Joint effects of long-term exposure to multiple air pollutants and breast cancer risk.

10572 Background: Human exposure to air pollution involves complex mixtures of multiple correlated air pollutants. To date, very few studies have assessed the combined effect of exposure to multiple air pollutants on breast cancer risk. We assessed the joint effects of multiple air pollutants and breast cancer risk. Methods: The study was based on a case-control study nested within the French E3N cohort, involving 5222 incident breast cancer cases and 5222 matched controls. For each woman, the average of the mean annual concentration estimates for eight air pollutants ((benzo(a)pyrene, cadmium, dioxins, polychlorinated biphenyls (PCB153), nitrogen dioxide (NO 2 ), particulate matters (PM 2.5 , PM 10 ), ozone) was estimated from cohort inclusion (in 1990) to the index date. We used Bayesian Profile Regression, which groups individuals according to their exposure profile and risk levels, and assigns a risk to each of these clusters. Odds ratios (OR) and their 95% credible intervals (CrI) were estimated. Results: Overall, 21 clusters were identified. The cluster characterized by low exposures to all pollutants, except ozone was taken as reference. A significant increase in breast cancer risk compared to the reference cluster was observed for 3 clusters, with the OR of 1.61 (CrI: 1.13;2.26), OR (1.00; 1.88), and OR 1.38 (1.00; 1.88) respectively. These three clusters share quite similar exposure profiles characterized by women in urban settings with high exposure to most pollutants, particularly to NO 2 , PM and PCB153. Conclusions: Overall, there is evidence of a positive joint effect of high level exposures to air several pollutants, namely NO 2 , PM and PCB153 and increased risk of breast cancer.