FDA again rejects Replimune melanoma drug RP1 over trial design concerns
Updated
Updated · Scientific American · May 2
FDA again rejects Replimune melanoma drug RP1 over trial design concerns
13 articles · Updated · Scientific American · May 2
An April 10 complete response letter repeated objections to IGNYTE data and said a new FDA review team had replaced the previous one before Replimune's 2025 resubmission was assessed.
The agency questioned the trial's heterogeneous patient group and whether responses came from RP1 rather than nivolumab, despite earlier data showing about 33% improvement in treatment-resistant advanced melanoma.
The decision has drawn backlash from oncologists and patients, triggered layoffs at Replimune, and raised wider concern that shifting FDA approval standards could hinder future melanoma drug development.
After approving a similar drug, why did the FDA suddenly shift its standards for this breakthrough melanoma therapy?
Why is the FDA demanding a trial design for a cancer drug that its own guidelines deem unethical?
RP1’s 33% Response Rate Overshadowed by FDA’s Demand for Controlled Data in Second Rejection of Replimune’s Melanoma Therapy
Overview
On April 10, 2026, the FDA issued a second rejection of Replimune's RP1 therapy for advanced melanoma, citing key flaws in the IGNYTE trial design: it was a single-arm study without a control group, enrolled a diverse patient population, and failed to isolate RP1's effect within combination therapy. Despite RP1 showing a 33% response rate in difficult-to-treat patients, these design issues led to the rejection. The decision triggered major consequences for Replimune, including layoffs of 224 employees, scaled-back manufacturing, and exploration of strategic alternatives. The FDA's move also sparked public criticism and political distancing, highlighting tensions between regulatory rigor and urgent patient needs.