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From OncoLog, September 2011, Vol. 56, No. 9

Colorectal Cancer Screening
Risk factors determine who should be screened and how often

Graphic: House CallRegular colorectal cancer screening has long been considered one of the best ways to prevent colorectal cancer or to find the disease early, when it is most treatable. More Americans than ever before are following recommendations for screening, and this has led to fewer deaths from colorectal cancer.

Yet a new report by the Centers for Disease Control and Prevention indicates that one in three Americans who should be screened for colorectal cancer is still not receiving the recommended screenings. If all people age 50 years and older were screened for colorectal cancer, the death rate from this disease would be cut in half, saving approximately 25,000 lives per year, the American Cancer Society reports.

Screening tests

After abnormal cells grow to become polyps on the inner wall of the colon or rectum, it usually takes 10–15 years before the polyps develop into colorectal cancer. Screening tests can detect these polyps, which, if found early, can be removed before they turn into cancer.

A variety of tests are used to screen for colorectal cancer and precancerous polyps in people who have no symptoms of the disease.

A colonoscopy, one of the most thorough tests, examines the rectum and entire colon with a lighted, flexible instrument called a colonoscope. Precancerous and cancerous growths found during the colonoscopy may be removed, or tissue samples may be taken for biopsy. Most patients receive some form of sedation before this test.

A virtual colonoscopy uses computed tomography (CT) or magnetic resonance imaging (MRI) to produce pictures of the colon and rectum that can show polyps and other abnormalities. No sedation is needed. If any polyps are detected, a standard colonoscopy is performed to remove them.

Other screening tests include sigmoidoscopy and double-contrast barium enema. A sigmoidoscopy is similar to a colonoscopy, but only the rectum and lower colon are examined. A double-contrast barium enema test uses a series of x-ray scans to examine the entire colon and rectum after the patient is given an enema with a barium solution and air is introduced into the colon.

To prepare for any of these tests, the patient’s colon and rectum must be empty. This usually means that the day before the test, the patient will consume only clear liquids and will take laxatives or enemas as prescribed by his or her doctor.

In another common screening procedure, the fecal occult blood test, tiny stool samples from the patient are tested to detect any blood in the stool. If the test is positive, a colonoscopy can determine the cause of the bleeding.

Screening guidelines

How often should these screening tests be done? That depends on a number of factors, including a patient’s risk of getting colorectal cancer.

Average risk
For people at average risk for colorectal cancer, MD Anderson physicians recommend any one of the following beginning at age 50 years: a colonoscopy every 10 years, a virtual colonoscopy every 5 years, or a fecal occult blood test every year.

Increased risk
People are considered at increased risk for colorectal cancer if they have a personal or family history of colorectal cancer or polyps.

For those who have had one or two small precancerous polyps removed, MD Anderson recommends a colonoscopy every 5 years. If they’ve had several polyps removed, they should be tested more often.

People with a first-degree relative (parent, brother, sister, daughter, or son) who had colorectal cancer or precancerous polyps before the age of 60 years—or two first-degree relatives who had these at any age—should have a colonoscopy every 5 years. These people can determine the age they should begin testing by subtracting 10 years from the relative’s age at diagnosis. For instance, if your brother was 50 years old when he was diagnosed with colorectal cancer, you should begin screening at age 40 years.

People with a first-degree relative who had colorectal cancer or precancerous polyps at age 60 years or older—or two second-degree relatives (grandparents, aunts, uncles, or cousins) with colorectal cancer—should start colorectal screening at age 40 years. For these people, MD Anderson recommends a colonoscopy every 10 years, a virtual colonoscopy every 5 years, or a fecal occult blood test every year.

High risk
People at the highest risk for colorectal cancer include those with a personal history of familial adenomatous polyposis, hereditary nonpolyposis colorectal cancer, Crohn disease, or chronic ulcerative colitis. For those in this risk category, MD Anderson recommends consulting a physician and undergoing screening every 1–2 years.

– K. Stuyck

For more information, talk to your physician, visit www.mdanderson.org, or call askMDAnderson at 877-632-6789.

Other articles in OncoLog, September 2011 issue:

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