Merck and Moderna’s Phase 3 results for a personalized mRNA cancer vaccine plus Keytruda were leaked ahead of an ESMO presentation, prompting an early public release and investor reaction. In high-risk melanoma patients after surgery, the combination cut the risk of recurrence or death by 42% versus pembrolizumab alone after a median follow-up of about two years. The leaked reporting also described a 38% reduction in the risk of spread or death compared with Keytruda alone, while overall survival data were not yet included in the early milestone framing. The episode highlights the fast pace of clinical-to-commercial decision cycles for personalized oncology vaccines, as companies prepare for regulatory engagement while the trial completes longer-term follow-up.