Long-term exposure to particulate air pollution and components in relation to breast cancer risk: A nested case-control study in the E3N-Generations cohort.

[BACKGROUND] Previous studies on the association between airborne particulate matter (PM), particularly PM and PM, and breast cancer have shown inconsistent results, potentially due to variations in particle composition. To address this, we investigated the relationship between breast cancer and exposure to individual PM and PM components, as well as their combined effects, in the French E3N-Generation cohort.

[METHODS] We conducted a nested case-control study within the cohort (1990-2011), including 5,222 incident breast cancer cases matched to 5,222 controls. Annual mean concentrations (µg/m) of pollutants at residential addresses were estimated using the CHIMERE chemistry-transport model from 1990 to the index date. Exposure assessment included nine PM components: ammonium, sulfate, black carbon, polychlorobiphenyl-153 (PCB153), nitrate, benzo[a]pyrene, cadmium, dioxins, and Saharan dust. We evaluated single-pollutant effects using logistic regressions, and mixture effects using Quantile G-computation (QGC) and Bayesian Kernel Machine Regression (BKMR).

[RESULTS] Significant positive associations with breast cancer (Odds Ratios and confidence intervals for one SD increase (controls distribution) were found for ammonium (OR = 1.19; 95%CI: 1.05-1.35), sulfate (OR = 1.17; 95%CI: 1.02-1.35), PCB153 (OR = 1.17; 95%CI: 1.08-1.26), nitrate (OR = 1.16; 95%CI: 1.01-1.33), black carbon (OR = 1.12; 95%CI: 1.05-1.20), cadmium (OR = 1.05; 95%CI: 1.00-1.11). QGC showed a positive association with breast cancer for a one-quartile increase in joint exposure (OR = 1.22; 95% CI: 1.00-1.50) with cadmium and nitrate as major contributors. BKMR confirmed a significant positive association between the exposure to the mixture and breast cancer.

[CONCLUSION] The consistency between single-pollutant and mixture analyses supports a role for multiple PM components acting jointly on breast cancer risk. These results suggest that the chemical composition of PM, rather than individual pollutants alone, is a key determinant of breast cancer risk, highlighting the importance of considering pollutant composition in air pollution research.