GRAIL’s multi-cancer blood test is meant to screen adults 50 and older for many cancers at once from a single blood draw. In FDA’s review of two large trials, it caught 35.0% and 31.6% of cancers diagnosed within a year, about 1 in 3.
That matters most for anyone who has had the test or is thinking about it. A “No Cancer Signal Detected” result misses about two out of three cancers.
A lung scan is one of the tests a negative result should not replace, and more former smokers qualify for one than know it.
Key takeaways
- In FDA’s review, Galleri caught 35.0% of cancers in the PATHFINDER 2 trial and 31.6% in the NHS-Galleri trial, about 1 in 3.
- Early cancers were missed more often: it caught 24.9% and 20.5% of stage I and II cancers, about 1 in 4 or fewer.
- When it flagged cancer, it was right 77.0% and 66.2% of the time, so roughly 1 in 4 to 1 in 3 positive results were false alarms.
What the study found
FDA reviewed two trials. The version tested in them is an earlier one, called MCED-V2. To judge the current Galleri version, GRAIL re-ran stored blood samples from both trials.
PATHFINDER 2 enrolled 35,878 adults aged 50 or older between December 2021 and July 2024. Among 303 people diagnosed with cancer within 12 months, Galleri caught 35.0%. For a prespecified group of 12 cancer types responsible for two-thirds of U.S. cancer deaths, it caught 61.3%. It caught 24.9% of stage I and II cancers. When it flagged cancer, it was right 77.0% of the time.
NHS-Galleri gave similar results. Among 820 people diagnosed with cancer, Galleri caught 31.6%, including 52.1% of the same 12 cancer types and 20.5% of stage I and II cancers. When it flagged cancer, it was right 66.2% of the time.
The NHS-Galleri trial did not find a statistically significant drop in combined stage III and IV cancers, according to OHSU’s summary of the results.
Dr. Kumar’s take
FDA’s numbers answer how many cancers the test misses. For a screening test you might lean on, that is the question that counts. Two out of three cancers slip past it, and early cancers slip past more often.
Finding more cancers is not the same as saving lives. Some cancers found by screening would never have caused harm, a problem mammogram research has argued about for years.
The argument for the test is real: most cancers it finds have no routine screening option. That is a reason to study it further. It is not proof that it works as a screen.
What it means for you
A negative Galleri result does not replace a colonoscopy, mammogram, Pap test or lung CT. FDA’s briefing tells people to keep up guideline-recommended screening. Some of those tests have been tied to fewer cancer deaths, including a simple mailed stool kit.
Whether the test adds anything for you depends on your age, history and risk. That is a conversation for your doctor.