After decades of decline, colorectal cancer rates are showing a concerning reversal.
Colorectal cancer rates in the United States are rising across a much wider range of ages than previously recognized, reversing a long period of declining diagnoses. A new study published in NEJM Evidence found that the increase is no longer concentrated among adults younger than 50, with rates now climbing in people approaching their 70s.
Colorectal cancer is the second leading cause of cancer-related deaths overall in the United States and the leading cause among adults younger than 50. As more generations reach ages when the disease becomes increasingly common, researchers warn that growing numbers of diagnoses could place additional demands on cancer treatment and long-term survivorship care.
Colorectal Cancer Rates Reverse a Decades-Long Decline
Researchers led by Caitlin Murphy, PhD, MPH, Professor of Pediatrics and Public Health Sciences at the University of Chicago, analyzed National Cancer Institute data to track changes in colorectal cancer incidence over more than two decades. The age-adjusted rate dropped from 55.2 cases per 100,000 people in 2000 to 36.7 in 2022, before increasing to 38.3 in 2023.
“This is the first time that we have seen an increase in the overall rate since in more than 20 years,” Murphy said. The study also found rising incidence across age groups through 65 to 69 years, indicating that the trend extends well beyond the younger populations that have received much of the attention.
The increase among older adults is particularly concerning because colorectal cancer screening has historically produced substantial benefits in these age groups. Rates are now rising among people ages 65 to 69 and have stopped declining among those ages 70 to 74, despite approximately 80% of people in these groups being up to date with screening. Researchers suspect that unidentified risk factors may be counteracting some of the progress achieved through earlier detection and prevention.
A Generational Pattern May Help Explain the Increase
Murphy believes the expanding age range reflects a phenomenon known as the “birth cohort effect,” in which people born during particular periods experience different disease risks as they grow older. In this case, evidence suggests that individuals born in the 1960s and afterward may face an elevated risk of colorectal cancer that persists as they advance into middle and older adulthood.
“I think of a birth cohort effect as the interaction of age and time,” Murphy explained. “As people born around the same time move through time and age together, we’re going to see more colorectal cancers being diagnosed.”
The pattern could help connect the growing incidence among younger adults with the increases now appearing in older populations. American Cancer Society statistics show that colorectal cancer incidence among people ages 20 to 49 rose approximately 3% annually from 2013 to 2022.
“There are many unique challenges when you’re diagnosed with cancer at a young age, so it’s important that we shine a spotlight on that problem,” Murphy said. “But in terms of understanding the root cause, I think our study shows that we can consider that whatever might be causing colorectal cancer in younger people is now also causing it to increase in older people as well.”
Screening Changes Explain Only Part of the Rise
The steepest increase occurred among adults ages 45 to 49, whose colorectal cancer incidence rose by 12.76% annually between 2019 and 2023. Researchers believe this unusually rapid increase largely reflects expanded screening following a change in national guidelines that lowered the recommended starting age from 50 to 45.
Screening can temporarily raise reported incidence by detecting cancers that were already present but had not yet been diagnosed. “That means that screening is doing as we intend it to do — it’s catching cancer earlier,” Murphy said.
However, increased screening cannot fully account for the broader rise across age groups, especially among older adults who already have high screening participation. The researchers also examined whether disruptions caused by the COVID-19 pandemic contributed to the trend. The increase persisted even when data from 2020 and 2021 were excluded, and screening activity had largely returned to pre-pandemic levels by January 2021. These findings suggest that pandemic-related delays are unlikely to explain the overall increase observed in 2023.
Scientists Investigate Environmental Exposures
The underlying causes of the rising incidence remain uncertain. Researchers are now examining whether exposure to chemicals in the environment could contribute to colorectal cancer risk, although no specific exposure has been established as responsible for the observed trends.
“These results motivate us to understand reasons for this rise, so risk factors can be identified and possibly reduced,” said Sonia Kupfer, MD, director of the Gastrointestinal Cancer Risk and Prevention Clinic at UChicago Medicine.
Murphy is collaborating with Xin Hu, PhD, a toxicologist at Emory University, to investigate thousands of environmental chemical exposures using small blood samples. This approach will help identify substances that may warrant closer examination.
The researchers then plan to work with Kupfer to study selected chemicals using colon organoids, laboratory-grown models that reproduce some features of human colon tissue. These models will allow scientists to investigate how particular exposures affect colon cells and potentially identify biological processes involved in cancer development.
Early Detection Remains Essential
Until the causes become clearer, colorectal cancer screening remains one of the most effective ways to identify the disease early and prevent deaths. Current national guidelines recommend routine screening for adults at average risk beginning at age 45 and continuing through age 75. Screening decisions outside that range should be individualized based on factors such as family history, symptoms, and other medical conditions.
Colonoscopy remains the gold standard because it can both detect cancer and remove precancerous polyps. Other screening methods include home-based stool tests and newer blood-based tests, although their capabilities and recommended testing intervals differ.
“There are several ways to do screening that should be discussed with a clinician, so people know what the different screening tests are intended for and how often these need to be repeated,” Kupfer added.
For adults younger than 45 who do not qualify for routine screening, recognizing possible warning signs is particularly important. Blood in the stool, persistent changes in bowel habits, and unexplained weight loss should prompt medical evaluation, even in people without a known family history or genetic risk.
The research team also recommends continued monitoring of national cancer registry data as new figures become available. If the upward trend persists as large generations of Americans grow older, healthcare systems may face increasing demand for cancer treatment, follow-up care, and long-term support for survivors.
Reference: “Colorectal Cancer among U.S. Adults, 2000–2023” by Caitlin C. Murphy, Folasade P. May, Sonia S. Kupfer, Xin Hu and Samir Gupta, 27 October 2026, NEJM Evidence.
DOI: 10.1056/EVIDpha2600217
The study was supported by funding from the National Institutes of Health and the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research Ablon Scholars Program.
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