How DNA Stool & Blood Tests Are Revolutionizing Early-Onset Colon Cancer Screening
- armantabesh
- Apr 29
- 4 min read
Colorectal cancer is diagnosed in 153,000 people annually in the U.S. and is the second most common cause of cancer-related death. Historically, CRC incidence rose with age, peaking in those over 65, but over the past three decades, rates in adults under 50 have climbed dramatically, nearly doubling in some populations. In high-income countries like the United States, Australia, and the UK, incidence in younger adults rose while rates in older adults fell. The American Cancer Society reported that in 2019, 20% of new CRC diagnoses occurred in those under 55—double the proportion seen in 1995. In response, screening guidelines have moved to begin average-risk screenings at age 45, most commonly in the form of a colonoscopy. Despite the effectiveness of colonoscopies in reducing the incidence and death rate of CRC, screening adherence was just under 60% in 2021, far below the recommended 80% target.
This post will discuss…
Possible reasons for the rise of cases in younger individuals
New ways to get screened for CRC and the difference between them
The effectiveness of these new tests compared to colonoscopies
Possible Reasons for Earlier Onset
Lifestyle and Environmental Factors
Sedentariness/ Lifestyle shift: Rates of sedentariness are consistently rising: A strong correlation to CRC. Today, one-third of the global population aged 15 years and older engages in insufficient physical activity. A sedentary lifestyle independently increases CRC risk by 20–24%
Dietary Patterns/Obesity: Diets high in processed meats and low in fiber are linked to CRC. In the past decades, obesity rates have risen in the U.S.. Slowly, however, the rates have plateaued in the recent years
Microbial Exposures: Recent research implicates more exposure to colibactin—a DNA-damaging toxin produced by certain E. coli strains—in early-onset CRC. A recent study from UCSD showed that out of 1,000 colorectal cancer patients tested across four continents, the majority had cancers bearing mutations that signaled a past encounter with colibactin. Tumors from patients under 40 show colibactin-associated mutations 3.3 times more often than those in patients over 70.
Genetic and Molecular Factors
Undiscovered Predisposition Genes: Lynch syndrome is the most common genetic condition associated with colon cancer. However CRC is happening sporadically, so experts are still trying to pinpoint more genes that produce CRC
New Routes for CRC Screening
Adherence for the strenuous colonoscopy process is lower than it needs to be so researchers have been searching for simpler, less invasive ways to get screened for CRC. Below are the two most common alternative screening methods:
Stool DNA Testing
In 2014, a noninvasive DNA stool test that assesses both DNA molecular markers and hemoglobin level was approved by the FDA. However, the diagnostic test only began receiving widespread traction several years ago. The test began with low sensitivity and specificity rates, but over the past 10 years, research drastically improved, and a next-generation multi-target stool DNA test was approved by the FDA in October of 2024.
The DNA stool test assesses several different biomarkers in the stool, looking for any abnormal or altered DNA and blood changes that occur as a result of cancer or polyps growing in the colon. The DNA changes are found in near-negligible amounts, so the test is sent to a lab where an advanced algorithm analyzes the molecular data of the stool. With a 95% sensitivity rate and a 94% specificity rate, receiving a negative DNA stool test helps avoid the strenuous colonoscopy process.
Pros
Convenience: No bowel prep or dietary restrictions are required; specimens are collected at home and mailed in
Non-Invasive: Avoids sedation and procedural discomfort.
Strong Sensitivity and Specificity for Cancer
Completely Free Under Majority of Insurance
Screening Interval: Recommended every three years for average-risk adults aged ≥45
Cons
Lower Polyp Detection: Detects only ~42% of large (≥1 cm) precancerous polyps versus ~95% for colonoscopy. Even if cancer hasn’t been formed yet, polyps are a major future danger
False Positives: Positive results require follow-up colonoscopy: Mostly accurate but false positives are possible
Blood-Based DNA Testing
How It Works
A blood-based DNA test looks for specific changes to cell-free DNA floating freely in the blood that indicate the presence of a tumor or polyps in the colon and rectum.
Pros
Cons
Lower Sensitivity for Precancerous Lesions: Detects ~13–20% of advanced adenomas, far less than stool-DNA tests or colonoscopy
Specificity Trade-Off: Although specificity for CRC is high (~80–90%), false positives still occur, necessitating colonoscopy follow-up.
Emerging Evidence: Long-term impact on CRC mortality remains under study; colonoscopy remains gold standard
Comparing Stool DNA and Blood Tests
Feature | Stool DNA (Cologuard®) | Blood-Based (Epi proColon®, Shield) |
Test Type | FIT + multi-target DNA | ctDNA / methylation biomarker |
Sample | Home-collected stool | Standard blood draw |
Cancer Sensitivity | ~95 % | ~80–83 % |
Advanced Adenoma Sens. | ~42 % | ~13–20 % |
Preparation | None | None |
Screening Interval | Every 3 years | Annually |
Follow-up | Colonoscopy if positive | Colonoscopy if positive |
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Ultimately, both the stool test and the blood test are works in progress and require extensive research to get it to a level of effectiveness similar to colonoscopies. But, this downward shift in the CRC average age displays the urgency of awareness and early detection. While colonoscopy remains the definitive screening and preventive tool,the DNA-based stool and blood tests are analogous options that can increase screening uptake among younger and average-risk individuals. To minimize the chance of getting CRC as a younger individual, exercise, maximize fiber intake, and reach out to a healthcare professional if bowel habits change.
Sources
Arnold M, et al. Colorectal cancer incidence trends in younger versus older adults. Lancet Oncol. 2024. The Lancet
Siegel RL, et al. Colorectal cancer in younger adults. PubMed Central. 2023. PMC
American Cancer Society. Colorectal Cancer Facts & Figures 2023-2025. 2023. Cancer Resources
Yale Medicine. Colorectal Cancer: What Millennials and Gen Zers Need to Know. 2023. Yale Medicine
Tryon Medical. The pros and cons of Cologuard®. 2021. tryonmed.com
Cologuard®. How the test works. Cologuard.com. 2025. Cologuard
St. Vincent’s Health. 8 Things to Know About the Blood Test for Colon Cancer. 2024. St. Vincent's
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