Colon and Rectal Cancers - Introduction

Highlights	Treatment	Radiation Treatment
Introduction	Surgery	Follow-up Testing
Causes	Chemotherapy	Treatment for Metastasized Colorectal Cancer
Risk Factors and Prevention	Radiation	Resources
Symptoms	Resources	References
Diagnosis and Screening	References

Introduction

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.

text continues below

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, stomach, and 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.

Esophagus

The esophagus is a narrow muscular tube, about 9 1/2 inches long, that begins below the tongue and ends at the stomach.

Stomach

In the stomach, acids and stomach motion break food down into particles small enough so that the small intestine can absorb nutrients.

Click the icon to see an image of stomach anatomy.

Small Intestine

The small intestine, despite its name, is the longest part of the gastrointestinal tract, extending for about 20 feet. Food passes from the stomach through its three parts: first the duodenum, then the jejunum, and finally the ileum. Most of the digestive process occurs in the small intestine.