Background: Smoking cessation is an important strategy for reducing the harmful effects of tobacco, particularly in the prevention of lung cancer; however, prospective data on the impact of smoking cessation on lung cancer risk in Asian populations are limited.
Methods: We studied a population-based cohort of Chinese men and women aged 45-74 years--participants of the Singapore Chinese Health Study. Information on smoking, lifestyle and dietary habits was collected at the time of recruitment in 1993-1998; and smoking status was assessed again at a second interview in 1999-2004 (mean interval 5.8 years). Participants were followed up to 31 December 2007, and incident cases of lung cancer were ascertained by linkage with population-wide registries.
Results: Among 45,900 participants, there were 463 incident cases of lung cancer. Relative to current smokers, those who quit smoking subsequent to baseline assessment had a 28% decrease in the risk of lung cancer (adjusted hazard ratio (HR) 0.72; 95% CI (95% confidence interval): 0.53-0.98). The risk was less than half in ex-smokers who had quit before the first interview and maintained their status (HR 0.42; 95% CI: 0.32-0.56).
Conclusions: Reduction in lung cancer incidence with smoking cessation in Asian populations is substantial and can be observed within a few years after quitting.