A clinical trial involving more than 140,000 NHS patients has found that a blood test designed to detect over 50 types of cancer did not meet its primary objective. The Galleri test, developed by California-based company Grail, failed to produce a statistically significant reduction in late-stage cancer diagnoses when added to standard screening. The findings were presented at the American Society of Clinical Oncology's annual meeting in Chicago.

The Galleri test works by analysing fragments of DNA shed by tumours into the bloodstream, with the goal of catching cancers before symptoms appear. Earlier diagnosis generally improves survival rates, which is why multi-cancer early detection tests have attracted considerable interest from researchers, health systems and investors. This trial was the first randomised controlled trial of such a test anywhere in the world, making its results significant for the field.

The trial enrolled 142,942 patients aged between 50 and 77, none of whom had cancer symptoms at the point of recruitment. Participants had blood drawn once a year for three years and continued to receive standard cancer screening throughout. Half had their samples analysed using the Galleri test; the other half formed the control group and their blood was not examined by it. Those who returned a positive Galleri result were referred for further diagnostic assessment.

The trial's primary endpoint was a combined measure: a reduction in stage three and stage four diagnoses across 12 pre-specified cancer types in the group receiving the Galleri test compared with those who did not. That target was not met. There was no statistically significant difference in advanced cancer diagnoses between the two groups.

Grail pointed to a secondary finding in which stage four cancers fell by 14% among those who received the test, suggesting some of the most serious cases may have been caught earlier. Harpal Kumar, the company's chief scientific officer, described the test as a potential shift in how cancer is detected. Dr Julie Gralow, chief medical officer of the American Society of Clinical Oncology, acknowledged some encouraging trends in the data towards earlier diagnosis, while noting the trial did not meet its predefined primary endpoint.

Independent experts were less willing to draw positive conclusions from the overall picture. Professor Richard Houlston, head of genetics and epidemiology at the Institute of Cancer Research in London, said the researchers had presented their findings more positively than the results warranted. He noted that while some secondary findings were of interest, they remained uncertain and required cautious interpretation. On the question of widespread adoption, he was direct: the results from this trial and smaller studies do not provide sufficient evidence to justify implementing the Galleri test across the general population.

Mortality data from the trial is expected to become available within the next two years, which will offer a clearer picture of whether earlier detection through the test translates into lives saved. NHS England said it would examine the full dataset before making any decisions about the test's future role in the health service.

Early cancer detection is an established priority for health systems globally. Catching cancers at an earlier, more treatable stage has the potential to reduce both mortality and the burden on treatment services. The ambition behind trials such as this one is well-founded. What the Galleri trial makes clear, however, is that technological promise and clinical utility are not the same thing. A test can function as designed and still fall short of what is needed to change patient outcomes at scale. For a tool to be adopted across a national health system, it must clear a high evidential bar, and on this occasion that bar was not cleared.