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A study 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 up to 65–69. Researchers say expanded screening may explain some of the rise among adults aged 45–49, but not the broader pattern; the causes remain unknown.
U.S. colorectal cancer incidence rose in 2023 after declining for more than 20 years, and the increase extends across age groups up to 65–69, a study published in NEJM Evidence found. Researchers say the trend goes beyond the rise among younger adults, while the reasons for the broader increase are still unknown.
Researchers led by Caitlin Murphy, a University of Chicago professor of pediatrics and public health sciences, 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. The study describes the 2023 change as the first increase in the overall rate in more than two decades.
The sharpest rise was among adults aged 45–49, whose incidence increased by 12.76% annually from 2019 through 2023, according to the study. The authors said increased screening may account for some of that change: national recommendations lowered the starting age for average-risk screening from 50 to 45. Murphy said screening is intended to detect cancers earlier, but the researchers said this shift does not account for increases in other age groups or the overall rate.
Incidence also rose among people aged 65–69, while rates plateaued among those aged 70–74. The researchers noted that screening has historically benefited older adults and that about 80% of people in these age groups are up to date with screening. They said the findings point to a need to investigate risks that screening alone does not explain.
The Rise Extends Beyond Younger Adults
The findings challenge the perception that rising colorectal cancer incidence is confined to people under 50. The disease remains a major health burden in the United States: the source report describes it as the second-leading cause of cancer-related death overall and the leading cause among adults younger than 50. A rise across a wider span of ages could increase demand for diagnosis, treatment and care after treatment.
The study does not establish what is causing the increase, nor does it show that screening is failing. Rather, its age-specific results suggest that the additional diagnoses among adults aged 45–49 may partly reflect more people being screened, while changes among older groups need further explanation. If the pattern persists, researchers warn, more cases across a large and aging population could add pressure to cancer-care services and survivorship support.
For readers, the practical message remains to follow screening recommendations and discuss personal risk with a clinician. Screening can find cancer earlier and some tests can detect precancerous growths, but the study’s findings are not a reason to assume an individual has cancer or to change a screening plan without medical advice.
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A Long Decline, Then a Reversal
For decades, U.S. colorectal cancer incidence had generally declined. The new analysis traces the rate from 55.2 per 100,000 in 2000 to 36.7 in 2022, before the increase to 38.3 in 2023. Those figures are age-adjusted rates, allowing comparisons that account for differences in population age structure; they are not a count of cases in a single age group.
Early-onset colorectal cancer has drawn attention as cases increased among younger adults. The UChicago Medicine report cites American Cancer Society statistics showing incidence among adults aged 20–49 rose by 3% annually from 2013 to 2022. Murphy and her colleagues argue the newer study broadens the issue: increases are also appearing among older groups, which may reflect shared risks or trends that develop as people born around the same time age.
The researchers describe a possible birth-cohort effect: people born in the 1960s and later may carry elevated risk as they move into middle and older adulthood. This is a proposed way to interpret the pattern, not an identified cause. The team also checked whether pandemic-era interruptions in screening and diagnosis could explain the rise. The increase remained when 2020 and 2021 data were excluded, and the report says screening had largely returned to pre-pandemic levels by January 2021.
“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 professor and study author
The Drivers of the Increase Remain Unknown
The study documents changes in incidence but does not identify the risk factors responsible. More screening is a likely contributor to the increase among adults aged 45–49, but researchers say it does not explain the rise across the overall population or in other age groups. The proposed birth-cohort effect is an interpretation of the timing and age pattern, not proof of a specific exposure or mechanism.
The researchers are investigating whether environmental chemical exposures could be involved. The planned work will measure thousands of exposures in small blood samples, then use colon organoids—laboratory models that grow colon tissue—to study selected chemicals. That research is ongoing, and the source report does not identify any particular chemical as a cause.
Future registry updates will also show whether the 2023 increase continues. The available data do not establish what happened after 2023, how much of the observed change reflects detection versus underlying disease risk, or whether the pattern will hold across subsequent years.
Researchers Plan Further Exposure Studies
The authors call for continued monitoring as cancer registry data are updated each year. They plan to examine environmental exposures with collaborators at Emory University, then study the effects of chemicals of interest using organoids with Kupfer’s team. Those steps may help identify candidates for further research, but they will not by themselves establish that an exposure causes cancer in people.
For now, U.S. guidelines recommend that adults at average risk begin regular colorectal cancer screening at age 45 and continue through age 75. Decisions for people younger than 45 or older than 75 should be individualized, taking account of factors such as family history, symptoms and other health conditions. Colonoscopy is one option; stool-based and blood-based tests are also available, with different uses and repeat schedules. People should discuss their circumstances and test choices with a clinician.
Key Questions
What did the study find?
Using National Cancer Institute data, researchers found the age-adjusted U.S. colorectal cancer incidence rate rose from 36.7 per 100,000 in 2022 to 38.3 in 2023, after a decline lasting more than two decades. Rates were rising across age groups up to 65–69.
Does the study explain why rates are rising?
No. The study identifies a trend, but the causes remain unknown. Researchers say increased screening may explain some of the rise among adults aged 45–49, but not the broader pattern.
Could pandemic disruptions explain the increase?
The researchers tested that possibility. The increase persisted when data from 2020 and 2021 were excluded, and the report says screening had largely returned to pre-pandemic levels by January 2021. The study therefore does not attribute the 2023 rise to pandemic disruptions.
When should average-risk adults begin screening?
U.S. guidelines recommend that adults at average risk start regular screening at age 45 and continue through age 75. Screening choices and timing outside those ages should be discussed individually with a clinician.
What research is planned next?
The research team plans to measure many environmental exposures in blood samples and then study selected chemicals using colon organoids. The work is exploratory; no specific chemical has been established as the cause of the rising rates.
Source: uchicagomedicine.org
