The effect of atmospheric particulate matter on survival of breast cancer among US females

Short-term effects of ambient particulate matter (PM) on cardiopulmonary morbidity and mortality have been consistently documented. However, no study has investigated its long-term effects on breast cancer survival. We selected all female breast cancer cases (n = 255,128) available in the California Surveillance Epidemiology and End Results cancer data. These cases were linked to 1999-2009 California county-level PM daily monitoring data. We examined the effect of PM on breast cancer survival. Results from Kaplan-Meier survival analysis show that female breast cancer cases living in areas with higher levels of PM10 and PM2.5 had a significant shorter survival than those living in areas with lower exposures (p < 0.0001). The results from marginal cox proportional hazards models suggest that exposure to higher PM10 (HR 1.13, 95 % CI 1.02-1.25, per 10 mu g/m(3)) or PM2.5 (HR 1.86, 95 % CI 1.12-3.10, per 5 mu g/m(3)) was significantly associated with early mortality among female breast cancer cases after adjusting for individual-level covariates such as demographic factors, cancer stage and year diagnosed, and county-level covariates such as socioeconomic status and accessibility to medical resources. Interactions between cancer stage and PM were also observed; the effect of PM on survival was more pronounced among individuals diagnosed with early stage cancers. This study suggests that exposure to high levels of PM may have deleterious effects on the length of survival from breast cancer, particularly among women diagnosed with early stage cancers. The findings from this study warrant further investigation.