Grail’s Galleri blood test screens for multiple cancer types using a single blood draw, analyzing DNA fragments for cancer signals and predicting their likely origin. As the test moves closer to a potential FDA decision, five cancer specialists highlighted its promise for detecting cancers that lack established screening methods, alongside concerns about sensitivity, follow-up testing, and whether earlier detection improves survival.
In the PATHFINDER 2 study, Galleri’s positive predictive value was approximately 62%, meaning positive results were confirmed as cancer in about six out of 10 cases. Reported specificity was 99.6%, while the test correctly predicted the cancer’s origin in more than 90% of positive cases. However, episode sensitivity remained relatively low, at approximately 30%–40% in the studies discussed. Performance also varied by cancer type: the test performed better for certain aggressive cancers, including colorectal, pancreatic, and liver cancers, than for breast and prostate cancers.