Replimune Group shares collapsed in premarket trading following news that the U.S. Food and Drug Administration issued a second complete response letter (RPL) for RP1, the company’s oncolytic virus therapy administered with nivolumab for advanced melanoma. By 05:10 ET the stock had plunged more than 57% in the premarket session.
Market reaction was swift. BMO Capital Markets cut its rating to Underperform and slashed its price target to $1 from $11. JPMorgan moved its view to Underweight from Neutral and withdrew a previously stated $10 price target outright.
The FDA’s rejection focused squarely on recurring concerns about the design and conduct of Replimune’s IGNYTE trial, many of which regulators first raised well before the company’s initial submission. In particular, the agency reiterated that the trial’s single-arm structure prevents clear attribution of response to each component of the combination therapy.
BMO analyst Evan David Seigerman highlighted that the FDA flagged problems as early as a March 2021 meeting, noting the agency’s view that a single-arm study "would not enable identification of the contribution of each component of the combination to the overall response rate" and that it "would not recommend that the Sponsor submit a BLA based on the results of a single-arm study."
Seigerman wrote that the detailed CRL makes it clearer which development-plan issues the FDA expects to see addressed, and that those issues will likely require an additional trial. "Such a path will likely be long and financially challenging for Replimune and shareholders," he said.
The FDA’s latest communication also raises technical concerns that undercut the regulator’s ability to assess systemic activity. Regulators pointed out that, for more than half of patients evaluated for efficacy, there were no noninjected lesions - a fact the agency said limited its ability to judge systemic drug response.
Additional protocol and operational features further complicated interpretation of the results. The FDA cited provisions allowing reinjection of lesions immediately before progression assessments, surgical procedures performed before tumor measurement, and histology assessments that were not centrally reviewed. Collectively, the agency said, these elements clouded the trial’s efficacy read.
Patient heterogeneity within the study population and the absence of a randomized control arm were also identified as factors that limited the regulator’s ability to determine how much benefit RP1 contributed beyond nivolumab alone.
JPMorgan analyst Anupam Rama said he had believed the totality of RP1 data supported approval, while acknowledging regulatory uncertainty prior to the decision. By contrast, Seigerman characterized prior resubmission efforts as appearing "grounded more on hope than true alignment with FDA," adding, "Hope is never a winning strategy, unfortunately."
Analysts pointed to the financial implications of the FDA’s stance. Replimune ended 2025 with less than $200 million in net cash, and market commentary suggested that significant cost reductions will be necessary. Seigerman suggested the company may need to consider returning capital to shareholders or seek a larger acquirer to assume responsibility for RP1’s continued development.
The FDA’s position and subsequent market reaction underscore the regulatory and funding risks facing companies developing combination immuno-oncology therapies, particularly when pivotal trials lack randomized comparators and include protocol features that complicate efficacy assessment. For Replimune specifically, the CRL appears to push the RP1 program back to a stage where additional, potentially extensive clinical work would be required to meet FDA expectations.
Key points
- Replimune shares plunged more than 57% premarket after the FDA issued a second complete response letter (RPL) for RP1 combined with nivolumab in advanced melanoma.
- BMO downgraded the stock to Underperform with a $1 target from $11, while JPMorgan moved to Underweight from Neutral and withdrew a $10 price target.
- FDA concerns focus on IGNYTE trial design, including the single-arm structure, lack of noninjected lesions in over half of efficacy-evaluable patients, protocol reinjection timing, pre-measurement surgeries, and non-centralized histology review, all of which limit interpretability of efficacy versus nivolumab alone.
Risks and uncertainties
- Regulatory risk: The FDA’s detailed CRL indicates the RP1 program may require an additional trial, creating a long and potentially costly regulatory pathway that affects biotech and capital markets for small-cap oncology developers.
- Funding risk: With under $200 million in net cash at the end of 2025, Replimune may need deep cost cuts, strategic alternatives, or a partner/acquirer to continue RP1 development, impacting investors and lenders exposed to the company.
- Clinical-readout uncertainty: Trial-design issues such as absence of a control arm and operational practices that cloud efficacy assessment increase uncertainty around potential approval and commercial prospects for RP1.