Introduction
Cancers of the colon and rectum, often referred to collectively as colorectal cancer, are life-threatening tumors that develop in the large intestine.
More than 80% of colorectal tumors evolve from adenomatous polyps. These are gland-like growths that develop on the mucous membrane that lines the large intestine. They are usually one of the following types:
- Tubular polyps, which protrude mushroom-like.
- Villous adenomas, which are flat and spreading and are more apt to become malignant (cancerous).
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It should be noted that these polyps are very common and almost always benign. Their numbers increase with age. Polyps are found in about 25% of people by age 50 and half of people by age 75. Fewer than one percent of polyps under one centimeter (slightly less than half an inch) become cancerous (malignant). About 10% of larger polyps become malignant within 10 years and about 25% of these larger polyps become cancerous after 20 years. Certain inherited polyps can become malignant more rapidly.
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.
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| The esophagus, stomach, large and small intestine, aided by the liver, gallbladder and pancreas convert the nutritive components of food into energy and break down the non-nutritive components into waste to be excreted. |
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