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Cancer of the colon or rectum is called colon or colorectal cancer. It develops in the digestive tract from polyps that initially are benign, but that over time mutate into a cancerous tumor. The cancer cells invade and destroy nearby tissue, and can break away to form new tumors in other parts of the body, a process called metastasis.
The three sections of the colon — ascending, transverse and descending (also called sigmoid colon) — and rectum are part of the body's gastrointestinal system that digests, processes and eliminates food, together forming a muscular tube more than 5 feet long. Most colon cancers begin in the sigmoid colon just above the rectum.
Colon cancer is the third most commonly diagnosed cancer and the second leading cause of cancer death in the United States. Approximately 55,000 Americans will die as a result of colon cancer in 2008.
Fortunately colon cancer is both preventable and highly treatable when detected early. Because people may be asymptomatic for many years — precancerous lesions or polyps may take 10 years to transform from benign to malignant — screening and early detection are keys to survival. More than 90 percent of patients with early stage colon cancer survive more than five years.
Very early colon cancer that develops within a polyp often can be cured by removing the polyp during a colonoscopy, a simple outpatient screening procedure. More-advanced tumors usually require surgical removal, which in many cases is followed by chemotherapy.
Colon-cancer symptoms may be few or nonexistent — patients may be asymptomatic for many years — which is a primary reason screening should begin at age 50 or earlier for those at high risk. When symptoms do occur, they may include:
Less-specific symptoms may include anemia, unexplained weight loss and weakness.