Smoking increases risks of all-cause and breast cancer specific mortality in breast cancer individuals: a dose-response meta-analysis of prospective cohort studies involving 39725 breast cancer cases

Abstract

Smoking is associated with the risks of mortality from breast cancer (BC) or all causes in BC survivors. Two-stage dose-response meta-analysis was conducted. A search of PubMed and Embase was performed, and a random-effect model was used to yield summary hazard ratios (HRs). Eleven prospective cohort studies were included. The summary HR per 10 cigarettes/day, 10 pack-years, 10 years increase were 1.10 (95% confidence interval (CI) = 1.04-1.16), 1.09 (95% CI = 1.06-1.12), 1.10 (95% CI = 1.06-1.14) for BC specific mortality, and 1.15 (95% CI = 1.10-1.19), 1.15 (95% CI = 1.10-1.20), 1.17 (95% CI = 1.11-1.23) for all-cause mortality, respectively. The linear or non-linear associations between smoking and risks of mortality from BC or all causes were revealed. Subgroup analyses suggested a positive association between ever or former smoking and the risk of all-cause mortality in BC patients, especially in high doses consumption. In conclusion, higher smoking intensity, more cumulative amount of cigarettes consumption and longer time for smoking is associated with elevated risk of mortality from BC and all causes in BC individuals. The results regarding smoking cessation and "ever or former" smokers should be treated with caution due to limited studies.

Keywords: all-cause mortality; breast cancer specific mortality; breast cancer survival; dose-response; smoking.

Figure 1. The flowchart of selecting eligible studies

Figure 2

Meta-analysis on (A) smoking intensity (cigarettes/day), (B) cumulative amount of cigarettes, (C) smoking duration, (D) smoking cessation and the risk of breast cancer specific mortality. The squares represent the hazard ratio per (A) 10 cigarettes/day, (B) 10 pack-years, (C-D) 10 years increase for each individual study, with the area reflecting the weight assigned to the study. The horizontal line across each square represents the 95% confidence interval. The diamond represents the summary hazard ratio per (A) 10 cigarettes/day, (B) 10 pack-years, (C-D) 10 years increase in smoking doses or duration, with width representing 95% confidence interval.

Figure 3

Meta-analysis on (A) smoking intensity (cigarettes/day), (B) cumulative amount of cigarettes, (C) smoking duration, (D) smoking cessation and the risk of all-cause mortality. The squares represent the hazard ratio per (A)10 cigarettes/day, (B) 10 pack-years, (C-D) 10 years increase for each individual study, with the area reflecting the weight assigned to the study. The horizontal line across each square represents the 95% confidence interval. The diamond represents the summary hazard ratio per (A) 10 cigarettes/day, (B) 10 pack-years, (C-D) 10 years increase in smoking doses or duration, with width representing 95% confidence interval.

Figure 4

The dose-response analyses on (A) smoking intensity (cigarettes/day), (B) cumulative amount of cigarettes, (C) smoking duration, (D) smoking cessation and the risk of breast cancer specific mortality. The circles represent the hazard ratios in each individual study, with the area reflecting the weight assigned to the study.

Figure 5

The dose-response analyses on (A) smoking intensity (cigarettes/day), (B) cumulative amount of cigarettes, (C) smoking duration, (D) smoking cessation and the risk of all-cause mortality. The circles represent the hazard ratios in each individual study, with the area reflecting the weight assigned to the study.