Cancers of the colon and rectum, often collectively referred to as colorectal cancer, are life-threatening tumors that develop in the large intestine.
More than 80% of colorectal tumors develop from adenomatous polyps. These gland-like growths develop on the mucous membrane that lines the large intestine. They are usually either:
- Tubular polyps, which protrude mushroom-like
- Villous adenomas, which are flat and spreading and are more apt to become malignant (cancerous)
Polyps are very common, and most of them are benign. Their numbers increase with age. Polyps are found in about 25% of people by age 50, and 50% of people by age 75. Fewer than 1% of polyps under 1 centimeter (slightly less than half an inch) become cancerous. About 10% of larger polyps become cancerous within 10 years, and about 25% of these larger polyps become cancerous after 20 years.
The Gastrointestinal Tract
Digestion takes place in the gastrointestinal (GI) tract, essentially a long tube that extends from the mouth to the anus. It is a complex organ system that first carries food from the mouth down the esophagus to the stomach. Food then travels through the small and large intestines before being excreted through the rectum and out the anus.
The esophagus is a narrow muscular tube, about 9 1/2 inches long, that begins below the tongue and ends at the stomach.
Review Date: 10/21/2010
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.