Galleri cancer test has limits, evidence shows.

The Galleri blood test screens cell-free DNA for cancer signals but misses many early-stage cancers and produces a notable share of false positives; no randomized trial has yet shown it reduces cancer deaths and large studies are ongoing.

The Galleri blood test has been marketed as a multi-cancer early detection tool that analyzes methylation patterns in cell-free DNA. It is sold direct-to-consumer and via clinicians, typically costs about $949, and returns either a "cancer signal detected" or "no cancer signal detected." The manufacturer recommends use for some adults at elevated risk, but published data show the test performs differently depending on cancer stage and setting. What is known: - Galleri detects methylation patterns in cell-free DNA and reports a likely tissue of origin when a signal is found. - In validation data, sensitivity was low for Stage I cancers (about 16.8%) and much higher for late-stage disease (over 90% for Stage IV). - Specificity is reported near 99%, but in the PATHFINDER study about 62% of positive results did not find cancer after follow-up. - A negative Galleri result did not identify many cancers found by standard screening or symptoms; in PATHFINDER, 71% of cancers were detected by usual care rather than the test. - No randomized controlled trial has yet shown that Galleri testing reduces cancer mortality; large trials such as the NHS-Galleri study are underway to address that question. Summary: The Galleri test is a promising technological advance but currently has important performance limits, especially for very early cancers, and produces a substantial number of false positives that can trigger lengthy and costly diagnostic evaluations. Its impact on population-level cancer deaths is unproven at this time, and definitive results are expected from ongoing large trials. Undetermined at this time.