Environmental tobacco smoke exposure and survival following breast cancer

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 to 1997 was interviewed shortly after diagnosis and again approximately 5 years later to assess ETS exposure, and women were followed for more than 18 years using the National Death Index; 597 deaths (237 associated with breast cancer) were identified. Multivariable Cox regression was used to estimate adjusted HRs and 95% confidence intervals (CI) for mortality among women with breast cancer as related to at-diagnosis and at-/postdiagnosis changes in ETS exposure. Results: There was little or no association between atdiagnosis 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 postdiagnosis ETS exposure up to 1 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. Postdiagnosis 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.