Replimune Shares Plunge 20% as FDA Staff Questions Melanoma Drug's Efficacy

Shares of Replimune Group Inc. (NASDAQ: REPL) plummeted more than 20% on Tuesday after the U.S. Food and Drug Administration (FDA) released highly critical briefing documents concerning the company's lead cancer therapy candidate. The documents, published ahead of a key advisory committee meeting, raised significant questions about the drug's efficacy in treating advanced melanoma.

FDA Outlines Efficacy Concerns

The FDA staff review identified what it termed "significant review issues" with Replimune’s Biologics License Application (BLA) for vusolimogene oderparepvec, also known as RP1. The therapy is intended for use in combination with nivolumab for adults with advanced cutaneous melanoma that has progressed after prior anti-PD-1 therapy.

In the documents, the agency outlined three primary concerns based on the single-arm IGNYTE study:

• Data Interpretation: The FDA stated that Replimune's application of the RECIST v1.1 criteria for assessing tumor response "confounds interpretation of the reported efficacy results and limits FDA’s ability to verify the reported results."
• Contribution of Effect: The agency questioned whether RP1 provides any additional benefit when combined with nivolumab. It noted that data from the single-arm study "are not of sufficient magnitude to overcome concerns" and that it "cannot be determined whether RP1 contributes to any observed effect."
• Survival Analysis: The overall survival analysis from the study was deemed "not interpretable" by the agency.

Trial Design Under Scrutiny

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The company's submission is based on the IGNYTE trial, which enrolled 140 patients. The FDA's critique centers on the study's single-arm design, which lacks a control group for direct comparison.

The agency noted that it had previously recommended Replimune conduct a randomized trial to definitively establish the contribution of RP1 when added to nivolumab. However, the company proceeded with its BLA submission based on the results from the single-arm study.

Market Reaction and Next Steps

The negative staff review introduces significant uncertainty regarding the approvability of RP1, prompting a sharp sell-off from investors. The briefing documents signal a challenging regulatory path for what is a key asset in Replimune's pipeline.

A public meeting of the FDA's Cellular, Tissue, and Gene Therapies Advisory Committee is scheduled for July 30 to discuss these review issues. The committee's subsequent recommendation, while not binding, will be a critical factor in the FDA's final decision and will be closely watched by the market.