Long-term exposure to residential radon and risk of skin cancer

Radon gas is a radioisotope which has a 3.8 day half-life, and builds up indoors. Exposure in the home to the progeny of this gas is responsible for about half of all non-medical population exposures to ionising radiation and the airways and lungs are the primary target organs followed by the skin (Kendall and Smith 2002). Skin cancer (malignant melanoma (MM) and non-melanoma skin cancer (NMSC)) are by far the most common form of cancers in the world, including Denmark (Madan et al. 2010) with exposure to ultraviolet (UV) radiation in sunlight as the key risk factor (Leiter and Garbe 2008). A recent estimation concluded that the attributable risk of radon exposure for skin cancer incidence was 0.5% to 5% at 20 Bq/m ³ provided that cancer can be initiated in the basal layer of the skin (Charles 2007). That review called for case-control or cohort studies to address the issue authoritatively. The most recent review highlighted that the epidemiological evidence relating to risks other than lung cancer was sparse and only evidence of miners exposed to high levels of radon was available for NMSC and MM. That review concluded that there is no epidemiological evidence suggesting that radon exposure contributes directly to excess disease other than lung cancer (Advisory Group on Ionising Radiation (AGIR) 2009). Despite these conclusions three British studies with ecological design have shown associations between radon exposure and NMSC (Etherington et al. 1996;Wheeler et al. 2012;Wheeler et al. 2013). However, a key limitation inherent to those studies is ecological fallacy as associations at the aggregate level do not necessarily reflect associations in individuals. In the present study we sought to confirm or refute this and we investigate the association between long-term exposure to residential radon and the risk for each of the three types of skin cancers (basal cell carcinoma (BCC), squamous cell carcinoma (SCC) and MM in Denmark.