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Screening for Colon

and Rectal Cancer

Colorectal cancer is the third most common cancer worldwide and the second leading cause of cancer deaths in the United States after lung cancer. It is estimated that in 2020 there will be 147,950 new cases of colorectal cancer in the United States and that 53,200 people will die of this disease. About 5% of Americans are expected to develop the disease within their lifetime and it occurs equally in men and in women.

Cancer is a disease characterized by the uncontrolled growth of abnormal cells. Genetic, experimental, and population studies suggest that colorectal cancer results from complex interactions between inherited susceptibility and environmental or lifestyle factors. Most bowel cancers come from polyps, which are small, benign (non-cancerous) growths on the lining of the colon and rectum. It is believed that ten to fifteen percent of all persons have colon polyps. Since most polyps cause no symptoms, people who have polyps usually are totally unaware of this condition.


Detection and removal of polyps before they become malignant can prevent cancer and save many lives. Even if cancer already is present, early detection, before the cancer has had a chance to spread, is the most important factor in curing cancer and saving lives.

Screening Guidelines

To detect colon cancers and colon polyps early, the American Cancer Society recommends performing certain screening examinations at regular intervals. While the risk of colon and rectal cancer starts to increase after age 50, the risk of colon polyps may begin to rise several years earlier. Patients are often divided into risk groups which help to define what screening they need.


For the person who is at average risk for developing colon polyps or cancer, minimum testing involves annually checking the stool for hidden blood and flexible sigmoidoscopy every five years, starting at age 45. Alternate testing is colonoscopy every 10 years. Barium enema combined with sigmoidoscopy every 5 years is another screening option. Most physicians believe that colonoscopy should be performed at least once in each person’s life to fully assess the individual risk. Average-risk individuals have a 1 in 17 lifetime chance of developing colorectal polyps or cancer.


Certain individuals have an above average risk for developing polyps or cancers of the colon and rectum. This risk group includes persons with: 

1. Personal history of polyps or cancer of the colon or rectum. 

2. A personal history of cancer of the breast or female organs. 

3. Certain kinds of inflammatory bowel disease, such as ulcerative colitis.

4. A closely-related family member with polyps or cancer of the colon or rectum. 

Above average risk individuals have a 1 in 6 lifetime risk of having colorectal polyps or cancer. These individuals should have colonoscopy beginning at age 40 (or 10 years younger than the affected relative’s age when first diagnosed, whichever is earlier). This test should be done every five years or more frequently if there are many polyps or aggressive polyps identified.

Some individuals have a high risk of colorectal cancer. These include those with hereditary (familial) cancer causing syndromes. These individuals have a 50 to 100% lifetime risk of colorectal cancer. These individuals should begin screening at puberty, and have annual colonoscopy beginning at age 20; they commonly will need surgery to remove the entire colon.

Frequently Asked Questions

  • What is stool testing?
    This is a non-invasive test during which you place samples of stool on testing cards. A chemical is added revealing digested blood or abnormal DNA from colon cells. This test is done annually and should be combined with direct inspection of the lowest part of the colon every five years (flexible sigmoidoscopy). If it is positive, colonoscopy must be performed.
  • What is flexible sigmoidoscopy?
    This is a test during which your physician directly inspects the lower third of the colon with a lighted flexible tube. This is usually done in the physician’s office after a cleansing enema. There is no sedative given and the test takes about 10 minutes. This test is done every 5 years, and must be combined with evaluation of the upper colon with Hemoccult testing. If polyps are found, then colonoscopy must be performed to remove them.
  • What is a barium enema?
    This is an X-ray test during which a special liquid (barium contrast) is placed into the colon to outline the bowel wall and identify any areas of abnormal contour which may be polyps, inflammation, or pockets. In order to perform this examination, the colon must be cleared of any waste material with a laxative preparation (or prep). If polyps are found, then colonoscopy should be performed to remove them.
  • What is virtual colonoscopy (CT colonography)?
    Virtual colonoscopy refers to the examination of computer-generated images of the colon constructed from data obtained from an abdominal computed tomographic (CT) examination. Patients must take laxatives before the procedure and a catheter is placed in the rectum to fill the colon with air during the study. No sedation is given during this test. If polyps are identified, then standard colonoscopy needs to be performed to remove them. In patients with a history of colon polyps or symptoms of colon disease, CT colonography has been shown to be less able to detect abnormalities and even cancers compared to conventional colonoscopy.
  • What is colonoscopy?
    During this test the entire large intestine is examined for abnormalities, using a lighted flexible tube with a video transmittal chip. The test is performed in an endoscopy unit with monitoring and intravenous sedation for comfort. Prior to the test the colon must be cleared of waste material with laxatives and a restricted diet. During colonoscopy, abnormal areas will be sampled and polyps or growths may be removed for microscopic examination. The exam takes about 30 minutes; you then rest in the recovery area until the sedatives have worn off. You must have someone drive you home.
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