Mortality from lung cancer among silicotic patients in Sardinia: an update study with 10 more years of follow up

Abstract

Objectives-To evaluate the association between silica, silicosis and lung cancer, the mortality of 724 patients with silicosis, first diagnosed by standard chest x ray film between 1964 and 1970, has been analysed by a cohort study extended to 31 December 1997. Methods-Smoking and detailed occupational histories were available for each member of the cohort as well as the estimated lifetime exposure to respirable silica dust and radon daughters. Two independent readers blindly classified standard radiographs according to the 12 point International Labour Organisation (ILO) scale. Lung function tests meeting the American Thoracic Society's criteria were available for 665 patients. Standardised mortality ratios (SMRs) for selected causes of death were based on the age specific Sardinian regional death rates. Results-The mortality for all causes was significantly higher than expected (SMR 1.35, 95% confidence interval (95% CI) 1.24 to 1.46) mainly due to tuberculosis (SMR 22.0) and to non-malignant chronic respiratory diseases (NMCRD) (SMR 6.03). All cancer deaths were within the expected numbers (SMR 0.93; 95% CI 0.76 to 1.14). The SMR for lung cancer was 1.37 (95% CI 0.98 to 1.91, 34 observed), increasing to 1.65 (95% CI 0.98 to 2.77) allowing for 20 years of latency since the first diagnosis of silicosis. Although mortality from NMCRD was strongly associated to the severity of radiological silicosis and to the extent of the cumulative exposure to silica, SMR for lung cancer was weakly related to the ILO categories and to the cumulative exposure to silica dust only after 20 years of lag interval. A significant excess of deaths from lung cancer (SMR 2.35) was found among silicotic patients previously employed in underground metal mines characterised by a relatively high airborne concentration of radon daughters and among ever smokers who showed an airflow obstruction at the time of the first diagnosis of silicosis (SMR 3.29). Mortality for lung cancer related to exposure was evaluated with both the Cox's proportional hazards modelling within the entire cohort and a nested case-control study (34 cases of lung cancer and 136 matched controls). Both multivariate analyses did not show any significant association with cumulative exposure to silica or severity of silicosis, but confirmed the association between mortality for lung cancer and relatively high exposure to radon, smoking, and airflow obstruction as significant covariates. Conclusions-The findings indicate that the slightly increased mortality for lung cancer in this cohort of silicotic patients was significantly associated with other risk factors-such as cigarette smoking, airflow obstruction, and estimated exposure to radon daughters in underground mines-rather than to the severity of radiological silicosis or to the cumulative exposure to crystalline silica dust itself. (Occup Environ Med 2001;58:786-793)

An update of a mortality study of talc miners and millers in Italy

“…Together with other recent reports, including experimental and epidemiological data evaluations [Chan et al, 2000;Hessel et al, 2000;Soutar et al, 2000;Carta et al, 2001;Cocco et al, 2001], the present study provides additional information of interest to further evaluate the association between silica and lung cancer [IARC, 1997;Steenland et al, 2001].…”

Exploring the joint effects of silicosis and smoking on lung cancer risks

“…An update study with 10 more years of followup among Sardinia silicotics was excluded from the analysis because only lung cancer SMR was shown among smoking silicotics (regional rates as reference), and the interaction indices could not be estimated. 45 Except for the studies of Chinese granite workers in Singapore and the refractory brick industry in Mainland, China, 12,42 the occupational exposures involved in the other studies were quite mixed, and might involve concomitant exposures to other occupational lung carcinogens. The cases of silicosis came from silicosis registries for the purpose of compensation 10,13,16,21,22,42,43 or from medical surveillance programs at the workplace.…”

Meta-analysis of silicosis and lung cancer

“…Five studies reported the risk of lung cancer according to the radiological severity of silicosis (29,31,37,45,47). One was excluded from the analysis because of a lack of data (42).…”