The FDA has twice refused to approve Replimune’s melanoma drug RP1, dealing the biotech company another setback for a treatment it once expected to move quickly toward the market. Replimune Group said the agency’s latest decision again blocked RP1, an oncolytic immunotherapy made from an engineered herpesvirus and injected directly into melanoma tumors.
Sushil Patel, Replimune’s chief executive, said, “I’ve just never seen the agency behave like this.” He added that the repeated denials leave the company “in a very, very difficult position.” The rejection lands after a phase 1/2 IGNYTE trial last year showed that nearly 33 percent of patients with treatment-resistant advanced melanoma improved with RP1 plus nivolumab, compared with about 6 to 7 percent who responded to nivolumab alone in the comparison described in the article.
The drug had already been given breakthrough therapy designation by the FDA after early trials showed promise, and the agency’s initial review panel recommended that RP1 be approved. Replimune had counted on that status to speed the drug through the review process, especially after development was placed on a fast track at the end of 2024. As of last month, though, the FDA had twice opted not to approve RP1.
The stakes are unusually high because melanoma is highly treatable when it is caught early, but once it spreads it becomes much harder to control. About 110,000 new cases are diagnosed in the U.S. each year, about 2.2 percent of people will be diagnosed with melanoma at some point in life, and advanced disease carries a five-year survival rate of roughly 16 percent. For patients at that stage, the treatment list can be thin. Yana Najjar said, “There’s really no second-line treatments,” and called it “a population that has been left behind,” adding, “This is where I had hoped RP1 would come in.”
That gap is what makes the FDA’s second rejection more than a routine regulatory delay. RP1 is not being turned away because it failed to show activity in a disease with little room for error; it is being blocked despite data that appeared strong enough to win a review panel’s support and a breakthrough tag meant to accelerate it. The next question is whether Replimune can persuade regulators to revisit the evidence without losing the momentum that had built around a drug aimed at one of the hardest-to-treat forms of cancer.
