Silica, silicosis and lung cancer among ceramic workers: a case-referent study.

A case-referent study has been carried out regarding a possible connection between silica exposure and lung cancer (ICD 162) in Central Italy, where the pottery industry has a long tradition. Silicosis among 72 cases of lung cancer and among 314 referents, all deceased, was ascertained through checking the individual files of compensated cases of silicosis. Questionnaires on past employments and smoking habits were blindly administered to the next-of-kin of the deceased subjects. Controlling for age, period of death, and smoking, workers in the ceramic industry were found to have a higher lung cancer risk than workers in other occupations free from silica exposure (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 nonsilicotic ceramic workers it was only 1.4 (95% CI = 0.7-2.8). The result of this study seems to suggest that lung cancer might be merely indirectly associated with exposure to silica through the silicotic process, although the dose may differ for silicotic and nonsilicotic individuals.