Background Occupational epidemiological studies among silicotics showed that long-term smoking cessation had lowered lung cancer risk by over 50%, but the beneficial effect for reducing risks of other diseases remains unknown. We aimed to evaluate the impact of smoking cessation on the mortality from all-cause and all-cancer using a large historical cohort of 3185 Chinese silicotics since 1981 and followed-up till 2014.

Methods Each silicotic’s baseline information was collected including socio-demographics, occupational history and medical history. Smoking habits were assessed at the baseline and reassessed during the follow-up. Multiple Cox proportional hazards model was performed to evaluate the impact of smoking cessation on all-cause and all-cancer mortality using adjusted hazard ratio (AHR) and 95% confidence interval (95% CI).

Results By the end of 2014, a total of 1942 deaths occurred and 360 silicotics died from cancer. Compared with never smokers, silicotics who were new quitters had 30% and 65% higher risk of all-cause of death [AHR=1.30, 95% CI: 1.06–1.58] and all-cancer (AHR=1.65, 95% CI: 1.04–2.62), while persistent quitters had a 52% and 49% excess risk of all-cause of death (AHR=1.52, 95% CI: 1.25–1.84) and all-cancer (AHR=1.49, 95% CI: 0.94–2.36), respectively. AHR for all-cause mortality among never quitters was 1.40 (95%CI: 1.14–1.73) while the HR for all-cancer was 2.08 (95%CI: 1.30–3.32). Both all-cause mortality and all-cause mortality decreased sharply after 5 years of smoking cessation and their risks almost equaled to those of the never smokers if the quitters could have kept abstained for more than 20 years.

Conclusions Smoking cessation sharply decreased all-cause and all-cancer mortality among workers with silicosis, and the beneficial effect was prominent for the long-term quitters.

Acknowledgement Pneumoconiosis Compensation Fund Board, Hong Kong