTING

Xuanwei County, Yunnan Province, China.

DESIGN

Retrospective cohort study (follow-up 1976-96) comparing mortality from lung cancer between lifelong users of "smoky coal" (bituminous) and "smokeless coal" (anthracite).

PARTICIPANTS

27,310 individuals using smoky coal and 9962 individuals using smokeless coal during their entire life.

MAIN OUTCOME MEASURES

Primary outcomes were absolute and relative risk of death from lung cancer among users of different types of coal. Unadjusted survival analysis was used to estimate the absolute risk of lung cancer, while Cox regression models compared mortality hazards for lung cancer between smoky and smokeless coal users.

RESULTS

Lung cancer mortality was substantially higher among users of smoky coal than users of smokeless coal. The absolute risks of lung cancer death before 70 years of age for men and women using smoky coal were 18% and 20%, respectively, compared with less than 0.5% among smokeless coal users of both sexes. Lung cancer alone accounted for about 40% of all deaths before age 60 among individuals using smoky coal. Compared with smokeless coal, use of smoky coal was associated with an increased risk of lung cancer death (for men, hazard ratio 36 (95% confidence interval 20 to 65); for women, 99 (37 to 266)).

CONCLUSIONS

In Xuanwei, the domestic use of smoky coal is associated with a substantial increase in the absolute lifetime risk of developing lung cancer and is likely to represent one of the strongest effects of environmental pollution reported for cancer risk. Use of less carcinogenic types of coal could translate to a substantial reduction of lung cancer risk.

Lung cancer in never smokers--a review

An estimated 10-25% of lung cancers worldwide occur in never smokers, i.e. individuals having smoked less than 100 cigarettes in their lifetime. Lung cancer in never smokers (LCINS) is more frequent in women, although large geographic variations are found. Histologically, adenocarcinomas predominate. The mere existence of LCINS suggests that risk factors other than smoking must be present. Exposure to environmental tobacco smoke (particularly in women) and exposure to workplace carcinogens (particularly in men) are the two most important alternative risk factors. However, a history of either is absent in more than a third of LCINS. The large proportion of women in LCINS suggest a hormonal element that may interact with other identified factors such as hereditary risks, a history of respiratory infections or disease, exposure to air pollution, cooking and heating fumes, or exposure to ionising radiation. The study of genomic polymorphisms finds constitutive DNA variations across subjects according to their smoking status, particularly in genes coding for enzymes that participate in the metabolism of certain carcinogens, in those coding for DNA repair enzymes, or in genes associated with tobacco addiction, or inflammatory processes. The type of molecular mutation in p53 or KRAS varies with smoking status. EGFR mutations are more frequent in never smokers, as are EML4-ALK fusions. The mutually exclusive nature of certain mutations is a strong argument in favour of separate genetic paths to cancer for ever smokers and never smokers. In the present paper we review current clinical and molecular aspects of LCINS.

The Diesel Exhaust in Miners study: a nested case-control study of lung cancer and diesel exhaust

Background

Most studies of the association between diesel exhaust exposure and lung cancer suggest a modest, but consistent, increased risk. However, to our knowledge, no study to date has had quantitative data on historical diesel exposure coupled with adequate sample size to evaluate the exposure–response relationship between diesel exhaust and lung cancer. Our purpose was to evaluate the relationship between quantitative estimates of exposure to diesel exhaust and lung cancer mortality after adjustment for smoking and other potential confounders.

Methods

We conducted a nested case–control study in a cohort of 12 315 workers in eight non-metal mining facilities, which included 198 lung cancer deaths and 562 incidence density–sampled control subjects. For each case subject, we selected up to four control subjects, individually matched on mining facility, sex, race/ethnicity, and birth year (within 5 years), from all workers who were alive before the day the case subject died. We estimated diesel exhaust exposure, represented by respirable elemental carbon (REC), by job and year, for each subject, based on an extensive retrospective exposure assessment at each mining facility. We conducted both categorical and continuous regression analyses adjusted for cigarette smoking and other potential confounding variables (eg, history of employment in high-risk occupations for lung cancer and a history of respiratory disease) to estimate odds ratios (ORs) and 95% confidence intervals (CIs). Analyses were both unlagged and lagged to exclude recent exposure such as that occurring in the 15 years directly before the date of death (case subjects)/reference date (control subjects). All statistical tests were two-sided.

Results

We observed statistically significant increasing trends in lung cancer risk with increasing cumulative REC and average REC intensity. Cumulative REC, lagged 15 years, yielded a statistically significant positive gradient in lung cancer risk overall (P_trend = .001); among heavily exposed workers (ie, above the median of the top quartile [REC ≥ 1005 μg/m³-y]), risk was approximately three times greater (OR = 3.20, 95% CI = 1.33 to 7.69) than that among workers in the lowest quartile of exposure. Among never smokers, odd ratios were 1.0, 1.47 (95% CI = 0.29 to 7.50), and 7.30 (95% CI = 1.46 to 36.57) for workers with 15-year lagged cumulative REC tertiles of less than 8, 8 to less than 304, and 304 μg/m³-y or more, respectively. We also observed an interaction between smoking and 15-year lagged cumulative REC (P_interaction = .086) such that the effect of each of these exposures was attenuated in the presence of high levels of the other.

Conclusion

Our findings provide further evidence that diesel exhaust exposure may cause lung cancer in humans and may represent a potential public health burden.