A recent study reported a lower than expected benefit of screening colonoscopies. But the study has important caveats, gastroenterologists say, making it open to misinterpretation if that context isn’t included.
The study was the first randomized controlled trial, widely considered the gold standard for evaluating medical interventions, of the procedure. Posted online October 9 in the New England Journal of Medicinethe study followed participants invited to undergo a colonoscopy and compared how they did with participants who were not invited to undergo the procedure. Colorectal cancer risk at 10 years was reduced by 18 percent in the invited group. But there was no significant difference in the risk of death from colorectal cancer between the two groups, the study reported.
This was disappointing, gastroenterologists say, as previous research has shown screening colonoscopies to be more effective in reducing the risks of developing and dying from colorectal cancer. Those earlier data came from observational studies, which don’t randomly assign patients to receive or not receive a treatment.
But a closer look at the details of the new study reveals why it shouldn’t be interpreted as a blow against screening. First, less than half of the people invited to have a colonoscopy actually did. The study also did not follow patients long enough to fully assess the risk of death from colorectal cancer. And some of the doctors who performed the procedure did not meet a minimum quality benchmark.
These issues limit what this study can tell us about screening colonoscopies. On top of that, this study shouldn’t be used to cast doubt on colorectal cancer screening in general, says Folasade May, a gastroenterologist and health services researcher at UCLA Health. “Screening is effective and saves lives,” she says. “We have enough data to promote detection.”
Importance of detection
Colorectal cancer is second leading cause of cancer death in men and women combined, according to the American Cancer Society. It is expected to kill more than 52,000 Americans by 2022. There are racial disparities in who gets and dies from the disease. The incidence and death rates are 21 percent and 44 percent taller in black men compared to white men; rates for black women compared to white women are 18 percent and 31 percent higher, respectively.
the US Preventive Services Task Force Recommends Colorectal Cancer Screening in adults from 45 to 75 years (Serial number: 05/31/18). There are different screening options, including stool-based tests; colonoscopy, which examines the entire colon; and sigmoidoscopy, which examines a part of the colon. People at average risk (those without 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 tested,” says gastroenterologist Sophie Balzora of New York University’s Grossman School of Medicine. “The best test is the one that is done.”
Fecal immunochemical testing, or FIT, and colonoscopy are commonly performed in the United States. FIT detects small amounts of blood in the stool, which can be a sign of colorectal cancer, and is done at home.
During a colonoscopy, a doctor looks for and removes polyps, tissue growths that can become cancerous. But the cost, time and preparation for the procedure can be prohibitive for some patients, says Carol Burke, a gastroenterologist at the Cleveland Clinic. People may not have the flexibility to take time off work for the procedure or have someone available to drive them home, for example. To complete a colonoscopy, “you have to be sure you can address patient barriers,” says Burke.
Important warnings
The potential barriers to having a colonoscopy mean that it’s not enough to simply tell someone to do it. That’s also the case in Poland, Norway and Sweden, where colonoscopies aren’t commonly used to screen for colorectal cancer. One-third of about 84,000 study participants from these countries were invited to have colonoscopies. The other two-thirds made up the “usual care” group. But “the intervention was an invitation, not a colonoscopy,” says Balzora. Only 42 percent of the participants invited to undergo the procedure had one. Most of the guests declined the invitation.
“If you don’t get tested, there’s no way it’s going to protect you,” says gastroenterologist Aasma Shaukat of New York University’s Grossman School of Medicine.
Another limitation of the new study has to do with time. Colon cancer develops slowly. Most polyps do not become cancerous, but those that do can take 10 years or more. It then takes time for the cancer to spread and become fatal. At least 15 years of follow-up is needed to really see the impact on colorectal cancer deaths, says Shaukat, so reporting the 10-year study isn’t enough.
And the quality of the colonoscopies performed in the study varied. One standard is the adenoma detection rate, the number of colonoscopies that reveal a precancerous polyp or adenoma, divided by the number of colonoscopies performed over a period of time. In the new study, nearly 30 percent of doctors who performed the procedures had rates below the minimum recommended quality rate.
In their article, the study authors acknowledge these limitations. They point out that the colonoscopy-by-invitation approach may have underestimated the benefits of the procedure. They say reductions in cancer risk are expected to come before reductions in death risk; the team will report the results again at 15 years of follow-up. And, they add, differences in quality benchmarks among doctors may have affected cancer detection.
The new study should be considered among other evidence of the effectiveness of screening colonoscopies, says Shaukat. For example, an analysis that combined observational colonoscopy studies, published in 2014 in the British medical journalreported that the procedure reduces both the incidence and mortality of colorectal cancer by about 70%.
Another observational study looked at an organized screening program that used colonoscopy, sigmoidoscopy, and FIT. The program led to a boost in screening that was linked to a 25 percent decline in the annual incidence of colorectal cancer from 2000 to 2015 and a 52 percent drop in cancer deathsthe researchers reported in gastroenterology in 2018.
A randomized controlled trial is also underway in the United States that will directly compare the effectiveness of screening with colonoscopy or FIT in people at average risk. So there is more data to come. The new study “is not the definitive study,” says May. “We haven’t closed the door on colonoscopy.”