Observational study indicates rising colorectal cancer rates among U.S. adults — Evidence Review
Published in NEJM Evidence, by researchers from University of Chicago, Emory University
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Table of Contents
Colorectal cancer rates in the U.S. have reversed a two-decade decline, now rising across multiple age groups, according to a new study. Related research generally supports the finding of increased incidence among younger adults but previously reported continued declines or stabilization in older populations, making this broader upward trend especially notable (2, 4, 5).
- Recent studies have consistently identified increasing colorectal cancer incidence among younger adults, but the new findings highlight a reversal in older age groups as well, extending previous observations of rising rates (2, 4, 5).
- Multiple sources attribute changing trends to a combination of birth cohort effects, shifting risk factors, and possibly environmental or lifestyle influences, echoing the new study’s focus on cohort-specific risk (4, 5, 6).
- The new study’s observation of incidence increases despite high screening rates in older adults suggests that factors beyond screening changes—such as unidentified environmental or lifestyle risks—may be driving recent trends, a point also raised in recent literature (6, 7, 8).
Study Overview and Key Findings
Colorectal cancer has long been a leading cause of cancer-related death in the United States, with previous decades marked by steady declines in incidence, largely attributed to widespread screening and changes in risk factor prevalence. However, the new study draws attention to a recent and concerning reversal of this trend, identifying rising incidence not just among younger adults—a pattern noted for several years—but also among older age groups that have traditionally benefited most from screening programs. This shift raises significant questions about emerging risk factors and the adequacy of current prevention strategies.
| Property | Value |
|---|---|
| Study Year | 2026 |
| Organization | University of Chicago, Emory University |
| Journal Name | NEJM Evidence |
| Authors | Caitlin C. Murphy, Folasade P. May, Sonia S. Kupfer, Xin Hu, Samir Gupta |
| Population | U.S. adults with colorectal cancer |
| Methods | Observational Study |
| Outcome | Colorectal cancer incidence rates across age groups |
| Results | Colorectal cancer rates increased from 36.7 in 2022 to 38.3 in 2023. |
The study, led by researchers at the University of Chicago and Emory University, analyzed over two decades of National Cancer Institute data. It found that after a long period of decline, the age-adjusted incidence rate of colorectal cancer in the U.S. rose from 36.7 per 100,000 people in 2022 to 38.3 in 2023. While previous concern focused on adults under 50, the new data show rising incidence through age 69 and a halt in decline among those aged 70–74, even as screening remains high in these groups. The researchers suggest a “birth cohort effect,” where individuals born after the 1960s may carry elevated risks as they age, and note that screening changes and COVID-19 disruptions do not fully explain the increase. The study calls for further investigation into environmental exposures and other potential drivers of these trends.
Literature Review: Related Studies
To provide context for these findings, we searched the Consensus paper database, which contains over 200 million research papers, using targeted queries. The following search queries were used:
- colorectal cancer incidence trends
- risk factors colorectal cancer 2023
- impact of diet on colorectal cancer
Below, we summarize key topics and findings from the related literature:
| Topic | Key Findings |
|---|---|
| What are the trends in colorectal cancer incidence and mortality across age groups? | - Incidence has declined overall in older adults but increased among younger adults, particularly since the mid-1990s (2, 3, 4, 5). - The birth cohort effect shows increased risk in more recent generations, reversing previous declines and raising the risk to levels seen in much earlier cohorts (5). |
| Which risk factors contribute to rising colorectal cancer rates? | - Modifiable lifestyle factors (e.g., obesity, low physical activity, red and processed meat, alcohol, smoking) are strongly associated with increased risk (6, 7, 8, 9, 10, 11, 12, 13, 14). - Non-modifiable factors include age, family history, and certain genetic conditions (7, 8, 9). |
| How do screening practices and guidelines affect incidence trends? | - Expanded screening, especially lowering the starting age to 45, has contributed to short-term increases in detected cases, especially among those aged 45–49 (2, 4). - High screening rates in older adults have historically driven declines, but recent increases in incidence suggest other factors are at play (3, 4). |
| What is the role of environmental exposures and the gut microbiome? | - Emerging research highlights possible links between environmental chemicals, dietary patterns, and the gut microbiome in colorectal cancer risk, but specific causal agents remain to be identified (6, 13, 14, 15). - Diets high in fiber, dairy, and whole grains and low in red/processed meat are protective (11, 12, 13). |
What are the trends in colorectal cancer incidence and mortality across age groups?
Recent studies have documented a shift in colorectal cancer epidemiology: while incidence and mortality declined for older adults for many years, rates among younger adults have increased since the mid-1990s. The new study extends these observations by reporting a reversal of declining trends in older populations as well, which had not been widely observed in previous research (2, 3, 4, 5).
- Previous declines in incidence and mortality were most pronounced in adults over 65, attributed largely to screening (2, 3, 4).
- Younger adults (under 50) have experienced increasing incidence rates, with the most rapid increases among those born after 1950 (4, 5).
- The “birth cohort effect” identified in recent studies aligns with the new findings, indicating that higher risk persists as affected cohorts age (5).
- The proportion of colorectal cancer cases in adults under 55 has doubled since the mid-1990s, a trend now seen extending into older age groups (4, 5).
Which risk factors contribute to rising colorectal cancer rates?
Multiple studies have established that both modifiable and non-modifiable risk factors contribute to colorectal cancer risk. The new study’s consideration of unidentified risk factors and environmental exposures is consistent with a growing body of evidence pointing to complex interactions among genetic predisposition, lifestyle, and environment (6, 7, 8, 9, 10, 11, 12, 13, 14).
- Modifiable risk factors such as obesity, physical inactivity, smoking, alcohol, and high consumption of red and processed meat are consistently linked to increased risk (6, 7, 9, 10, 11, 12, 13, 14).
- Family history and certain medical conditions (e.g., inflammatory bowel disease) also substantially elevate risk (7, 8, 9).
- Dietary patterns play a significant role: diets rich in fiber, dairy, and whole grains are protective, while pro-inflammatory diets and high red/processed meat intake increase risk (11, 12, 13, 14).
- The new study’s focus on environmental exposures reflects emerging research but definitive links to specific chemicals remain to be established (6, 15).
How do screening practices and guidelines affect incidence trends?
Changes in screening guidelines—particularly the recommendation to begin screening at age 45—have led to increased detection rates in younger age groups, which can partially explain recent rises in incidence. However, the plateau or increase in older adults, despite high screening participation, points to additional factors (2, 3, 4).
- Expanded screening has contributed to short-term increases in incidence among newly eligible age groups (45–49), but cannot explain broader incidence rises (2, 4).
- Declines in incidence and mortality among older adults in previous decades were closely linked to high screening uptake (3, 4).
- The new data suggest screening alone does not account for recent trends, particularly in age groups with already high screening rates (4).
- Screening remains a key tool for early detection and prevention, but other strategies are needed to address the observed increases (2, 4).
What is the role of environmental exposures and the gut microbiome?
There is increasing interest in the potential contribution of environmental chemicals, dietary patterns, and the gut microbiome to colorectal cancer risk. The current study’s planned investigation into environmental exposures and biological mechanisms reflects a broader trend in research (6, 13, 14, 15).
- Environmental exposures, including chemicals, are suspected contributors but have not yet been definitively linked to the observed trends (6, 15).
- The gut microbiome, influenced by diet and lifestyle, may mediate some of the risk associated with environmental and dietary factors (15).
- Diets characterized by high fiber, dairy, and whole grains and low in red and processed meats are associated with lower risk, potentially via anti-inflammatory effects and microbiome modulation (11, 12, 13, 14).
- Pro-inflammatory diets and ultraprocessed foods increase colorectal cancer risk, underlining the importance of dietary interventions (14, 15).
Future Research Questions
Given the reversal of declining colorectal cancer trends across a wide age range and the uncertainty surrounding the underlying causes, further research is needed to clarify the contributions of environmental, lifestyle, and biological factors. Understanding these drivers is essential for developing effective prevention and intervention strategies.
| Research Question | Relevance |
|---|---|
| What environmental exposures are linked to recent rises in colorectal cancer incidence? | Identifying specific environmental chemicals or exposures that may contribute to rising incidence rates could inform targeted prevention strategies (6, 15). Further research could clarify whether environmental factors are responsible for the observed trends in various age cohorts. |
| How do birth cohort effects impact colorectal cancer risk over time? | Investigating the mechanisms underlying the birth cohort effect may help explain why certain generations are experiencing higher risks as they age (5). This could reveal early-life exposures or behaviors that increase susceptibility to colorectal cancer later in life. |
| What is the role of the gut microbiome in colorectal cancer development? | Research into how the gut microbiome mediates or modifies colorectal cancer risk could lead to new prevention and treatment approaches (13, 15). The interaction between diet, microbiome, and carcinogenesis is a promising area for intervention. |
| How effective are current screening strategies for older adults amid changing incidence trends? | Understanding whether existing screening guidelines are sufficient for early detection in older adults as incidence rises could help optimize recommendations (2, 3, 4). This is essential as increases are now seen even among populations with high screening uptake. |
| Which modifiable lifestyle factors most strongly influence colorectal cancer risk in younger versus older adults? | Determining the relative impact of factors such as diet, obesity, physical activity, and alcohol on different age groups could inform tailored prevention strategies (6, 7, 8, 10, 11, 12). This may help slow or reverse the rising incidence in both younger and older populations. |