Air pollution has been classified as a human carcinogen based largely on epidemiological studies of lung cancer. Recent research suggests that exposure to ambient air pollution increases the risk of breast cancer.
Our aim was to characterize associations between residential exposure to ambient fine particulate matter (PM2.5) and the incidence of breast cancer in a cohort of 89,247 women enrolled in the Canadian National Breast Screening Study between 1980 and 1985. Vital status and incident cancers were determined through record linkage to the national registry data through 2005. Individual-level estimates of exposures to PM2.5 at baseline were derived from satellite observations. Six thousand five hundred three incident breast cancers were identified during follow-up. We classified menopausal status using self-reported information collected at baseline and by attained age (50, 52, and 54 years) as women were followed-up. We computed hazard ratios (HRs) and their 95% confidence intervals (CI) using age as the time axis. Models were adjusted for several individual risk factors, including reproductive history, as well as census-based neighborhood-level characteristics.
The median residential concentration of PM2.5 was 9.1 μg/m3. In models adjusted for personal and contextual risk factors, a 10-μg/m3 increase in PM2.5 was associated with an elevated risk of premenopausal (HR = 1.26; 95% CI = 0.99, 1.61) but not postmenopausal breast cancer (HR = 1.01; 95% CI = 0.94, 1.10). The elevated risk of premenopausal breast cancer from PM2.5 was only evident among those randomized to the screening arm of the study.
Our findings support the hypothesis that exposure to low concentrations of PM2.5 increase the risk of premenopausal breast cancer.
This is an open access article distributed under the Creative Commons Attribution License 4.0 (CCBY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
aDepartment of Health Sciences, Carleton University, Ottawa, Canada;
bCHAIM Research Centre, Carleton University, Ottawa, Canada;
cDepartment of Medicine, McGill University, Montreal, Canada;
dDepartment of Sociology, University of New Brunswick, Fredericton, Canada;
eThe Hospital for Sick Children, Toronto, Canada;
fDalla Lana School of Public Health, University of Toronto, Toronto, Canada; and
gDepartment of Epidemiology, Biostatistics, and Occupational Health and Gerald Bronfman Department of Oncology, McGill University, Montreal, Canada
Published online 9 July 2018
Dr. Weichenthal received support from a GRePEC salary award funded by the Cancer Research Society, the Quebec Ministry of Economy, Science and Innovation, and FRQS (Fonds de Recherche du Québec- Santé).
Sponsorships or competing interests that may be relevant to content are disclosed at the end of the article.
*Corresponding author: Address. Department of Health Sciences, Carleton University, Health Sciences Building, Room 3305, Ottawa, ON, Canada K1S 5B6. Tel.: (613) 520–2600. E-mail: Paul.Villeneuve@carleton.ca (P.J. Villeneuve).
Received: 22 December 2017; Accepted 11 May 2018