Long‐term exposure to fine particulate matter air pollution and the risk of lung cancer among participants of the Canadian National Breast Screening Study

Abstract

Recently, air pollution has been classified as a carcinogen largely on the evidence of epidemiological studies of lung cancer. However, there have been few prospective studies that have evaluated associations between fine particulate matter (PM2.5 ) and cancer at lower concentrations. We conducted a prospective analysis of 89,234 women enrolled in the Canadian National Breast Screening Study between 1980 and 1985, and for whom residential measures of PM2.5 could be assigned. The cohort was linked to the Canadian Cancer Registry to identify incident lung cancers through 2004. Surface PM2.5 concentrations were estimated using satellite data. Cox proportional hazards models were used to characterize associations between PM2.5 and lung cancer. Hazard ratios (HRs) and 95% confidence intervals (CIs) computed from these models were adjusted for several individual-level characteristics, including smoking. The cohort was composed predominantly of Canadian-born (82%), married (80%) women with a median PM2.5 exposure of 9.1 µg/m(3) . In total, 932 participants developed lung cancer. In fully adjusted models, a 10 µg/m(3) increase in PM2.5 was associated with an elevated risk of lung cancer (HR: 1.34; 95% CI = 1.10, 1.65). The strongest associations were observed with small cell carcinoma (HR: 1.53; 95% CI = 0.93, 2.53) and adenocarcinoma (HR: 1.44; 95% CI = 1.06, 1.97). Stratified analyses suggested increased PM2.5 risks were limited to those who smoked cigarettes. Our findings are consistent with previous epidemiological investigations of long-term exposure to PM2.5 and lung cancer. Importantly, they suggest associations persist at lower concentrations such as those currently found in Canadian cities.

Ambient PM 2.5 exposure and risk of lung cancer incidence in North America and Europe

“…Summaries of the study characteristics, methods, and key findings of each of these studies are shown in table 1. The pollution levels were similar in five of the six included studies with mean concentrations of these five studies ranging from 9.5±3.4 μg m −3 to 13.1±3.7 μg m −3 ; [23][24][25][26][27] the sixth study, one of the European-based study populations, had much higher pollution exposures with a mean of 28.3±2.5 μg m −3 [28].…”

“…Six studies met the inclusion criteria for the meta-analysis. Four of these were based in North American study populations [23][24][25][26] with two studies based in European study populations [27,28]. The European study by Beelen and colleagues (2008) [29] was excluded, because updated results on that cohort with extended follow up time was provided in the later published study by Hart and colleagues (2015) [28].…”

Exposure to ambient air pollution and the incidence of lung cancer and breast cancer in the Ontario Population Health and Environment Cohort

“…All models were stratified by region (living in Toronto or not) at baseline. We conducted subgroup analyses to investigate potential effect modification by age group (35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54), 55-64, 65-74 and 75-85 years), sex (for lung cancer only), income level and selected comorbidities. Because we lacked information on menopausal status (a known risk factor for breast cancer) and the average age of menopause in Canada is 51 years, we conducted an additional stratified analysis by using 51 years as a cutoff to investigate whether there are potential differences for pre/postmenopausal breast cancer risk in relation to air pollution.…”

“…conducted in North America and Europe that typically contained a small number of cases (with lung cancer cases ranging from 250 to 2,309), 7-10,41-43 which showed the increases in incident lung cancer per 10 μg /m 3 increase in PM 2.5 exposure varying from 6% to 43%, but was higher than that from a study in Netherlands (HR: 0.81; 1,940 cases). 8 These differences might be due to inherent difference in the characteristics of study subjects (e.g., females, 41,42 males, 43 nonsmokers 10 and general populations [7][8][9] ), different study designs (i.e., case-control 7 and cohort design [8][9][10][40][41][42][43] ), possible differences in the assessment of outcomes and PM 2.5 (e.g., land use regression models 9 and spatiotemporal interpolation methods 7,10,42 ), and differences in the sources and compositions of PM 2.5 , or chance. Interestingly, we found a somewhat strong association between lung cancer and NO 2 exposure (HR = 1.05; 95% CI: 1.03-1.07 for every 14 ppb increase in NO 2 ).…”

Relationships between chronic obstructive pulmonary disease and lung cancer: biological insights

“…The investigators concluded that in certain regions of China, PM 2.5 imposes significant health risks that are even greater than those so far attributed to CS, thus action plans for Air Pollution Prevention and Control should be enforced, at least in specific geographical areas (76). Recently, strong associations between small cell LC and adenocarcinoma (hazard ratios: 1.53 and 1.44, respectively) and exposure to high levels of PM 2.5 have also been reported in a cohort of women of the Canadian Cancer Registry (77). In other studies, however, the effects of air pollution as a risk factor of LC were significantly attenuated after adjusting for several factors such as CS and occupational exposure, even if the influence of urbanization persisted (1,78).…”