Worth the Hype: Colonoscopies are the most useful tool we have to prevent colorectal cancer


Numerous studies over the years have found that colonoscopies significantly reduce the risk of developing colorectal cancer — one of the leading causes of cancer deaths in the U.S. So when a new study published in the New England Journal of Medicine last month cast doubt on the effectiveness of colonoscopies, doctors were puzzled.

The study found a meager 18 percent reduction in colorectal cancer among thousands of men and women who were “invited” to get a colonoscopy. That’s a disappointing figure compared to previous studies, such as a 2018 Kaiser Permanente study that found a 67 percent reduction in cancer deaths among people who got a screening colonoscopy.

Upon further review, many doctors found major design flaws — not in colonoscopies, but in the study itself. It turns out that more than half of the participants “invited” for a colonoscopy in the new study never actually showed up for the procedure.

“It’s hard to know the value of a screening test when the majority of people in the study didn’t get it done,” Dr. William Dahut, chief scientific officer at the American Cancer Society, told NPR.

But while doctors have largely rejected the study’s results, it nonetheless generated headlines declaring colonoscopies “overrated,” potentially swaying patients who might have been looking for a reason not to get the procedure in the first place.

That makes Dr. Seifeldin Hakim nervous. Dr. Hakim, a gastroenterologist with Memorial Hermann Medical Group, stresses that colonoscopies are the most valuable tool we have in the fight against one of America’s deadliest, but most preventable, forms of cancer.

“Colonoscopies save lives and prolong lives, period,” he says.

Still, no one looks forward to a colonoscopy. Some people refuse to get them altogether, for a number of reasons, Dr. Hakim says.

“Many people are resistant to colonoscopies. Some don’t like the bowel prep; some are afraid of anesthesia,” he says. “For some people it’s a cultural issue, because of the stigma of having a colon inspection, and it can be especially challenging to convince them. If I can’t, I’ll say, ‘OK, let’s do a stool test — it’s better than nothing. But if it’s positive, we have to do a colonoscopy.’”

Colonoscopies remain the gold standard when it comes to screening for colorectal cancer, Dr. Hakim says, even though most people would prefer to do a stool test. While stool tests are less invasive and can be useful for detecting cancer or advanced adenoma (precancerous tumors), they can miss benign polyps, which are clusters of abnormal cells that develop on the lining of the colon. Colonoscopies, meanwhile, enable doctors to remove polyps before they develop into cancer.

“Most colorectal cancer forms from these small benign polyps that grow over the years and become cancerous,” Dr. Hakim explains. “No stool test that we have now can detect the smaller polyps.”  

That doesn’t mean they won’t be able to do so eventually.

“Everyone anticipates that, down the line, there will be less invasive screening tests that are more advanced,” Dr. Hakim says. “There could be a stool test one day that will be just as good as a colonoscopy, or maybe we’ll have a blood test that works as well.”

But colonoscopies already have significant benefits — they’re part of the reason the death rate from colorectal cancer has been dropping for several decades, according to the American Cancer Society. And they’ve become less onerous in recent years, Dr. Hakim says.

“We have better bowel prep formulas now that are smaller in amount and more effective,” he says. “It used to be a gallon, and it tasted nasty. The newer version is a half-gallon, and it’s much more palatable. There’s another prep that’s just coming out in tablet form, and you just have to drink a lot of water with it.”

While the overall death rate from colorectal cancer has declined in recent years, however, deaths among people younger than 55 have increased alarmingly, rising 1 percent per year from 2008 to 2017, according to the American Cancer Society. In response, the medical community recently lowered the recommended age for a first colonoscopy, from 50 to 45.

“We don’t know why it seems to be happening younger — whether it’s from diet or lack of exercise or something else. As with every cancer, you don’t know if environmental causes like pollution might have an effect. Are there more carcinogenic substances in what we eat or drink because we have more food preservatives than before? It could be any number of things,” Dr. Hakim says. “It could also be a factor of the screenings themselves — we could just be detecting more colorectal cancers than we otherwise would have. If you don’t do a colonoscopy and you don’t know a patient has colon cancer, in a few years he’ll have cancer all through his body, so at that point you won’t necessarily know where it started.”

The fact that colorectal cancer is very deadly in its advanced stages and very treatable if caught early makes it an ideal candidate for preventive screening, Dr. Hakim stresses.

“We don’t do screening for every kind of cancer, and there’s a reason for that. We don’t screen for brain cancer, partly because we don’t have very good treatment options if we find it,” he says. “With colonoscopies, like with mammograms, we have a minimally invasive test we can do, and catching this type of cancer early means we can treat it very successfully.”

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