Objective: To investigate the effect of smoking cessation on the risk of cancer among male subjects.
Methods: Participants of this study were derived from the workers in Kailuan Group who took the health check-up examination in its 11 affiliated hospitals. The check-up examinations were given biennially based on uniformed standard. From May 2006 to December 2011, health examinations were given for 3 rounds and a total of 104 809 male workers involved. The date of being enrolled in this study was defined as that of taking first check-up, and the date of end-of-observation was defined as that of cancer diagnosis, death or end of follow-up.
Inclusion criteria: age ≥18 while being enrolled in this study, and there was no information missing in the questionnaire for age (or date of birth), smoking status, the age of starting smoking, the age of quitting smoking, and smoking amount. The information of smoking status was collected by questionnaires, and the information of newly-diagnosed cancer cases was obtained by follow-up. After adjusted for age, education background, drinking habits, working environment and BMI, multi-variate Cox proportional hazard regression models were used to analyze the association between smoking cessation and cancer risk (all sites of cancers, smoking-related cancers, and lung cancer) by calculating the values of HR (hazard ratio) and 95% CI (confidence interval).
Results: Totally, 104 809 subjects were followed up for 450 639.6 person-years, including 46 013 smokers (43.90%), 51 624 never-smokers (49.26%), and 7 172 smoking quitters (6.84%). Among all these subjects, 1 323 were diagnosed as cancer cases, including 1 082 smoking-related cancers, of which 378 were lung cancer cases. The results showed that, compared with never-smokers, smokers had increased risks for all sites of cancers (HR=1.38, 95% CI: 1.20- 1.59), smoking-related cancers (HR=1.45, 95% CI: 1.24- 1.69) and lung cancer (HR=1.70, 95% CI: 1.31- 2.21). While compared with the smokers, smoking quitters had decreased risk of lung cancer (HR=0.36, 95% CI: 0.20- 0.65). For the smokers with smoking history ≥20 pack-years, HR (95% CI) of lung cancer incidence was 0.09 (0.01- 0.65). For people age ≥60 smoke quitter, HR (95% CI) of lung cancer incidence was 0.33 (0.16- 0.68). For people who quit ≥10 years, HR (95% CI) of lung cancer incidence was 0.19(0.06- 0.58).
Conclusion: Smoking cessation might decrease the risk of lung cancer among male smokers. The risk of lung cancer was lower among the smoking quitters with longer history of smoking, older age, and longer years of quitting smoking.