Types Definition of lung cancer: Cancer that forms in tissues of the lung, usually in the cells lining air passages. The two main types are small cell lung cancer and non-small cell lung cancer. These types are diagnosed based on how the cells look under a microscope. 
Estimated new cases and deaths from lung cancer (non-small cell and small cell combined) in the United States in 2008:
- New cases: 215,020
- Deaths: 161,840