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A study using U.S. National Cancer Institute data found colorectal cancer incidence rose from 36.7 per 100,000 in 2022 to 38.3 in 2023, following a long decline. Rates increased across age groups through 65–69, while the causes of the broader rise remain unknown.
A study published in NEJM Evidence found that U.S. colorectal cancer incidence rose in 2023 after more than two decades of decline, with rates increasing across age groups up to 65–69. The finding extends concern beyond younger adults and could mean greater demand for treatment and survivorship care, researchers said, though the reasons for the broader increase are not yet known.
Researchers led by Caitlin Murphy, a professor of pediatrics and public health sciences at the University of Chicago, analyzed the latest available National Cancer Institute data across a 20-year period. The age-adjusted incidence rate fell from 55.2 per 100,000 in 2000 to 36.7 in 2022, then rose to 38.3 in 2023. The 2023 figure is higher than the 2022 rate, but remains below the 2000 rate.
The increases were not limited to people under 50. The study found rising incidence in age groups through 65–69. The steepest reported increase was among adults aged 45–49: incidence rose by 12.76% annually from 2019 to 2023. The authors said expanded screening after U.S. recommendations lowered the starting age from 50 to 45 likely contributed to the increase in that group by detecting cancers earlier.
That screening explanation does not account for the rise across all age groups, the researchers said. Incidence increased among people aged 65–69 and plateaued among those aged 70–74, groups that have historically benefited from screening. The study also found that the overall trend persisted when data from 2020 and 2021 were excluded, making pandemic-related interruptions an unlikely explanation for the 2023 increase.
Rising Rates Extend Beyond Younger Adults
The findings matter because colorectal cancer has commonly been discussed as a growing concern among younger adults, but the new analysis points to a wider age pattern. Colorectal cancer is the second-leading cause of cancer-related deaths in the United States overall and ranks first among adults younger than 50, according to the UChicago Medicine report.
If increased incidence continues across large age groups, health systems may face more demand for diagnosis, cancer treatment and survivorship services. Researchers cautioned that the data show a trend, not its cause. The 45–49 increase may partly reflect more screening, while screening alone does not explain the pattern among older adults.
For individuals, the results reinforce the importance of following screening guidance and discussing personal risk with a clinician. They do not establish that a particular exposure or behavior is responsible, nor do they predict an individual’s likelihood of developing cancer.
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Screening, Age and the Trend
Colorectal cancer rates among adults aged 20–49 had already been rising: American Cancer Society statistics cited in the report show an average annual increase of 3% from 2013 to 2022. The new study adds evidence that the rise is not confined to that younger age range. Murphy described a possible birth-cohort effect, in which people born around the same time carry changing risks as they age. This is a proposed way to interpret the pattern, not a confirmed cause.
U.S. guidelines recommend that adults at average risk begin regular screening at age 45 and continue through 75. Screening options include colonoscopy and stool-based tests, among others; which test to use and how often to repeat it should be discussed with a health professional. Decisions for people younger than 45 or older than 75 are individualized, taking account of factors such as family history and other health concerns.
“This is the first time that we have seen an increase in the overall rate since in more than 20 years.”
— Caitlin Murphy, study author and University of Chicago professor
The Drivers of the Increase Remain Unknown
The study documents changing incidence, but does not establish why rates are rising across the age groups examined. Increased screening likely contributed to the 45–49 pattern, according to the authors, but it does not explain the overall increase or the findings among older adults. The researchers said that unknown risk factors may be offsetting gains associated with screening.
Murphy and colleagues are investigating environmental chemical exposures as one possible line of inquiry. They plan to measure many exposures in blood samples, then use colon organoids—specialized models grown in a laboratory—to study the effects of chemicals that merit further research. Those investigations have not yet identified a cause. The study also cannot show from incidence figures alone whether changes in diagnosis, underlying risk or both explain each age-group trend.
Researchers Plan Further Exposure Studies
Researchers expect to keep tracking colorectal cancer incidence as registry data are updated annually. The University of Chicago team’s next research steps include screening blood samples for a range of environmental exposures and testing selected chemicals in colon organoids. Results could help determine which exposures warrant closer study, but the work is still investigative.
In the meantime, the report advises adults to follow screening guidance suited to their age and risk and to discuss test options with a clinician. People under 45 who are not eligible for routine screening should seek medical advice about concerning symptoms, particularly if they have a family history or other known risk factors. The study does not specify a timeline for identifying the causes of the rising rates.
Key Questions
What did the study find?
Using National Cancer Institute data, researchers found that the U.S. age-adjusted colorectal cancer incidence rate rose from 36.7 per 100,000 in 2022 to 38.3 in 2023, after declining for more than two decades. Increases extended across age groups through 65–69.
Did the study identify why rates are rising?
No. The study describes incidence trends but does not identify their cause. The authors said expanded screening likely contributed to the increase among adults aged 45–49, while other factors behind the wider pattern remain uncertain.
Who had the sharpest reported increase?
Adults aged 45–49 had the sharpest increase reported: 12.76% annually from 2019 through 2023. Researchers said more screening after the recommended starting age was lowered to 45 likely contributed to this result.
When should adults begin screening?
U.S. guidelines recommend that adults at average risk start regular colorectal cancer screening at age 45 and continue through 75. People should discuss the appropriate test and schedule with a clinician; decisions outside that age range are individualized.
Could the COVID-19 pandemic explain the increase?
The researchers found that the increase persisted when 2020 and 2021 data were excluded. They said pandemic disruptions are therefore unlikely to explain the rise recorded in 2023, though the study does not resolve the causes of the broader trend.
Source: uchicagomedicine.org
