SILICOSIS, RADON, AND LUNG-CANCER RISK IN ONTARIO MINERS

The presence of radiographic silicosis was assessed as a risk factor f or lung cancer in a cohort and case-control study of miners in the Ont ario Silicosis Surveillance Database. Subjects were 328 miners with si licosis matched on age to 970 miners with normal radiographs. In a can cer incidence followup, there was a significant excess of lung cancer among miners with silicosis (Standardized Incidence Ratio 2.55; 95% Co nfidence Interval 1.43-8.28). Miners with normal radiographs had lung cancer incidence about the same as the Ontario average (Standardized I ncidence Ratio 0.90; 95% Confidence Interval 0.51-1.47). In a matched case-control analysis of lung cancer, cumulative radon exposure was as sociated with lung cancer risk (increase in odds ratio 0.4% per WLM; 9 5% Confidence Interval -0.3% to 1.1%). When the presence of silicosis was added to the model, silicosis was a highly significant risk factor for lung cancer (Odds Ratio 6.99 95% Confidence Interval 1.91 - 25) a nd the risk factor for radon was diminished (increase in Odds Ratio -0 .5% per WLM; 95% confidence Interval -1.4% to 0.4%). This finding sugg ests that additional study is warranted before concluding that radon r isk factors derived from mining populations do not need to be modified for application to the general population.