You may have heard about a new study in the New England Journal of Medicine that evaluated the effectiveness of colonoscopies in reducing the risk of developing colon cancer as well as dying from the disease. This randomized controlled trial (RCT) involved 84,585 participants, ages 55 to 64, in Norway, Sweden, the Netherlands, and Poland, who were divided into two groups—one that was offered screening colonoscopy and another that received usual care without screening (the control group).

RCTs are considered the most reliable way of determining that something being evaluated is effective or not, so this study had the potential to shed more light on the topic than prior studies that have been observational in nature.

The researchers found that that there was an 18 percent reduction in colon cancer in the colonoscopy group compared to the control group—a figure that was statistically significant but unexpectedly low. Moreover, there was no significant reduction in colon cancer deaths.

Not surprisingly, the study immediately grabbed national news attention in early October and was widely reported on social media, with responses ranging from calling the study nonsense and stating that colonoscopy is still the best colon cancer screening test available to asserting that colonoscopy should be entirely abandoned as a screening test. The truth lies somewhere in the middle, as there were significant flaws in how the data were presented, despite the good experimental design of the study.

Here are four main issues I have with the study:

1. Only 42 percent of the participants invited to undergo colonoscopy actually got one. When this group was evaluated separately, there was a 31 percent reduction in colon cancer and a 50 percent reduction in deaths from colon cancer—a far higher percentage than what was reported as the overall results.
2. Any polyps (potential precursors to cancer) in participants receiving colonoscopy were removed during the procedure; of course, no polyps could be removed from the usual-care group, since they did not undergo screening. The follow-up period for the study, however, averaged seven years, which is not long enough to know whether any undetected polyps in the usual-care group would become malignant. A longer follow-up might have led to stronger results in favor of colonoscopy.
3. A significant number of the endoscopists performing the procedure fell short in meeting the polyp detection rate standard established in the U.S., where more colonoscopies are performed. That makes it harder to generalize the results of the study to the U.S.
4. Participants in the colonoscopy group were scheduled to receive the procedure just one time; the data weren’t clear about follow-up, which is needed in people who have polyps and who thus may need additional screening.

So what can we take away from this important and widely publicized study? First and foremost, it is incorrect to conclude that colonoscopy is not a valid and useful tool for colon cancer screening, based on these results. But it’s also incorrect to conclude that colonoscopy is the “gold standard” screening test. There are other tests available, including the fecal immunochemical test (FIT), which screens for human blood in the stool as a way of detecting possible cancer. Trials are currently underway to see if there is a difference in outcomes between colonoscopy screening and FIT screening.

Keep in mind that fewer than half of the participants in the study agreed to undergo colonoscopy, suggesting that other methods would have increased participation in screening. Studies in the U.S. and Europe have shown that screening rates increase when different screening options are offered.

BOTTOM LINE: I believe the most important message to convey to our readers is to undergo colon cancer screening, beginning at age 45, by one of the methods currently recommended by the various medical organizations and societies (such as the American Cancer Society and the U.S. Multi-Society Task Force on Colorectal Cancer) involved in preventing colon cancer deaths. If you are at increased risk of colon cancer (because of a strong family history, for example), you should talk with your doctor about earlier or more frequent screening.

For more on FIT, you can read the Expert Q&A from March 2022. And for other colon cancer prevention strategies beyond screening, see our Expert Q&A with two doctors from NYU Langone Health.