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Definition of lung cancer: Cancer that forms in tissues of the lung, usually in the cells lining air
passages. The two main types are small cell lung cancer and non-small cell lung cancer. These types are
diagnosed based on how the cells look under a microscope.

Estimated new cases and deaths from lung cancer (non-small cell and small cell combined) in the
United States in 2008:

• New cases: 215,020
• Deaths: 161,840
• Risk Factors

Doctors cannot always explain why one person develops lung cancer and another does not. However, we
do know that a person with certain risk factors may be more likely than others to develop lung cancer. A
risk factor is something that may increase the chance of developing a disease.
Studies have found the following risk factors for lung cancer:

• Tobacco smoke: Tobacco smoke causes most cases of lung cancer. It’s by far the most
  important risk factor for lung cancer. Harmful substances in smoke damage lung cells. That’s why
  smoking cigarettes, pipes, or cigars can cause lung cancer and why secondhand smoke can cause
  lung cancer in nonsmokers. The more a person is exposed to smoke, the greater the risk of lung
  cancer. For more information, see the NCI fact sheets Quitting Smoking and Secondhand Smoke.
• Radon: Radon is a radioactive gas that you cannot see, smell, or taste. It forms in soil and rocks.
  People who work in mines may be exposed to radon. In some parts of the country, radon is found in
  houses. Radon damages lung cells, and people exposed to radon are at increased risk of lung
  cancer. The risk of lung cancer from radon is even higher for smokers. For more information, see
  the NCI fact sheet Radon and Cancer.
• Asbestos and other substances: People who have certain jobs (such as those who work in the
  construction and chemical industries) have an increased risk of lung cancer. Exposure to asbestos,
  arsenic, chromium, nickel, soot, tar, and other substances can cause lung cancer. The risk is
  highest for those with years of exposure. The risk of lung cancer from these substances is even
  higher for smokers.
• Air pollution: Air pollution may slightly increase the risk of lung cancer. The risk from air pollution
  is higher for smokers.
• Family history of lung cancer: People with a father, mother, brother, or sister who had lung
  cancer may be at slightly increased risk of the disease, even if they don’t smoke.
• Personal history of lung cancer: People who have had lung cancer are at increased risk of
  developing a second lung tumor.
• Age over 65: Most people are older than 65 years when diagnosed with lung cancer.
  Researchers have studied other possible risk factors. For example, having certain lung diseases (such
  as tuberculosis or bronchitis) for many years may increase the risk of lung cancer. It’s not yet clear
  whether having certain lung diseases is a risk factor for lung cancer.

People who think they may be at risk for developing lung cancer should talk to their doctor. The doctor may be able to suggest ways to reduce their risk and can plan an appropriate schedule for checkups.  For people who have been treated for lung cancer, it’s important to have checkups after treatment.  The lungtumor may come back after treatment, or another lung tumor may develop.