Cancer mortality among silicotics in China's metallurgical industry.

BACKGROUND We conducted a retrospective cohort study of lung cancer among silicotics in China's metallurgical industries. The study cohort consisted of 4372 male silicotics diagnosed and alive before 1 January 1980. The follow-up period was 1 January 1980 to 31 December 1989. RESULTS Standardized mortality ratios (SMR) of all deaths, all cancers, chronic bronchopneumonia, pneumonia and pulmonary heart disease, and pulmonary tuberculosis showed statistically significant excesses. The SMR for lung cancer for the total cohort was 237 (P < 0.01). When the total study cohort was divided into various categories by occupation (including iron ore mining, ore-sintering, refractory brick manufacturing, iron and steel smelting, and steel casting), significant excess lung cancer risk was observed among silicotics in all categories (SMR > 200, P < 0.01) except for casting (SMR = 157, P > 0.05). Excess lung cancer was not related to years since diagnosis of silicosis or years of exposure to silica. There was more than twofold excess lung cancer risk among both smoking (SMR = 257, P < 0.01) and non-smoking silicotics (SMR = 209, P < 0.01). Silicosis increased the risk of lung cancer.