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The National Cancer Institute estimates there will be nearly 230,000 new cases of lung cancer in the United States in 2013, and approximately 160,000 Americans will die from this disease. While smoking accounts for the vast majority of lung cancers, 10 to 15 percent of all lung cancer deaths are related to factors other than smoking. According to a 2009 review in Clinical Cancer Research, lung cancer in “never smokers” may be attributable to a variety of causes. Unfortunately, the risks imposed by most of these entities are not easily quantified, nor are there many clear-cut measures for dealing with them.

Radon Is the Second Leading Cause of Lung Cancer

Second only to tobacco smoke as a cause of lung cancer, radon is responsible for approximately 20,000 deaths each year in the U.S. Radon is a colorless, tasteless, odorless gas that emanates from decaying uranium in geological formations around the world. In outdoor environments radon is present in concentrations too low to cause health problems. However, when this radioactive gas concentrates in closed spaces – basements, homes and workplaces – it can be inhaled in amounts that damage your cells’ genetic machinery and trigger tumor development.

A never smoker’s risk for radon-induced lung cancer is directly related to the level of exposure. On average, being exposed to radon increases your background risk for lung cancer by 10 to 20 percent. The only way to know if you are getting more than your share of radon is to place detectors in places where you spend a significant amount of time. High radon concentrations can be mitigated with specialized venting techniques.

Secondhand Smoke Is an Important Risk Factor

Dozens of studies and multiple expert reviews have confirmed that secondhand smoke causes lung cancer, and the Environmental Protection Agency has classified secondhand smoke as a known human carcinogen. A 2004 analysis in the International Journal of Cancer estimated that nonsmoking spouses of smokers have a 23 percent excess risk for developing lung cancer, meaning they are 23 percent more likely to get lung cancer than the nonsmoking spouses of nonsmokers. (If you are the nonsmoking spouse of a smoker and you are also exposed to radon, your excess risk jumps to 30 to 45 percent.) According to the American Lung Association, approximately 3,400 nonsmokers die from lung cancer every year solely as a result of exposure to secondhand smoke.

Occupational Exposures Are In the Running

A number of agents – beryllium, coal dust, pesticides, paint fumes, asbestos, silica dust, chromium, arsenic and many others – have been implicated in lung cancers arising from occupational exposures. For people who have never smoked, research shows a consistent link between lung cancer and occupational exposure to asbestos, silica and arsenic. For other agents the data is less consistent. The specific risks due to any one agent are difficult to assess, as many people are exposed to more than one hazardous substance, both in and out of the workplace. In addition, most studies linking lung cancer to occupational exposures have included smokers, whose risk for lung cancer may be greatly magnified by exposure to certain agents.

For example, a smoker who is not exposed to asbestos is 13 times more likely to develop lung cancer than a never smoker. If a smoker is also exposed to asbestos, the risk for lung cancer jumps to at least 50 times that of a nonsmoker.

As If That Wasn’t Enough…

Some studies have suggested an increased risk for lung cancer in never smokers who are exposed to high levels of air pollution. Other studies, however, do not support this association. Similarly, a link between lung cancer and diet or certain infections – human papillomavirus and HIV, for example – has not been firmly established in nonsmokers, although such associations have been found in smokers. While chronic lung diseases, such as tuberculosis, asthma and chronic obstructive pulmonary disease, have been linked to lung cancer in smokers, only asthma has been associated with increased rates of lung cancer in never smokers.

Finally, recent research suggests your genetic makeup may be the final determinant of whether you develop lung cancer in a given situation. A 2012 review in Human Molecular Genetics demonstrated associations between several common genetic mutations and an increased risk for lung cancer. This supports what many people already know intuitively: since most smokers never develop lung cancer, genetics must be a potent force in determining an individual’s risk. Eventually, genetic testing may be used for identifying people at risk for lung cancer so they can begin screening – with low-dose chest CT, for example – at a time when diagnosis of lung cancer could make a difference in their long-term prognosis.


  1. National Cancer Institute: Lung Cancer
  2. Clinical Cancer Research: Lung Cancer in Never Smokers: Clinical Epidemiology and Environmental Risk Factors
  3. International Journal of Cancer: Secondhand Smoke Exposure in Adulthood and Risk of Lung Cancer among Never Smokers: A Pooled Analysis of Two Large Studies
  4. American Lung Association: Lung Cancer Fact Sheet
  5. Human Molecular Genetics: Influence of Common Genetic Variation on Lung Cancer Risk: Meta-Analysis of 14,900 Cases and 29,485 Controls