Grail reported that its large NHS-Galleri multicancer early detection (MCED) trial failed to meet the study's primary endpoint, triggering a sharp sell-off in the company's stock. The company disclosed topline results showing no statistically significant reduction in combined stage III–IV cancers among screened participants versus controls, though it reported favorable trends in a pre-specified group of 12 deadly cancers. Grail said it will extend follow-up by 6–12 months to let the signal mature and plans to submit more detailed results to ASCO. The trial enrolled 142,000 participants in England and was a key piece of evidence for Grail’s regulatory and reimbursement push in the U.S. and U.K. NHS leaders and regulators will scrutinize whether the study design, population selection, or test performance drove the outcome. Grail management argued the result should not derail ongoing FDA review of its PMA package and said it will press forward with commercial and regulatory efforts. Investors reacted immediately: Grail shares plunged roughly half their value in after-hours trading. The setback reignites debate over MCED clinical endpoints and whether earlier detection via blood-based methylation tests translates into population-level outcome improvements.