World-First Melanoma Vaccine Cuts Recurrence or Death Risk by 42% in Landmark Trial

A personalized mRNA cancer vaccine, developed by Moderna and Merck, has achieved a world-first milestone by reducing the risk of melanoma recurrence or death by 42% when combined with Keytruda, compared to Keytruda alone. The Phase 2b trial results, published in The Lancet, followed 157 patients with high-risk stage III/IV melanoma after surgical removal. At two years, 78.6% of those receiving the vaccine plus Keytruda remained recurrence-free, versus 62.2% for Keytruda alone. The vaccine, mRNA-4157 (V940), encodes up to 34 neoantigens unique to each patient’s tumor, training the immune system to attack cancer cells. Side effects were mostly mild, including fatigue and injection site reactions. This is the first randomized trial to show such benefit for a personalized cancer vaccine, marking a potential turning point in oncology. A Phase 3 trial is now underway, with results expected by 2029. The breakthrough could pave the way for personalized immunotherapy across other cancers.