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 increases the 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 in cells that line the airways and often invade adjacent tissues or spread elsewhere in the body before symptoms are noticed.
About 20% of all lung cancer cases are small cell lung cancer, meaning about 30,000 patients each year are diagnosed with this disease.
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