Multi-cancer blood test fails primary trial goal in 142,000-patient NHS study

A blood test designed to detect more than fifty types of cancer in their earliest stages has failed to accomplish what it was built to do. The Galleri test, which arrived in clinical trials with considerable promise, did not reduce the number of people diagnosed with advanced cancer when added to standard screening protocols. Researchers presented these results at the American Society of Clinical Oncology's annual conference in Chicago on Saturday, marking the first major setback for a technology that had been positioned as a potential breakthrough in oncology.

The trial itself was substantial in scope. It enrolled 142,942 people in the UK aged fifty to seventy-seven who had no cancer symptoms. For three years, every participant gave blood samples annually and received whatever cancer screening tests were already recommended for their age group. Half of them had their blood analyzed using the Galleri test; the other half served as a control group, receiving standard care alone. Those who tested positive on Galleri underwent follow-up diagnostic work. The study's primary goal was straightforward: determine whether adding this blood test to routine screening would shift diagnoses toward earlier, more treatable stages—specifically, whether it would reduce the proportion of people diagnosed with stage three or stage four cancer across twelve cancer types.

It did not. The data showed no statistically significant reduction in advanced cancers among those screened with Galleri compared with those who received standard care only. This was the trial's main objective, and it was not met. The failure was blunt enough that one senior cancer figure, speaking anonymously to the Guardian, described it simply: "The trial flopped."

Yet the company behind Galleri, Grail, and some researchers involved in the study emphasized secondary findings that suggested a different picture. When researchers looked at stage four cancers alone—the most advanced and deadly form—they found a fourteen percent reduction in the group screened with Galleri. This suggested that the test might be catching the most serious cancers earlier, even if it had not moved the needle on advanced cancers overall. Harpal Kumar, Grail's chief scientific officer and a former chief executive of Cancer Research UK, called the test "a potential transformational shift in cancer detection."

Independent experts were considerably more cautious. Richard Houlston, head of genetics and epidemiology at the Institute of Cancer Research in London, noted that while this was the largest randomized trial of a multi-cancer blood test to date, the company and researchers had presented their findings "far more positively than the overall results justify." The primary endpoint—the measure the trial was designed to test—was not met. Secondary findings, while potentially encouraging, remained uncertain and should be interpreted with care. Houlston emphasized that the failure to meet the primary endpoint was the central issue. Mortality data will become available in two years, he said, and those results will be worth examining closely. But based on current evidence, he concluded, there is no justification for rolling out Galleri across the NHS population.

Peter Johnson, the national clinical director for cancer at NHS England, said the health service would review the detailed trial data before deciding what the results might mean for the future. The question now is whether a test that failed to achieve its main goal in the world's largest trial of its kind can still find a clinical role—and whether the secondary findings, however encouraging they appear, are enough to justify the cost and complexity of adding another screening layer to an already stretched health system.