A new report on RP1, an oncolytic immunotherapy from Replimune Group, details why the FDA twice declined to approve the melanoma drug despite breakthrough therapy designation and early trial signals. Replimune CEO Sushil Patel criticized the agency’s behavior as unusually stringent. The article frames the challenge around the unmet need for patients with limited second-line options in melanoma, describing RP1’s approach: an engineered herpesvirus injected into tumors to trigger immune-mediated cancer cell destruction. The setbacks highlight the gap between early clinical enthusiasm and the FDA’s expectations for late-stage evidence, with the company still pushing to resolve the agency’s remaining issues for approval.