FDA Executive in Charge of Cancer Drug Approvals Vetoes Melanoma Treatment by Replimmune
In a surprising turn of events, Replimmune's advanced melanoma drug, RP1, received a Complete Response Letter (CRL) from the Food and Drug Administration (FDA) two weeks ago. This decision came as a shock, as the agency had not raised any of the concerns during earlier mid- and late-cycle reviews, and Replimmune had aligned on the confirmatory study design with the FDA.
RP1 is an engineered herpes simplex virus designed to replicate in tumors and stimulate an immune response against melanoma cells. The drug was being tested in combination with BMS' immunotherapy Opdivo.
The FDA's top cancer regulator, Richard Pazdur, directly intervened to issue the CRL. Pazdur is the director of the FDA's Oncology Center of Excellence (OCE) and acting director of the Office of Oncologic Diseases, both offices within the Center for Drug Evaluation and Research (CDER).
According to STAT, the design of the trials that provided supporting data for RP1 was a concern for Pazdur and his team. They felt that the drug's tumor killing effect could not be separated from the effect elicited by Opdivo.
The rejection may have been due to a late intervention from CDER into a review at its sister office, the Center for Biologics Evaluation and Research (CBER), where RP1 was under review. An anonymous FDA official suggested that CBER had "mishandled" the review, prompting Pazdur to get involved.
Vinay Prasad, who was then the chief of CBER, presided over the regulatory environment leading to this decision. Prasad, who was seen as a data-driven regulator, had a conservative, evidence-demanding approach and was in opposition to the approval of RP1 during a conference in early July. Despite the consensus from the CBER side that RP1 should be approved, Prasad ultimately deferred to Pazdur.
Replimmune's stock crashed 75% after the rejection and was down another 30% Monday morning after market open. The company intends to request a follow-up meeting with the FDA to understand how to move forward.
Dan Samorodnitsky, a journalist, reported on this news on BioSpace's platform. A week after the Replimmune CRL, Vinay Prasad left the FDA following a hail of criticism from conservative figures.
References:
[1] Samorodnitsky, D. (2025). FDA Surprises Replimmune with Rejection of Advanced Melanoma Drug RP1. BioSpace.
[2] Samorodnitsky, D. (2025). FDA's Prasad Plays Key Role in Replimmune's RP1 Rejection. STAT News.
- The advanced melanoma drug, RP1, developed by Replimmune, was rejected by the Food and Drug Administration (FDA) due to concerns about its trial design.
- The rejection of RP1, designed to replicate in tumors and stimulate an immune response against melanoma cells, has significant implications for the health-and-wellness sector, especially in relation to cancer.
- The FDA's decision to reject RP1, which was being tested in combination with BMS' immunotherapy Opdivo, has implications for the finance and investing world, as Replimmune's stock plummeted after the rejection.
- The business sphere has been abuzz with news about RP1's rejection, with politicians discussing the implications of the decision for general-news outlets.
- The technology sector is also closely watching the RP1 saga, as the rejection highlights the intricacies involved in approving new drugs, including the coordination between different FDA offices.
- The crime-and-justice arena might also be impacted, as some have questioned if the late intervention from CDER into CBER's review of RP1 may have constituted a misuse of power or a mishandling of the review process.
