TL;DR
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A study published in NEJM Evidence found that the U.S. age-adjusted colorectal cancer incidence rate rose to 38.3 cases per 100,000 people in 2023, up from 36.7 in 2022, after falling for decades. Rates increased across age groups through 65–69, but researchers have not identified the causes; expanded screening may explain part of the rise among adults aged 45–49.
A study published in NEJM Evidence found that U.S. colorectal cancer incidence rose in 2023 after more than two decades of overall decline, with rates increasing across age groups through 65–69. The findings extend concern beyond adults under 50, though researchers say the reasons for the broader increase remain unknown.
Researchers led by Caitlin Murphy, a professor of pediatrics and public health sciences at the University of Chicago, analyzed National Cancer Institute data covering a 20-year period. The age-adjusted rate fell from 55.2 cases per 100,000 people in 2000 to 36.7 in 2022, then rose to 38.3 in 2023. Murphy said this was the first increase in the overall rate in more than 20 years.
The largest recent rise was among adults aged 45–49: incidence increased by 12.76% annually from 2019 through 2023, according to the study. The authors said the increase in this age group is likely partly related to national screening recommendations lowering the starting age from 50 to 45. More screening can detect cancers that might otherwise have been found later, but it does not explain increases in other age groups.
The study also found rising rates among people aged 65–69 and a plateau among those aged 70–74. Researchers noted that these older groups have historically benefited from screening, and about 80% are up to date. The team tested whether pandemic-era interruptions to screening and diagnosis could account for the pattern; excluding 2020 and 2021 data did not remove the increase.
Rising Rates Extend Beyond Younger Adults
Colorectal cancer is the second-leading cause of cancer-related deaths overall in the United States and ranks first among adults younger than 50, according to the source report. A rise spanning younger and older groups may mean more people need diagnosis, treatment and follow-up care—not only the younger patients whose increasing rates have drawn public attention.
Murphy told UChicago Medicine that a growing number of diagnoses among a large, aging population could place added demand on cancer treatment and survivorship services if the trend continues. The findings also make it harder to explain the pattern as a screening issue affecting only people newly eligible for testing. They do not establish what is causing the rise or how much screening contributes to changes in each age group.
For patients, the study reinforces the value of following screening guidance, while it does not establish that any one test or prevention measure can account for the population-level trend. People making screening decisions should discuss options with a clinician, taking account of age, family history, symptoms and other health factors.
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Screening and the Age Pattern
Earlier attention focused on early-onset colorectal cancer, diagnosed before age 50. U.S. American Cancer Society statistics cited in the UChicago Medicine report show that incidence among adults aged 20–49 increased by 3% annually from 2013 to 2022. The new study adds evidence that the upward pattern is not confined to that younger population.
Murphy described the possibility of a birth cohort effect: people born around the same time may share exposures or other risks, and rates could change as those groups grow older. This is a proposed way to understand the age-and-time pattern, not an identified cause. The researchers say the data cannot yet show which factors are driving increases among older adults.
National guidance cited in the report recommends that adults at average risk begin regular colorectal cancer screening at age 45 and continue through age 75. The report says colonoscopy is one option and that stool-based and blood-based tests are also available. Screening schedules and choices vary; people under 45 or over 75 are advised to discuss individual circumstances with a clinician.
“This is the first time that we have seen an increase in the overall rate since in more than 20 years.”
— Caitlin Murphy, University of Chicago epidemiologist
Causes of the Increase Remain Unknown
The study documents changes in incidence but does not identify the risk factors behind the wider rise. Screening likely contributes to the sharp increase recorded among 45–49-year-olds, the authors said, but it cannot account for the overall increase or the patterns in other age groups. The researchers also found that removing pandemic-disruption years from the analysis did not eliminate the trend.
Murphy and colleagues are investigating whether environmental chemical exposures could play a role. The team plans to measure many exposures in blood samples and then study chemicals of interest using colon organoids, laboratory models of colon tissue. That work is a research direction, not evidence that a particular chemical has caused the increase. The available report does not specify when results from those investigations will be published.
Researchers Will Track Rates and Risks
The researchers call for continued surveillance as cancer registry data are updated annually. Future data will show whether the 2023 rise persists and whether incidence continues to increase in the same age groups. One year of higher rates does not by itself establish how the trend will develop.
The team also plans to investigate environmental exposures through blood testing and follow-up laboratory work. In the meantime, the report says screening remains an important way to detect colorectal cancer early and reduce the chance that it becomes deadly. Adults should discuss appropriate screening tests and timing with a qualified clinician, particularly if they have a family history, symptoms or other risk factors.
Key Questions
What did the study find?
It found that the U.S. age-adjusted colorectal cancer incidence rate rose from 36.7 per 100,000 people in 2022 to 38.3 in 2023, after declining for more than two decades. Rates rose across age groups through 65–69.
Which age group had the sharpest increase?
Adults aged 45–49 had the sharpest increase reported: incidence rose by 12.76% annually from 2019 through 2023. The authors said expanded screening after the recommended starting age fell to 45 likely contributed to this age group’s increase.
Do researchers know what is causing the rise?
No. The study identifies incidence patterns but does not establish their cause. Researchers are investigating possible risk factors, including environmental chemical exposures, but have not confirmed a specific cause.
When should adults begin colorectal cancer screening?
The report cites national guidance recommending that adults at average risk begin regular screening at age 45 and continue through age 75. Screening decisions, including for people outside that age range or with risk factors, should be discussed with a clinician.
Source: uchicagomedicine.org
