Replimune Receives Complete Response Letter from FDA for RP1 Melanoma Treatment

Biotech company disappointed by regulatory setback for promising cancer immunotherapy.

Apr. 13, 2026 at 4:42am

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An abstract, ghostly X-ray image showing the intricate internal structures of a melanoma tumor cell, conveying the complex biological challenges of developing effective cancer treatments.The FDA's rejection of Replimune's melanoma treatment leaves patients and their families waiting for new therapeutic options to fight this deadly form of skin cancer.Woburn Today

Replimune Group, Inc., a clinical-stage biotech company, announced that it received a complete response letter (CRL) from the U.S. Food and Drug Administration (FDA) for the company's Biologics License Application (BLA) for RP1 in combination with nivolumab for the treatment of advanced melanoma. The company disagrees with the FDA's decision and believes the data supports the efficacy and safety of RP1, but the regulatory process has been inconsistent and slow-moving, putting U.S. innovation at risk.

Why it matters

Melanoma is the fifth most common cancer in the U.S., with approximately 112,000 new cases estimated in 2026 and nearly 8,500 deaths annually. Standard of care therapies fail to help about half of patients, so new treatment options are desperately needed. The FDA's decision not to approve RP1 is a major setback for Replimune and the melanoma community.

The details

In the IGNYTE trial, patients with confirmed progression on an anti-PD-1 based regimen who received RP1 plus nivolumab had a 34% response rate with a median duration of 24.8 months and a favorable safety profile. Replimune says the FDA raised several issues related to tumor assessment methodology, but the company provided detailed analyses addressing the agency's concerns. Replimune also says the FDA's communication and decision-making process has been inconsistent, with the agency contradicting previous positions and replacing the review team without meeting the company.

  • In March 2021, the FDA suggested in a Type B meeting that a single-arm trial could be acceptable for consideration under accelerated approval if the data was sufficiently compelling.
  • In the subsequent pre-BLA meeting, the FDA stated it did not object to Replimune submitting a BLA based primarily on data from the Phase 2 IGNYTE trial.
  • Replimune submitted the BLA, which was accepted with breakthrough therapy designation and priority review.
  • In July 2025, Replimune received an initial CRL from the FDA.
  • In April 2026, Replimune received the latest CRL, leading the company to say the RP1 development will not be viable without timely accelerated approval.

The players

Replimune Group, Inc.

A clinical-stage biotechnology company pioneering the development of novel oncolytic immunotherapies, headquartered in Woburn, Massachusetts.

U.S. Food and Drug Administration (FDA)

The federal agency responsible for regulating and supervising the safety of food, drugs, and biological products in the United States.

Sushil Patel, Ph.D.

CEO of Replimune.

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What they’re saying

“It is deeply disappointing that the FDA has not exercised regulatory flexibility to meet patients' needs given the data supporting strong efficacy and the favorable safety profile. Approximately 8,500 Americans with advanced melanoma die every year. The country's foremost melanoma specialists stood behind the RP1 data. Patients and caregivers pleaded for urgency. All of it was met with inconsistent communication and a fragmented and slow-moving regulatory process which clearly puts U.S. innovation at risk.”

— Sushil Patel, Ph.D., CEO of Replimune

What’s next

Without timely accelerated approval, Replimune says the development of RP1 will not be viable, and the company will be forced to eliminate jobs, including substantially scaling back its U.S. manufacturing operations.

The takeaway

This regulatory setback for Replimune's promising melanoma treatment highlights the challenges biotech companies face in navigating the complex and sometimes inconsistent FDA approval process, which can significantly impact the availability of innovative therapies for patients with serious unmet medical needs.