Smoking and survival of breast cancer patients: A meta-analysis of cohort studies.

OBJECTIVES: Published articles reported controversial results about the association of breast cancer survival with smoking. Hence, a meta-analysis was performed to investigate this association.

METHODS: A comprehensive search was performed to identify relevant cohort studies (up to May 31st, 2016). In the current smoking and former smoking v. never smoking analyses, the fixed- or random-effect model was selected based on the heterogeneity test among studies. And the heterogeneity was measured using Q test and I2 statistic. Publication bias was estimated using Egger's regression asymmetry test.

RESULTS: Thirteen articles with 44 studies were included. Compared with never smokers, current smokers have a higher breast cancer-specific mortality and all-cause mortality, with pooled hazard ratio (HR) (HR = 1.30 95%CI: 1.16-1.45; I2  = 52.4%) and (HR = 1.59, 95%CI: 1.41-1.78; I2  = 87.1%), respectively. While former smokers tend to have a moderately increased all-cause mortality (HR = 1.10, 95%CI: 1.07-1.12; I2  = 0.0%), but there was no significant association between former smoking and breast cancer-specific mortality (HR = 0.95, 95%CI: 0.90-1.02; I2  = 0.0%).

CONCLUSION: The present evidence indicates that current smoking leads to higher breast cancer-specific mortality and all-cause mortality than never smoking in breast cancer patients. However former smoking just causes a mild increase in all-cause morality, but not breast cancer-specific mortality.