Colon Cancer

Risks

Nearly half of all colon cancers occur in the rectum and sigmoid colon.

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The colon comprises the upper four to six feet of the large intestine. The colon absorbs water, salt and other minerals from food, and waste is stored in the lower colon until it is eliminated from the body. The colon is a continuous tube with four sections: the ascending colon, the transverse colon, the descending colon, and the sigmoid colon.

Most colon cancers begin as small clusters of cells called adenomatous polyps. Over a long time — up to several years — some polyps may become cancerous. Large polyps are more likely to become cancerous than small ones.

In later stages of the disease, cancerous tumors may penetrate the colon wall. These tumors may also spread (metastasize) to nearby lymph nodes or other organs.

The cause of colon cancer is unknown. Knowing the risk factors for colon cancer is an important step in prevention. Colon cancer risk factors include:

• A diet that includes foods high in fat, especially from animal sources
• Physical inactivity
• Aging (about 90 percent of people with colon cancer are over 50)
• A history of intestinal polyps
• Ulcerative colitis or Crohn's disease
• A family history of colon cancer