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.