Most lung cancers are caused by cigarette smoking. The more cigarettes you smoke per day and the earlier you started smoking, the greater the risk of lung cancer.

Second-hand smoke has also been shown to increase risk. Government surveys show that as many as 3,000 people each year develop lung cancer from second-hand smoke. High levels of pollution, radiation, and asbestos exposure may also increase risk.

Lung cancer begins by changes in cells that line the airways and can invade adjacent tissues before symptoms are noticed.

There are many types of lung cancer, but most can be categorized into two basic types, "small cell" and "non-small cell." Small cell lung cancer is generally faster growing than non-small cell, but more likely to respond to chemotherapy.

• Small cell cancer is divided into "limited stage" (generally cancer confined to the chest) and "extensive stage" (cancer that has spread outside the chest).
• Non-small cell cancer is divided into four stages, I-IV. Most patients with stage I and II non-small cell tumors and some patients with stage III tumors can undergo surgery with the goal of cure. Stage IV denotes cancer that has spread to other sites in the body (most often bone, brain, or liver) and is, in most cases, not curable.

Men and women die from lung cancer more than any other type of cancer. Lung cancer occurs most often in people between 55 and 65 years old.