Study finds colonoscopy only works if you have one.
Still, the results of a large trial were less encouraging than hoped.
Colonoscopy: common in the United States. Not common elsewhere. The procedure aims at removing suspicious growths before they become cancerous. It’s an expensive test and—many are surprised to learn—not backed up by data from randomized clinical trials.
Still, the general medical consensus, in the US anyway, is that colonoscopy reduces colon cancer rates and saves lives. But we don’t know how well they work here (if at all) because it would be unethical to run a randomized clinical trial in which tests which would otherwise be recommended were denied to people randomly selected to be in a control group.
However, in places where views on colonoscopies are less rosy, such trials are possible; It’s fair to do a study when experts are unsure of whether the thing being studied actually helps (what researchers call “equipoise”).
Three such countries (Poland, Norway, and Sweden) have been running a massive trial on colonoscopy since 2009. Tens of thousands of people ages 55-64 were invited either to have colon cancer screenings or not. Researchers have been following the patients in databases ever since.
Today, researchers unveiled the first set of results from the study in the New England Journal of Medicine. The results were disappointing, though not indicative of total failure.
The hope had been that colonoscopy would decrease colon cancer mortality rates by 25%; those tested would have a 50% reduction in death (but only half of the people invited to have the tests actually would). Unfortunately, the researchers found that offering colonoscopy led to no decrease in cancer mortality (0.28% versus 0.31%, an insignificant difference that missed the trial’s goals). Ten years out, the risk of death from all causes was 11% in both those invited to have colonoscopy and in the control group. Colonoscopy did lead to an 18% reduction in cancer diagnoses, a finding smaller than anticipated. Surprisingly though, on average, the cancers found were not in earlier stages. An editorial published alongside the report described the overall findings as “discouraging.”
Before we flush colonoscopies down the toilet, there are some glimmers of hope to discuss.
First, among those who actually received colonoscopy, there was a reduction in colon cancer and mortality. In the purest sense, this study assessed whether offering colonoscopy to the population at large works, to reflect the reality that many advised to receive these tests never do. That means educating the public might make this all work, as those who had colonoscopy fared better; narrow benefits might still be worthwhile on a population level, if enough people do these tests.
Second, some self-selection might have made colonoscopy look less effective than it is. Consider two subgroups: people who were invited to get colonoscopy but did not get one and people who were never invited to get one. No one in either group received colonoscopy screening so, in theory, their cancer rates ought to be identical. But ten years on, cancer rates in the first group (i.e., those invited for colonoscopy but who did not receive them) is lower. That means people invited to have a colonoscopy were more likely to say yes if they had some symptoms that were bothering them (or if a relative had been diagnosed with cancer). That indicates that the group actually receiving colonoscopy was enriched with people more likely to develop colon cancer later on in the study, stacking the statistical deck against the procedure.
Third, the rate of complications in the study was exceedingly low. One problem with cancer screening generally is that risks often get downplayed. For example, prostate cancer screening leads to many unnecessary surgeries. One advantage of colonoscopy, however, is that it rarely leads to fruitless downstream procedures. The procedure is both diagnostic and therapeutic. Doctors find and remove the suspicious lesions in one go. Still, colonoscopy itself can cause bowel perforation and massive bleeding. The good news is that the rates of these complications were incredibly low in the new study—almost to the point where it’s difficult to believe, according to one expert I spoke with. That means any benefit versus harm assessment carries less harm than we might have anticipated.
Should we abandon colonoscopy? No. Not yet anyway. The study results are not a win, but it’s still early. Patients who received colonoscopy had much higher rates of cancer in the first 3 years after their procedures, which makes perfect sense and was predicted; if you look for something, you’re more likely to find it. But cancer rates in the non-colonoscopy group quickly caught up after that and have already overshot the rates among the screened. In addition, comparing people who actually had colonoscopies to those who didn’t indicated encouraging trends. Among the screened, many more cancers were discovered early on (it took 6 years for rates to even out). But by ten years, 30% fewer cancers had been found among the screened, with differences increasing over time. It’s possible that by 15 years (which the researchers will assess), the results will increasingly favor colonoscopy.
Also, these findings are not necessarily applicable in areas outside of Northern and Eastern Europe. In the US, for example, Black people have higher rates of colon cancer. While the results of this European study suggest some groups may not benefit from colonoscopy, others almost certainly do.
Currently, US expert guidelines recommend colonoscopy or a stool-based test every 10 years starting at age 45 for average risk persons (or even earlier if a close relative has previously been diagnosed with colon cancer, or if the person has certain medical conditions including inflammatory bowel disease). It might be that some populations should start screening even earlier, say at age 40, while those in groups without such risks (i.e. like those in this latest study) might be able to wait until perhaps age 60. Time will tell.
For those without risks who still want peace of mind but aren’t sure whether colonoscopy is worth the trouble (or risk), other options exist. There’s sigmoidoscopy (which examines a small but important part of the colon near the end of the GI tract). There’s also stool-based testing. In fact, doctors in many nations like the U.K. don’t routinely offer colonoscopy not because they’re convinced it doesn't work, but because less invasive testing of patients’ stool for signs of cancer are thought to accomplish almost as much as colonoscopy, but with less hassle, risk, and expense.
I’m 43 years old. I have no family history of colon cancer. I’m supposed to have a colonoscopy in a couple of years. Will I? I’m not sure. I’ll definitely have some kind of colon cancer screening. Whether it involves a fiberoptic camera (colonoscopy) or a fancy biochemical stool test, remains as-yet determined.
We doctors love screening patients for undiagnosed chronic diseases. It makes us feel like we’re getting ahead of problems. It works less often that we'd like. That said, I don’t think today’s results mean that colonoscopy is a failed paradigm for everyone. But we have work to do. We have to identify the people who need colonoscopy the most—and also work out the optimal timing to maximize the benefits.
More may not be better. But too little could also be a problem.
Did you like this? Share it! Better yet, upgrade to Premium and get exclusive articles, audio versions of articles, interviews with big names in medicine and health, and access to the Inside Inside Medicine community on Facebook, where I answer questions and more.
❓💡🗣️ What are your questions? Comments? Join the conversation below.
Follow me on Twitter, Instagram, and on Facebook and help me share accurate frontline medical information!
📬 Subscribe to Inside Medicine here and get updates from the frontline at least twice per week.