TEMPORAL MODIFIERS OF THE RADON-SMOKING INTERACTION

Data on lung cancer mortality in a cohort of 3,347 Colorado Plateau ur anium miners was reanalyzed to investigate the role of time-related mo difiers of the radon-smoking interaction. A nested case-control sample of the cohort was drawn, matching each of the 258 lung cancer deaths with 15 controls drawn at random from the subjects who were born in th e same year and still alive at the time the case died. As reported ear lier, the dose response was sublinear for both total radon and total s moking, and their joint effect was approximately multiplicative. We fi tted linear multiplicative models to these data, transforming the rado n and smoking variables to improve their fit, and then added variables testing various temporal modifying effects and interactions. The stro ngest modifiers of the main effects of each variable taken separately were latency and duration of exposure. The strongest modifier of the i nteraction effect was the timing of radon and smoking exposures: Expos ure to radon followed by smoking produced a significantly more-than-mu ltiplicative effect, whereas the reverse sequence produced a significa ntly less than-multiplicative effect. These findings suggest that smok ing may act as a promoter of radon-initiated cells.