Merck and Moderna’s Phase 3 melanoma vaccine data arrived early at ESMO, following a leak, forcing the companies to release initial results ahead of presentation. The personalized mRNA vaccine, intismeran autogene, combined with pembrolizumab (Keytruda), reduced the risk of recurrence or death by 42% versus Keytruda alone at a median follow-up of about two years. The report described a 38% reduction in risk of cancer spread or death over pembrolizumab and showed more patients remaining relapse-free in the combination arm (82.2% vs. 70% at two years). Overall survival data were still maturing at the time of disclosure, according to the coverage. Market reaction reflected the mismatch between expectations and timing, but oncology experts flagged the trial’s endpoint performance as the central development. Regulators will now become the focus as the companies seek authorization for the combination approach. The leak-and-release sequence also highlighted how manufacturing and commercialization questions for personalized mRNA platforms could become a parallel storyline alongside efficacy as the companies move toward potential approvals.