Radon I. Lung cancer risks.

Radon is a rare natural radioactive gas. It produces solid progeny which emit alpha particles implicated in inducing cellular lesions in human bronchial epithelial tissue after inhalation. As early as the 15th century, increased rates of mortality due to respiratory diseases were observed in Eastern European mine workers. In the middle of the 20th century, increased incidence of lung cancer was recorded in uranium mine workers. Subsequent epidemiological studies conducted on lung cancer in miners confirmed that it was of occupational origin and proportional to levels of exposure. More recently, the risk of residential exposure has been evoked by case-control studies whose data were pooled to ensure adequate statistical power. Radon exposure is the second leading risk factor for lung cancer after smoking in the general population. There is epidemiological evidence for an increased risk of lung cancer caused by synergism between radon exposure and smoking in mine workers and in the general population. No predominant histological type was detected in the tumours under observation and clinical research into the molecular signature of radon is still in its infancy. International recommendations have prescribed housing and construction standards to mitigate exposure to radon and its progeny. Recommended thresholds vary considerably from one country to another. Reducing radon exposure in the general population is entirely warranted, but the necessary measures must go hand in hand with measures against smoking and exposure to other lung carcinogens.