Nationwide Cancer U-Turn – No Clear Cause

Tablet displaying the word Colonoscopy with a stethoscope beside it — Photo: Zerbor / Shutterstock

Colorectal cancer rates in American adults rose last year for the first time in more than two decades, and the doctors who found it cannot say why.

Story Snapshot

A new national study found colorectal cancer rates climbed from 36.7 cases per 100,000 people in 2022 to 38.3 in 2023.
Rates had fallen almost every year since 2000, when they stood at 55.2 per 100,000.
The increase showed up in nearly every age group under 70, not just younger adults.
Researchers say screening expansion explains part of the rise but not all of it.

A Twenty-Year Decline Just Broke

For two decades, colorectal cancer was one of America’s quiet public health wins. Rates dropped from 55.2 cases per 100,000 people in 2000 down to 36.7 by 2022, thanks largely to colonoscopies catching precancerous polyps before they turned deadly. That steady progress ended in 2023, when the rate jumped to 38.3 per 100,000, the first annual increase since federal cancer tracking began under the current system.

The study behind this finding comes from Caitlin Murphy and her team, published in NEJM Evidence on October 27, 2026. They used data from the National Cancer Institute’s Surveillance, Epidemiology, and End Results program, which tracks cancer cases across roughly 46 percent of the United States population. That is not every American, but it is a large enough sample that cancer researchers treat it as the gold standard for spotting national trends.

The numbers behind the headline matter here. From 2000 through 2019, colorectal cancer rates fell every single year, with annual declines ranging from under 1 percent to nearly 4 percent. Then the trend flipped. Researchers modeled a 2.76 percent yearly increase from 2021 through 2023, a shift large enough that statisticians are confident it is not just noise in the data.

This Is Not Only A Young Adult Story

Much of the recent colorectal cancer conversation has focused on younger patients, and for good reason. Reuters reported the sharpest increase, nearly 13 percent per year between 2019 and 2023, hit adults aged 45 to 49. Researchers believe expanded screening deserves real credit there, since federal guidelines lowered the recommended starting age from 50 to 45, meaning doctors are simply finding more cancers that were already present.

But that explanation runs into a problem. The same analysis found rising rates across nearly every age group under 70, including people well past the point where screening changes would explain new detections, according to reporting from the University of Chicago. If screening alone drove this, the increase should cluster tightly around the newly screened age group. It did not.

Doctors Admit They Do Not Have An Answer Yet

What stands out about this study is the researchers’ own restraint. Instead of offering a tidy explanation, they called the 2023 increase a finding that “warrants additional surveillance and investigation,” language that signals genuine scientific uncertainty rather than a settled conclusion. ScienceDaily’s coverage put it bluntly: scientists do not know why this is happening.

That honesty matters for readers trying to make sense of the headlines. A single year of higher numbers, even a well-documented one, is not the same as proof of a permanent new trend. The researchers compared just one year against the prior one for their core finding, while their broader modeled trend only covers three years, 2021 through 2023. Context from outside this study shows younger-onset colorectal cancer has been climbing since the 1990s, long before this new reversal, suggesting something deeper than screening schedules may be at work.

Colorectal cancer is on the rise in younger adults and appears to be different from colorectal cancer in older adults. The disease is often more aggressive in young people, and less responsive to treatment.

“Up until now, we were frustrated by not being able to identify the… pic.twitter.com/Kr6dqM7iJR

— Dana-Farber (@DanaFarber) November 12, 2026

For now, the honest answer is that nobody has pinned down the cause. Could be diet, obesity, gut bacteria, medications, or something researchers have not even considered yet. The study’s authors are not pretending otherwise, and neither should the headlines covering it. What is certain is the data itself: a two-decade decline in colorectal cancer has stalled, and reversed, and the medical community is now racing to figure out why before the trend goes any further.