An experimental blood test detected 81% of advanced adenomas, high-risk colorectal polyps that can develop into cancer, in a new international study involving more than 1,500 adults.
It also detected about 92% of stage I to III colorectal cancers, while correctly identifying around 85% of people without advanced precancerous lesions. The findings were published this week in The Lancet Gastroenterology & Hepatology.
The result is notable because detecting colorectal cancer in blood is no longer the only challenge. The harder problem has been finding the abnormal growths that come before cancer.
Finding cancer before it becomes cancer
Many colorectal cancers develop from polyps known as adenomas.
Most adenomas will not become cancerous, but certain characteristics, including their size, number and degree of abnormal cellular change, can identify lesions at greater risk of progressing. These are generally classified as advanced adenomas.
Finding and removing them during a colonoscopy can interrupt that progression.
This is what makes colorectal screening different from screening for some other cancers: doctors are not necessarily waiting to find an early tumour. They can sometimes identify and remove the precursor lesion before a cancer develops.
Existing blood-based screening tests have been considerably better at detecting established colorectal cancers than these precancerous lesions. The American Cancer Society’s updated 2026 screening guideline specifically notes that current blood-based tests have lower sensitivity for advanced precancerous lesions and stage I cancers than established stool-based approaches.
The new DENEB test was developed with that weakness in mind.
More than 1,500 people across three countries
Researchers tested DENEB using participants from colorectal screening programmes in China, Japan and Spain.
The study used separate cohorts to develop and validate the test, comparing the blood results with colonoscopy findings. Colonoscopy provided the reference because doctors could directly determine whether participants had no significant lesions, lower-risk adenomas, advanced adenomas or colorectal cancer.
In the validation results, sensitivity for advanced adenomas reached 81%, while the test identified approximately 92% of stage I to III colorectal cancers. Specificity for advanced neoplasia was about 85%.
Sensitivity describes how often a test correctly identifies people who have the condition being sought. An 81% sensitivity therefore does not mean the test is 81% “accurate” overall. It means roughly four out of five advanced adenomas in the study produced a positive result.
Some lesions were still missed.
The blood carries molecular clues
DENEB does not look for a physical polyp circulating through the bloodstream.
Instead, it analyses microRNAs, small molecules involved in controlling how genes are expressed.
The research programme behind DENEB combines microRNAs circulating freely in blood with microRNAs carried inside tiny membrane-bound particles called exosomes. These molecules can reflect biological changes associated with colorectal abnormalities.
The idea is to identify a molecular signature that changes as normal colorectal tissue progresses towards higher-risk adenomas and cancer.
That distinction matters because some existing liquid-biopsy approaches are particularly effective once a tumour is shedding detectable material into the bloodstream. A precancerous polyp presents a more difficult biological signal to find.
DENEB’s performance against advanced adenomas is therefore the central result of the study, rather than simply its ability to detect cancers that have already formed.
Why blood-based screening is being discussed now
The findings arrive as blood testing moves closer to mainstream colorectal screening.
In May, the American Cancer Society updated its colorectal cancer screening guideline to include blood-based testing as an option. However, it currently recommends these tests specifically for people who decline or do not complete preferred screening methods, because existing blood tests remain comparatively weak at detecting important precancerous lesions. A positive blood test must also be followed by colonoscopy.
JAMA returned to the issue on 14 August 2026, publishing an overview of what the new guideline means for blood-based colorectal screening. Reuters separately highlighted the DENEB results on the same day.
The debate is therefore moving beyond whether cancer can be detected in a tube of blood.
The more clinically important question is whether a convenient blood test can retain enough of colonoscopy’s preventive value to identify people who need further investigation before cancer develops.
DENEB offers encouraging evidence, but it has not answered that question yet.
What this could mean for South Africa
South Africans currently have access to more established approaches to colorectal screening. CANSA encourages colonoscopy based on age and individual risk and also provides home faecal-occult-blood testing.
A reliable blood test would potentially offer another route into screening because drawing blood is already routine throughout healthcare.
But even a highly sensitive future blood test would not remove the need for colonoscopy.
If DENEB identifies an advanced adenoma, the growth still needs to be located and removed. The blood test would therefore act as a way of identifying who should undergo the invasive procedure, rather than performing the preventive treatment itself.
For health systems with limited specialist capacity, that distinction could eventually become useful: the value may lie in directing colonoscopies towards people most likely to benefit from them.
That remains a potential application rather than something demonstrated by this study.
The 81% result still needs a harder test
The current findings require caution.
The validation study was outcome-enriched, meaning it contained a greater proportion of people with cancers and advanced adenomas than would be expected in an ordinary population invited for routine screening. The researchers themselves conclude that larger prospective studies in real screening populations are required before the test’s clinical utility can be established.
The assay was also less successful at detecting some sessile or flatter lesions, which can be particularly challenging abnormalities.
Those limitations matter because a screening test eventually has to work among thousands of mostly healthy people, not only distinguish carefully selected groups inside a diagnostic study.
Still, the finding addresses one of the more stubborn problems in blood-based cancer screening.
Detecting a cancer earlier is valuable.
Detecting the lesion before it becomes cancer could be more valuable still.
Whether DENEB can do that reliably enough in everyday screening is now the question the next generation of trials will need to answer.
Source Information
Study Title: A blood-based test for detection of advanced adenomas and colorectal cancer (DENEB): a multicentre diagnostic accuracy study
Authors: Alessandro Mannucci et al.
Journal: The Lancet Gastroenterology & Hepatology
Published: 10 August 2026
DOI: 10.1016/S2468-1253(26)00180-9
Clinical trial: DENEB: DEtection of colorectal NEoplasias in Blood
ClinicalTrials.gov: NCT06342440
Contextual guideline: American Cancer Society 2026 colorectal cancer screening guideline
DOI: 10.3322/caac.70083
