Objectives To evaluate the beneficial effect of smoking cessation on lung cancer mortality among workers with silicosis in Hong Kong.

Methods We recruited all 3202 incident cases of silicosis in Hong Kong from 1981 to 2005 and followed up them till 2014 to ascertain the causes of death. Only 79 workers were loss to follow-up and the rate of follow-up was 97.5%. We collected each worker’s smoking habits and other important information including socio-demographics, occupational history, and medical history at the time of diagnosis of silicosis. We further collected smoking information for workers who received regular medical assessment at the clinic during the follow-up period, and the effect of smoking cessation was assessed based on the following categories: never smokers, persistent quitters, new quitters, and never quitters. We performed multiple Cox’s regression analysis to evaluate the impact of smoking cessation on lung cancer mortality.

Results During 1981–2014, a total of 1984 deaths (62%) occurred and 196 of them were from lung cancer. Compared with never smokers, lung cancer mortality was strongly associated with never quitters [hazard ratio (HR) = 7.69, 95% CI: 2.81–20.90], followed by persistent quitters (HR = 4.39, 95% CI: 1.60–12.09), and new quitters (HR = 3.30, 95% CI: 1.17–9.26). Lung cancer mortality started to decreasing after 10 years of cessation (HR = 0.90, 95% CI: 0.60–1.37) and a substantial decrease was observed after the abstinence of smoking for 30 or more years (HR = 0.40, 95% CI: 0.25–0.65).

Conclusions Smoking cessation has a beneficial effect on lung cancer mortality among workers with silicosis, with a significant impact for those who quit smoking for 30 years or more.

Acknowledgement Pneumoconiosis Compensation Fund Board, Hong Kong [Correspondence: shelly@cuhk.edu.hk]