Silicosis, Radon, and Lung Cancer Risk in Ontario Miners

The presence of radiographic silicosis was assessed as a risk factor for lung cancer in a cohort and case-control study of miners in the Ontario Silicosis Surveillance Database. Subjects were 328 miners with silicosis matched on age to 970 miners with normal radiographs. In a cancer incidence follow-up, there was a significant excess of lung cancer among miners with silicosis (Standardized Incidence Ratio 2.55; 95% Confidence Interval 1.43-8.28). Miners with normal radiographs had lung cancer incidence about the same as the Ontario average (Standardized Incidence Ratio 0.90; 95% Confidence Interval 0.51-1.47). In a matched case-control analysis of lung cancer, cumulative radon exposure was associated with lung cancer risk (increase in odds ratio 0.4% per WLM; 95% 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) and 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 suggests that additional study is warranted before concluding that radon risk factors derived from mining populations do not need to be modified for application to the general population.