Radon-associated lung cancer risk among French uranium miners: modifying factors of the exposure-risk relationship.

Radon is classified as a known pulmonary carcinogen in humans. A better understanding of the effects of low exposure and time-dependent factors, modifying the lung cancer risk is of continued interest. We present analyses of the exposure-risk relationship in the French cohort of uranium miners updated until 1999 and including five additional years of follow-up. These new analyses provide a better opportunity to look at low radon exposures with longer follow-up intervals, and allow consideration of new modifying factors, such as physical activity, mine location and job type. The cohort includes 5,086 miners, and 159 lung cancer deaths have been observed among these over a follow-up of more than 30 years. The exposure-risk relationship was estimated using excess relative risk models, which allow investigation of several modifying factors such as period of exposure, time since exposure, age at exposure, duration of exposure, exposure rate, job type, mine type and physical activity. The analysis confirms the association between radon exposure and lung cancer risk (ERR per 100 WLM = 0.58, P < 0.01). Period of exposure and physical activity appear as major modifying factors. Higher risks are observed for hard physical activity works. The effect of hard physical activity persists when the period of exposure is taken into account (ERR per 100 WLM = 2.95, P < 0.01).

Lung cancer risk associated to exposure to radon and smoking in a case-control study of French uranium miners.

A case-control study nested in the cohort of French uranium miners took smoking information into account in investigating the effect of radon exposure on lung cancer risk. This study included 100 miners who died of lung cancer and 500 controls matched for birth period and attained age. Data about radon exposure came from the cohort study, and smoking information was retrospectively determined from a questionnaire and occupational medical records. Smoking status (never vs. ever) was reconstructed for 62 cases and 320 controls. Statistical analyses used conditional logistic regression. The effect of radon exposure on lung cancer risk was assessed with a linear excess relative risk model, and smoking was considered as a multiplicative factor. Mean cumulative radon exposures were 114.75 and 70.84 Working Level Months (WLM) among exposed cases and controls, respectively. The crude excess risk of lung cancer per 100 WLM was 0.98 (95% CI: 0.18-3.08%). When adjusted for smoking, the excess risk was 0.85 per 100 WLM (95% CI: 0.12-2.79%), which is still statistically significant. The relative risk related to smoking was equal to 3.04 (95% CI: 1.20-7.70). This analysis shows a relative risk of lung cancer related to smoking similar to that estimated from previous miners' cohorts. After adjustment for smoking, the effect of radon exposure on lung cancer risk persists, and its estimated risk coefficient is close to that found in the French cohort without smoking information.