Blood Test That Screens For Multiple Cancers At Once

Gloved hands manipulating samples under a microscope in a petri dish — Photo: Svitlana Hulko / Shutterstock

One blood draw may someday flag cancer in a person who feels perfectly healthy, and a trial of nearly 36,000 adults just gave that idea its biggest test yet.

Quick Take

The PATHFINDER 2 study enrolled 35,878 adults age 50 and older in the United States and Canada with no cancer symptoms.
Grail’s Galleri blood test picked up cancer signals across 17 different cancer types, including ovarian, lung, breast and colorectal cancers.
Researchers say the technology shows promise but stress that larger trials must still prove it actually lowers cancer deaths.
A separate, larger United Kingdom trial of the same test found mixed results, missing its main goal while still catching more early-stage cancers.

A Blood Test Built To Catch Cancer Before Symptoms Show

The study, published in Nature Medicine, tracked adults who had no clinical suspicion of cancer and no cancer diagnosis or treatment in the prior three years. That design matters. It means the test was being judged in the exact group doctors hope to help most: people who feel fine but might be carrying an undetected tumor. Researchers call this early detection, and it is the entire premise behind the Galleri test.

Among participants, the blood test flagged cancer signals tied to 17 different cancer types, including ovarian, lung, breast and colorectal cancers. Of the 151 people who had at least one positive signal followed up closely, researchers confirmed cancer in a meaningful share of cases, giving the test a track record across cancers that often get caught late and prove harder to treat.

What The Numbers Actually Show

When researchers looked only at participants tracked for more than a year, the test caught 40.4% of cancer cases, a measure known as sensitivity. That number tells doctors how often the test correctly spots cancer when cancer is actually there. It is an improvement over earlier versions of the technology, but it also means more than half of cancers in this group were not flagged by the blood draw alone.

Grail, the company behind Galleri, says it plans to file for approval with the Food and Drug Administration (FDA) based on this newer trial data. Of the almost 36,000 total participants, close to 26,000 had the Galleri test added on top of their regular screening routine, like colonoscopies or imaging scans, rather than replacing it. That detail matters for anyone picturing this test as a stand-alone replacement for existing screening.

A Bigger British Trial Tells A More Complicated Story

Across the Atlantic, a much larger study called NHS-Galleri enrolled 142,000 adults ages 50 to 77 in England, making it the largest randomized trial of its kind. Its main goal was to prove the test reduces late-stage cancer diagnoses population-wide. That primary goal was not met, according to results reported by the Guardian and the trial’s own organizers.

Still, the same trial found a four-fold higher cancer detection rate and more stage I and stage II cancers caught early among those tested, compared with standard care alone. One expert reviewing the results for the Science Media Centre noted that based on this trial and smaller ones, there is not yet enough evidence to justify rolling the test out to the general population.

Why Regulators And Doctors Are Moving Carefully

A systematic review of 36 studies covering 13 different multi-cancer blood tests found that most of the existing evidence comes from diagnostic-accuracy studies rather than trials tracking real-world outcomes like survival. Reviewers flagged notable risk-of-bias concerns across the research and found no completed randomized trial in an asymptomatic population that had yet reported full outcome data at the time.

🧬 What if cancer could leave a molecular fingerprint in your blood—before you ever knew it was there?

That future may be closer than we think.

GRAIL’s Galleri multi-cancer early detection (MCED) blood test recently received a favorable vote from an FDA advisory committee.… pic.twitter.com/Z6dHoRJxsm

— Dr. Nicole M. Batty MD, MBA, MSF, FACP, FASCP, (@Echelonmednyc) September 28, 2026

That caution makes sense. A test that flags false positives can send healthy people through unnecessary biopsies and scans, while a test that misses real cancers offers false comfort. Medicine demands proof that new technology helps patients live longer before it gets pushed into routine checkups and billed to Medicare or private insurance. The PATHFINDER 2 results are encouraging, but the harder questions about saving lives still await answers.