What Is Lung Cancer?

Outline of male figure with arrows showing lung cancer spreading to liver, other lung, bone, and brain.Your body is made up of tiny building blocks called cells. Normal cells grow when your body needs them, and die when your body doesn't need them. Lung cancer starts when cells in the lungs are damaged and grow out of control. These cells grow even though your body doesn't need them. These cells are called cancer cells. Cancer cells grow at a different rate than normal cells. Their size and shape are also not normal. Over time, enough of them can grow in one area to form a mass or tumor. Cancer cells can spread to other areas in the lungs. Or, they can travel to other parts of the body.

There are 2 main types of lung cancer:

Non-small cell lung cancer

Most cases of lung cancer are called non-small cell. There are a few different types of non-small cell lung cancer. These include 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. (The cells are shaped like oats when viewed under a microscope.) This type of lung cancer may grow and spread faster than non-small cell cancer.

How cancer spreads

Cancer cells don’t always stay in one place. Cancer cells can break off from the place they started. They can spread to other parts of the body if they enter the bloodstream. They can also spread if they enter the lymph system. The lymph system is a network of nodes and vessels that help your body fight disease. When cancer spreads, the process is called metastasis. Lung cancer that spreads (metastasizes) often goes to the other lung or the liver, brain, or bones.