Ambient fine particulate matter and breast cancer incidence in a large prospective US cohort.

Background Fine particulate matter (PM2.5) has been inconsistently associated with breast cancer incidence, however, few studies have considered historic exposure when levels were higher. Methods Outdoor residential PM2.5 concentrations were estimated using a nationwide spatiotemporal model for women in the National Institutes of Health–AARP Diet and Health Study, a prospective cohort located in 6 states (California, Florida, Louisiana, New Jersey, North Carolina, and Pennsylvania) and 2 metropolitan areas (Atlanta, GA, and Detroit, MI) and enrolled in 1995-1996 (n = 196 905). Annual average PM2.5 concentrations were estimated for a 5-year historical period 10 years prior to enrollment (1980-1984). We used Cox regression to estimate adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for the association between a 10 µg/m3 increase in PM2.5 and breast cancer incidence overall and by estrogen receptor status and catchment area. Results With follow-up of participants through 2017, a total of 15 870 breast cancer cases were identified. A 10 ug/m3 increase in PM2.5 was statistically significantly associated with overall breast cancer incidence (HR = 1.08, 95% CI = 1.02 to 1.13). The association was evident for estrogen receptor–positive (HR = 1.10, 95% CI = 1.04 to 1.17) but not estrogen receptor–negative tumors (HR = 0.97, 95% CI = 0.84 to 1.13; P heterogeneity = .3). Overall breast cancer hazard ratios were more than 1 across the catchment areas, ranging from a hazard ratio of 1.26 (95% CI = 0.96 to 1.64) for North Carolina to a hazard ratio of 1.04 (95% CI = 0.68 to 1.57) for Louisiana (P heterogeneity = .9). Conclusions In this large US cohort with historical air pollutant exposure estimates, PM2.5 was associated with risk of estrogen receptor–positive breast cancer. State-specific estimates were imprecise but suggest that future work should consider region-specific associations and the potential contribution of PM2.5 chemical constituency in modifying the observed association. [ABSTRACT FROM AUTHOR]