Observational study finds colorectal cancer as leading cause of deaths in under-50 population — Evidence Review

Colorectal cancer is now the leading cause of cancer deaths in Americans under 50, according to a new study from the American Cancer Society. Related research largely supports these findings, documenting a sustained increase in colorectal cancer incidence and mortality among younger adults.

• Multiple studies report that while colorectal cancer rates and deaths are declining in older adults, they are rising in people under 50, with a particular increase in advanced-stage diagnoses and left-sided tumors 1 2 3.
• The trend toward earlier onset is observed not only in the United States but also internationally, with similar increases in Europe and other high-income countries 4 6.
• Although the causes remain unclear, related research points to a combination of non-modifiable risk factors (such as family history and race) and modifiable exposures (including obesity, diet, and lifestyle) as contributors to increasing risk among younger cohorts 11 12 13 15.

Study Overview and Key Findings

Colorectal cancer has historically been considered a disease of older adults, but recent data show a shifting pattern. This new study is particularly relevant as it analyzes incidence and mortality trends using national data, highlighting a concerning reversal: while overall colorectal cancer rates have declined due to screening and treatment advances, younger adults are now facing increased risk and mortality, often at advanced stages of diagnosis. The findings prompt renewed focus on early detection, awareness, and research into underlying causes.

Property	Value
Study Year	2023
Organization	American Cancer Society
Authors	Rebecca Siegel, Nikita Sandeep Wagle, Ahmedin Jemal
Population	People under 50 with colorectal cancer
Methods	Observational Study
Outcome	Colorectal cancer incidence and mortality rates
Results	Colorectal cancer is now the leading cause of cancer deaths in people under 50.

Literature Review: Related Studies

To contextualize these findings, we searched the Consensus database—containing over 200 million research papers—using the following queries:

1. colorectal cancer deaths under 50
2. young adults cancer mortality rates
3. risk factors colorectal cancer younger population

Below is a summary of key topics and findings from the literature:

Topic	Key Findings
Why is colorectal cancer increasing among younger adults?	• Rising incidence and mortality in people under 50, despite declines in older adults 1 2 3 4 6 • Possible contributors include generational shifts in diet, environmental exposures, and lifestyle factors, but the exact causes remain unclear 13 15
What are the major risk factors for early-onset colorectal cancer?	• Non-modifiable risk factors: family history, race (Black, Asian), male sex, inflammatory bowel disease 11 12 14 • Modifiable risk factors: obesity, smoking, alcohol use, metabolic syndrome, diet high in processed meats 13 14 15
How does stage at diagnosis and tumor location differ in younger patients?	• Younger patients more often present with advanced-stage and left-sided (distal colon/rectal) tumors 3 11 13 • These patterns are associated with poorer prognosis and may contribute to increased mortality in younger age groups 3 11
What is the global and long-term impact of early-onset colorectal cancer?	• Early-onset colorectal cancer is increasing in high-income countries globally 4 6 8 • Survivors of adolescent and young adult cancers face elevated long-term mortality and risk of chronic health conditions compared to the general population 9 10

Why is colorectal cancer increasing among younger adults?

Recent studies consistently demonstrate a rise in colorectal cancer incidence and mortality among adults under 50, contrasting with declines seen in those over 65. This reversal is observed in the U.S. and internationally, with the trend particularly pronounced for advanced-stage and left-sided tumors. The literature suggests that generational changes in environmental exposures, dietary patterns, and lifestyle may contribute, but no single cause has been definitively identified 1 2 3 4 6 13 15.

• Incidence among adults aged 20-49 has risen steadily in the U.S. and Europe over the last two decades 1 2 4 6.
• Declines in older adults are attributed to effective screening and treatment, while lack of screening in younger adults may contribute to later-stage diagnoses 1 2 3.
• International data suggest this is not a U.S.-specific phenomenon but part of a broader pattern in high-income countries 4 6.
• The "birth cohort effect" observed in the new study is echoed in related research, indicating a real generational change in risk factors 3.

What are the major risk factors for early-onset colorectal cancer?

Both non-modifiable and modifiable risk factors play roles in early-onset colorectal cancer. Family history, race, and certain pre-existing conditions increase risk, while lifestyle factors such as obesity, smoking, and diet are also significant. Notably, most young patients lack a family history, suggesting environmental or behavioral exposures are important 11 12 13 14 15.

• Non-modifiable risks include male sex, family history of colorectal cancer, Black and Asian race, and inflammatory bowel disease 11 12 14.
• Modifiable risks include obesity, metabolic syndrome, smoking, alcohol consumption, and diets high in processed foods and red meat 13 14 15.
• Many early-onset cases occur in patients without traditional risk factors, highlighting the need for broader research into etiological pathways 13 15.
• Regular exercise and aspirin use may lower risk, as indicated in certain population studies 12 15.

How does stage at diagnosis and tumor location differ in younger patients?

Younger patients are more likely to be diagnosed with advanced-stage disease and with tumors located in the distal colon or rectum. These factors are associated with poorer outcomes and may explain rising mortality rates in this age group 3 11 13.

• The proportion of advanced-stage diagnoses has increased among those under 55 since the mid-1990s, reversing earlier gains from screening 3.
• Early-onset colorectal cancer is more likely to affect the left side of the colon and rectum compared to later-onset cases 3 11 13.
• Advanced-stage presentation is linked to lower survival rates and higher mortality 3 11.
• These patterns underscore the need for earlier diagnosis and increased awareness of symptoms in younger populations 3 11 13.

What is the global and long-term impact of early-onset colorectal cancer?

Globally, early-onset colorectal cancer is rising in incidence, particularly in high-income regions. Survivors of adolescent and young adult cancers face increased long-term risks of mortality and chronic health conditions, emphasizing the growing public health impact 4 6 8 9 10.

• The trend of increasing incidence in young adults is mirrored across North America, Europe, and Australia 4 6 8.
• Cancer is a leading cause of death and disability-adjusted life-years among adolescents and young adults worldwide 8 10.
• Survivors of early-onset cancers have elevated risks of late mortality and chronic health issues, necessitating long-term follow-up and surveillance 9 10.
• The societal and economic burden is substantial, given the years of life lost and the impact on working-age populations 8 10.

Future Research Questions

Although the new study highlights a critical shift in colorectal cancer epidemiology, many questions remain regarding causes, prevention, and optimal screening strategies in younger adults. Addressing these gaps is essential to inform public health policies and reduce early-onset colorectal cancer deaths.

Research Question	Relevance
What are the primary environmental and lifestyle drivers of rising colorectal cancer incidence in adults under 50?	Understanding the causes of increased early-onset colorectal cancer is critical for targeted prevention. Current evidence points to diet, obesity, and environmental exposures, but precise factors remain unclear 13 15.
How effective are current screening guidelines at reducing mortality in adults aged 45-49?	The majority of deaths in adults under 50 occur in those aged 45-49, but screening uptake remains low. Evaluating guideline effectiveness could inform updates to screening recommendations 3.
What are the barriers to early diagnosis of colorectal cancer in younger populations?	Many younger patients are diagnosed at advanced stages, suggesting delays in symptom recognition or healthcare access. Identifying and addressing these barriers could improve outcomes 3 11.
Are novel biomarkers or genetic factors associated with early-onset colorectal cancer risk?	Although family history accounts for some cases, most early-onset patients lack known genetic risks. Research into novel biomarkers and genetic factors may enhance risk stratification and screening 11 13.
What public health strategies most effectively reduce modifiable risk factors for colorectal cancer in young adults?	Interventions targeting obesity, physical inactivity, and unhealthy diets could potentially slow rising incidence rates. Determining the most effective strategies is essential for prevention efforts 13 14 15.