Imagine going to your doctor, having a single blood sample taken and finding out whether you might have cancer before experiencing any symptoms. No complicated scans or invasive procedures, just a simple blood test that could potentially detect dozens of different cancers.
It sounds like a major breakthrough in medicine, and that is exactly what scientists have been working toward with a test called Galleri.
Developed by American biotechnology company GRAIL, the test is designed to detect cancer-related signals in the bloodstream, potentially identifying more than 50 types of cancer before symptoms appear.
But a major clinical trial involving more than 142,000 people has delivered disappointing results.
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According to a study published in the New England Journal of Medicine on September 22, 2026, the Galleri test failed to significantly reduce the number of cancers diagnosed at advanced stages, the main outcome researchers had hoped to demonstrate.
The findings do not mean the technology is useless, but they raise serious questions about whether it is ready to become part of routine cancer screening.
More than 142,000 people took part in the experiment
The research, known as the NHS-Galleri trial, was conducted in England and is the largest randomized trial of a multicancer early detection blood test published to date.
Researchers recruited 142,250 adults aged between 50 and 77 and randomly divided them into two groups. Both groups continued receiving normal healthcare and existing NHS cancer screening.
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One group had their blood samples analyzed using the Galleri test, while the other group had their samples stored without being tested. Participants were invited to provide blood samples once a year over three screening rounds.
The researchers wanted to answer a straightforward question: Could adding Galleri to existing screening programs reduce the number of people diagnosed with advanced cancer?
Their main focus was on 12 types of cancer that are frequently diagnosed late, including cancers of the lung, pancreas, ovary, bowel, liver and stomach.
These are particularly important because cancers discovered after they have spread are often more difficult to treat successfully.
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The main result was not what researchers had hoped for
After three screening rounds, the researchers compared how many people in each group had been diagnosed with stage III or stage IV cancer.
Stage III generally describes cancer that has grown locally or spread to nearby tissues or lymph nodes, while stage IV means it has spread to distant parts of the body. The precise definitions vary between cancer types.
The researchers hoped that regular blood testing would reduce the number of diagnoses in these advanced stages.
However, the results showed no statistically significant difference between the two groups.
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In other words, people who received the additional Galleri blood test were not significantly less likely to be diagnosed with stage III or IV cancer than those who received standard healthcare alone.
This meant the trial failed to achieve its primary objective.
But that was not the end of the story.
One finding offered a reason for optimism
Although the trial did not demonstrate an overall reduction in advanced cancers, researchers noticed something interesting when they examined stage IV diagnoses separately.
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According to the official NHS-Galleri trial findings, people offered the blood test had approximately 14 percent fewer stage IV cancer diagnoses among the 12 cancer types studied.
Researchers also found 16 percent more stage I and II cancers in the group receiving the test.
These findings suggest that Galleri may help identify some cancers before they reach their most advanced stage.
The difference became more noticeable in later rounds of screening, when researchers observed fewer stage IV diagnoses among participants who had repeated blood tests.
Professor Peter Sasieni, a cancer epidemiologist at Queen Mary University of London and one of the study's leading researchers, discussed the findings in a statement published by the university.
He acknowledged that the study had failed to achieve its primary objective but highlighted the lower number of stage IV diagnoses and the increase in cancers detected at earlier stages.
However, these encouraging findings came from secondary analyses. They do not overturn the main result, and researchers still need to determine whether the differences will eventually translate into fewer cancer deaths.
The test looks for tiny traces of cancer in your blood
To understand why Galleri has attracted so much attention, it helps to know how the technology works.
Our cells constantly release tiny fragments of DNA into the bloodstream. Cancer cells can release DNA too, and those fragments may contain chemical patterns that differ from DNA released by healthy cells.
Galleri analyzes these patterns, particularly changes known as DNA methylation, to look for signs that cancer might be present.
If it detects a suspicious signal, the test also attempts to predict where in the body the cancer originated. Doctors can then investigate that area using established diagnostic methods, such as scans or other tests.
The appeal is obvious. Instead of developing a separate screening program for every possible cancer, doctors could potentially use one blood sample to look for signs of many different diseases.
But detecting a cancer-related signal is not the same as proving someone has cancer, and a negative result does not guarantee that a person is healthy.
The test missed many cancers despite its high accuracy in another measure
A separate study published in Nature Medicine examined how accurately Galleri performed across the three screening rounds.
The findings revealed both strengths and important limitations.
Only around one percent of participants received a positive cancer-signal result in each screening round. Among those who tested positive, approximately 46 to 58 percent were subsequently diagnosed with cancer.
That means roughly half of the positive results corresponded to confirmed cancer diagnoses, while the remaining positive results were not confirmed as cancer during the study's follow-up period.
The test also had high specificity, correctly producing negative results for approximately 995 out of every 1,000 people who did not have cancer.
However, a different measurement revealed a significant weakness.
Across the three rounds, Galleri returned positive results for only around 27 to 37 percent of participants who were subsequently diagnosed with cancer within the study's defined follow-up period.
This measurement included all cancer types, not just the 12 cancers that formed the trial's main focus.
Put simply, the test was good at avoiding false alarms, but it still missed a substantial proportion of cancers that were diagnosed during the following year.
That distinction matters because someone receiving a negative result might mistakenly believe they have no reason to worry about cancer.
In reality, a negative Galleri test cannot reliably rule out cancer.
Why detecting cancer earlier does not always mean saving more lives
The ultimate purpose of cancer screening is not simply to detect more cancers. It is to reduce the number of people who become seriously ill or die from the disease.
Finding cancer earlier can create more treatment opportunities, particularly when a tumor can still be removed or treated before spreading.
However, screening tests must also demonstrate that their benefits outweigh potential harms.
Some positive results turn out to be false alarms, potentially leading to additional scans, invasive examinations, anxiety and unnecessary medical costs.
Screening can also identify cancers that might never have caused symptoms or threatened a person's life, a problem known as overdiagnosis.
As Cancer Research UK explains in its guidance on Galleri, a positive result requires further investigation, and the test can sometimes return an incorrect result.
The crucial question is therefore whether detecting additional cancers at earlier stages will ultimately prevent deaths rather than simply increase the number of diagnoses.
The NHS-Galleri trial has not yet provided a definitive answer to that question.
Should you consider paying for the Galleri test?
The Galleri test is already available through some private healthcare providers, including in the United States and England, but it has not become part of routine NHS cancer screening.
According to the official NHS-Galleri trial information, health authorities are reviewing the research before deciding whether the technology could have a place in future screening programs.
For people considering a private test, the new findings are an important reminder that more testing does not automatically mean better protection against cancer.
Galleri should not replace established screening methods, such as mammograms, cervical screening, bowel cancer screening or recommended lung cancer screening for people at increased risk.
Those programs have been studied separately and have evidence supporting their use in specific populations.
Anyone experiencing worrying symptoms, including unexplained weight loss, persistent bleeding, unusual lumps or lasting changes in bowel habits, should speak to a healthcare professional rather than relying on a screening blood test.
Researchers are still waiting for the most important answer
Despite failing to meet its main objective, the NHS-Galleri trial is not finished.
Researchers plan to continue following participants to understand whether the differences in cancer diagnoses become more significant over time.
One of the most important questions is whether the lower number of stage IV cancers in the blood-test group eventually leads to fewer deaths.
The research team will also continue examining the potential disadvantages of screening, including unnecessary investigations and the possibility of overdiagnosis.
The technology remains an important area of medical research, and future improvements could potentially make multicancer blood testing more useful.
For now, however, the message is clear: a test that can detect signals from dozens of cancers is a remarkable scientific achievement, but it must also demonstrate that using it improves patients' lives.
Until researchers can establish that benefit, the promise of detecting cancer through a single blood sample remains more complicated than the advertising might suggest.
This article is made and published by Aksel Kryhlmand, who may have used AI in the preparation.