Long Term-Exposure To Fine Particulate Matter Air Pollution And The Incidence Of Breast Cancer: Findings From The Canadian National Breast Screening Study

Paul VILLENEUVE, Carleton University, Canada
MILLER A. 2 , WEICHENTHAL S. 3 , CROUSE D. 4 , TO T. 2,5 , MARTIN R. 6 , VAN DONKELAAR A. 6 , WALL C. 2 , GOLDBERG M. 3

1 Department of Health Sciences, Carleton University, Ottawa, Canada
2 Dalla Lana School of Public Health, University of Toronto, Toronto, Canada
3 Department of Epidemiology, Biostatistics & Occupational Health, McGill University, Montreal Quebec
4 New Brunswick Institute for Research, Data and training, University of New Brunswick, Fredericton, Canada
5 Hospital for Sick Children, Toronto, Canada
6 Department of Physics and Atmospheric Sciences, Dalhousie University, Halifax, Canada

Long-term exposure to fine-particulate matter air pollution (PM2.5) is classified as a human carcinogen based largely on findings from epidemiological studies of lung cancer.  A few studies suggest that exposure to air pollution may increase the risk of breast cancer, but to our knowledge, only one of these has been longitudinal and it was limited to a 6 year follow-up interval and did not specifically examine PM2.5. Our aim was to characterize associations between residential exposure to PM2.5 and the incidence of breast cancer in a prospective cohort of 89,248 women who first enrolled in the Canadian National Breast Screening Study between 1980 and 1985. Incident cases of cancer were determined through probabilistic record linkage to national registry data through the end of 2005.  Individual-level estimates of long-term exposure to PM2.5 were derived from satellite observations. In total, 6,549 incident cases of breast cancer were identified during the two decade long follow-up interval. The hazard ratios (HR) and their 95% confidence intervals (CI), computed from these models were adjusted for several individual risk factors, including reproductive history, as well as neighborhood-level characteristics.  Stratified analyses were undertaken to determine whether the associations differed by menopausal status.  The average residential concentration of PM2.5 was 9.50 µg/m3 (standard deviation=3.44). In fully adjusted models, a 10-µg/m3 increase in PM2.5 exposure was positively associated with an elevated risk of incident premenopausal breast cancer (HR, 1.34; 95% CI, 1.05 – 1.71), but not those diagnosed in postmenopausal women (HR=0.99, 95% CI=0.91-1.07). The findings from this study provide additional support for the hypothesis that exposure to very low-levels of ambient PM2.5 increase the risk of breast cancer in premenopausal women.