Abstract Background: Breast cancer is a complex and multifactorial disease, and environmental factors have been suggested to increase its risk. However, prior research has largely focused on studying exposures to one factor/contaminant at a time, which does not reflect the real-world environment. Methods: Herein, we investigate associations between breast cancer and the environmental quality index (EQI), a comprehensive assessment of five domains of environmental quality (air, water, land, sociodemographic, and built environments) at the county level. Breast cancer diagnoses for North Carolina women were obtained from the North Carolina Central Cancer Registry (2009–2014) and the county of residence at the time of diagnosis was linked with the EQI. We evaluated the odds of localized, regional, or distant metastatic breast cancer in categories of environmental quality using women with carcinoma in situ as registry-based controls. Results: Overall environmental quality was generally not associated with invasive breast cancer; however, all breast cancer types tended to be inversely associated with land quality, particularly in more rural communities [distant metastatic breast cancer was 5%–8% more likely (OR, 1.08; 95% confidence interval, 1.02–1.14; P = 0.02) compared with carcinoma in situ]. Conclusions: Cumulatively, our results suggest that some broad measures of environmental quality are associated with invasive breast cancer but that associations vary by environmental domain, cancer stage, subtype, and urbanicity. Impact: Our findings suggest that components of land quality (e.g., pesticide applications and animal facilities) warrant additional investigation in relation to invasive breast cancer. See all articles in this CEBP Focus section, “Environmental Carcinogenesis: Pathways to Prevention.”

Environmental Quality and Invasive Breast Cancer