New Study Questions Effectiveness of Colonoscopies

Colonoscopy screenings prevent just 1 case of colon cancer for every 455 people who undergo this invasive test, in which a camera is snaked through the intestines, according to a new study that calls into question the benefit of the procedure.

For the study, researchers randomly selected about 28,000 adults in Poland, Norway, and Sweden to undergo colonoscopies and compared colon cancer diagnoses and deaths with a randomly selected control group of about 56,000 people who didn’t get these screenings. Over a median follow-up period of 10 years, there were 259 cases of colon cancer detected in the group invited to get colonoscopies and 622 cases in the control group.

At 10 years, the group invited to get colonoscopies had an 18 percent lower risk of colon cancer and a 10 percent lower risk of death from these tumors than the group that didn’t get screened, according to study results published October 9 in the New England Journal of Medicine.

“I am surprised that a larger benefit was not shown,” says Samir Gupta, MD, a professor of medicine at the University of California in San Diego and a staff physician at the Jennifer Moreno VA San Diego Healthcare System.

Colonoscopy Has a Lower Acceptance Rate Among Younger Adults

“However, the lower benefit can in part be explained by the low rate of acceptance of colonoscopy,” says Dr. Gupta, who wasn’t involved in the study.

Just 42 percent of the study participants who were asked to get colonoscopies did so.

When researchers compared outcomes for only the subset of participants who went through with requested colonoscopies, they found that the screening was associated with a 31 percent lower risk of colon cancer over 10 years. In this analysis, colonoscopies were associated with a 50 percent lower risk of death from colon cancer.

“Colonoscopy can only be effective if colonoscopy gets done,” says Jason Dominitz, MD, the executive director of gastroenterology for the Veterans Health Administration and a professor of medicine at the University of Washington in Seattle.

Most U.S. adults age 50 and older — the age group that has long been advised to get colonoscopies once a decade — do get these screenings. But colonoscopies have been slower to catch on among adults ages 45 to 49 in the five years since rising colon cancer death rates in this age group prompted the American Cancer Society to lower the starting age for screening to include them.

While about 70 percent of people 50 and up get colonoscopies as recommended, colon cancer screening rates are much lower for people in their mid- to late-forties, Gupta says. “That’s because this group is newly eligible.”

When people don’t get screened, it’s often because they’re unaware that it’s important, because their doctor doesn’t recommend it, or because they don’t realize they can opt for less-invasive alternatives to colonoscopies, Gupta adds.

Patients who undergo a colonoscopy — the most common screening method for colon cancer — may need to use laxatives or an enema to empty their bowels before the exam, and go under some type of sedation during the procedure.

Alternatives to Colonoscopies

One less-invasive option is fecal occult blood testing (FOBT), which looks for blood — a possible sign of cancer — in stool samples. Another option involves doing FOBT along with a sigmoidoscopy exam of just the lower colon. Some patients who have abnormal findings on these tests may require a follow-up colonoscopy.

Most adults at average risk — people without inflammatory bowel disease or a family history of colon cancer — should start screening with a colonoscopy or one of the less-invasive alternatives at age 45, according to recommendations issued in 2021 by the U.S. Preventive Services Task Force.

“For those who don’t want colonoscopy, fecal occult blood tests are a great option,” says Dr. Dominitz, the coauthor of an editorial accompanying the new study. “The bottom line is that people should definitely not lose confidence in screening for colorectal cancer.”

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