LAUSR

INTRODUCTION Previous investigations found elevated mortality after breast cancer in association with biomarkers of persistent organochlorine pesticides in non-occupationally exposed women. We hypothesized that lifetime residential pesticide use, which includes persistent and non-persistent pesticides, would also be associated with increased mortality after breast cancer. METHODS A population-based cohort of 1505 women with invasive or in situ breast cancer was interviewed in 1996-1997, shortly after diagnosis, about pre-diagnostic lifetime residential pesticide use. Participants were followed for mortality through 2014 (595 deaths from any cause and 236 from breast cancer, after 17.6 years of follow-up). Pesticides were examined as 15 individual categories; a group of seven used for lawn and garden purposes; a group of eight used for nuisance-pest purposes; and all combined. Cox regression was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for all-cause and breast cancer-specific mortality. Modification by estrogen receptor (ER) status, body mass index, and long-term residence was examined. RESULTS Ever use (HR = 0.77, 95%CI = 0.63-0.95) and higher lifetime applications (4th quartile: HR = 0.62, 95%CI = 0.47-0.81, ptrend = 0.3) of the lawn and garden group of pesticides were inversely associated with all-cause mortality, compared to never use. The inverse association for lawn and garden pesticide use was limited to ER positive (vs. negative) tumors (pinteraction = 0.05). Nuisance-pest pesticides, and all groups combined, were not associated with all-cause or breast cancer-specific mortality. CONCLUSIONS Contrary to our hypothesis, lifetime residential use of lawn and garden pesticides, but not all combined or nuisance-pest pesticides, was inversely associated with all-cause mortality after breast cancer.