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Colon Cancer Screening Guidelines - Colonoscopy Better Than Sigmoidoscopy? The Truth and the Myth

Posted Mar 07 2011 12:52am
Colon cancer screening has a particular personal interest for me.  One of my colleagues in residency training had her father die of colon cancer when she was a teenager.

No one should lose a love one to a disease when caught early is often treatable.  Although for both men and women, colon cancer is the third most common behind lung and prostate cancer in men and behind lung and breast cancer in women, it is the second most lethal.

The problem is that patients are often confused about which test is the right one.  Is it simply a stool test?  Flexible sigmoidoscopy?  Colonoscopy?  Virtual colonoscopy?   Isn't there just a blood test that can be done? (No.)

In real simple terms, this is all you need to know. 

All men and women age 50 and older should be screened for colon cancer.  Even if you feel healthy and well and have no family history, it must be done.  Note that Oprah's doctor, Dr. Oz, arguably a very health conscious individual learned that he had a colon polyp at age 50 after a screening test.  Left undetected, it could have cut his life short.  This wake-up call caused him to abort his original second season premier on weight loss and instead show the country why colon cancer screening matters.  He admitted that if it wasn't for the show and the need to demonstrate the importance of screening to America, he would have delayed having any test done.

The least invasive test is a stool test.  If it is to screen for colon cancer, then the test is done at home and NOT in the doctor's office.   Either the fecal occult blood (FOBT) or the fecal immunochemical test (FIT) are available to screen for unseen microscopic blood that could be a sign of a colon polyp or cancer.  Research shows that when done annually the risk of dying from colon cancer can fall by 15 to 33 percent.   If you don't want any fiber optic cameras in the rectum and lower colon, this is the test for you.  You must do it annually.

The next two tests are similar but often confused - the flexible sigmoidoscopy and the colonoscopy.

The flexible sigmoidoscopy examines the lower third of the colon, known as the sigmoid and the descending colon.  Patients cleanse the lower colon by ingesting a small amount of laxative the day before the procedure.  If a colon growth or polyp is found, it can be biopsied or completely removed during the procedure.  The test is typically done in 15 to 20 minutes.  Patients are awake for the procedure and can go home.  Research shows this test can decrease the number of deaths due to colon cancer.  The risk of the procedure is very small with about 1 in every 5,000 patients having a small tear or perforation.  This flexible sigmoidoscopy test is done every 5 years. 

Like the sigmoidoscopy, the colonoscopy also requires cleansing of colon, however, a gallon of laxative is require to empty the entire colon.  Colon growths and polyps can be removed similarly.  Unlike the sigmoidscopy, however, the colonoscopy requires that patients be sedated.  As a result, you will need someone to take you to the appointment and drive you home.  Although the procedure itself takes about 30 minutes, it can be a few hours from arriving to going home due to the anesthesia.  Out of all of the screening tests, it is the most risky with an estimated perforation rate and cause of serious bleeding affecting in 1 in 1,000 patients.   A colonoscopy is done every 10 years.

Would checking the entire colon with a colonoscopy be better than evaluating the lower third of the colon with a sigmoidoscopy?  Evidence that colonoscopies save lives from colon cancer is lacking.  This subtle but important point is often not mentioned in media reports.  Even the NY Times perpetuated this belief that colonoscopy is the preferred test in its January 20th, 2011 article, " Why People Aren't Screened for Colon Cancer. "  When family medicine doctor and lecturer in health care policy at Harvard medical school, Dr. John Abramson, wrote a letter to the NY Times editor in February 15th, 2011, noting the this fact in an unrelated article, the American College of Gastroenterology (ACG) wrote a letter indicating that a colonoscopy is their preferred test for screening.

No wonder patients are confused.

If one dissects the ACG letter carefully , we note the following language (words bolded for emphasis):

American College of Gastroenterology’s 2009 colorectal cancer screening guidelines recommend colonoscopy as the preferred cancer prevention strategy, and guidelines by the American Society for Gastrointestinal Endoscopy in 2006 also endorse colonoscopy because of its ability to view the entire colon and remove potentially precancerous polyps, reflecting a strong opinion of these experts that prevention should be the primary goal of colorectal cancer screening.

While public health experts have recently debated the exact parameters to measure the impact of these screening strategies on mortality, a clinical picture that is muddied by the many variables affecting the quality of the examination, the jury is still out. Indeed colonoscopy’s protective power may lie in a growing appreciation that the biology of precancerous polyps and cancer is different in the right compared to the left colon.

In other words, the recommendation is based on opinion.  There is no language indicating that there is evidence.  The "protective power may lie" in such and such, but hasn't been confirmed.  Examples of when doctors made opinions when evidence was lacking only to change their minds later include hormone replacement after menopause, bone marrow transplant for breast cancer treatment, and prostate cancer screening with PSA .

A study that appeared in the Annals of Internal Medicine in the January 6th, 2009 issue, researchers found that colonoscopies did cut down colon cancer deaths, but it was due to detection of the left sided colon cancers (sigmoid and descending colon) and not to the right side, of which only the colonoscopy can reach.  In other words, a flexible sigmoidoscopy would have detected the cancers as well, which has been observed in previous studies. 
Researchers reviewed health records for persons aged 52 to 90 who received a colorectal cancer diagnosis between 1996 and 2001 and died of colorectal cancer by 2003. These patients were compared to a control group who were selected from the population of Ontario and had not died of colorectal cancer.
According to the researchers, complete colonoscopy was strongly associated with fewer deaths from left-sided colorectal cancer. Conversely, the data showed that colonoscopy seemed to have almost no mortality prevention benefit for right-sided colorectal cancer.
So who do you listen to?  I typically review the guidelines from the American Cancer Society (ACS).  As a group advocating cancer screening and awareness, they should have no bias about what test to use to screen for colon cancer.   For individuals at average risk for colon cancer, ACS notes that to find colon polyps or cancer, either a sigmoidoscopy every 5 years or colonoscopy every 10 years.  Their recommendations don't say the preferred option is a colonoscopy.  The Centers for Disease Control the US Preventive Services Task Force , and the National Cancer Institute also say little about which is preferred. 

What does this mean to you?  For those at average risk and no family history of colon cancer, get screened for colon cancer at age 50.  At the bare minimum, do an annual stool test if you don't want an invasive procedure.  Know that at this time there is no evidence that colonoscopy is better than a flexible sigmoidscopy. 

If people tell you otherwise ask them to show you the evidence.

And let me know.
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