Don't Be Afraid of Colorectal Cancer Screening
Just talking about a colonoscopy makes most people cringe. That's probably because the idea of having a tube inserted into your rectum and colon is disturbing.
But even more disturbing for many people is the thought of getting colorectal cancer. Colorectal cancer is the third most diagnosed cancer in the US, but second deadliest cancer in the US. It is the third deadliest cancer worldwide. But when diagnosed at an early stage, before the cancer has invaded the colon wall or spread to distant sites, the chances of survival are much higher.
Still, by definition, all screening tests are performed on people who feel fine except for the anxiety they have about their future health. And while some screening tests clearly decrease the risk of dying, that is certainly not true of all of them.
What about colorectal screening? Is the unpleasant prospect of having a colonoscopy or some other equally disagreeable procedure really worth it? For many of us, the answer is “yes”.
Screening Tests: What Do They Entail?
All colorectal screening tests are designed to detect, either directly or indirectly, fingerlike projections of tissue, called polyps. Polyps may be cancerous or precancerous. Although most polyps are not cancerous, the vast majority of colorectal cancers are believed to begin as polyps. Fortunately, not all the screening tests for colorectal cancer are invasive.
Here's what's involved with each test:
Fecal Occult Blood Test
The fecal occult blood test is a test for hidden blood in a sample of stool (feces) you have already passed. Blood in your feces may be the result of bleeding from a cancerous polyp in your colon or rectum, or it may be a sign of a more benign condition.
Stool DNA Test
This is a newer non-invasive method of testing an entire specimen of stool (feces) for altered DNA which is shed by colon cancer or polyps into the stool. It is more expensive than fecal Occult Blood Testing. The sensitivity for detecting cancer with this test is variable. One limitation is that this test does not detect all types of colon cancer.
For a flexible sigmoidoscopy, a thin, lighted tube is inserted into the rectum and lower colon to examine their internal mucosal lining. Images can be recorded on a video tape while the doctor looks for polyps and other abnormalities through an eyepiece.
For a colonoscopy, a thin, lighted tube similar to a flexible sigmoidoscope, only much lighter, is used. This time, the lighted tube goes all the way through to the end of your colon where it connects to the small intestine. Polyps that are detected can be removed during the same procedure.
Digital Rectal Exam
A digital rectal exam involves the insertion of a lubricated, gloved finger into the rectum to check for lumps, polyps, or other abnormalities inside of the rectum.
Double-Contrast Barium Enema
A double-contrast barium enema involves the injection of a fluid called barium followed by air into your rectum. This makes your entire colon visible on an x-ray, allowing doctors to see abnormal growths, like polyps.
Computed Tomography (CT) Colography
Computed tomography colography (“virtual colonoscopy”) is a new technique that takes computer generated x-ray images after injection of air into the colon. This approach may not be quite “ready for prime time,” but it’s getting close. It can detect some lesions that colonosocopy cannot, but misses others. It has a major advantage over colonoscopy in that it is less expensive and safer; however, if a polyp is discovered during colonoscopy it can be removed right then and there, while if one is detected with virtual colonoscopy, a follow up real colonoscopy will be necessary.
The American Cancer Society suggests that starting at age 50, men and women should be screened for colorectal cancer with one of the following options:
- Yearly fecal occult blood test (preferably the take-home, multiple sample method); or
- Flexible sigmoidoscopy every 5 years; or
- Fecal occult blood test every year and flexible sigmoidoscopy every 5 years; or
- Double-contrast barium enema every 5 years; or
- Colonoscopy every 10 years
However, people at increased risk of colorectal cancer may need to have some of these tests earlier in life and more often. You're considered to be at increased risk if you have any of the following:
Colonoscopy can undoubtedly detect and remove precancerous polyps throughout the colon and rectum. And since some people who have no polyps in the rectum and lower colon (where sigmoidoscopy reaches) turn out to have them farther up, colonoscopy is more likely to find polyps and tumors than any of the other tests.
But here's the controversy. Some of these tests have been shown to help prevent deaths from colorectal cancer and others have not. And they may not be the ones you'd expect.
Digital rectal exam is a simple test, but not very effective at detecting polyps. Although barium enema is effective at detecting larger polyps throughout the colon, studies have shown that it is a less effective screening tool than colonoscopy. There is evidence that annual or biennial fecal occult blood tests in people aged 50 to 80 decreases the risk of dying from colorectal cancer. However, since many other problems produce blood in the colon, a lot of people end up having false positive results. Having the test every two years instead of annually can reduce this risk.
The US Preventive Services Task Force recently determined that regular sigmoidoscopy alone or in combination with FOBT reduces colorectal mortality. There is insufficient evidence, however, to know exactly how often people should undergo sigmoidoscopy, although many authorities say every five years is probably reasonable.
As for colonoscopy, there is currently no evidence that screening everyone irrespective of their risk would save lives. Although colonoscopy is considered generally safe, it is more risky than any other colorectal screening test and far more expensive. On the other hand, one-half of people who have polyps or tumors in the upper part of the colon, where only a colonoscopy reaches, have no polyps or tumors in the lower colon, where the sigmoidoscopy reaches. This means that many patients who only undergo sigmoidoscopy will have polyps missed. It is here that virtual colonoscopy makes a contribution; however, it may miss certain small polyps, and is less accurate when done in some centers than in others.
What Tests Do You Need?
While it now seems clear that screening for colorectal cancer after age 50 in average risk individuals is better than not screening at all, the best combination of screening tests and their frequency has yet to be determined. So, how do you know what screening tests you need and when?
For starters, you ought to at least have the yearly fecal occult blood test starting at age 50, and you should probably consider having a sigmoidoscopy at least every five years, since most of the evidence indicates that these tests save lives. Talk to your doctor about the advantages and disadvantages of a full colonoscopy, especially if your risk for colorectal cancer is greater than average. Also consider a virtual colonoscopy. These tests may save your life.
American Cancer Society
National Cancer Institute
National Institutes of Health
Canadian Cancer Society
Colon Cancer Canada
American Cancer Society. Available at http://www.cancer.org/.
American Gastroenterological Association. Available at http://www.gastro.org/.
Centers for Disease Control and Prevention. Available at http://www.cdc.gov/.
Levin B, Lieberman DA, McFarland B, et al. Screening and surveillance for the early detection for colorectal cancer and adenomatous polyps, 2008: a joint guidline from the American cancer society, the US multi-society task force on colorectal cancer, and the American college of radiology. Gastroenterology. Feb 8, 2008.
National Cancer Institute. Available at http://www.nci.nih.gov/.
U.S. Preventive Services Task Force. Available at http://www.ahcpr.gov.
Last reviewed April 2008 by Rimas Lukas, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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