Impact of Smoking Cessation Duration on Lung Cancer Mortality: A Systematic Review and Meta-Analysis

Smoking history is a heterogeneous situation for different populations, and numerous studies suggest that smoking cessation is conducive to reduce the mortality of lung cancer. However, no quantitative meta-analysis regarding smoking cessation duration based on different populations has demonstrated it clearly. We systematically searched four electronic databases (PubMed, Embase, the Cochrane Central Register of Controlled Trials, and Scoups) till February 2023. Eligible studies reported the association between lung cancer survival and duration of smoking cessation. Additionally, we stratified the study population according to whether they had lung cancer at the time they quit smoking. Studies were pooled with the random-effects model. Out of the 11,361 potential studies initially identified, we included 24 studies involving 969,560 individuals in our analysis. Lung cancer mortality varied across two groups: general quitters and peri-diagnosis quitters. For general quitters, those who had quit smoking for less than 10 years exhibited an RR of 0.64 (95% CI [0.55-0.76]), while those who quit for 10-20 years had an RR of 0.33 (0.25-0.43), over 20 years had an RR of 0.16 (0.11-0.24), and never-smokers had an RR at 0.11 (0.07-0.15). Among peri-diagnosis quitters, the 1-year Overall Survival (OS) showed an RR of 0.80 (0.67-0.96), the 2-year OS had an RR of 0.89 (0.80-0.98), the 3-year OS had an RR of 0.93 (0.84-1.03), and the 5-year OS had an RR of 0.85 (0.76-0.96). Earlier and longer smoking cessation is associated with reduced lung cancer mortality, no matter in which cessation stage for two different populations.