By Donnie Yance
Over the past year, many of my patients have asked me whether the Galleri multi-cancer blood test is something they should consider, so I took the dive and carefully reviewed all the data to date.
Blood-based cancer screening sounds like a breakthrough we’ve all been waiting for: a single blood draw that can detect dozens of cancers, including many that currently have no routine screening options. The Grail–Galleri Multi-Cancer Early Detection (MCED) test promises exactly that.
But a promise is not the same as proof.
Based on the published research available so far, I urge caution—and I do not recommend the Galleri test for routine use. Below, I explain how the test works, what the studies actually show, and why leading experts believe the evidence is not yet strong enough to justify widespread adoption.
How the Galleri Test Works
The Galleri test uses advanced DNA sequencing technology to analyze cell-free DNA (cfDNA) fragments circulating in the blood. Some of these fragments originate from tumors—known as circulating tumor DNA (ctDNA)—and carry distinct molecular signals that can differ from DNA released by healthy cells.
Unlike traditional screening tools that look for one cancer at a time (such as mammograms or colonoscopies), Galleri claims to detect over 50 different cancer types through a single blood sample. It does this by identifying aberrant DNA methylation patterns, which are chemical modifications that regulate gene expression and are often altered in cancer cells.1
One advantage of methylation-based testing is that these changes can occur early in cancer development and are more stable than genetic mutations. Additionally, methylation patterns tend to be tissue-specific, allowing the test to predict where in the body a cancer may have originated—information that could guide follow-up diagnostic work.2
On paper, this technology is impressive. In practice, the performance data tell a more complicated story.
What the Performance Data Really Show
A widely cited 2021 validation study reported a specificity of 99.5% and an overall sensitivity of 51.5%, with the test correctly identifying the cancer’s tissue of origin nearly 89% of the time when a cancer signal was detected.3
At first glance, that specificity looks reassuring—but even a small false-positive rate can have major real-world consequences. A 0.5% false-positive rate, if applied to population-wide screening, would result in more than 100,000 people undergoing additional testing each year in the UK alone. This raises concerns about unnecessary procedures, healthcare system burden, and patient anxiety.
More concerning is the test’s limited sensitivity for early-stage cancers—the very stage where screening is meant to help the most. In other clinical studies, Galleri detected only 27.5% of early-stage cancers overall, meaning it missed nearly three-quarters of cases.
When researchers focused on 12 so-called “high-need” cancers—those without established screening tools—sensitivity improved to 52.8%, but that still means almost half of these cancers went undetected.4
In February 2026, maker Grail Inc. announced the trial’s primary endpoint failure: adding Galleri to standard screenings did not reduce stage III-IV cancer diagnoses over 3 years among adults aged 50-77. The test increased early-stage detection by 16% and showed reduced stage IV diagnoses in a subset of 12 cancers during later screening rounds—findings Grail framed as evidence the test shifts cancers toward more treatable stages, even if the primary metric didn’t reach statistical significance.
Leading experts rejected this interpretation. Dr. H. Gilbert Welch argued the fourfold increase in cancer detection without corresponding reduction in late-stage disease is a classic signature of overdiagnosis—finding cancers that grow so slowly they would never cause symptoms or death, yet trigger invasive treatment. While GRAIL investigators argued the findings suggest the test can shift cancers toward potentially more treatable stages, several independent experts urged caution in interpreting the results.
Key Points
- >142,000 asymptomatic adults randomized; primary endpoint not met.
- Galleri + usual care did not ↓ combined stage III/IV cancers (IRR 1.03; P=.63).
- Secondary analyses: stage IV ↓ in later rounds; stage I-II dx ↑ 16% over 3 rounds.
- Test performance: 0.91% positive; ~52% of positives cancer-confirmed; ~70% of 12-mo cancers missed.
- Mortality benefit unproven; no major oncology society recommends routine MCED screening.5
Why Experts Are Urging Restraint
Supporters of MCED testing argue that artificial intelligence and improved molecular analysis could enhance performance over time. While that may eventually prove true, it does not solve the core problem: current evidence does not demonstrate clear clinical benefit.
Several prominent researchers have publicly urged physicians not to move ahead of the data. Dr. Welch has stated plainly that doctors “should not use or recommend these tests,” citing added cost, anxiety, overdiagnosis, and overtreatment.
Dr. Hoffman echoed this concern, emphasizing that professional guidelines—including those from the American Cancer Society—already stress caution and warn against premature adoption.
A major issue is the lack of long-term follow-up data. We still don’t know whether detecting these cancers earlier with Galleri actually improves survival, reduces advanced disease, or avoids harm. Reduction in late-stage diagnoses—a commonly cited endpoint—remains controversial and may not translate into better outcomes for patients.6
Regulatory and Coverage Considerations
Importantly, no MCED test has yet been approved by the FDA. However, the recently passed Nancy Gardner Sewell Medicare MCED Screening Coverage Act authorizes Medicare coverage for any FDA-approved MCED test beginning in 2028.
Coverage decisions by the Centers for Medicare & Medicaid Services are supposed to be based on demonstrated clinical benefit—not surrogate endpoints or preliminary findings. As Dr. Hoffman noted, a negative or inconclusive study does not meet that standard.
What Comes Next?
Grail has stated that additional analyses of the NHS-Galleri trial are underway. However, independent experts agree that larger studies with longer follow-up and more meaningful endpoints are still needed before MCED tests can be responsibly integrated into routine care.7
Until such evidence exists, widespread use risks doing more harm than good.
Bottom Line
The Galleri test represents an exciting scientific concept—but excitement should not replace evidence. At present, the test misses too many early cancers, risks unnecessary follow-up for false positives, and lacks proof that it improves patient outcomes.
For these reasons, and based on the research to date, I currently do not recommend the Galleri test for routine cancer screening.
References
- Klein EA, Richards D, Cohn A, et al. Clinical validation of a targeted methylation-based multi-cancer early detection test using an independent validation set. Ann Oncol. 2021;32(9):1167-1177. doi:10.1016/j.annonc.2021.05.806
- Brito-Rocha T, Constâncio V, Henrique R, Jerónimo C. Shifting the cancer screening paradigm: the rising potential of blood-based multi-cancer early detection tests. Cells. 2023;12(6):935. doi:10.3390/cells12060935
- Old R, Pharoah P, Wald N. NHS announces a pilot of a blood test for early detection of many cancers. J Med Screen. 2021;28:1-2.
- Turnbull C, et al. GRAIL-Galleri: why the special treatment? The Lancet. 2024;403(10425):431-432.
- Swanton, R.C., NHS-Galleri: Primary results from a randomised controlled trial to assess the clinical utility of a multi-cancer early detection (MCED) test in population screening.. J Clin Oncol 44, LBA100-LBA100(2026). DOI:10.1200/JCO.2026.44.17_suppl.LBA100
- Worchester S. Galleri Cancer Detection Test Fails in Key Trial: Now What? Medscape Medical News. February 26, 2026.
- American Cancer Society. Consensus statement on discussing MCED tests with primary care patients. Cancer. Accessed online.
