Lung cancer is caused by malignant (cancer) cells that form in the tissues of the lung, usually in the cell's lining air passages. The two main types are small cell lung cancer and non-small cell lung cancer. These different types are diagnosed based on how the cells look under a microscope. Finding lung cancer early is the key to treatment success.
Doctors cannot always explain why one person develops lung cancer and another does not. However, we do know that smoking is by far the most important risk factor for lung cancer and causes most cases.
Other factors that may increase the chance of developing lung cancer include exposure to radon (a radioactive gas) and a variety of naturally-occurring substances used in industry including asbestos, arsenic, chromium and nickel, air pollution, a family history of lung cancer, age over 65, and a history of having other lung diseases such as bronchitis or tuberculosis over time.