Environmental Tobacco Smoke Exposure and Survival Following Breast Cancer

Abstract

Background: Environmental tobacco smoke (ETS) exposure is hypothesized to influence survival after breast cancer, but few studies have examined this association. Methods: A population-based cohort of women (N=1,508) diagnosed with first primary invasive or in situ breast cancer in 1996-1997 was interviewed shortly after diagnosis and again approximately 5 years later to assess ETS exposure, and women were followed for over 18 years using the National Death Index; 597 deaths (237 associated with breast cancer) were identified. Multivariable Cox regression was used to estimate adjusted hazard ratios (HR) and 95% confidence intervals (CI) for mortality among women with breast cancer as related to at-diagnosis and at-/post-diagnosis changes in ETS exposure. Results: There was little or no association between at-diagnosis ETS exposure and all-cause (HR=1.04, 95% CI=0.78-1.40) or breast cancer-specific (HR=0.98, 95% CI=0.63-1.52) mortality. Mortality was elevated among women who reported cessation in post-diagnosis ETS exposure up to one year before the follow-up assessment, for all-cause (HR=1.81, 95% CI=0.87-3.74) and breast cancer mortality (HR=1.89, 95% CI=0.68-5.24); however, estimates were imprecise. Conclusions: We found little evidence of an association between at-diagnosis ETS exposure and mortality after breast cancer. Post-diagnosis cessation of ETS exposure was positively associated with mortality, although we could not rule out chance and reverse causation as possible explanations. Impact: Exposure to ETS does not appear to influence mortality after breast cancer.