TL;DR
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A study published in NEJM Evidence found that U.S. colorectal cancer incidence, after declining for decades, rose from 36.7 cases per 100,000 people in 2022 to 38.3 in 2023. Rates increased across age groups through 65 to 69, but researchers have not identified the factors behind the broader rise.
A study published in NEJM Evidence found that U.S. colorectal cancer rates rose in 2023 after more than two decades of overall decline, with increases extending beyond younger adults to age groups through 65 to 69. The findings, based on National Cancer Institute data, point to a wider pattern than early-onset disease alone, although researchers say the causes of the broader increase are not yet known.
Researchers led by Caitlin Murphy, an epidemiologist at the University of Chicago, examined cancer incidence across a 20-year period using the most recent available National Cancer Institute data. The age-adjusted rate fell from 55.2 cases per 100,000 people in 2000 to 36.7 in 2022, before rising to 38.3 in 2023. That one-year increase follows a long decline, and the study describes rising rates across age groups up to 65 to 69.
The sharpest reported annual increase was among people aged 45 to 49: incidence rose by 12.76% annually from 2019 through 2023. The researchers said expanded screening may account for some of that rise. U.S. recommendations lowered the starting age for average-risk screening from 50 to 45, meaning more people in this age range are being tested and cancers may be detected earlier.
That explanation does not account for the overall increase or the changes in other age groups, according to the study. Rates also increased among adults aged 65 to 69, while they plateaued among those aged 70 to 74. The researchers said these patterns merit attention because older adults have historically benefited from screening, and about 80% of people in those groups are up to date with it.
The Rise Extends Beyond Younger Adults
The results shift the focus from early-onset colorectal cancer alone to a trend affecting a wider span of ages. Cases among adults younger than 50 have received substantial attention, but the study suggests that the increase is not confined to them. That matters for prevention and care planning: more diagnoses across a large population could add demand for treatment and survivorship care, the researchers said.
The study does not show that screening has stopped working. The authors suggest that increased testing may be contributing to the sharp rise recorded among people aged 45 to 49, because more screening can find cancers that otherwise might have been detected later. But screening does not explain the pattern in every age group. The rise among 65- to 69-year-olds, despite substantial screening participation, leaves open the possibility that other factors are contributing or offsetting screening gains.
For readers, the findings are a reason to pay attention to screening guidance, not to assume that the study identifies an individual’s risk or establishes a new cause. The data describe population-level incidence. They do not establish why rates are changing or predict what will happen to any one person.
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A Long Decline Reverses in 2023
Colorectal cancer has long been a major cause of cancer death in the United States. The source report identifies it as the second-leading cause of cancer-related deaths overall and the leading cause among adults younger than 50. Earlier research had drawn attention to increasing cases among younger adults; American Cancer Society statistics cited in the report found incidence among people aged 20 to 49 rose by 3% annually from 2013 through 2022.
Murphy and her colleagues interpret the spread into older age groups as potentially consistent with a birth-cohort effect: people born in the 1960s and later may carry elevated risk as they age. This is a proposed way to understand the pattern, not a proven explanation for it. The researchers also checked whether disruption during the COVID-19 pandemic could account for the findings. The increase persisted when data from 2020 and 2021 were excluded, and screening had largely returned to pre-pandemic levels by January 2021.
Current U.S. guidance recommends regular screening for adults at average risk from age 45 through 75. The source report says screening options include colonoscopy and stool-based and blood-based tests. Which test to use and how often to repeat it can vary; the report advises discussing options with a clinician. Screening decisions for people younger than 45 or older than 75 should be individualized, taking factors such as family history and other medical conditions into account.
“This is the first time that we have seen an increase in the overall rate in more than 20 years.”
— Caitlin Murphy, University of Chicago professor of pediatrics and public health sciences
The Causes Remain Unidentified
The study reports incidence patterns but does not pinpoint the risk factors driving the increase. Screening may explain part of the sharp rise among people aged 45 to 49, but the authors say it cannot explain the overall increase or the pattern in other groups. The birth-cohort explanation is a hypothesis about how risk may vary across generations, not a confirmed cause.
The researchers are investigating whether environmental chemical exposures could play a role. Their planned work includes measuring many exposures in blood samples and then studying selected chemicals in colon organoids, laboratory-grown models. That work is still in progress; the source report does not provide results or establish that any particular chemical causes colorectal cancer.
Incidence data also depend on continued updates to cancer registries. One year of overall increase, even after a long decline, does not by itself establish how rates will move in the future. Researchers call for ongoing surveillance to see whether the trend continues.
Researchers Plan Exposure Studies
The research team plans to continue analyzing registry data as annual updates become available. It also intends to test thousands of environmental exposures in a small blood sample, identify candidates for further study, and examine their effects on colon organoids with Kupfer’s team. These steps may help identify possible lines of investigation, but they do not yet offer an explanation for the trend.
For now, the source report says screening remains an important way to detect colorectal cancer early and prevent it from becoming deadly. Adults should discuss appropriate screening options and timing with a qualified clinician, particularly if family history, symptoms or other health factors affect their risk. The next key evidence will be whether subsequent data confirm a continued increase and whether research can identify factors behind it.
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 people in 2022 to 38.3 in 2023, after declining from 55.2 in 2000. Rates were rising across age groups through 65 to 69.
Which age group had the sharpest reported increase?
Among people aged 45 to 49, incidence rose by 12.76% annually from 2019 through 2023. Researchers said increased screening after the recommended starting age was lowered from 50 to 45 may account for some of that rise.
Do researchers know what is causing the increase?
No. The study identifies incidence trends but does not determine their cause. The team is investigating possible environmental exposures, among other questions, but has not reported findings that establish a specific risk factor.
When should average-risk adults begin screening?
The source report says U.S. guidelines recommend regular colorectal cancer screening for adults at average risk from age 45 through 75. Screening choices and timing can depend on individual circumstances; discuss them with a qualified clinician.
Source: uchicagomedicine.org
