What Causes Lung Cancer?

Avoiding risk factors and increasing protective factors may help prevent lung cancer.

Avoiding cancer risk factors may help prevent certain cancers. Risk factors include smoking, being overweight, and not getting enough exercise. Increasing protective factors such as quitting smoking, eating a healthy diet, and exercising may also help prevent some cancers. Talk to your doctor or other health care professional about how you might lower your risk of cancer.

The following are risk factors for lung cancer:

Cigarette, cigar, and pipe smoking

Tobacco smoking is the most important risk factor for lung cancer. Cigarette, cigar, and pipe smoking all increase the risk of lung cancer. Tobacco smoking causes about 9 out of 10 cases of lung cancer in men and about 8 out of 10 cases of lung cancer in women.

Studies have shown that smoking low tar or low nicotine cigarettes does not lower the risk of lung cancer.

Studies also show that the risk of lung cancer from smoking cigarettes increases with the number of cigarettes smoked per day and the number of years smoked. People who smoke have about 20 times the risk of lung cancer compared to those who do not smoke.

Secondhand smoke

Being exposed to secondhand tobacco smoke is also a risk factor for lung cancer. Secondhand smoke is the smoke that comes from a burning cigarette or other tobacco product, or that is exhaled by smokers. People who inhale secondhand smoke are exposed to the same cancer -causing agents as smokers, although in smaller amounts. Inhaling secondhand smoke is called involuntary or passive smoking.

Family history

Having a family history of lung cancer is a risk factor for lung cancer. People with a relative who has had lung cancer may be twice as likely to have lung cancer as people who do not have a relative who has had lung cancer. Because cigarette smoking tends to run in families and family members are exposed to secondhand smoke, it is hard to know whether the increased risk of lung cancer is from the family history of lung cancer or from being exposed to cigarette smoke.

HIV infection

Being infected with the human immunodeficiency virus (HIV), the cause of acquired immunodeficiency syndrome (AIDS), is linked with a higher risk of lung cancer. People infected with HIV may have more than twice the risk of lung cancer than those who are not infected. Since smoking rates are higher in those infected with HIV than in those not infected, it is not clear whether the increased risk of lung cancer is from HIV infection or from being exposed to cigarette smoke.

Environmental risk factors

• Radon exposure: Radon is a radioactive gas that comes from the breakdown of uranium in rocks and soil. It seeps up through the ground, and leaks into the air or water supply. Radon can enter homes through cracks in floors, walls, or the foundation, and levels of radon can build up in the home.
• Studies show that high levels of radon gas inside homes and other buildings increase the number of new cases of lung cancer and the number of deaths caused by lung cancer. The risk of lung cancer is higher in smokers exposed to radon than in nonsmokers exposed to radon. In people who have never smoked, about 30% of deaths caused by lung cancer have been linked to being exposed to radon.
• Workplace exposure: Studies show that being exposed to the following substances increases the risk of lung cancer:
• Asbestos.
• Arsenic.
• Chromium.
• Nickel.
• Beryllium.
• Cadmium.
• Tar and soot.

These substances can cause lung cancer in people who are exposed to them in the workplace and have never smoked. As the level of exposure to these substances increases, the risk of lung cancer also increases. The risk of lung cancer is even higher in people who are exposed and also smoke.

• Air pollution: Studies show that living in areas with higher levels of air pollution increases the risk of lung cancer.

  Beta carotene supplements in heavy smokers

  Taking beta carotenesupplements (pills) increases the risk of lung cancer, especially in smokers who smoke one or more packs a day. The risk is higher in smokers who have at least one alcoholic drink every day.

  The following are protective factors for lung cancer:

  Not smoking
  The best way to prevent lung cancer is to not smoke.
  Quitting smoking
  Smokers can decrease their risk of lung cancer by quitting. In smokers who have been treated for lung cancer, quitting smoking lowers the risk of new lung cancers.Counseling, the use of nicotine replacement products, and antidepressanttherapyhave helped smokers quit for good.
  In a person who has quit smoking, the chance of preventing lung cancer depends on how many years and how much the person smoked and the length of time since quitting. After a person has quit smoking for 10 years, the risk of lung cancer decreases 30% to 50%.
  See the following for more information on quitting smoking:
  • Smoking Home Page (Includes help with quitting)
  • Cigarette Smoking: Health Risks and How to Quit

  Lower exposure to workplace risk factors

  Laws that protect workers from being exposed to cancer-causing substances, such as asbestos, arsenic, nickel, and chromium, may help lower their risk of developing lung cancer. Laws that prevent smoking in the workplace help lower the risk of lung cancer caused by secondhand smoke.
  Lower exposure to radon
  Lowering radon levels may lower the risk of lung cancer, especially among cigarette smokers. High levels of radon in homes may be reduced by taking steps to prevent radon leakage, such as sealing basements.

  It is not clear if the following decrease the risk of lung cancer:

  Diet
  Some studies show that people who eat high amounts of fruits or vegetables have a lower risk of lung cancer than those who eat low amounts. However, since smokers tend to have less healthy diets than nonsmokers, it is hard to know whether the decreased risk is from having a healthy diet or from not smoking.
  Physical activity
  Some studies show that people who are physically active have a lower risk of lung cancer than people who are not. However, since smokers tend to have different levels of physical activity than nonsmokers, it is hard to know if physical activity affects the risk of lung cancer.

  The following do not decrease the risk of lung cancer:

  Beta carotene supplements in nonsmokers
  Studies of nonsmokers show that taking beta carotenesupplements does not lower their risk of lung cancer.
  Vitamin E supplements
  Vitamin E supplements does not affect the risk of lung cancer.
  Cancer prevention clinical trials are used to study ways to prevent cancer.
  Cancer preventionclinical trials are used to study ways to lower the risk of developing certain types of cancer. Some cancer prevention trials are conducted with healthy people who have not had cancer but who have an increased risk for cancer. Other prevention trials are conducted with people who have had cancer and are trying to prevent another cancer of the same type or to lower their chance of developing a new type of cancer. Other trials are done with healthy volunteers who are not known to have any risk factors for cancer.
  The purpose of some cancer prevention clinical trials is to find out whether actions people take can prevent cancer. These may include eating fruits and vegetables, exercising, quitting smoking, or taking certain medicines, vitamins, minerals, or food supplements.

  New ways to prevent lung cancer are being studied in clinical trials.

  Clinical trials are taking place in many parts of the country. Information about clinical trials can be found in the Clinical Trials section of the NCI Web site. Check NCI’s list of cancer clinical trials for prevention trials for non-small cell lung cancerand small cell lung cancer that are now accepting patients. These include trials for quitting smoking.