Lung cancer: What is it?

Lung cancer starts in the lungs. It is a tumor of abnormal cells that reproduce rapidly and do not grow into normal lung tissue. A lung cancer tumor can grow in one or both lungs.

There are two main types of lung cancer.

Non-small cell lung cancer is the most common lung cancer.

Non-small cell lung cancer accounts for about 80 percent of lung cancers. There are three types of non-small cell lung cancer:

  • Adenocarcinoma starts in the outer part of the lungs.
  • Squamous cell carcinoma is usually found in the middle of the lungs.
  • Large cell undifferentiated carcinoma can start anywhere in the lungs and spreads more rapidly than other non-small cell lung cancers.

Small cell lung cancer is a fast-growing lung cancer.

Small cell lung cancer accounts for about 20 percent of lung cancers. The cells are small but multiply quickly and spread to other organs.

Small cell lung cancer is also called small cell carcinoma or oat cell cancer.


Malignant mesothelioma is a cancer that involves the lining of the lung. Although it occurs in the chest, it is not considered a form of lung cancer.

Lung cancer facts

  • Lung cancer causes more deaths than any other type of cancer.
  • Lung cancer is the most preventable type of cancer.
  • To prevent most lung cancer cases, all you need to do is stop smoking—or never start.

Get more lung cancer facts from our health encyclopedia.


Reviewed By: Katie Schwarzkopf, manager, Lung Program at the Virginia Piper Cancer Institute - Abbott Northwestern Hospital
First Published: 09/30/2009
Last Reviewed: 09/01/2011

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