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What is the Definition of Lung Cancer?


Updated May 08, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Question: What is the Definition of Lung Cancer?

The definition of lung cancer is a cancer (malignancy) that originates in the tissues of the lungs or the cells lining the airways. Lung cancer originates when normal lung cells become cancer cells, usually after a series of mutations, and begin to divide out of control.

A malignant (cancerous) lung tumor is distinguished from a benign (non-cancerous) lung tumor in that it can spread (metastasize) to areas of the body distant from the original tumor.

It is important to distinguish primary lung cancer from other forms of cancer that may spread to the lungs. Primary lung cancer begins in the lungs, but may spread to other regions of the body. If it spreads to the brain, it would be referred to as lung cancer metastatic to the brain. Likewise, if a cancer begins in the breast and spreads to the lungs, it would be referred to as breast cancer metastatic to the lungs.

Approximately 80% of lung cancers are classified as non-small cell lung cancers, while small cell lung cancers are responsible for 20% of cases. Lung cancer is now the leading cause of cancer deaths in both men and women in the United States and worldwide.

Though smoking is responsible for at least 80% of lung cancers, lung cancer is a multifactorial disease –- that is, many factors work together to either cause or prevent cancer. Exposure to radon in the home is the second leading cause of lung cancer in the U.S. and the leading cause in non-smokers.


National Cancer Institute. Lung Cancer. Accessed 06/22/10. http://www.cancer.gov/cancertopics/types/lung

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