[A retrospective cohort study on mortality among silicotic workers in Hong Kong with emphasis on lung cancer].
OBJECTIVE
To investigate the relationship between silica or silicosis and lung cancer in a large cohort of silicotic workers in Hong Kong.


METHODS
All workers with silicosis in Hong Kong diagnosed between 1981 and 1998 were followed up till the end of 1999 to ascertain their vital status and causes of death, using the corresponding mortality rates of Hong Kong males of the same period as external comparison. Standardized mortality ratios (SMR) for lung cancer and other major causes of death were calculated. Person-year method was used. Axelson's indirect method was performed to adjust for the confounding effect of smoking. Penalized smoothing spline (p-spline) models were used to evaluate the exposure-response relationship between silica dust exposure and lung cancer mortality.


RESULTS
A total of 2789 newly diagnosed cases of silicosis were included in the cohort, with an overall 24 992.6 person-years of observations. The loss-to-follow-up rate was only 2.9%. Surface construction workers (51%) and underground caisson workers (37%) constituted the major part of the cohort. There were 853 silicotics observed with an average age at death of 63.8 years. The SMR for all causes and all cancers increased significantly. The leading cause of death was non-malignant respiratory diseases. About 86 deaths were from lung cancer, giving a SMR of 1.69 (95% CI: 1.35 approximately 2.09). The risk of lung cancer death among workers in surface construction, underground caisson, and entire cohort was reduced to 1.12 (95% CI: 0.89 approximately 1.38), 1.09 (95% CI: 0.82 approximately 1.42) and 1.56 (95% CI: 0.98 approximately 2.36) respectively, after indirectly adjusting for smoking.


RESULTS
from P-spline model did not show a clear exposure-response relationship between silica dust (CDE and MDC) and lung cancer mortality.


CONCLUSIONS
This cohort study did not show an increased risk of lung cancer mortality among silicotic workers. P-spline model does not support an exposure-response relationship between silica dust exposure and lung cancer mortality.
Yu
Ignatius Ts
ITs
Department of Community & Family Medicine, The Chinese University of Hong Kong, Hong Kong SAR, China.
Tse
Lap Ah
LA
Chi
Chiu-leung
CL
Tze
Wai-wong
WW
Cheuk
Ming-Tam
MT
Alan
Ck-chan
CC
D000328:Adult; D000368:Aged; D004391:Dust; D005500:Follow-Up Studies; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D008175:Lung Neoplasms / Q000209:etiology / Q000401:mortality*; D008297:Male; D008875:Middle Aged; D016273:Occupational Exposure / Q000009:adverse effects; D012189:Retrospective Studies; D012829:Silicosis / Q000150:complications* / Q000401:mortality
D004391:Dust