Colorectal cancer rates are rising across younger and older age groups, according to a study published in NEJM Evidence.

Colorectal cancer, the second leading cause of cancer-related deaths overall in the U.S., ranks first in adults younger than 50 years. The new study found that rising incidence now extends beyond younger adults to nearly all age groups, which has implications for the healthcare system as more diagnoses will create a greater demand for treatment and survivorship care.

Caitlin Murphy, PhD, MPH, Professor of Pediatrics and Public Health Sciences at the University of Chicago, and her colleagues used the most recent data from the National Cancer Institute to examine incidence rates of colorectal cancer over a 20-year period. The data showed that 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.

“This is the first time that we have seen an increase in the overall rate since in more than 20 years,” Murphy said, noting that for decades, incidence rates had been declining. This latest study shows that the rates are rising across all age groups up to 65-69.

As an epidemiologist studying colorectal cancer trends, she anticipated that a swelling tidal wave of colorectal cancer rates would occur in older populations in addition to those under 50. She describes this phenomenon as the “birth cohort effect,” whereby people born in the 1960s and later face higher risk of colorectal cancer as they reach middle age 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 authors saw the sharpest increase in incidence rates among the 45-49-year-old age group, with an increase of 12.76% annually from 2019-2023. They said that this increase is likely driven by more people undergoing colorectal cancer screening after national recommendations lowered the age to begin screening from 50 to 45.

“That means that screening is doing as we intend it to do — it’s catching cancer earlier,” Murphy said.

However, that does not explain the rise in incidence overall or for other age-specific groups. Increasing rates among those aged 65-69 and plateaus among 70-74-year-olds are concerning as these groups were historically the biggest beneficiaries of screening and are about 80% up-to-date with screening. This suggests unknown risk factors may be offsetting the gains made by screening.

The researchers also explored the potential impact of disruptions to screening and diagnoses during the COVID-19 pandemic, but found that even when data from 2020-2021 were excluded, the increase persisted. Screening had largely returned to pre-pandemic levels by January 2021, making COVID unlikely to explain the increase seen in 2023.

“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.

Not just a problem for young people

According to American Cancer Society statistics from 2013-2022, colorectal cancer incidence rates among adults aged 20-49 years increased by 3% annually. This troubling rise in cases of early-onset colorectal cancers among people younger than 50 has received mainstream attention.

“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.”

Although researchers cannot yet pinpoint which risk factors are driving the trend, Murphy and colleagues are looking into environmental chemical exposures as a possible culprit. With Xin Hu, PhD, a toxicologist at Emory University, the team will measure thousands of environmental exposures at once in a small blood sample to identify which chemicals warrant further research. They will then work with Kupfer to study the effects of those chemicals on the colon by using organoids, specialized models that can grow colons in a dish.

The importance of screening

The authors call for continued surveillance as registry data are updated annually. If these trends continue, Murphy warns that the increases in diagnoses across a large, aging population may create a heavy burden on the healthcare system for cancer treatment and survivorship care.

Until more is known about the risks factors driving these trends, screening remains the best chance to detect colorectal cancer early and prevent it from becoming deadly.

National guidelines recommend that adults at average risk should begin regular screening at age 45 and continue through age 75. For those younger than 45 or older than 75, discussion about screening should be individualized based on family history, symptoms, and other medical problems.

Colonoscopies remain the gold standard, but there are now newer options such as blood-based and home-based stool tests that screen for colorectal cancer.

“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 those younger than 45 without risk factors such as genetics or family history who are not yet eligible for screening, she stressed the importance of paying attention to symptoms — such as blood in the stool, changes in bowel habits or unexplained weight loss — and seeing a doctor.

The study, “Colorectal cancer among U.S. adults, 2000-2023,” 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.

Additional authors include Folasade P. May from the University of California Los Angeles, Xin Hu from Emory University in Atlanta, and Samir Gupta from the University of California San Diego.

UChicago Medicine and the Biological Sciences Division continue to be at the forefront of cancer care and research. In April 2027, UChicago Medicine will open the AbbVie Foundation Cancer Pavilion, Chicago’s first freestanding cancer pavilion, to bring advanced diagnostics, innovative treatments, translational discoveries, and comprehensive support to patients and the community.