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Understanding Tests That Screen for Colon Cancer

Article date: February 28, 2014

By Stacy Simon

Over the past few decades, more people have been surviving colon cancer, and fewer people have been dying from it. This is thanks partly to improvements in colon cancer screening. Screening is the process of looking for cancer or pre-cancer in people who have no symptoms of the disease. It can find colon cancer early, before symptoms develop, when it’s easier to treat. Screening can also sometimes find growths called polyps so they can be removed before they turn into cancer. That means screening can sometimes prevent colon cancer altogether.

The American Cancer Society recommends regular colon cancer screening for most people starting at age 50. People with a family history of the disease or other risk factors should talk with their doctor about beginning screening at a younger age.

Several different tests can be used to screen for colon cancer. Some are less able to find polyps and more likely to find cancer. Other tests not only can find cancer, but also are better at finding polyps; these tests may be more likely to prevent colon cancer.

Tests that can find polyps and cancer:

  • Colonoscopy uses a flexible lighted tube with a small camera on the end to examine the entire length of the colon and rectum. If polyps are found, they may be removed during the test. To prepare for the test, you may be asked to follow a special diet for a day or two before the test. You will also need to clean out your colon with strong laxatives (called a bowel prep) and sometimes with enemas, as well. Most people are sedated during the test. If nothing is found during the test, you won’t need another one for 10 years.
  • Flexible sigmoidoscopy is similar to colonoscopy, but examines only part of the colon and rectum. If polyps are found, they may be removed during the test, or you may need to have a colonoscopy later. Bowel prep may be required, but is not as extensive as the one used for colonoscopy. Most people do not need to be sedated during this test. If polyps or suspicious areas are seen, a colonoscopy will be needed to look at the rest of the colon. Flexible sigmoidoscopy must be done every 5 years.
  • Double-contrast barium enema is a type of x-ray test. It involves injecting a liquid called barium into the rectum, which spreads through the colon. Air is then pumped in to spread the barium in a thin, smooth layer to show better detail. Then x-rays are taken. It requires bowel prep, but no sedation. If polyps or suspicious areas are seen on the test, a follow-up colonoscopy will be needed. Barium enemas also need to be repeated every 5 years.
  • CT colonography (also called virtual colonoscopy) is a scan of the colon and rectum that produces detailed cross-sectional images so the doctor can look for polyps or cancer. It requires bowel prep, but no sedation. Air is pumped into the rectum and colon , and then a CT scanner is used to take images of the colon. If something is seen that may need to be biopsied, a follow-up colonoscopy will be needed. CT colonography must be done every 5 years.

Tests that mainly find cancer:

  • Fecal occult blood test and fecal immunochemical test are used to detect tiny amounts of blood in the stool that could indicate the presence of cancer or large polyps. People take these tests at home with a kit they receive from their doctor’s office, along with instructions. A positive result will need to be followed up with a colonoscopy. However, many times the cause is a non-cancerous condition, such as ulcers or hemorrhoids. Stool tests like these need to be done every year.

What’s new in colon cancer screening

New imaging and lab tests that can be used for colon cancer screening continue to be developed and tested. Some of the tests are newer, more accurate ways to look for changes in the stool that might indicate colon cancer.

Also new is a pill with a tiny camera inside that can take pictures of the colon after the patient swallows it. For now it is only available as a follow-up procedure for people who have not been able to complete a colonoscopy, not as its own screening test. The pill still requires a bowel prep and some limitations on activity while the pill camera makes its way through the intestinal tract, which can take up to 10 hours. If suspicious areas are seen, surgery, CT colonography, or another procedure may be recommended.

Talk to your doctor about screening

Regular screening is one of the most powerful weapons for preventing colon cancer. If polyps are found during colon screening, they can usually be removed before they have the chance to turn into cancer. Screening can also result in finding cancer early, when it is easier to treat and more likely to be curable.

If you’re 50 or older, talk to your doctor about which test is right for you and get tested as often as recommended.

Reviewed by: Members of the ACS Medical Content Staff

ACS News Center stories are provided as a source of cancer-related news and are not intended to be used as press releases. For reprint requests, please contact permissionrequest@cancer.org.

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