The Galleri Cancer Blood Test Just Failed Its Most Important Trial. Here Is What That Means.

In previous essays, I wrote about the aggressive marketing of blood-based multi-cancer early detection tests to consumers who are understandably eager for any tool that might catch cancer before it becomes life-threatening. My central argument at the time was that the existence of a test on the market carries no guarantee that the test has been validated as accurate, useful, or safe — and that the advertising campaigns surrounding these products were running substantially ahead of the evidence. The results are now in from the trial that was supposed to settle that question, and they do not support the optimism the marketing had generated.

The Galleri test, developed by a company called Grail, screens for more than 50 types of cancer by looking for tiny fragments of tumor-associated DNA circulating in the blood. It has been sold in the United States since 2021 for $949, without Food and Drug Administration approval, under a regulatory framework that permits certain laboratory-developed tests to be marketed without prior FDA review. The company ran a large, rigorous clinical trial in partnership with the UK’s National Health Service on 142,000 healthy adults aged 50 to 77 — exactly the kind of prospective, large-scale, diverse-population study that the field genuinely needed. The hope was to demonstrate a 20% reduction in advanced cancer diagnoses among people who received the test.

The study failed to meet that primary endpoint. There was no statistically significant reduction in Stage 3 or Stage 4 cancers in the group that received Galleri testing compared to the control group.

What the Trial Result Actually Means

Most experts have interpreted this result to mean that the Grail test should not be funded as part of routine cancer screening for adults in either the United Kingdom or the United States, and I share that interpretation as the appropriate population-level conclusion. The trial was well-designed, the sample was large, and the endpoint — reduction in late-stage cancer diagnoses — was the clinically meaningful outcome that matters most to patients and health systems alike. When a test of this quality, run at this scale, fails to demonstrate that benefit, the evidence base for broad routine use is simply not there.

That conclusion, however, leaves room for a more nuanced clinical judgment. I believe there may be benefit to this and similar tests in selected populations — people with elevated cancer risk due to family history, known genetic abnormalities such as BRCA mutations, or prior cancer diagnoses — where the pre-test probability of finding something meaningful is substantially higher than in the general healthy adult population. The trial result speaks primarily to population-level screening, and the question of targeted use in high-risk groups deserves continued investigation with appropriately designed studies.

The Deeper Problem the Trial Exposes

The Galleri trial result is significant not only for what it tells us about one specific test, but for what it illustrates about the broader relationship between evidence, regulation, and the commercialization of medical technology. The test has been sold at $949 per use since 2021, marketed directly to consumers through channels including Super Bowl advertising, without FDA approval and before the large-scale trial that might have established — or failed to establish — its clinical value had been completed. The UK NHS trial was, in effect, the rigorous evidence generation that should have preceded or accompanied the commercial launch rather than following it by several years.

This sequence — commercial launch first, rigorous evidence later — is a pattern that the consumer health testing space has repeated across multiple products and companies, and its consequences fall disproportionately on the people who spent money on tests that have not been proven to work, who may have experienced anxiety from false positives, or who derived false reassurance from results that, as the trial now suggests, were not reliably predictive of what they claimed to detect.

The broader question the trial raises is one that public health has always struggled to answer effectively: how do we, as a society, align what we invest in with what the evidence actually supports? The evidence is clear that cutting Medicaid leads to more sickness and death. The evidence is equally clear that a $949 blood test marketed to the worried well does not reduce advanced cancer diagnoses at the population level. The policy environment that allows one while pursuing the other is not making decisions on the basis of evidence. Changing that alignment — building regulatory frameworks and funding priorities that reward demonstrated benefit rather than marketing ambition — remains among the most consequential and most difficult challenges in American public health.