FDA staff tell advisers Replimune's skin cancer drug still falls short, on its third try

Replimune's third attempt to win FDA approval for its injected skin cancer drug runs into the same roadblock it has hit in its two prior tries: the agency's own staff are publicly telling the advisory committee that the company's main study cannot tell whether the drug is doing any work, because every patient received the drug together with Opdivo.

The Cellular, Tissue, and Gene Therapies Advisory Committee meets Thursday, July 30, 2026, to weigh whether to recommend approval of vusolimogene oderparepvec, a herpesvirus-based oncolytic that Replimune has named RP1. The drug is injected directly into melanoma tumors and is meant to prime the immune system against the cancer. In the pivotal study, every patient who had already failed a checkpoint inhibitor, a class of drugs that release the brakes on immune cells, received RP1 on top of Opdivo (nivolumab), the Bristol-Myers Squibb checkpoint inhibitor. There was no arm that received Opdivo alone.

In pre-meeting briefing documents, agency reviewers wrote that the single-arm trial "cannot adequately evaluate RP1's efficacy on its own" or determine whether the locally-injected virus contributes anything beyond the systemic PD-1 blockade the patient was already getting, according to STAT+ coverage of the materials. Without a comparator, the briefing materials argue, there is no way to tell how much of the tumor shrinkage came from RP1 and how much came from re-treating with Opdivo.

Replimune's counter, laid out in the company's own briefing document for the committee, is that a randomized study is "not feasible or ethical" in this patient group. Patients enrolled in the trial had already progressed on a PD-1 inhibitor. Replimune argues that "there is no evidence that continued anti-PD-1 monotherapy provides any level of clinical benefit" to that population, so randomizing them to Opdivo alone would withhold what those patients and their physicians might consider standard care. The company's argument is that the single-arm design is the only one that can be run in this population at all.

The FDA's posture, distilled from the staff briefing materials, is that "not feasible" is not the end of the evidentiary conversation. The agency has pointed to alternative trial structures, including randomized add-on designs, external controls, and synthetic comparator arms drawn from real-world PD-1-failed populations, as ways to disentangle the contribution of the injected drug. The disagreement is therefore not just about this study's results. It is about what kind of evidence can be required when a new agent is added to an existing therapy in a population that has already failed that therapy.

The advisory committee vote is not the final word. CTGTAC is an outside panel whose recommendation the FDA typically follows but is not bound by. The actual decision on BLA 125827, the Biologics License Application Replimune filed for vusolimogene oderparepvec, will come from the agency after the meeting. A Federal Register notice published July 8, 2026 established the meeting and opened a public docket; Replimune's investor relations release confirms FDA accepted the current BLA resubmission for advanced melanoma after the company's earlier Complete Response Letter.

What is at stake for Replimune is the regulatory pathway for a locally-injected oncolytic that the company argues can convert so-called "cold" tumors, tumors the immune system cannot see, into "hot" ones that respond to checkpoint blockade. If the committee and FDA accept the single-arm evidence, RP1 would become one of the first approved oncolytic immunotherapies used in combination with a PD-1 inhibitor in PD-1-failed melanoma. If they do not, the company would face a third rejection and a hard question about whether the trial design it has run three times is the one the agency will ever accept.

The committee meets July 30. The docket is open for public comment through the meeting date.