IO Biotech’s off-the-shelf therapeutic cancer vaccine Cylembio narrowly missed its primary endpoint in a pivotal Phase 3 melanoma study, falling just short of statistical significance despite promising progression-free survival improvements over Merck’s Keytruda alone. Subgroup analyses suggest stronger benefits in key patient populations, galvanizing confidence in potential FDA approval pathways. The vaccine aims to stimulate immune responses against checkpoint proteins, representing a simpler alternative to personalized mRNA-based vaccines. IO plans to pursue regulatory discussions despite the narrow miss.