A new generation of multi-cancer early detection (MCED) blood tests promises to identify dozens of cancers from a single blood sample, but scientists remain divided on whether the technology is ready for widespread use.
One of the most prominent tests, Galleri, developed by Grail, is part of a growing group of nearly 40 MCED tests currently available or in development. These tests aim to detect cancer by identifying fragments of tumor DNA circulating in the bloodstream — a method known as liquid biopsy.
However, early evidence suggests the technology may still face significant limitations.
Mixed Evidence From Early Trials
Results from the first randomized trial of Galleri, conducted with the National Health Service, found that the test did not significantly reduce the number of cancers detected at advanced stages, one of the key goals of early screening.
Researchers say the main challenge lies in detecting circulating tumor DNA (ctDNA) in early-stage cancer, where the amount of tumor DNA in blood can be extremely small — sometimes less than 0.006% of total circulating DNA.
Despite these challenges, advances in DNA sequencing and epigenetic analysis are improving the ability to identify cancer signals in blood.