NHS cancer blood test fails primary trial goal despite some positive signs

A three-year trial of what researchers had called the "Holy Grail" of cancer detection has ended without delivering what the NHS hoped for. The Galleri test, a blood test designed to spot more than fifty different cancers from a single draw, was meant to prove it could catch the disease earlier and reduce the number of people diagnosed at advanced stages. Instead, when the results were presented at an American cancer research conference in Chicago, the test had failed to meet its primary goal—despite some numbers that looked encouraging on their surface.

The trial was substantial in scale and cost. More than 142,000 NHS patients aged 50 to 77 participated over three years, with half receiving the blood test annually while the other half received standard NHS screening. The study cost £150 million. What researchers were testing was straightforward: whether the Galleri test, which detects fragments of tumor DNA in blood before symptoms appear, could reduce the proportion of cancers diagnosed at stages three and four—the later, more difficult-to-treat phases of the disease.

It did not. The trial missed that primary endpoint. But the results contained a wrinkle that has now become the center of debate. Stage four cancers—the most advanced—fell by more than a fifth. This led GRAIL, the American biotechnology company that developed the test, to suggest that what had happened was not failure but redistribution. Some of those stage four cancers, they argued, had been caught earlier and reclassified as stage three. If true, that would mean the test was working as intended, just in a way the trial's original design had not fully captured. The problem was that the overall number of stage three cancers had increased, which meant the primary goal—reducing late-stage diagnoses as a whole—remained unmet.

Julie Gralow, GRAIL's chief medical officer, was direct about the implications: the test would not receive NHS approval based on this data. That statement closed a door that had seemed open just years earlier. In 2021, Amanda Pritchard, then the chief executive of the NHS, had spoken of the Galleri test as potentially marking "the beginning of a revolution in cancer detection and treatment here and around the world." The language had been expansive. The hope had been real.

But the scientific community has not accepted the company's interpretation without scrutiny. Richard Houlston, a cancer researcher at The Institute of Cancer Research in London, warned that presenting positive secondary findings while missing the primary goal amounted to "moving the goal posts." He pointed out that the only way to truly know whether the test saves lives would be a trial that followed patients over time and measured survival rates. Such a trial, he noted, would take close to two decades to complete. By then, the technology itself would likely be obsolete—a catch-22 that leaves the question of the test's real-world value fundamentally unanswered.

The NHS has not closed the door entirely. Peter Johnson, the national clinical director for cancer at NHS England, said the health service would examine the trial data in detail and explore what it might mean for the future. But approval, at least for now, appears off the table. The test that was meant to transform cancer screening in Britain has instead become a case study in the gap between promising early signals and the harder evidence required to change how millions of people are screened.