Ambient particulate matter and females breast cancer survival after breast cancer diagnosis: The French E3N study

Abstract

Background: While breast cancer (BC) is associated with long-term survival, especially in early stage cases, factors influencing BC progression and survival are not perfectly understood. Residential exposure to ambient particulate matter <2.5 μg/m3 (PM2.5) has been associated to increased BC incidence; but only three studies focused on BC survival, with no consistent findings. Objective: To assess the associations between mean annual PM2.5 exposure after diagnosis, and total and BC specific mortality. Methods: A total of 4,804 women from the French E3N cohort study and diagnosed with BC between 1990 and 2008 were followed through December 2011. Mean residential PM2.5 exposure was derived from Europe-wide hybrid land use regression models at a 100 m spatial grid (ELAPSE project). Cox regression analysis was used to estimate hazard ratios (HR) and 95% confidence intervals (CI) of total and BC-specific mortality per increase in annual PM2.5 exposure, controlling for BC risk factors. We also evaluated possible non-linear dose-response relationship by using restricted cubic splines, and investigated potential effect modification by clinical and lifestyle factors. Results: A total of 608 women died over the follow-up (among whom 52% of BC-specific deaths). Mean annual PM2.5 concentration was 3.6 μg/m3 (inter-quartile range= 19.6 μg/m3). Overall, a 10 μg/m3 increase in PM2.5 was associated with modest increased total (HR= 1.18; 95% CI: 0.85-1.63) and BC-specific (HR= 1.17; 95% CI: 0.74-1.84) mortality. Associations per 10 μg/m3 increase in PM2.5 were stronger among stage 1 BC cases [HR= 1.57 (95% CI: 0.95-2.60) and HR= 2.43 (95% CI: 1.17-5.08), respectively] with total and BC-specific mortality, respectively, than in higher stage BC (PInteraction = 0.05 and 0.02, respectively). There was no evidence of a non-linear relationship. Conclusion: Our findings suggest that exposure to high levels of PM2.5 could reduce long-term survival after diagnosis of a good-prognosis BC.