Long-Term Exposure to Ambient Air Pollution and Incidence of Postmenopausal Breast Cancer in 15 European Cohorts within the ESCAPE Project.

Background: Epidemiological evidence on the association between ambient air pollution and breast cancer risk is inconsistent.

Objective: We examined the association between long-term exposure to ambient air pollution and incidence of postmenopausal breast cancer in European women.

Methods: In 15 cohorts from nine European countries, individual estimates of air pollution levels at the residence were estimated by standardized land-use regression models developed within the European Study of Cohorts for Air Pollution Effects (ESCAPE) and Transport related Air Pollution and Health impacts – Integrated Methodologies for Assessing Particulate Matter (TRANSPHORM) projects: particulate matter (PM) ≤2.5μm, ≤10μm, and 2.5–10μm in diameter (PM, PM, and PM, respectively); PM absorbance; nitrogen oxides (NO and NO); traffic intensity; and elemental composition of PM. We estimated cohort-specific associations between breast cancer and air pollutants using Cox regression models, adjusting for major lifestyle risk factors, and pooled cohort-specific estimates using random-effects meta-analyses.

Results: Of 74,750 postmenopausal women included in the study, 3,612 developed breast cancer during 991,353 person-years of follow-up. We found positive and statistically insignificant associations between breast cancer and PM {hazard ratio (HR)=1.08 [95% confidence interval (CI): 0.77, 1.51] per 5 μg/m}, PM [1.07 (95% CI: 0.89, 1.30) per 10 μg/m], PM[1.20 (95% CI: 0.96, 1.49 per 5 μg/m], and NO [1.02 (95% CI: 0.98, 1.07 per 10 μg/m], and a statistically significant association with NO [1.04 (95% CI: 1.00, 1.08) per 20 μg/m, =0.04].

Conclusions: We found suggestive evidence of an association between ambient air pollution and incidence of postmenopausal breast cancer in European women. https://doi.org/10.1289/EHP1742.