Lung cancer in never-smokers: radon exposure and environmental tobacco smoke.

Lung cancer occurs in subjects with no history of active smoking in 15–25% of all cases, mainly females. Lung cancer in never-smokers is a recent field of investigation, with differences in clinical, pathological and molecular aspects compared with lung cancer in smokers [1, 2]. Chronic exposure to radon and its decay products is recognised as the second leading cause of lung cancer, after active cigarette smoking. Alpha particle emissions from inhaled radon decay products, and not radon itself, cause lung cancer [3]. Alpha particles, which can only penetrate a short distance into bronchial epithelium, induce more biological damage than beta or gamma radiation, and can induce DNA base mutations and chromosomal strand breaks.