Why Does Lung Cancer Occur in Non-Smokers?

Medical Author: Melissa Conrad Stoppler, MD
Medical Editor: Jay W. Marks, MD

While cigarette smoking is an undisputed cause of lung cancer, not all cases of lung cancer occur in smokers or former smokers. Each year, over 170,000 Americans develop lung cancer, and approximately ten per cent of lung cancers, or 17,000 cases, occur in non-smokers. Although not every non-smoker suffering from lung cancer will have an identifiable risk factor for development of the disease, a number of conditions and circumstances have been identified that will increase a non-smoker's chance of developing lung cancer.

Passive smoking, or the inhalation of tobacco smoke from other smokers sharing living or working quarters, is an established risk factor for the development of lung cancer. Non-smokers who reside with a smoker have a 24% increase in risk for developing lung cancer when compared with other non-smokers. Each year, up to 3,000 lung cancer deaths are estimated to occur in the U.S. that are attributable to passive smoking. For more, please read the The Dangers Secondhand Smoke article.

Radon gas, a naturally-occurring gas that forms when uranium decays, is another known cause of lung cancer. An estimated 12% of total lung cancer deaths in both smokers and non-smokers, or 15,000 to 22,000 lung cancer-related deaths annually in the U.S, are believed to be at least partially related to radon gas exposure. Those who do smoke and are exposed to radon have an even greater risk of developing lung cancer than non-smokers who are exposed to radon gas. Radon gas can travel up through soil and enter homes through gaps in the foundation, pipes, drains, or other openings. The U.S. Environmental Protection Agency estimates that one out of every 15 homes in the U.S. contains dangerous levels of radon gas. Radon gas is invisible and odorless but can be detected with simple test kits. For more, please read the Radon FAQ and Test Your Home for Radon articles.

Asbestos is a compound that was widely used in the past as both thermal and acoustic insulation material. Microscopic fibers of asbestos break loose from the insulation material and are released into the air where they can be inhaled into the lungs. Asbestos fibers can persist for a lifetime in lung tissue following exposure to asbestos. Both lung cancer and a type of cancer known as mesothelioma are associated with exposure to asbestos. Cigarette smoking drastically increases the chance of developing an asbestos-related lung cancer among workers exposed to asbestos; nevertheless, asbestos workers who do not smoke have a five fold greater risk of developing lung cancer than other non-smokers. Today, asbestos use is limited or banned in many countries including the Unites States. For more, please read the Asbestos-Related Disease article.

Since all smokers do not eventually develop lung cancer, it is likely that other factors, such as individual genetic susceptibility, may play a role in the causation of lung cancer. Numerous studies have shown that lung cancer is more likely to occur in both smoking and non-smoking relatives of those who have had lung cancer than in the general population.

Air pollution from vehicles, industry, and power plants, can raise the likelihood of developing lung cancer in exposed individuals. It has been estimated that up to 2,000 lung cancer deaths per year may be attributable to breathing polluted air, and many experts believe that prolonged exposure to highly polluted air can carry a risk for the development of lung cancer similar to that of passive smoking. For more, please read the Deaths Rise with Ground-Level Ozone Warning article.

For more, please read our Lung Cancer article.