Abstract
Some dioxins are carcinogenic, but few studies have investigated the relationship between ambient polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) and risk of breast cancer. We evaluated associations between proximity-based residential exposure to industrial emissions of PCDD/F and breast cancer risk in a large U.S. cohort. Sister Study participants at enrollment (2003-2009) were followed for incident breast cancer through September 2018. After restricting to participants with ≥10 years of residential history prior to enrollment (n = 35,908), we generated 10-year distance- and toxic equivalency quotient (TEQ)-weighted average emissions indices (AEI [g TEQ/km(2)]) within 3, 5, or 10 km of participants' residences, overall and by facility type. Multivariable Cox regression models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the association between AEI quartiles (vs. zero AEI) and risk of breast cancer [invasive or ductal carcinoma in situ]. There were 2670 incident breast cancer cases over 11 years (median) of follow-up. Breast cancer risk was increased for those in the highest quartile [Q] of AEI exposure within 3 km (HR(Q4):1.18, 95% CI: 0.99,1.40, P(trend) = 0.03). The HR was higher for the 10-year AEI at 3 km from municipal solid waste facilities (HR (≥ median.vs.0):1.50, 95% CI: 0.98, 2.29; P(trend) = 0.07). Risk was higher among ever smokers (vs. never smokers) in the top quartile of the 3 km AEI (HR(Q4):1.41, 95% CI:1.12,1.77, P(trend) = 0.003; P(interaction) = 0.03) and higher risk for ER negative tumors was suggested (HR(Q4):1.47, 95% CI: 0.95, 2.28, P(trend) = 0.07, P(heterogeneity) = 0.17). Our findings suggest that residential exposure to PCDD/F emissions may confer an increased risk of breast cancer.