A case-referent study on lung cancer mortality among ceramic workers.

A case-referent study has been carried out to test the hypothesis that silica-exposed ceramic workers have an increased risk of lung cancer. Next-of-kin interviews were conducted for 72 lung cancer cases and 319 referents, all deceased, to collect work histories and smoking habits. The diagnosis of silicosis was ascertained by checking the individual files of cases of silicosis where compensation had been received. It was found that, after controlling for age, period of death and smoking, workers in the ceramic industry had a higher lung cancer risk than those in other occupations in which there was no exposure to silica (Mantel-Haenszel rate ratio = 2.0; 95% confidence interval (CI) = 1.1-3.5). This increased risk was mainly due to a rate ratio of 3.9 (95% CI = 1.8-8.3) for silicotic individuals, while for non-silicotic ceramic workers it was only 1.4 (95% CI = 0.7-2.8). Exposure to other carcinogens in the workplace seems not to play any role in the development of lung cancer. Furthermore, the data do not suggest an increased risk for silicotic non-smokers. The results of the study tend to confirm previous evidence of an excess risk among silicotic subjects and points to a possible etiological role of the silicotic process itself in lung cancer.