Postdiagnosis Changes in Cigarette Smoking and Survival Following Breast Cancer

BACKGROUND: The purpose of this study was to examine whether at-diagnosis smoking and postdiagnosis changes in smoking within five years after breast cancer were associated with long-term all-cause and breast cancer-specific mortality. METHODS: A population-based cohort of 1508 women diagnosed with first primary in situ or invasive breast cancer in 1996 to 1997 were interviewed shortly after diagnosis and again approximately five years later to assess smoking history. Participants were followed for vital status through December 31, 2014. After 18+ years of follow-up, 597 deaths were identified, 237 of which were breast cancer related. Multivariable Cox regression was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). RESULTS: Compared with never smokers, risk of all-cause mortality was elevated among the 19% of at-diagnosis smokers (HR = 1.69, 95% CI = 1.36 to 2.11), those who smoked 20 or more cigarettes per day (HR = 1.85, 95% CI = 1.42 to 2.40), women who had smoked for 30 or more years (HR = 1.62, 95% CI = 1.28 to 2.05), and women who had smoked 30 or more pack-years (HR = 1.82, 95% CI = 1.39 to 2.37). Risk of all-cause mortality was further increased among the 8% of women who were at-/postdiagnosis smokers (HR = 2.30, 95% CI = 1.56 to 3.39) but was attenuated among the 11% women who quit smoking after diagnosis (HR = 1.83, 95% CI = 1.32 to 2.52). Compared with never smokers, breast cancer–specific mortality risk was elevated 60% (HR = 1.60, 95% CI = 0.79 to 3.23) among at-/postdiagnosis current smokers, but the confidence interval included the null value and elevated 175% (HR = 2.75, 95% CI = 1.26 to 5.99) when we considered postdiagnosis cumulative pack-years. CONCLUSIONS: Smoking negatively impacts long-term survival after breast cancer. Postdiagnosis cessation of smoking may reduce the risk of all-cause mortality. Breast cancer survivors may benefit from aggressive smoking cessation programs starting as early as the time of diagnosis.