Industrial air emissions and breast cancer incidence in a United States-wide prospective cohort

Background: We evaluated air emissions of industrial compounds, many of which have carcinogenic or endocrine disrupting properties, in relation to breast cancer incidence. Methods: Using the United States Environmental Protection Agency’s Toxics Release Inventory, we quantified air emissions of 28 compounds near Sister Study participants’ residences during the 10 years leading up to study enrollment (2003-2006; n=46,150). We used Cox proportional hazards regression to estimate adjusted hazard ratios (HR) and 95% confidence intervals (CI) for associations of residential emission levels of single pollutants with incident breast cancer. We assessed pollutant mixtures using an Exposure Continuum Mapping (ECM) framework and characterized associations using a joint-exposure response function. Results: During follow-up (median=13.4 years), we identified 4,155 breast cancer cases. We observed non-monotonic but elevated associations with breast cancer for emissions within 3km of the residence for nickel compounds (HR quintile5vs.none = 1.3; 95% CI 1.0, 1.6) and trichloroethylene (HR quintile5vs.none = 1.3; 95% CI 1.0, 1.6). ECM identified 25 mixture profiles that explained 72% of the variance in emissions patterns, with most participants experiencing relatively low emissions profiles. The joint-exposure response function suggested that higher incidence of breast cancer occurred among individuals with relatively rare, high emissions profiles; however, the overall trend was not associated with breast cancer (p=0.09). Conclusions: In our study, breast cancer incidence was associated with air emissions of certain industrial carcinogens. Although the overall emissions mixture did not show a trend related to breast cancer, this may not reflect the importance of individual compounds or specific emissions sources.