MANAGING PATIENTS EXPOSED TO RADON
Screen for lung cancer in smokers only
The National Lung Screening Study (NLST) was a large multicenter trial of annual low-dose computed tomography (CT) to screen for lung cancer in a cohort at high risk: age 55 to 74, at least a 30 pack-year history of smoking in a current smoker, or a former smoker who quit within the past 15 years. The trial demonstrated a 20% reduction in lung cancer deaths in the CT screening group.31
Since the publication of the NLST results, many societies have endorsed screening for lung cancer with low-dose CT using the study criteria. The National Comprehensive Cancer Network (NCCN) expanded these criteria and has recommended screening in patients over age 50 who have a history of smoking and one additional risk factor, such as radon exposure.
However, radon exposure has not been incorporated into a lung cancer risk-prediction model, and there is no empirical evidence suggesting that people who have such a history would benefit from screening.32,33 The joint guidelines of the American College of Chest Physicians and American Society of Clinical Oncology recommend annual low-dose CT screening only for patients who meet the NLST criteria.34
What to do about indeterminate lung nodules
The widely used guidelines from the Fleischner Society35 on how to manage small lung nodules stratify patients into groups at low and high risk of developing lung cancer on the basis of risk factors. The guidelines apply to adults age 35 and older in whom an indeterminate solid nodule was recently detected.
If a patient is at high risk, the recommended approach includes follow-up in shorter intervals depending on the nodule size. History of smoking is recognized as a major risk factor, and the statement also lists family history and exposure to asbestos, uranium, and radon.35
Although the association of radon with lung cancer has been shown in epidemiologic studies, radon exposure has not been included in validated statistical models that assess the probability that an indeterminate lung nodule is malignant. We would expect the risk to be higher in miners, who suffer a more intense exposure to higher levels of radon, than in the general population, which has a low and constantly variable residential exposure. Furthermore, there are no data to support a more aggressive follow-up approach in patients with indeterminate lung nodules and a history of radon exposure.
RADON AND OTHER CANCERS
When a person is exposed to radon, the bronchial epithelium receives the highest dose of ionizing radiation, but other organs such as the kidneys, stomach, and bone marrow may receive doses as well, although lower. Several studies have looked into possible associations, but there is no strong evidence to suggest an increased mortality rate related to radon from cancers other than lung.24,36 However, there seems to be a positive association between radon and the incidence of lymphoproliferative disorders in uranium miners.37,38
Radon can be measured in drinking water, and a few studies have looked at a possible association with gastrointestinal malignancies. The results did not reveal a consistent positive correlation.39,40 The risk of cancer from exposure to radon in the public water supply is likely small and mostly from the transfer of radon particles into the air and not from drinking the water. On the other hand, the risk could be higher with private wells, where radon levels are variable and are possibly higher than from public sources.41
DATA ARE INSUFFICIENT TO GUIDE MANAGEMENT
Radon is a naturally occurring and ubiquitous radioactive gas that can cause tissue damage. Cohort and case-control studies have demonstrated that radon exposure is associated with increased risk of lung cancer. It is recommended that radon levels be measured in every home in the United States and mitigation measures instituted if levels exceed 4 pCi/L.
There are insufficient data to help guide the management of patients with a history of radon exposure, and prospective studies are needed to better understand the individual risk of developing lung cancer and the appropriate management of such patients.
Smoking cessation is an integral part of lung cancer risk reduction from radon exposure.