Although lung cancer accounts for only 15% of all newly-diagnosed cancers in the United States, it is the leading cause of cancer death in U.S. men and women. It is more deadly than colon, breast, and prostate cancers combined. About 160,000 patients die from lung cancer each year. Death rates have been declining in men over the past decade, and they have about stabilized in women.
The lungs are two spongy organs surrounded by a thin moist membrane called the pleura. Each lung is composed of smooth, shiny lobes: the right lung has three lobes, and the left has two. About 90% of the lung is filled with air. Only 10% is solid tissue.
- Air is carried from the trachea (the windpipe) into the lung through flexible airways called bronchi.
- Like the branches of a tree, the bronchi in turn divide into over a million smaller airways called bronchioles.
- The bronchioles lead to grape-like clusters of microscopic sacs called alveoli.
- In each adult lung, there are about 300 million of these tiny alveoli. A thin membrane makes up the alveoli sacs. Oxygen and carbon dioxide pass through this membrane to and from capillaries.
- Capillaries, the smallest of our blood vessels, carry blood throughout the body.
Lung cancer develops when genetic mutations (changes) occur in a normal cell within the lung. As a result, the cell becomes abnormal in shape and behavior, and reproduces endlessly. The abnormal cells form a tumor that, if not surgically removed, invades neighboring blood vessels and lymph nodes and spreads to nearby sites. Eventually, the cancer can spread (metastasize) to locations throughout the body.
The two major categories of lung cancer are small cell lung cancer and non-small cell lung cancer. Most lung cancers are non-small cell cancer, the subject of this report. Less common cancers of the lung are known as carcinoids, cylindromas, and certain sarcomas (cancer in soft tissues). Some experts believe all primary lung cancers come from a single common cancerous (malignant) stem cell. As it copies itself, that stem cell can develop into any one of these cancer types in different people.
Review Date: 07/01/2010
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.