Radon is the 2nd leading cause of all lung cancers and is the primary cause of disease in never-smokers. In Canada, this has accounts for 110,000 cases since 2001 –an enormous burden of disease.
The connection between residential radon and lung cancer was proven directly by several large studies each involving >10,000 lung cancer patients and another >10,000 healthy controls.
The data indicated that there is a ~16% increase in relative lifetime risk of lung cancer for every 100 Bq/m3 of long term radon exposure.
References: Krewski, et al. Residential radon and risk of lung cancer: a combined analysis of 7 North American case-control studies. Epidemiology 16, 137-45 (2005) and also Darby et al. Radon in homes and risk of lung cancer: collaborative analysis of individual data from 13 European case-control studies. Brit. Med. J. 330, 223 (2005).