Medical ‌groups have been sounding the alarm about the recent rise of colorectal cancers among younger adults in the United States, but a new analysis found that the increased incidence extends to nearly all age groups.

Colorectal cancer incidence rates among adults aged 20-49 years increased by 3% annually between 2013 and 2022, and by 2026 the disease was the leading cause of cancer deaths in that age group, according to data from the American Cancer Society.

The new analysis of National Cancer Institute data ​looked at all ages up to 70. Researchers found the incidence fell from 55.2 per 100,000 in 2000 to 36.7 in 2022, but then rose to 38.3 in 2023.

“This is the ​first time that we have seen an increase in the overall rate in more than 20 years,” study leader Caitlin Murphy of the University of ⁠Chicago said in a statement.

The sharpest increase — 12.76% annually from 2019-2023 — was seen in 45- to 49-year-olds, likely driven by more people undergoing colorectal cancer screening after US recommendations lowered the recommended age for ​the testing to 45 from 50, the researchers reported in NEJM Evidence, opens new tab.

“That means that screening is doing as we intend it to do. It’s catching cancer earlier,” Murphy said.

But screening increases do not explain the rise ​in incidence overall or in other age groups, which suggests unknown risk factors, including environmental, may be offsetting the gains made by screening, the researchers said.

A separate team of researchers has identified new clues to help explain why colorectal cancer is often more aggressive in younger patients.

They analyzed 189 tumors from adults of all ages, looking for factors that changed gradually with age.

Among tumors of the most common colorectal cancer subtype, younger patients’ tumors had significantly more connective and supporting cells ​than cancer cells, a finding that has been linked to chemotherapy resistance in several types of solid cancer, the researchers reported in Nature Medicine.

Younger patients also had higher activity of long non-coding RNAs, molecules that ​can regulate genes without making proteins. Many are “dark” RNAs, whose functions remain largely unknown.

The researchers also saw gene activity suggesting stronger signaling between cells that can help cancer cells move and invade nearby tissue in younger patients.

“While we’re ‌still at the ⁠beginning of understanding what these differences mean, our work gives researchers a new direction to pursue in tackling this urgent problem in human disease,” study co-author Ana Anderson of Harvard Medical School said in a statement.