Silicosis and risk of lung cancer or lung tuberculosis: a cohort study.
This is a study of cancer mortality, cancer incidence, and incidence of lung tuberculosis among cases of silicosis reported to the National Swedish Pneumoconiosis Register during 1959-1977. Two occupational categories were extracted--"mining, tunneling, and quarrying" (n = 284) and "iron and steel foundries" (n = 428), respectively. Control groups were drawn from a national register of persons undergoing periodic health examinations with regard to silicosis risk. The controls were matched for occupation, age, and time of first exposure. The follow-up was performed through record-linkage operations to computerized information in Swedish Death Statistics, Swedish Cancer Register, and the Swedish Tuberculosis Index. End of follow-up was set at December 31, 1980. In cases drawn from mining, quarrying, and tunneling workers seven deaths in lung cancer were observed and two among the controls. Among iron and steel foundry workers the corresponding numbers were 10 and 6. The values for expected numbers, based on general population statistics, were 1.3 and 2.6, respectively, for these two occupational groups. When cancer incidence statistics were used, the case/control ratio for lung cancer was 2.1 for "mining, quarrying, and tunneling" and 0.6 for "iron and steel foundries." There were 29 cases of lung tuberculosis registered among the silicosis cases during the follow-up period. Only one tuberculosis case was observed among the controls. The results demonstrate that persons with silicosis contracted in the mining, quarrying, and tunneling occupations are subject to an increased risk of lung cancer. The risk is observed when both the general population and a closely matched control population from the same occupations are used for values of reference. The results also demonstrate the high risk of persons with silicosis to contract lung tuberculosis.