A recent study reported a smaller-than-expected benefit from screening colonoscopies. But the study has important caveats, gastroenterologists say, making it ripe for misinterpretation if that context isn’t included.
The study was the first randomized controlled trial — widely considered the gold standard for testing medical interventions — of the procedure. Online publication October 9, 2009. New England Journal of MedicineThe study followed participants invited to have a colonoscopy and compared how they fared with participants who weren’t invited to undergo the procedure. The invited group saw a 18% decrease in colorectal cancer risk at 10 years. But there wasn’t a meaningful difference in the risk of death from colorectal cancer between the two groups, the study reported.
The gastroenterologists said that this was disappointing as previous research had shown that screening colonoscopies were more effective in reducing the chances of developing or dying from colorectal disease. Those previous data were from observational studies, which don’t randomly assign patients to get, or not get, a treatment.
But a closer look at the details of the new study reveals why it shouldn’t be interpreted as a slam-dunk against the screening test. First, less than half of those who were invited to have a coloscopy did. The study also didn’t follow patients long enough to fully assess the risk of death from colorectal cancer. And some of the physicians who did the procedure didn’t meet a minimum quality benchmark.
These limitations limit the information this study can provide about screening colonoscopies. Folasade Mai, a UCLA Health gastroenterologist, said that this study shouldn’t be used to doubt colorectal screening. “Screening is effective, and it saves lives,” she says. “We have enough data to promote screening.”
Important screening
Colorectal cancer can be prevented by early detection. Second-leading cause of death from cancer for both men and women is combinedAccording to the American Cancer Society, this is a staggering number. It’s expected to kill more than 52,000 Americans in 2022. There are significant racial differences in who is affected by the disease. The rates of death and incidence are 41 percent to 44 percent respectivelyBlack men have a higher rate of suicide than white men. Black women’s rates are 31% and 18% higher than white women.
The U.S. Preventive Services Task Force recommends screenings for colorectal CancerAdults Ages 45-75 years (SN: 5/31/18). There are several screening options: stool-based tests, colonoscopy (which examines the entire colon), and sigmoidoscopy (which only examines a part of it). Average-risk individuals — those who don’t have a family history of colorectal cancer or other conditions that increase risk — can choose the option that works for them. “We just want people to get screened,” says gastroenterologist Sophie Balzora of the New York University Grossman School of Medicine. “The best test is the one that gets done.”
Coloscopy and the fecal immune chemical test (or FIT), are common procedures in the United States. The FIT is a home test that detects small amounts of blood in stool. This can indicate colorectal cancer.
A doctor performs a colonoscopy to look for and remove polyps. But the procedure’s expense, time and preparation can be prohibitive for some patients, says Carol Burke, a gastroenterologist at the Cleveland Clinic. Some people may not be able to leave work to have the procedure performed or they might need someone to drive them home. To complete a colonoscopy, “you have to be sure that you can address the patient’s barriers,” Burke says.
Important caveats
The potential barriers to getting a colonoscopy mean it’s not enough to just tell someone to do it. That’s also the case in Poland, Norway and Sweden, where colonoscopies are not commonly used to screen for colorectal cancer. These countries represented about one-third of the approximately 84,000 participants in the study. They were all invited to have colonoscopies. The other two-thirds made up the “usual care” group. But “the intervention was an invitation, not a colonoscopy,” Balzora says. Only 42 percent had one of the procedures. The invitation was rejected by most of the people who received it.
“If you don’t actually have the test, it can’t possibly protect you,” says gastroenterologist Aasma Shaukat of the New York University Grossman School of Medicine.
Another limitation of this study is the lack of time. Colon cancer develops slowly. Most polyps don’t become cancerous, but for those that do, it can take 10 years or more. It takes time for cancer to spread and then become fatal. At least 15 years of follow up are needed to really look at the impact on colorectal cancer deaths, Shaukat says, so the study’s report at 10 years isn’t long enough.
There were many variables in the quality of colonoscopies that were performed during the study. One standard is the adenoma discovery rate. This is the ratio of the number or colonoscopies which reveal a precancerous polyp (or adenoma) divided by the time span. Nearly 30 percent of physicians who performed the procedures did not meet the minimum quality standard.
In their paper, the study’s authors acknowledge these limitations. They note that the colonoscopy-by-invitation approach may have underestimated the benefits of the procedure. The team expects that a reduction in cancer risk will be seen before a reduction in death risk. They will again report the results after 15 years. They also mention that differences in quality standards among practitioners could have contributed to the delay in detecting cancer.
Shaukat said that this new study should be considered alongside other evidence supporting the effectiveness of screening colonoscopies. One example is the 2014 publication in The Observational Studies of Colonoscopy. British Medical JournalAccording to a report by, the procedure was successful. Close to 70% reduction in colorectal cancer mortality and incidence.
Another observational study examined an organized screening program using colonoscopy and sigmoidoscopy. The screening program resulted in a 25% increase in screening, which was linked to a 25% drop in the incidence of colorectal carcinoma from 2000 to 2015. There was a 52 percent decline in cancer-related deathsResearchers reported in GastroenterologyIn 2018.
In the United States, a randomized controlled study is currently underway that will evaluate the effectiveness and safety of screening with colonoscopy in people at average risk. So there’s more data to come. The new study “isn’t the end-all, be-all study,” May says. “We haven’t closed the door on colonoscopy.”
