IO Biotech announced clinical improvement in progression-free survival (PFS) in its pivotal Phase 3 trial of the cancer vaccine Cylembio combined with Merck's Keytruda (pembrolizumab) for the treatment of first-line advanced melanoma. Despite demonstrating an improved median PFS of 19.4 months and showing efficacy in PD-L1-negative patients along with a favorable safety profile, the trial narrowly missed achieving statistical significance on its primary endpoint. Following these results, IO Biotech plans to pursue FDA approval, with the regulatory pathway potentially focusing on overall survival (OS) for a broader label or a PD-L1-negative biomarker strategy for a more targeted indication. The company has indicated it will meet with the FDA later this year to discuss next steps. The market reaction to the announcement was volatile, with IO Biotech's stock price initially rising by as much as 60% before fluctuating. The company also reported its second quarter 2025 financial results and business highlights amid these developments.