Combined Effect of Radon Exposure and Smoking and Their Interaction in Czech Studies of Lung Cancer

The aim is to compare lung cancer risks from radon in smoking categories in Czech residential radon and uranium miners studies and to evaluate interactions between smoking and radon exposure. The residential and occupational studies are based on one hospital based case-control study and three case-control studies nested within cohort studies, two among uranium miners and one in the general population in a radon prone area. Controls in the nested studies are individually matched by sex, age and year of birth. Smoking data were collected in person or from relatives of deceased subjects. In the occupational studies, some smoking data were obtained from medical files. Radon exposures were based on measurements of radon in houses by open track detectors LR115 in the radon prone area and by closed detectors and electrets in the hospital based study. Exposures in uranium mines were based on extensive measurements and personal dosimetry. The analyses are based on conditional logistic regression with linear dependence of the risk on radon exposure adjusted for smoking. The study resulted in 300 cases and 1035 controls in the residential study and 672 cases and 1491 controls in the study of uranium miners. The dependence of lung cancer risk on radon exposure adjusted for smoking was not substantially different from analyses when smoking was ignored and reflected mainly the risk among smokers. However, the excess relative risk per unit exposure among non-smokers was 3-10 fold higher in comparison to that in smokers. The relative risk from radon among non-smokers was consistently higher in the occupational and residential studies, reflecting probably differences in lung morphometry, clearence and unattached fraction of radon progeny in houses of non-smokers. Risks from combined effects are substantially lower than the risk derived from the multiplicative model, but consistent with the additive model.