Colorectal cancer rates in American adults have climbed for the first time in two decades, and the scientists who found it admit they do not know why.
Story Snapshot
- A new analysis of national cancer data shows colorectal cancer rates rose in 2023, reversing a 20-year decline.
- Rates fell from 55.2 cases per 100,000 people in 2000 to 36.7 in 2022, then jumped to 38.3 in 2023.
- The increase showed up in almost every age group under 70, not just younger adults.
- Researchers say expanded screening explains part of the rise but not all of it, and the cause remains unclear.
A Two-Decade Decline Just Hit A Wall
For twenty years, colorectal cancer was one of the few cancer success stories in America. Screening caught tumors early, often before they turned deadly. The rate of new cases per 100,000 people dropped steadily, falling from 55.2 in the year 2000. By 2022, it had been cut nearly in half, down to 36.7.
Then the numbers moved the wrong way. In 2023, the rate climbed to 38.3 cases per 100,000 people, according to the study published in NEJM Evidence. Researchers say this marks the first increase since the current national tracking system began. The data came from the Surveillance, Epidemiology, and End Results program, a federal cancer registry covering close to half the U.S. population.
The Numbers Behind The Reversal
This was not a single bad year compared to a single good one. Researchers built a statistical model covering the full stretch from 2000 to 2023. Rates dropped every single year from 2000 through 2019, sometimes by as much as 3.74 percent annually. Then the trend flipped, rising by an estimated 2.76 percent per year from 2021 through 2023. That is a real, measured shift, not a rounding error.
What makes the finding harder to explain away is how widespread it was. Reuters reported the increase showed up across nearly every age group under 70, not just the younger adults who have drawn headlines for years. The University of Chicago’s review of the data reached the same conclusion, describing rates rising in nearly all age brackets. That breadth is the detail doctors are watching closest.
Why Screening Alone Doesn’t Add Up
The sharpest jump happened among adults aged 45 to 49, where rates rose nearly 12.76 percent per year from 2019 through 2023. That group lines up with a 2021 change in guidelines, when health officials lowered the recommended screening age from 50 to 45. More screening naturally finds more cancers, and researchers call that a likely factor here. But finding more cancer in one newly screened group does not explain why rates also rose among people in their 50s, 60s, and up to 70, ages that were already being screened under the old rules.
That gap is the real puzzle. If screening alone drove the number up, the increase should cluster tightly around the newly eligible age group and fade elsewhere. Instead it spread. The researchers themselves were careful not to overreach, writing that the apparent 2023 increase “warrants additional surveillance and investigation” rather than claiming they had solved it.
Part Of A Longer, Quieter Trend
None of this comes entirely out of nowhere. Scientists have tracked rising colorectal cancer in younger adults since at least the mid-1990s, well before this latest data point. What is new in 2023 is that the rise appears to have broadened beyond the youngest patients into older age brackets that had been reliably improving for years. That shift in pattern, more than the single-year number itself, is what has researchers paying closer attention now.
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
One brief caution is worth noting. The reversal rests on just a few years of data following the 2021 screening age change, and the study’s own authors call for more tracking before drawing firm conclusions. That does not undercut the finding. It simply means the next few years of data will matter as much as this one did.
What Comes Next For Patients And Doctors
For readers over 40, the practical takeaway is straightforward. Screening guidelines exist because they catch cancer early, when it is most treatable. The fact that rates rose even among already-screened age groups is a reason to keep up with colonoscopies and other tests, not skip them. A rising case count paired with earlier detection is a very different story than a rising case count paired with people avoiding doctors altogether.
Public health agencies and researchers now face the task of figuring out what is driving the broader rise, whether it involves diet, environment, obesity trends, or something not yet identified. Until that work is done, the honest answer is the one the study’s own authors gave: the trend is real, it is broader than expected, and the cause is not yet known.
Sources:
evidence.nejm.org, reuters.com, news.uchicago.edu
