Colorectal Cancer Rates Rise Again in U.S. After 20 Years of Decline
U.S. colorectal cancer incidence rose from 36.7 to 38.3 per 100,000 in 2023, with increases in nearly every age group under 70, an NEJM Evidence study found.
Colorectal cancer incidence in the United States rose from 36.7 cases per 100,000 people in 2022 to 38.3 in 2023, the first overall increase in more than 20 years, according to a study in NEJM Evidence. The University of Chicago Medical Center, which released the findings, said rates are now climbing in nearly every age group under 70, not only among younger adults.
Colorectal cancer is already the second leading cause of cancer deaths in the United States and the leading cause among adults younger than 50.
How the researchers measured it
Caitlin Murphy of the University of Chicago and her colleagues analyzed National Cancer Institute incidence data covering 2000 through 2023. The work is an analysis of cancer registry statistics, so it describes who is being diagnosed rather than why. The age-adjusted rate was 55.2 per 100,000 in 2000 and fell to 36.7 by 2022 before turning upward. The authors also include researchers from the University of California, Los Angeles, Emory University and the University of California, San Diego.
The team checked whether the pandemic distorted the picture, since screening and diagnoses were disrupted in 2020 and 2021. The upward trend stayed even after they removed those two years. Screening had also largely returned to its earlier levels by January 2021, so the authors consider pandemic disruption an unlikely explanation for the 2023 rise.
Where the increase is largest
Adults ages 45 to 49 showed the steepest change: from 2019 through 2023, incidence in that group rose 12.76% per year. The researchers think much of it reflects a change in national guidelines, which lowered the recommended screening start age from 50 to 45. More testing finds more cancers that would have gone undetected. “Screening is doing as we intend it to do,” Murphy said.
Screening does not explain the whole pattern. Rates are also rising among adults ages 65 to 69, and the decline has stalled for ages 70 to 74. About 80% of people in those age groups are up to date with recommended testing.
What scientists suspect and what is unknown
The causes remain uncertain. Murphy expected the rise seen in younger adults to reach older ones through what she calls a birth cohort effect: people born in the same period carry shared risks that show up as they age. People born in the 1960s and later appear to face higher risk as they reach middle age and beyond. American Cancer Society data show incidence among adults ages 20 to 49 grew by about 3% per year between 2013 and 2022.
The team is working with Xin Hu, a toxicologist at Emory University, to test small blood samples for thousands of environmental chemical exposures at once. They then plan to study how candidate chemicals affect colon tissue using organoids, which are laboratory-grown models that reproduce features of the colon. This work is at an early stage, and the study does not show that any chemical causes the increase.
Why it matters
If the trend continues, Murphy said, many Americans born in recent decades will reach older ages with higher incidence, which would raise demand for treatment and long-term support. Current national recommendations advise adults at average risk to begin screening at age 45 and continue through age 75. Sonia Kupfer, who directs the Gastrointestinal Cancer Risk and Prevention Clinic at UChicago Medicine, said people should talk with a clinician about the available tests, which include colonoscopy, newer blood-based tests and stool tests done at home. She added that people under 45 who notice blood in the stool, persistent bowel changes or unexplained weight loss should seek medical attention.
The paper, “Colorectal Cancer among U.S. Adults, 2000-2023,” appeared in NEJM Evidence (DOI 10.1056/EVIDpha2600217). It was funded by the National Institutes of Health and the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research Ablon Scholars Program.
Source: ScienceDaily
