A combined analysis of three case-control studies nested in three European uranium miner cohorts was performed to study the joint effects of radon exposure and smoking on lung cancer death risk. Occupational history and exposure data were available from the cohorts. Smoking information was reconstructed using self-administered questionnaires and occupational medical archives. Linear excess relative risk models adjusted for smoking were used to estimate the lung cancer risk associated with radon exposure. The study includes 1046 lung cancer cases and 2492 controls with detailed radon exposure data and smoking status. The ERR/WLM adjusted for smoking is equal to 0.008 (95% CI: 0.004-0.014). Time since exposure is shown to be a major modifier of the relationship between radon exposure and lung cancer risk. Fitting geometric mixture models yielded arguments in favor of a sub-multiplicative interaction between radon and smoking. This combined study is the largest case-control study to investigate the joint effects of radon and smoking on lung cancer risk among miners. The results confirm that the lung carcinogenic effect of radon persists even when smoking is adjusted for, with arguments in favor of a sub-multiplicative interaction between radon and smoking.

Background:A determination of the risk of lung cancer at low levels of radon exposure is important for occupational radiation protection.Methods:The risk of death from lung cancer at low radon exposure rates was investigated in the subcohort of 26 766 German uranium miners hired in 1960 or later.Results:A clear association between lung cancer mortality (n=334 deaths) and cumulative exposure to radon in working level months (WLM) was found. The excess relative risk per WLM was 0.013 (95% confidence intervals: 0.007; 0.021).Conclusions:The present findings provide strong evidence for an increased lung cancer risk after long-term exposure to low radon exposure rates among Wismut miners. The results are compatible to those from residential radon studies and miner studies restricted to low levels.

It is still not fully understood whether and how factors such as time, age and smoking modify the relationship between lung cancer and radon at low exposures and exposure rates. Improved knowledge is necessary for the dose conversion of radon in working level month (WLM) into effective dose, as currently discussed by the International Commission on Radiological Protection (ICRP). An update of the German uranium miner cohort study (n = 58,974 men) with a 10-year extension of mortality follow-up (1946-2013) was used to further examine this issue. Internal Poisson regression was applied to estimate the excess relative risk (ERR) for lung cancer mortality per unit of cumulative radon exposure in WLM with exponential time-related effect modifiers. In the full cohort restricted to <100 WLM the estimated overall ERR/WLM was 0.006 [95% confidence interval (CI): 0.003; 0.010] based on 1,254 lung cancer deaths and 1,620,190 person-years at risk. Both age at and time since exposure turned out to be important modifiers of the ERR/WLM and were included in the final model. Here, the ERR/WLM centered on age at exposure of 30 years, and 20 years since exposure was 0.016 (95% CI: 0.008; 0.028). This value decreased statistically significantly by approximately 40% and 60% for each 10-year increase in age at exposure and time since exposure, respectively. The joint effect of smoking and radon exposure was investigated in the sub-cohort of miners hired in 1960 or later, which includes data on smoking status. The centered ERR/WLM was slightly higher for non/light smokers compared to moderate/heavy smokers (0.022 versus 0.013). The current findings provide evidence for an increased lung cancer risk at low radon exposures or exposure rates that is modified by age and time. The observed risk is lower, but statistically compatible to those of other miner studies at low exposures or exposure rates. These findings reject an additive- and support a sub- to (supra-) multiplicative interaction between smoking and radon.

Data from the German miners' cohort study were analysed to investigate whether radon in ambient air causes cancers other than lung cancer. The cohort includes 58 987 men who were employed for at least 6 months from 1946 to 1989 at the former Wismut uranium mining company in Eastern Germany. A total of 20 684 deaths were observed in the follow-up period from 1960 to 2003. The death rates for 24 individual cancer sites were compared with the age and calendar year-specific national death rates. Internal Poisson regression was used to estimate the excess relative risk (ERR) per unit of cumulative exposure to radon in working level months (WLM). The number of deaths observed (O) for extrapulmonary cancers combined was close to that expected (E) from national rates (n=3340, O/E=1.02; 95% confidence interval (CI): 0.98–1.05). Statistically significant increases in mortality were recorded for cancers of the stomach (O/E=1.15; 95% CI: 1.06–1.25) and liver (O/E=1.26; 95% CI: 1.07–1.48), whereas significant decreases were found for cancers of the tongue, mouth, salivary gland and pharynx combined (O/E=0.80; 95% CI: 0.65–0.97) and those of the bladder (O/E=0.82; 95% CI: 0.70–0.95). A statistically significant relationship with cumulative radon exposure was observed for all extrapulmonary cancers (ERR/WLM=0.014%; 95% CI: 0.006–0.023%). Most sites showed positive exposure–response relationships, but these were insignificant or became insignificant after adjustment for potential confounders such as arsenic or dust exposure. The present data provide some evidence of increased risk of extrapulmonary cancers associated with radon, but chance and confounding cannot be ruled out.

From 1946 to 1990 extensive uranium mining was conducted in the southern parts of the former German Democratic Republic. The overall workforce included several 100 000 individuals. A cohort of 59 001 former male employees of the Wismut Company was established, forming a large retrospective uranium miners' cohort for the time period 1946 -1998. Mean duration of follow-up was 30.5 years with a total of 1 801 630 person-years. Loss to follow-up was low at 5.3%. Of the workers, 16 598 (28.1%) died during the study period. Based on 2388 lung cancer deaths, the radon-related lung cancer risk is evaluated. The excess relative risk (ERR) per working level month (WLM) was estimated as 0.21% (95% CI: 0.18 -0.24). It was dependent on time since exposure and on attained age. The highest ERR/WLM was observed 15 -24 years after exposure and in the youngest age group (o55 years of age). While a strong inverse exposure-rate effect was detected for high exposures, no significant association was detected at exposures below 100 WLM. Excess relative risk /WLM was not modified by duration of exposure. The results would indicate the need to re-estimate the effects of risk modifying factors in current risk models as duration of exposure did not modify the ERR/WLM and there was only a modest decline of ERR/WLM with increasing time since exposure.