Replimune (NASDAQ: REPL) shares fell nearly 31% on Tuesday after US Food and Drug Administration (FDA) staff reviewers raised concerns over the effectiveness of the company’s lead cancer therapy, RP1, ahead of a key advisory committee meeting.
The decline followed the release of FDA briefing documents that questioned whether Replimune had provided sufficient evidence to demonstrate RP1’s efficacy in advanced melanoma. The stock has now fallen for five consecutive sessions, down about 47% over that period.
Replimune is seeking approval for RP1 in combination with Bristol Myers Squibb’s Opdivo for patients with advanced melanoma. The company’s application is based on data from the IGNYTE study, a single-arm trial that reported an objective response rate of 33.6% and a median duration of response of 24.8 months.
FDA reviewers raised concerns about how tumor responses were assessed in the study, stating that the methodology may have overstated both the response rate and duration of response. Because RP1 is injected directly into tumors, the agency noted that tumor shrinkage observed in treated areas could reflect a local injection effect rather than a broader systemic anti-cancer benefit.
The reviewers also highlighted challenges with the single-arm design of the IGNYTE study, noting that the lack of a comparison group makes it difficult to determine the extent of RP1’s contribution to the reported outcomes. The FDA also questioned whether the submitted overall survival data could reliably demonstrate a treatment benefit.
The FDA is scheduled to hold an advisory committee meeting on July 30 to discuss the application, with a final decision targeted for August 2.
In May 2026, the FDA agreed to prioritize its review of RP1 following discussions with Replimune, citing the significant unmet need in advanced melanoma. The company’s application had previously received Complete Response Letters from the agency in July 2025 and April 2026.