FDA Again Rejects Replimune’s Advanced Skin Cancer Treatment

The U.S. Food and Drug Administration (FDA) on April 10, 2026, declined to approve an experimental treatment for advanced skin cancer developed by Replimune Group. This marks the second time the agency has rejected the therapy, which is designed to treat advanced melanoma.

The FDA issued a Complete Response Letter regarding the Biologics License Application for RP1. According to reports from Reuters, the agency cited insufficient data from studies as the reason for the decision.

The news had an immediate impact on the company’s valuation, with Replimune shares falling 58% in extended trading following the announcement.

The Science Behind RP1

The experimental drug, RP1, is an engineered virus. We see designed to stimulate and rev up the immune system to better target and fight melanoma, a serious form of skin cancer.

The development of this therapy has become a focal point in a broader debate regarding the standards used by the FDA to approve new biologics and oncology treatments.

Regulatory Shifts and the FDA

What we have is not the first time Replimune has faced a setback with this specific treatment. The drug was initially rejected by the FDA in July 2025.

The timing of the initial July 2025 rejection occurred just two months after Vinay Prasad was appointed as the FDA’s head of biologics. Prasad, an academic oncologist, has previously criticized regulatory bodies for approving medications based on limited data.

Industry observers have viewed the decisions regarding Replimune’s therapy as a potential indicator of a stricter regulatory stance under Prasad’s leadership at the agency.

Impact on Drug Development

The repeated rejection of RP1 highlights the challenges biotech companies face when meeting the FDA’s evidentiary requirements for biologics. The agency’s insistence on more robust data suggests a high threshold for proving the efficacy and safety of engineered virus therapies in advanced skin cancer.

For patients with advanced melanoma, the lack of approval means this specific engineered virus remains an experimental treatment rather than a clinically available option.

The current situation underscores a simmering tension between the need for innovative cancer therapies and the FDA’s mandate to ensure that approved drugs are supported by sufficient clinical evidence.