Replimune's RP1 oncolytic virus therapy, designed for anti-PD-1 refractory melanoma, received a complete response letter from the FDA, signaling a significant regulatory hurdle despite encouraging trial data. The IGNYTE trial demonstrated a 32.9% overall response and 15% complete response rate, surpassing previous approvals like T-VEC. However, the FDA's rejection has sent Replimune's stock plummeting, highlighting an evolving and tougher regulatory environment for cancer immunotherapies. This shift may demand more stringent clinical evidence despite previous accelerated pathways and breakthrough designations.