We don’t know what causes each case of lung cancer. But we do know many of the risk factors for these cancers (see Non-Small Cell Lung Cancer Risk Factors) and how some of them cause cells to become cancerous.
Smoking
Tobacco smoking is by far the leading cause of lung cancer. About 80% of lung cancer deaths are caused by smoking, and many others are caused by exposure to secondhand smoke.
Smoking is clearly the strongest risk factor for lung cancer, but it often interacts with other factors. Smokers exposed to other known risk factors such as radon and asbestos are at even higher risk. Not everyone who smokes gets lung cancer, so other factors like genetics likely play a role as well (see below).
Lung cancer in non-smokers
Not all people who get lung cancer are smokers. Many people with lung cancer are former smokers, but many others never smoked at all.
Lung cancer in non-smokers can be caused by exposure to radon, secondhand smoke, air pollution, or other factors. Workplace exposures to asbestos, diesel exhaust or certain other chemicals can also cause lung cancers in some people who don’t smoke.
A small portion of lung cancers occur in people with no known risk factors for the disease. Some of these might just be random events that don’t have an outside cause, but others might be due to factors that we don’t yet know about.
Lung cancers in non-smokers are often different in some ways from those that occur in smokers. They tend to occur at younger ages. Lung cancers in non-smokers often have certain gene changes that are different from those in tumors from smokers. In some cases, these changes can be used to guide treatment.
Gene changes that may lead to lung cancer
Scientists know how some of the risk factors for lung cancer can cause certain changes in the DNA of lung cells. These changes can lead to abnormal cell growth and, sometimes, cancer. DNA is the chemical in our cells that makes up our genes, which control how our cells function. We usually look like our parents because they are the source of our DNA. But DNA also can influence our risk for developing certain diseases, including some kinds of cancer.
Some genes help control when cells grow, divide to make new cells, and die: