Cancer starts when cells change (mutate) and grow out of control. The changed (abnormal) cells often grow to form a lump or mass called a tumor. Cancer cells can also grow into (invade) nearby areas. They can spread to other parts of the body, too. This is called metastasis.
Lung cancer is cancer that starts in the cells that make up the lungs. The lungs are sponge-like organs in your chest. Their job is to bring oxygen into the body and to get rid of carbon dioxide. When you breathe air in, it goes into your lungs through your windpipe (trachea).
Lung cancer is divided into 2 main types:
Non-small cell lung cancer. Most lung cancers are non-small cell. They're named for how cancer cells look under a microscope. There are a few different types, such as squamous cell carcinoma, adenocarcinoma, and large cell carcinoma.
Small cell lung cancer. Small cell lung cancer is less common than non-small cell lung cancer. Small cell cancer is sometimes called oat cell cancer. This is because the cancer cells are shaped like oats when looked at under a microscope. This type of lung cancer may grow and spread faster than non-small cell cancer.