Lung cancer is a cancer that forms in the lung or surrounding tissue. There are two major types of lung cancer: non-small cell lung cancer and small cell lung cancer. Non-small cell lung cancer is much more common. It usually spreads to different parts of the body more slowly than small cell lung cancer. Squamous cell carcinoma, adenocarcinoma, and large cell carcinoma are three types of non-small cell lung cancer. Small cell lung cancer also called oat cell cancer, accounts for about 20% of all lung cancer.