In a commentary published this week in JAMA, colon cancer experts at Columbia University Medical Center are raising questions about the effectiveness of colonoscopies, which may be no better at preventing deaths from colon cancer than other, less arduous screening methods.
“It is disconcerting to realize that 20 years have passed since we first started using colonoscopy for screening, and we still don’t have adequate data to back the long-held belief that it is superior to other methods,” says the commentary’s co-author Alfred Neugut, MD, the Myron M. Studner Professor of Cancer Research in the College of Physician and Surgeons and professor of epidemiology in the Mailman School of Public Health.
“If further studies continue to find that colonoscopy is not an improvement, we should be prepared to consider returning to sigmoidoscopy for screening while we explore ways to enhance colonoscopy’s effectiveness,” Dr. Neugut says.
Colonoscopy Popularized in 1990s
Today, most people who are screened for colon cancer choose colonoscopy. Before colonoscopy became popular for screening in the late 1990s, physicians used a similar method called sigmoidoscopy. In both methods, a camera attached to a flexible endoscope is inserted into the colon to look for cancer and pre-cancerous polyps. The difference lies in the length of the scope: a sigmoidoscope only examines the left side of the colon, while a colonoscope can inspect the entire colon.
Restricting the exam to the left side of colon seemed reasonable in the 1970s when most cancers were located on the left. Studies eventually showed that sigmoidoscopy reduces deaths from colon cancer by about 40-60 percent. But during the 1980s, the cancer distribution changed, and cancers are now evenly scattered throughout the entire colon.
The change in distribution prompted Dr. Neugut in 1988 to publish the first article suggesting that physicians switch from sigmoidoscopy to colonoscopy. “I essentially said that if you think sigmoidoscopy is good, you’ll love colonoscopy. It made sense to change to a method that could detect the increasing number of cancers showing up on the right side.”
In the 1990s, colonoscopy grew increasingly popular as a screening method. In 2001, Medicare and private insurers started reimbursing doctors for performing screening colonoscopies.
“There used to be a saying that getting a sigmoidoscopy is like getting a mammography on one breast,” says Benjamin Lebwohl, MD, a gastroenterologist at Columbia University Medical Center and co-author of the JAMA commentary.
Today, colonoscopy is the preferred option for screening in the American College of Gastroenterology’s guidelines, and sigmoidoscopy screening in the United States is almost obsolete.
Colonoscopy Vs. Sigmoidoscopy
But Drs. Neugut and Lebwohl now say that three recent studies cast doubt on the idea that colonoscopy – as currently performed – is better than sigmoidoscopy at reducing deaths from colon cancer.
The first study, an analysis published in 2008 of a claims database in Canada, found that colonoscopy reduces the number of deaths from colon cancer, but only by about 40 percent, the same amount as sigmoidoscopy. More surprisingly, the study found that colonoscopy did not reduce mortality from right-sided colon cancers.
“It was very surprising. The logic for using colonoscopy is based on its extended range into the right side of the colon, and this paper showed the entire mortality reduction from colonoscopy came from the left side,” Dr. Neugut says. “The paper raised a lot of eyebrows, but it was only one study, and there could be several reasons why the results could have been aberrant.”
However, two new papers were published in the past six months that confirm the Canadian findings.
“We now have three studies that show colonoscopy gives you the same overall results as sigmoidoscopy with no apparent benefit on the right side,” Dr. Lebwohl says. “The data so far are not living up to the high hopes we have for colonoscopy.”
That doesn’t mean people should stop having colonoscopies just yet, both researchers say.
“If we had this kind of data before introducing colonoscopy, we probably wouldn’t have started doing them,” Dr. Neugut says. “But colonoscopy is now widely accepted and used among doctors and patients. The evidence isn’t strong or persuasive enough at the moment to go back to sigmoidoscopy.”
One reason to stick with colonoscopy, Dr. Lebwohl says, is that all three studies were conducted in Canada or Europe, where a large percentage of colonoscopies are not done by gastroenterologists. In the United States, about 75 percent of colonoscopies are performed by gastroenterologists.
“It’s possible that the physicians performing the colonoscopies in the three studies did not inspect the entire length of the colon,” Dr. Lebwohl says. Colonoscopies require special training to guide the scope around several bends in the colon until the scope reaches the cecum, where the colon meets the small intestine.
“It’s not always obvious when you’ve reached the cecum,” Dr. Lebwohl says. “Physicians should photograph landmarks to document that the cecum has been reached, but recognizing the cecum takes experience. Other structures in the colon can mislead you.”
Another explanation for colonoscopy’s disappointing data may be failure to fully prepare the bowel before the procedure.
“If you ask patients what’s the hardest thing about colonoscopy, it’s not the procedure, it’s the bowel preparation,” Dr. Lebwohl says. “Although the preparation is extremely safe, it can be difficult. It can cause nausea, bloating, and abdominal cramping, and the intended effect—emptying the colon—is unpleasant. I often tell patients who arrive for their colonoscopy: ‘The worst part is over.’”
In a study published this month, Drs. Lebwohl and Neugut found that 19 percent of patients had not fully emptied their bowels, which can lead the physician to miss suspicious polyps during the examination. Because clearing the right colon is more difficult than clearing the left, poor bowel preparation may contribute to the mortality differences between right- and left-sided cancers after colonoscopy.
At the very least, until more data come in, the authors say sigmoidoscopy shouldn’t be disparaged or relegated to a non-preferred status. “Sigmoidoscopy is less arduous for the patient. There’s no bowel prep, no need for sedation, no need for the patient to miss a day of work, and sigmoidoscopy has fewer complications,” Dr. Neugut says.
Although colon cancer rates in the United States are declining, colon cancer is still the second leading cause of cancer deaths in men and women.
“Colonoscopy, sigmoidoscopy, and fecal blood tests all have excellent evidence behind them,” Dr. Lebwohl says. “The best screening method for colon cancer is the one that we can persuade patients to undergo.”