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What Causes Lung Cancer?

Lung cancer is a malignant disease in which the cells of the lung tissues become abnormal, characterized by uncontrollable, unlimited growth. As they grow, these abnormal cells can form tumors and interfere with the functioning of the lung. These lung cancer cells can then invade nearby tissue and destroy organ structure.

Lung Cancer Facts

What you need to know

  • Lung cancer is the leading cause of cancer death and the second most common cancer among both men and women in America.
  • Each year, more people die of lung cancer than of colon, breast, and prostate cancers combined.
  • About two out of three people diagnosed with lung cancer are 65 or older.
  • Only one in every ten people with lung cancer are alive 5 years after diagnosis.

Lung Cancer Causes and Risk Factors

There are some factors that make one person more likely to develop lung cancer. These include:


Cigarette smoking is by far the leading risk factor for lung cancer, accounting for approximately 90 percent of lung cancer cases.

Tobacco smoke contains over 4,000 chemicals, including more than 60 carcinogens (cancer causing agents). When you smoke, you inhale these cancer-causing substances that may cause damage to the cells in the lungs. Over time, the damaged cells may become cancerous.

The more you smoke and the longer amount of time you smoke, the higher your risk is of developing lung cancer. Also, if you started smoking at a young age, you will be at greater risk later in life.

Secondhand smoke

Breathing in other people’s cigarette smoke can also cause lung cancer. Though it comes in smaller amounts, the same cancer-causing agents are inhaled through secondhand smoke.

The more secondhand smoke you breathe in, the greater your risk of the disease. Secondhand smoke is thought to cause more than 7,000 deaths from lung cancer each year.

Exposure to radon gas

Radon is an odorless, radioactive gas that results from the natural breakdown of uranium in soil and rocks. In the outdoors, radon gas is diluted by fresh air, so it is not usually a concern. But radon can seep into buildings through various openings, such as dirt floors, cracks in foundation walls and other underground openings. Without proper ventilation, radon can accumulate to high levels.

Exposure to high levels of radon can increase the risk of developing lung cancer. In fact, radon is the leading cause of lung cancer in non-smokers and the second leading cause of lung cancer among smokers, according to the US Environmental Protection Agency (EPA).

The risk of developing lung cancer depends on how much radon you are exposed to and how long you are exposed to it. The risk for lung cancer from radon is much higher in people who smoke than in those who don’t.

Exposure to asbestos

People exposed to large amounts of asbestos also have a greater risk of developing lung cancer.

Asbestos fibers easily break into particles. When inhaled, these dust particles can lodge in the lungs and cause damage that leads to an increased risk of lung cancer. Approximately 5 percent of the lung cancer cases diagnosed each year are caused by asbestos.

Air pollution

Air pollution can contain trace amounts of diesel exhaust, coal products, and other industrial substances that are harmful to the health of humans.

Outdoor air pollution poses the greatest environmental lung cancer risk due to the high number of people exposed to it every day. The more air pollution you are exposed to, the greater your risk of developing lung cancer. Researchers estimate that about 5% of all deaths from lung cancer may be due to outdoor air pollution.

Family history

Your risk of lung cancer may be higher if your parents, siblings, or children have had lung cancer. This might be due to shared genes among family members and/ or they live in the same place where they are exposed to radon and other substances that can cause lung cancer.

Radiation therapy to the lungs

Having previous radiation therapy to the chest area for another disease can increase your chances of developing lung cancer.

Examples include people treated for Hodgkin disease or women who get radiation after a mastectomy for breast cancer.

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