Residential proximity to emissions of dioxins and furans and risk of breast cancer in the Sister Study cohort

Abstract

BACKGROUND AND AIM: 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 U.S. cohort. METHODS: Sister Study participants, who have a sister with breast cancer but no history of breast cancer themselves at enrollment, were followed for incident breast cancer. PCDD/F exposures were estimated using a historical U.S. Environmental Protection Agency database of 4,478 facilities (85% of PCDD/F air emissions) and their toxic equivalency quotient (TEQ) emissions. After restricting to participants with at least 10 years of continuous residential history prior to enrollment (2003-2009; n=34,103), we generated 10-year distance- and TEQ-weighted average emissions indices (AEI [g TEQ/km2]) within 3, 5, or 10km of participants’ residences, overall and by facility type. Cox regression was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the association between AEI (dichotomized, quartiles) and risk of breast cancer (invasive or ductal carcinoma in situ). Models were adjusted for breast cancer risk factors and residential outdoor air pollutants. We evaluated whether associations differed by smoking status and tumor estrogen receptor (ER) status. RESULTS:There were 2,583 incident breast cancer cases over a median of 11 years of follow-up. We found an increased risk of breast cancer associated with AEI exposure within 3km (HR Q4.vs.0:1.19, 95% CI: 1.00,1.42, Ptrend=0.03). The relationship was stronger for exposure to emissions from municipal solid waste facilities (HR ≥median.vs.0:1.46, 95% CI: 0.96,2.24; Ptrend=0.08) and among former smokers (HR Q4.vs.0: 1.46, 95% CI: 1.14,1.87, Ptrend=0.004), but did not differ by ER status (Pheterogeneity=0.47). No associations were observed for the AEI at 5 or 10km. CONCLUSIONS:Our findings suggest that increased residential exposure to PCDD/F emissions may confer a higher risk of breast cancer. KEYWORDS: air pollution, chemical exposures, long-term exposure, cancer and cancer precursors, female, environmental epidemiology