Medical Express | Tuesday, November 25, 2025 
The cancer blood test making waves, and what the numbers really show

Progress in cutting the global toll of cancer remains painfully slow, but a new blood test has sparked unusual levels of hope. Researchers say it could one day make routine screening far more effective by catching cancers earlier, when treatment has the best chance of saving lives. The Galleri blood test, developed by US firm Grail, is the latest entrant to attract worldwide attention, after early trial results were described as “exciting” by researchers. A press release claims the test, currently being trialed by the NHS, can detect signals from 50 cancers and correctly identify the disease in 62% of people who receive a positive result. It also appears to be highly accurate at ruling cancer out, with a reported 99.6% success rate among those who were disease-free. At first glance, these headline figures appear to represent a significant step forward. But before we reach for the champagne, it’s worth looking more closely at what these numbers really mean. Early promise does not always translate into real-world performance. The Pathfinder 2 trial, involving 23,161 people aged over 50 from the US and Canada with no prior cancer diagnosis, produced the figures now circulating widely. Of the 216 participants who tested positive, 133 were later found to have cancer, giving the “positive predictive value” (PPV) of…Read more