Moderna and Merck’s personalized mRNA melanoma vaccine, intismeran autogene, cleared a major Phase 3 checkpoint after leaked results reached the market before formal presentation at ESMO. In the trial of 1,137 patients with high-risk melanoma, the combination with pembrolizumab reduced the risk of recurrence or death by 42% versus pembrolizumab alone after a median follow-up of about two years. Additional efficacy signals also pointed to reduced spread risk: the dual treatment cut the risk of distant metastasis or death by 38%. The companies said overall survival data are still pending, setting up an adoption question that depends not only on efficacy but also on the practical requirements of personalized manufacturing. Market reaction was sharp—shares fell after the disclosed readout—underscoring how tightly priced expectations were heading into ESMO. Regulators are next, with the companies saying they are engaging with authorities for potential approval steps. The trial results widen the competitive field for perioperative melanoma strategies and add another datapoint for the clinical viability of neoantigen-directed mRNA approaches beyond earlier proof-of-concept datasets.