Mini-reviewResidential radon and lung cancer in never smokers. A systematic review☆
Introduction
Lung cancer is the first cause of cancer mortality in the World, with more than 1,400,000 annual deaths [1], [2]. Tobacco consumption is its main risk factor, and between 10% and 25% of all lung cancer cases occur among never smokers [3]. Though at first sight it could seem a low percentage, if we consider lung cancer in never smokers as a specific cancer it would rank the seventh cause of cancer death worldwide [4]. Many authors state than lung cancer in never smokers should be considered as a different disease than lung cancer due to tobacco consumption [4], [5], [6]. Residential radon exposure is the second cause of lung cancer after tobacco consumption and it is the main risk factor among never smokers [7]. It is estimated that radon exposure could play a role in 30% of lung cancer deaths occurred in never smokers [8].
Many countries have depicted residential radon exposure maps in order to characterize those areas with the highest indoor radon concentrations. The Environmental Protection Agency (USA) established in 1987 148 Bq/m3 as the action level [9] and the World Health Organization has recently lowered the recommended levels below 100 Bq/m3 [7]. WHO recommendation is based on the results of the two most relevant studies regarding residential radon and lung cancer performed in Europe and North America, respectively [10], [11].
Both studies observed a linear and statistically significant increase on the risk of lung cancer with residential radon exposure.
Despite of this evidence there are scant studies on residential radon and lung cancer performed exclusively in never smokers. Among the published investigations we should highlight a Swedish study [12] which included never smokers from 5 different case-control studies. This study observed a relative risk of 1.44 (95%CI 1.0–2.1) for those exposed to concentrations higher than 140 Bq/m3 compared with those exposed to concentrations lower than 50 Bq/m3. This is one of the three available studies performed exclusively in never smokers [13], [14]. The other published studies did not make a difference between smokers and never smokers or the subgroup of never smokers had a very low sample size when it was analyzed independently.
Taking into account the importance of residential radon as a risk factor for lung cancer and the limited and fragmented available evidence for never smokers, we aim to assess the effect of residential radon exposure on lung cancer risk in never smokers through a systematic review of the published literature.
Section snippets
Literature search
We performed a literature search in Pubmed (Medline) and EMBASE. To retrieve information we used a predefined search strategy employing keywords (radon; lung neoplasms; never smokers; systematic review) complemented with free text. We also searched in the databases of the Center for Reviews and Dissemination (CRD databases) of the York University and on the Cochrane Library. The search period comprised between the first of January 1985 and 31st of December 2012. We used as search languages
Search results
We obtained 195 papers through the literature search. After reading all the abstracts we selected 48 for full text reading. Of them, 14 finally fulfilled the established inclusion criteria. Among them, we included the European and North American pooling studies (with two publications each one), a cohort study and nine case-control studies. Most of the investigations were performed in Europe and North America. Individual studies had a sample size ranging between 56 and 844 never smokers. The
Discussion
This is the first systematic review focused exclusively on the effect of residential radon in never smokers. The available studies suggest a possible relationship between residential radon exposure and lung cancer risk in never smokers. Though some studies have not reached a statistically significant association or do not even show a p-value, the investigations with better design and higher sample size point to an association between residential radon and lung cancer in never smokers.
While the
Funding
This paper has been funded by a competitive research grant of the Xunta de Galicia: 10CSA208057PR “Risk factors of lung cancer in never smokers: a multicenter case-control study in the Northwest of Spain.”
Conflict of Interest
The authors declare not to have any conflict of interest.
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This work is part of the research conducting to the PhD degree of María Torres Durán, MD.