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A study published in NEJM Evidence found that U.S. colorectal cancer incidence rose in 2023 after falling for more than two decades, with increases across age groups through 65-69. Researchers say expanded screening may explain part of the sharp rise among people aged 45-49, but not the broader pattern; the causes 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 increases across age groups up to 65-69. The findings extend concern beyond younger adults and could mean greater demand for cancer treatment and survivorship care, though researchers say the causes of the broader rise are not yet known.
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 incidence rate fell from 55.2 cases per 100,000 people in 2000 to 36.7 in 2022, then rose to 38.3 in 2023. The figures describe incidence, or new diagnoses, rather than deaths.
The study found rising rates across age groups through ages 65-69. The steepest increase was among people aged 45-49: incidence rose by 12.76% annually from 2019 through 2023. The authors said increased screening after national recommendations lowered the starting age from 50 to 45 likely accounts for some of that rise, because screening can find cancers that might otherwise be diagnosed later.
That screening change does not explain the increase across the other age groups, according to the researchers. Rates also rose among people aged 65-69, while they plateaued among those aged 70-74. The team found that the overall increase persisted when it excluded 2020 and 2021 data, suggesting pandemic-era interruptions alone do not account for the 2023 rise.
A Rise Beyond Younger Adults
For years, public concern about colorectal cancer has focused in part on its growing incidence among people younger than 50. The new findings suggest the pattern is not limited to early-onset disease: increases are now visible in older age groups as well. That distinction matters because a rise affecting more age groups can mean more people needing diagnosis, treatment and follow-up care.
Murphy told UChicago Medicine that researchers had expected higher rates to appear as people born in the 1960s and later grew older. She described this as a possible birth cohort effect—a pattern in which people born around the same time carry elevated risk as they age. It is a proposed way to interpret the trend, not an identified cause. The study does not establish which exposures or behaviors are driving the changes.
The increase among people aged 65-69 also deserves attention because these adults have historically benefited from screening, and the source report says roughly 80% of people in this group are up to date. Researchers said the pattern may indicate that unknown risk factors are offsetting some screening gains. That possibility remains under investigation, not a conclusion about any single factor.
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Screening and the Long-Term Trend
Colorectal cancer is the second-leading cause of cancer-related deaths overall in the United States, according to the source report, and ranks first among adults younger than 50. Earlier American Cancer Society statistics cited by UChicago Medicine found that incidence among adults aged 20-49 rose by 3% annually from 2013 to 2022. The new study adds evidence that the trend reaches beyond that younger group.
National guidelines recommend that adults at average risk begin regular screening at age 45 and continue through age 75. Screening options include colonoscopy and certain home-based stool tests; the source report also notes newer blood-based options. Different tests have different purposes and repeat schedules, so patients can discuss appropriate choices with a clinician. Recommendations for people younger than 45 or older than 75 are individualized based on factors including family history and health status.
Murphy said the age-adjusted rate had declined for decades before the 2023 increase. She told UChicago Medicine, “This is the first time that we have seen an increase in the overall rate since in more than 20 years.” The statement refers to the trend described in the study; the data show a rise from 2022 to 2023, not a confirmed explanation for it.
““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, as quoted by UChicago Medicine
The Causes Remain Unidentified
The study documents changes in incidence but does not identify the risk factors behind the increase. Screening likely contributed to the sharp rise among people aged 45-49 after the recommended starting age fell, but it does not account for the wider pattern or the increase among older adults. Researchers are examining environmental chemical exposures as one possible area of investigation; the source report presents this as a research direction, not an established explanation.
The team also considered whether disruptions to screening and diagnosis during the COVID-19 pandemic could have distorted the figures. The increase remained when 2020-2021 data were removed, and screening had largely returned to pre-pandemic levels by January 2021, according to the source report. That analysis makes the pandemic an unlikely explanation for the rise seen in 2023, but it does not rule out every effect of delayed diagnosis or identify what is driving the trend.
The available figures end in 2023, so it is not yet clear whether the increase will persist in later years. The study also cannot establish whether the trend reflects changes in exposures, detection, other factors or a combination. Annual registry updates will help show whether the pattern continues.
Researchers Pursue Risk Clues
Murphy’s team plans to investigate possible environmental exposures with Xin Hu, a toxicologist at Emory University. The researchers intend to measure thousands of exposures in a small blood sample to identify chemicals that may warrant closer study. They then plan to work with Kupfer to examine effects on the colon using organoids, laboratory models grown to represent colon tissue. These steps may point researchers toward candidates for further investigation; they will not, by themselves, establish that a chemical causes colorectal cancer.
Researchers also call for continued surveillance as cancer registry data are updated annually. The next updates will help establish whether the increase persists beyond 2023 and how it develops across age groups. For readers, the study does not change screening guidance: average-risk adults are advised to start at 45 and continue through 75, while individual circumstances may call for a clinician’s advice about screening and symptoms.
Key Questions
What did the study find?
Researchers 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?
People aged 45-49 had the steepest reported increase: incidence rose by 12.76% annually from 2019 to 2023. The researchers said expanded screening after the recommended starting age was lowered to 45 likely contributed to this group’s increase.
Do researchers know what is causing the broader rise?
No. The study identifies a trend but does not establish its cause. Researchers are investigating possible factors, including environmental chemical exposures, but those remain under study.
What are the current screening recommendations?
National guidelines recommend regular screening for adults at average risk from age 45 through 75. People outside that age range, or with factors such as family history, should discuss their circumstances and options with a qualified clinician.
Source: uchicagomedicine.org
