FDA rejects Replimune RP1 twice after fast-track designation
replimune’s melanoma drug RP1 has been rejected by the FDA twice, even after the agency placed it on a fast track at the end of 2024. The drug is designed for advanced melanoma, a disease that carries a five-year survival rate of roughly 16 percent once it spreads.
Replimune Group’s chief executive, Sushil Patel, said, "I’ve just never seen the agency behave like this," and added that it was "putting us in a very, very difficult position." The company had pointed to an IGNYTE phase 1/2 trial showing nearly 33 percent of patients with treatment-resistant advanced melanoma improved with RP1 plus nivolumab.
RP1 and the FDA panel
RP1 is an oncolytic immunotherapy made from an engineered virus, a modified version of a herpesvirus. Replimune injects it directly into melanoma tumors, where the virus causes cancer cells to burst and trigger the immune system to kill similar cancer cells without damaging healthy tissue.
The FDA gave RP1 breakthrough therapy designation after early trials were so effective. Last year, the same drug drew support from the initial FDA review panel, which recommended that RP1 be approved. That sequence made the later refusal more difficult for the company to absorb.
Melanoma patients and options
Yana Najjar, director of the Clinical and Translational Research Center at the University of Pittsburgh Medical Center Hillman Cancer Center, said, "There’s really no second-line treatments" for some patients. She also said, "This is a population that has been left behind. This is where I had hoped RP1 would come in."
Those patients are part of a large group: about 110,000 new cases of melanoma are diagnosed each year in the U.S., and about 2.2 percent of people will be diagnosed with it at some point in their life. Early-stage disease has a greater than 99 percent survival rate, but the outlook worsens sharply after it spreads.
Replimune after last month
The contrast in RP1’s data is central to the dispute. The IGNYTE phase 1/2 trial found nearly 33 percent response in one treatment group, while 6 to 7 percent of similar patients responded to nivolumab alone. That gap is the strongest case Replimune can make as it tries to push back against the FDA’s second rejection.
Patel’s comments point to a company that had expected a different path after the breakthrough designation and fast-track status. The practical result for patients is that RP1 is still not available as an approved option, even for the group Najjar described as having few other treatments left.
