Long-term Particulate Matter Exposures During Adulthood and Risk of Breast Cancer Incidence in the Nurses' Health Study II Prospective Cohort

Background: There is increasing concern that environmental exposures, such as air pollution, may be related to increasing rates of breast cancer; however, results from cohort studies have been mixed. We examined the association between particulate matter (PM) and measures of distance to roadway with the risk of incident breast cancer in the prospective nationwide Nurses' Health Study II (NHSII) cohort.

Methods: Incident invasive breast cancer from 1993 to 2011 (N = 3,416) was assessed among 115,921 women in the NHSII cohort. Time-varying Cox proportional hazards models were used to calculate HRs and 95% confidence intervals (95% CI) for increases in ambient exposures to PM10, PM2.5-10, and PM2.5 and residential roadway proximity categories.

Results: In multivariable adjusted models, there was little evidence of an increased risk of breast cancer (or any of the receptor-specific subtypes) overall or by menopausal status with PM exposure. There was, however, a suggestion of increased risks among women living <50 m of the largest road type (HR = 1.60; 95% CI, 0.80-3.21) or within <50 m of the two largest road types (1.14; 95% CI, 0.84-1.54) compared with women living farther (≥200 m) away.

Conclusions: Among women in the NHSII, we found no statistically significant associations between particulate matter exposures and incidence of breast cancer overall, by menopausal status, or by hormone receptor subtype. There was, however, a suggestion that residential proximity to major roadways may be associated with increased risk.

Impact: These results suggest no elevated breast cancer risk with increasing exposures to particulate matter air pollution, but that other traffic-related exposures may be important. Cancer Epidemiol Biomarkers Prev; 25(8); 1274-6. ©2016 AACR.