CLINICAL MEASURES, SMOKING, RADON EXPOSURE, AND RISK OF LUNG-CANCER IN URANIUM MINERS

Objectives-Exposure to the radioactive daughters of radon is associate d with increased risk of lung cancer in mining populations. An investi gation of incidence of lung cancer following a clinical survey of Onta rio uranium miners was undertaken to explore whether risk associated w ith radon is modified by factors including smoking, radiographic silic osis, clinical symptoms, the results of lung function testing, and the temporal pattern of radon exposure. Methods-Miners were examined in 1 974 by a respiratory questionnaire, tests of lung function, and chest radiography. A random selection of 733 (75%) of the original 973 parti cipants was followed up by linkage to the Ontario Mortality and Cancer Registries. Results-Incidence of lung cancer was increased threefold. Risk of lung cancer among miners who had stopped smoking was half tha t of men who continued to smoke. There was no interaction between smok ing and radon exposure. Men with lung function test results consistent with airways obstruction had an increased risk of lung cancer, even a fter adjustment for cigarette smoking. There was no association betwee n radiographic silicosis and risk of lung cancer. Lung cancer was asso ciated with exposures to radon daughters accumulated in a time window four to 14 years before diagnosis, but there was little association wi th exposures incurred earlier than 14 years before diagnosis. Among th e men diagnosed with lung cancer, the mean and median dose rates were 2.6 working level months (WLM) a year and 1.8 WLM/year in the four to 14 year exposure window. Conclusions-Risk of lung cancer associated wi th radon is modified by dose and time from exposure. Risk can be subst antially decreased by stopping smoking.