Lung cancer occurs when cells inside the lungs grow out of control.

The cancer can start in the bronchi, the tubes that allow air to move from the trachea into the lungs; bronchioles, the tiny tubes that carry air farther inside the lungs; or alveoli, the air sacs within the lungs.

Smoking is the leading risk factor for lung cancer. Others include secondhand smoke; exposure to radon, asbestos or workplace chemicals; radiation therapy to the lungs; air pollution; and a personal or family history of lung cancer.

Lung cancer often causes no symptoms until it has grown past the early stage. Symptoms can include a persistent, worsening cough that may bring up blood; chest pain, especially with deep breathing or laughing; hoarseness; loss of appetite; shortness of breath; fatigue; wheezing; and bronchitis or pneumonia.

Lung cancer that spreads to other parts of the body can cause bone pain, such as in the back or hips; nervous system changes such as headache, dizziness or seizures; yellowed skin or eyes; or swollen lymph nodes.