A Simple Blood Test Detects 7 Times More Cancers Than Standard Screening

A revolutionary blood test can detect more than 50 types of cancer with just a single blood draw, finding seven times more cancers than traditional screening methods like mammograms and colonoscopies combined. The Galleri multi-cancer early detection (MCED) test analyzes tiny DNA fragments in the blood to identify cancer signals and pinpoint where in the body the cancer originated with 92% accuracy.

How Does This Blood Test Actually Work?

The test works by examining circulating cell-free DNA (cfDNA) that cancer cells shed into the bloodstream. Using machine-learning algorithms, it analyzes methylation patterns—chemical tags that act like "on" and "off" switches for genes—to distinguish between DNA from healthy cells versus cancerous cells. This process happens in three key steps:

• Blood Analysis: The test examines blood samples for circulating cfDNA fragments
• Pattern Recognition: It "reads" specific methylation patterns to identify if the DNA came from a cancer cell
• Origin Detection: If cancer is detected, the test uses pattern recognition technology to predict which organ the cancer may have originated in

What Did the Largest Study Find?

The PATHFINDER 2 study, the largest interventional multi-cancer early detection trial in North America, enrolled 35,878 participants aged 50 and older across the United States and Canada. When researchers analyzed results from 23,161 participants with 12 months of follow-up, they discovered remarkable improvements in cancer detection rates.

Adding the Galleri test to standard screenings for breast, cervical, colorectal, and lung cancers increased cancer detection by more than seven-fold. The test detected approximately three times as many cancers when added to standard screening that also included prostate cancer. Most importantly, 73% of the cancers detected by Galleri had no existing screening options, including pancreatic, liver, head-and-neck, and ovarian cancers.

"MCED tests have the potential to fill one of the biggest gaps in cancer screening today," said Nima Nabavizadeh, M.D., Associate Professor of Radiation Medicine at Oregon Health & Science University. "While we have effective screening tools for a handful of cancers like breast, colon and cervical, the vast majority of cancers are discovered only after symptoms develop—often when they are much harder to treat."

How Accurate Is This New Test?

The test demonstrated impressive accuracy with a positive predictive value of 61.6%, meaning it correctly identified cancer in about six out of 10 participants who received a positive result. This represents a significant improvement from the earlier PATHFINDER study, which had a 43% positive predictive value.

The false-positive rate remained remarkably low at just 0.4%, meaning very few people received unnecessary follow-up testing. When the test did detect cancer, it correctly identified the cancer's origin 92% of the time, helping doctors focus their diagnostic efforts more efficiently. More than half (53.5%) of detected cancers were caught in early stages I or II, when treatment is most effective.

However, the test did miss about 60% of cancers that appeared within a year, highlighting that traditional screening methods like mammograms and colonoscopies remain essential. The episode sensitivity—the test's ability to detect cancer within 12 months—was 40.4% for all cancers but reached 73.7% for the 12 cancer types responsible for two-thirds of cancer deaths in the United States.

Safety data showed that fewer than 1% of all participants underwent an invasive procedure because of the test, and no serious study-related adverse events were reported during diagnostic workups. The median time to diagnostic resolution was 46 days.

Oregon Health & Science University led enrollment in the study, recruiting 6,125 of the 35,000 participants and making it the highest-enrolling interventional study in the Knight Cancer Institute's history. The research team deliberately expanded enrollment beyond Portland to reach rural and urban communities across Oregon, ensuring representation from underserved populations.

GRAIL expects to submit data from PATHFINDER 2 to the Food and Drug Administration (FDA) as part of the Galleri premarket approval application in the first quarter of 2026, with a potential decision expected in 2027. Currently, the test is commercially available as a laboratory-developed test for those not eligible for clinical trials, typically costing $700-$1,000 out of pocket without insurance coverage.