EXPOSURE TO RADON PROGENY, TOBACCO USE AND LUNG-CANCER IN A CASE-CONTROL STUDY IN SOUTHERN CHINA

A case-control study of lung cancer in underground tin miners in south ern China was conducted to examine the interplay between exposure to r adon progeny and tobacco use. A total of 460 incident cases and 1,043 controls were evaluated. Among the exposed, mean radon progeny exposur es were 600 and 427 working level months (WLM) for cases and controls, respectively. The excess relative risk per WLM (ERR/WLM) was 0.28% ov erall, with a 95% confidence interval of 0.1-0.6%, similar to the esti mate from a cohort study in a related population of underground miners . The established patterns of lung cancer associated with radon were s een; the ERR/WLM decreased with attained age and time since last expos ure. Conditional on total exposure, risk was highest for exposures del ivered at a low rate. The ERR/WLM did not differ significantly among c urrent and former smokers or within categories of time since last expo sure. The relative risk relationship between exposure to radon progeny and tobacco use was consistent with a multiplicative model, but the b est-fitting model was intermediate between additive and multiplicative ; an additive association was rejected. Adjustment for exposure to ino rganic arsenic, a known lung carcinogen, reduced the estimate of the E RR/WLM from 0.86% to 0.28%. The ERR/WLM estimate was homogeneous acros s subgroups defined by workers not exposed to arsenic and quartiles of cumulative arsenic exposure. Although squamous cell carcinoma was the predominant cell type, small cell and adenocarcinoma histologies appe ared more strongly associated with exposure to radon progeny. The find ing of a stronger trend with exposure with small cell carcinomas and a denocarcinomas, compared to squamous cell carcinomas, occurred primari ly at