A study of silicosis and lung cancer among North Carolina (NC) workers employed in dusty trades was conducted. The cohort consisted of 760 males employed in dusty trades, defined as foundry work and the mining, quarrying, stone crushing, asbestos (1332214) and silica (14808607) product manufacturing, and construction industries, who were diagnosed by the NC Industrial Commission between 1940 and 1983. The vital status of the cohort was determined at the end of 1983. Death certificates were obtained for the decedents and reviewed. Standardized mortality ratios (SMRs) were calculated using mortality rates of the general white male United States (US) population and a group of 9,543 white NC male nonsilicotic miners as the reference groups. A total of 550 silicotics had died by the end of the followup period. When compared to US rates, mortality was significantly increased for tuberculosis, intestinal cancer, pneumonia, bronchitis, emphysema, pneumoconiosis and other respiratory diseases, and infectious kidney disease, SMRs 30.7, 2.3, 2.4, 7.9, 3.6, 32.9, and 6.5, respectively. Mortality from lung cancer was significantly increased when compared with both US and NC rates, SMRs 2.6 and 3.0, respectively. The lung cancer SMR was 2.3 for silicotics who had no known exposure to other carcinogens and 4.5 for those who had been exposed to asbestos or other workplace carcinogens. The lung cancer SMR was 3.4 for silicotics with a history of smoking and 1.7 for nonsmokers. For those diagnosed with silicosis during their employment in a dusty trade, the lung cancer SMR was 2.5, a significantly increased risk. For those diagnosed after leaving employment, the lung cancer SMR was 2.9, a nonsignificant increase. The authors conclude that the results of this analysis, which has effectively controlled for age, smoking, exposure to other carcinogens, and detection bias, are consistent with the view that silicosis is associated with an increased risk of lung cancer.
Dr HE Amandus, National Institute for Occupational Safety and Health, 944 Chestnut Ridge Road, Mailstop P 1133, Morgantown, WV 26505, USA