Colon Cancer Screening May Be Even More Effective Than Experts Thought

Posted December 27, 2023

Colon Cancer Screening May Be Even More Effective Than Experts Thought

Getting your preventive screening colonoscopy could be even more of a lifesaver than you thought, a new analysis finds.

The two gold standard tests for spotting cancers and polyps of the colon -- colonoscopy and sigmoidoscopy -- offer double the benefit determined in prior studies, conclude a team from the Massachusetts Institute of Technology (MIT), in Cambridge, Mass.

They explained that, in multiple studies, about 1 percent of people in colon cancer screening trials will go on to develop the disease over the next decade.

Prior colon cancer screening studies found that regular colonoscopy/sigmoidoscopy reduced that rate by 25% -- to 0.75%.

But the new analysis took into account the number of participants in a colon cancer screening trial who decided, for whatever reason, to skip screening.

When these "non-adherent" folks were eliminated from statistical calculations, the actual percentage of people who went on to develop colon cancer over a 10-year span fell to just 0.5%.

"The effect of actually getting screened is about half a percentage point, double previously published results, which focus on the effect of being invited to screen,"explained MIT econometrician Josh Angrist.

He believes the new findings give even more weight to current recommendations to get screened for colon cancer.

Right now, the American Cancer Society recommends that "people at average risk of colorectal cancer start regular screening at age 45. This can be done either with a sensitive test that looks for signs of cancer in a person's stool [a stool-based test], or with an exam that looks at the colon and rectum [a visual exam]."

Stool-based tests should be conducted annually, and colonoscopy should be done every 10 years. If an individual opts for the noninvasive stool test, any suspicious result should be followed up with colonoscopy, the ACS says.

In the new study, Angrist and his colleagues analyzed data from five major clinical trials focused on colon cancer screening. Four of the trials used sigmoidoscopy (which doesn't probe as deeply into the colon as a colonoscopy does) while the fifth used colonoscopy.

The rate at which participants in the five trials who were offered sigmoidoscopy/colonoscopy actually opted to get one done varied widely -- from 42 percent to 87 percent, the MIT group discovered.

"In many clinical trials, there can be quite a few people who aren't treated as planned,"Angrist explained in an institute news release. "Cancer screening trials are a setting where that's especially problematic."

Once Angrist's group adjusted for that key confounding factor, the benefit from regular colon cancer screening more than doubled, compared to that seen in prior analyses.

Factoring in non-adherence also "smoothed" out any discrepancies seen in the results of the five trials, he noted, with all now finding that screening cut the odds of developing a colon cancer over the following decade from 1% to 0.5%.

Angrist hopes this new information will boost screening rates.

"If you want to encourage a reluctant colonoscopy patient, you shouldn't tell them the effect of being invited to screen, you should tell them the effect of actually being screened,"Angrist said. "And that's a much bigger number."

The study was published recently in Proceedings of the National Academies of Science.

More information

For more details on colon cancer screening guidelines, head to the American Cancer Society.

SOURCE: Massachusetts Institute of Technology, news release, Dec. 19, 2023