Exploring Associations between Traffic-Related Air Pollution and Female Breast and Prostate Cancer using a Multi-Site Population-Based Case-Control Study in Can

Abstract

Background: Recent studies have reported positive associations between exposure to traffic-related air pollution and breast and prostate cancer incidence; however, few studies have been conducted and the findings are mixed. Methods: We used the National Enhanced Cancer Surveillance System, a population-based case-control study conducted in 8 of 10 Canadian provinces from 1994 to 1997. Our analyses are based on 1,829 post-menopausal incident breast cancer cases and 2,432 female controls, and 1,763 incident prostate cancer cases and 2,477 male controls. Residential histories over a 20 year period were used with a geographic information system to estimate urbanicity, population density, and road proximity measures. Long-term nitrogen dioxide (NO2) exposure measures were estimated from fixed-site air pollution monitors as well as spatiotemporal modeling methods. We calculated odds ratios (ORs) using logistic regression and adjusted for several known and suspected risk factors from self-reported questionnaires for each cancer site. Results: Preliminary analyses showed no consistent associations between breast cancer and long-term exposure measures, including years residing in large urban areas, average population density within 1, 5 and 10 km's of residences, proximity to major roads, and measured and modelled NO2 exposure. For example, the odds of breast cancer associated with a 10 ppb increase in modelled NO2 exposure was 1.07 (95% CI: 0.88-1.28). Similarly for prostate cancer, no associations were observed with years residing in large urban areas and average population density within 1, 5 and 10 km's of residences. Increased associations were observed for prostate cancer and 10 ppb increases in measured (OR: 1.11; 95% CI: 0.92-1.33) and modelled (OR: 1.12; 95% CI: 0.96-1.31) NO2, although the results varied by province. Conclusions: No consistent associations were observed between traffic-related air pollution measures and post-menopausal breast cancer incidence, while some evidence was seen for increased associations for prostate cancer incidence.