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NEWS & VIEWS

RADON RISK FOR LUNG CANCER BACK IN THE SPOTLIGHT

A recent study in the BMJ (2005;330:223–228) serves as a potent reminder that smoking isn’t the only factor physicians and patients should consider when discussing lung cancer risk. European researchers report that exposure to radon gas in the home accounts for about 9% of lung cancer deaths and about 2% of overall cancer deaths in Europe.

The findings are based on an analysis of 13 case-control studies of residential radon and lung cancer involving 7,148 lung cancer patients and 14,208 control subjects. The authors, led by Sarah Darby, PhD, of the Clinical Trials Service Unit and the Epidemiological Studies Unit of Radcliffe Infirmary, Oxford, UK, assessed lung cancer risk based on measurements of household radon and personal characteristics such as smoking history, age, sex, and area of residence.

Radon is an odorless, colorless, flavorless radioactive gas that arises naturally from the breakdown of uranium in the earth. Because it emanates from soil, it is found throughout the environment. Outdoors, radon amounts are so small that they pose virtually no risk; indoors, however, the gas can become concentrated. Over time, breathing radon exposes the lungs to radiation that can increase the risk of lung cancer.

Darby and colleagues calculated that lung cancer risk increases by 8.4% for every 100 Becquerels per cubic meter (Bq/m³). The US Environmental Protection Agency (EPA) recommends taking action to remediate indoor radon when the gas reaches concentrations of 4 picocuries per liter (pCi/L), which is equivalent to 148 Bq/m³.

"These results are consistent with those of earlier studies, including one from the United States," said Elizabeth Ward, PhD, Director of Surveillance Research for the American Cancer Society (ACS). "But this study has larger numbers of people resulting in greater statistical power and better ability to separate the results of radon exposure from the results of smoking."

The European group found that the increase in relative risk of lung cancer for every 100 Bq/m³ of radon was similar for smokers and nonsmokers. However, the absolute risks of lung cancer associated with radon exposure are much greater among smokers. For example, among nonsmokers exposed to 800 Bq/m³ of radon, the lifetime risk of developing lung cancer by age 75 is about 1%, about double the absolute risk among individuals with no radon exposure (0.5%). Among current smokers of 15 to 24 cigarettes a day, the absolute risk of developing lung cancer after 800 Bq/m³ radon exposure is about 22%, about double the risk in smokers not exposed to radon (10%).

The risks of radon have been known for decades and were based primarily on studies of miners exposed to extremely high levels of the gas while working underground. Calculating the potential risks to the general public is more difficult because radon exposure is highly variable depending on where people live and what type of residence they occupy—radon levels vary according to soil type and concentrations tend to be greater in lower levels of a home, such as the basement.

The EPA has recommended radon testing in homes for years, and in January 2005 the US Surgeon General issued a national health advisory on the subject. The advisory said radon is the second leading cause of lung cancer in the US (smoking is first) and causes more than 20,000 lung cancer deaths in the country each year. Venting systems can be installed in homes to lower indoor radon levels and reduce the risk.

"It would be good for doctors to talk to their patients about the risks of radon," Ward said, "particularly in those parts of the country where the potential for radon exposure in homes is high."

The EPA estimates that 1 in 15 US homes have excessive levels of radon. The agency provides a county-by-county map of estimated radon levels on its Web site at http://www.epa.gov/iaq/radon/zonemap.html. Consumer information describing the risks of radon, home modifications to lower the risk, and ways to find qualified contractors to perform the work are available at http://www.epa.gov/iaq/radon/pubs/index.html. The booklet A Physician’s Guide—Radon: The Health Threat with a Simple Solution, developed by the EPA and the American Medical Association, is also available online at http://www.epa.gov/radon/pubs/physic.html.

Doctors should talk with patients about the lung cancer risks posed by radon exposure in the home.

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