Colorectal Cancer Rates Are Now Climbing in Nearly Every Age Group, Study Finds

Colorectal cancer incidence in the United States, after decades of steady decline, has begun to rise again — and not only among the young adults who have dominated headlines in recent years. A new study published in NEJM Evidence reports that rates are climbing across nearly all age groups, a shift that researchers say could reshape the demands placed on the American healthcare system for years to come. The findings, based on the most recent data from the National Cancer Institute, suggest that the well-documented surge of early-onset colorectal cancer may be only one part of a broader, population-wide change in disease patterns.

Colorectal cancer is the second leading cause of cancer-related death overall in the United States, and it ranks first among adults younger than 50. The new analysis, led by Caitlin Murphy, PhD, MPH, Professor of Pediatrics and Public Health Sciences at the University of Chicago, examined incidence rates 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 — a long decline that public health experts had come to regard as a durable success story — and then rose to 38.3 in 2023. That reversal, Murphy noted, is the first increase in the overall rate seen in more than 20 years.

The latest study shows that rates are now rising across all age groups up to 65-69. As an epidemiologist who has long studied colorectal cancer trends, Murphy said she anticipated that a swelling tidal wave of diagnoses would eventually reach older populations in addition to those under 50. She describes the underlying phenomenon as the birth cohort effect, in which people born in the 1960s and later carry a higher risk of colorectal cancer as they move into middle age and older adulthood.

Murphy frames the birth cohort effect as the interaction of age and time. As people born around the same time move through time and age together, she explained, more colorectal cancers are diagnosed among them. In practical terms, the elevated risk carried by younger generations does not disappear as they grow older; it travels with them. The sharp rise in early-onset disease among people under 50 that has attracted so much attention in recent years may therefore be an early signal of what happens when those same birth cohorts reach the ages at which colorectal cancer has historically been most common.

The study found the sharpest increase in incidence among adults aged 45 to 49, with rates rising 12.76% annually from 2019 to 2023. The authors said this spike is likely driven in part by more people undergoing colorectal cancer screening after national recommendations lowered the age to begin screening from 50 to 45. In that sense, Murphy said, screening is doing exactly what it is intended to do: catching cancer earlier.

But that screening effect cannot explain the rise in incidence overall or in other age-specific groups. Increasing rates among adults aged 65 to 69 — and plateaus among those aged 70 to 74 — are particularly concerning, the researchers noted, because these groups were historically the biggest beneficiaries of screening and are roughly 80% up-to-date with recommended screening. If screening is working as intended in the populations where it is most widely used, yet incidence is still climbing, the authors suggest that unknown risk factors may be offsetting the gains made by early detection. Identifying those factors, they argue, is now an urgent research priority.

The researchers also examined whether disruptions to screening and diagnosis during the COVID-19 pandemic could account for the 2023 increase. They found that even when data from 2020 and 2021 were excluded from the analysis, the increase persisted. Screening had largely returned to pre-pandemic levels by January 2021, making the pandemic an unlikely explanation for the rise seen in 2023. Sonia Kupfer, MD, director of the Gastrointestinal Cancer Risk and Prevention Clinic at UChicago Medicine, said the results motivate researchers to understand the reasons for the rise so that risk factors can be identified and possibly reduced.

The findings build on an already troubling pattern in younger adults. According to American Cancer Society statistics covering 2013 to 2022, colorectal cancer incidence rates among adults aged 20 to 49 increased by 3% annually. Murphy emphasized that there are many unique challenges when someone is diagnosed with cancer at a young age, and that the problem deserves a spotlight. But she argued that the new study points toward a common cause: whatever is driving colorectal cancer in younger people appears to now also be driving increases in older people as well.

Researchers cannot yet pinpoint which risk factors are behind the trend, but Murphy and her colleagues are pursuing a systematic search for answers. Working with Xin Hu, PhD, a toxicologist at Emory University, the team plans to measure thousands of environmental chemical exposures at once in small blood samples to identify which chemicals warrant further investigation. They will then collaborate with Kupfer to study the effects of those chemicals on the colon using organoids — specialized laboratory models that can grow colons in a dish. The approach reflects a growing suspicion among researchers that environmental exposures may play a role in the changing epidemiology of the disease, though the authors stress that no specific culprit has yet been identified.

The authors call for continued surveillance as registry data are updated annually. If these trends continue, Murphy warns, the increases in diagnoses across a large, aging population could create a heavy burden on the healthcare system for cancer treatment and survivorship care. Until more is known about the risk factors driving the trends, screening remains the best available chance to detect colorectal cancer early and prevent it from becoming deadly. National guidelines recommend that adults at average risk begin regular screening at age 45 and continue through age 75, with individualized discussions for those younger than 45 or older than 75 based on family history, symptoms and other medical problems. Colonoscopy remains the gold standard, but newer options — including blood-based and home-based stool tests — have expanded the ways people can be screened. Kupfer urged people to discuss the different screening tests with a clinician so they understand what each is intended for and how often each needs to be repeated. 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 if they occur.

Subject of Research: Rising colorectal cancer incidence across age groups in the United States

Article Title: Rising rates of colorectal cancer found in nearly all age groups

Article References: Rising rates of colorectal cancer found in nearly all age groups. Original publication (Bibliographic details unavailable.)

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Keywords: colorectal cancer, cancer incidence, early-onset cancer, birth cohort effect, cancer screening, NEJM Evidence, epidemiology, National Cancer Institute, environmental exposures, public health, colonoscopy, healthcare burden