UC Davis

BACKGROUND: Although particulate matter (PM) has not been consistently associated with breast cancer risk, two studies have reported harmful associations for breast cancer survival. We examined PM exposures and breast cancer survival in two U.S.-based prospective cohort studies. METHODS: The Nurses Health Study (NHS) and NHSII are cohorts with detailed data on medical history, lifestyle factors, and causes of death. Women with Stage I-III breast cancer (n = 8,936) were followed through June 2014. Residential PM was estimated using spatio-temporal models. We performed Cox regression to estimate hazard ratios (HR) of breast cancer-specific mortality and all-cause mortality for 10 μg/m3 increases in post-diagnosis PM. RESULTS: There were 1,211 breast cancer-specific deaths. Overall, PM was not associated with breast cancer-specific mortality [PM2.5: HR, 1.09; 95% confidence interval (CI), 0.87-1.36; PM2.5-10: HR, 1.03; 95% CI, 0.85-1.24; PM10: HR, 1.05; 95% CI, 0.89-1.24], but was associated with modest increases in all-cause mortality (PM2.5: HR, 1.12; 95% CI, 0.96-1.30; PM2.5-10: HR, 1.12; 95% CI, 1.00-1.24; PM10: HR, 1.09; 95% CI, 1.01-1.18). However, among participants with Stage I disease, PM2.5 was associated with higher breast cancer-specific mortality (HR, 1.64; 95% CI, 1.11-2.43). CONCLUSIONS: PM was not associated with breast cancer-specific death overall; however, higher PM was associated with all-cause mortality. Higher PM2.5 was associated with higher breast cancer-specific mortality among patients with Stage I breast cancer even after adjustment. IMPACT: Studies on ambient PM and breast cancer survival demonstrate that PM2.5 may have broader health effects than previously recognized and warrants further research on breast tumor progression.