The Food and Drug Administration’s recent decision to withhold approval of Replimune’s experimental melanoma treatment, RP1, landed hard on physicians and patients who saw dramatic responses in a clinical trial and raised broader questions about the agency’s direction under Commissioner Marty Makary.
Clinicians described the ruling as devastating. Trisha Wise-Draper, a dermatologist at the University of Cincinnati who had patients in the trial, said it felt like a serious setback. Eric Whitman, medical director of oncology at Atlantic Health System, estimated the drug could be life-saving for as many as 2,000 to 2,500 people if the trial results hold up. A Wall Street Journal editorial warned the decision could chill drug development.
RP1 is a genetically engineered virus designed to kill tumor cells and stimulate the immune system. Replimune sought accelerated approval by presenting data from a single-arm trial in which about one-third of 140 participants experienced tumor shrinkage or disappearance when treated with RP1 plus the immunotherapy drug Opdivo. The company has argued that adding a control arm using Opdivo alone would have been unethical because enrolled patients had already stopped responding to checkpoint inhibitors.
But FDA reviewers flagged significant design concerns. The agency warned Replimune months earlier that the trial’s lack of a control arm made it difficult to determine how much of the benefit came from RP1 itself rather than from the combination with Opdivo. In its denial statement the FDA said it was not convinced the observed benefits could be attributed solely to RP1. Replimune now has a larger randomized trial that includes a control arm, but the FDA’s rejection jeopardized investor support and prompted the company to shed staff and scale back operations.
Observers noted that single-arm studies have previously supported approvals in melanoma; Keytruda was approved on that basis more than a decade ago. Still, some oncologists and industry analysts say Replimune declined repeated FDA suggestions to alter its development plan, and regulators concluded the evidence did not meet the threshold for accelerated approval.
The timing and context of the decision amplified scrutiny. Makary, who resigned this week after 13 months as commissioner, reshaped agency culture in ways critics say have undermined trust in regulatory norms. Steven Grossman, a regulatory consultant and former HHS official, said people now speculate about the standards and processes behind FDA decisions, and that uncertainty harms patients, sponsors and investors.
Makary publicly attacked Replimune after the denial, accusing the company of “corruption” and of trying to make the FDA look bad. HHS Secretary Robert F. Kennedy Jr. defended Makary during a congressional hearing but misstated aspects of the trial, incorrectly saying patients had also received chemotherapy.
Former FDA staffers and industry consultants said the pattern of decision-making under Makary has been inconsistent. Paul Kim, a former FDA staffer and Senate aide, said the agency’s actions have left stakeholders guessing whether denials reflect solid scientific reasoning or political motives. Evan Seigerman of BMO Capital Markets said that even if the Replimune decision was warranted, the broader chaos at the agency has mired legitimate regulatory choices in controversy.
The controversy over RP1 is part of a larger stream of policy shifts and interventions at the agency during Makary’s tenure. Critics point to instances in which senior officials either blocked or pushed approvals and policy changes at the behest of political leadership, sometimes overriding career staff recommendations. Vinay Prasad, an oncologist who held leadership roles at the FDA and frequently intervened in approval processes, resigned three weeks after the Replimune decision, prompting further questions about whether individual interventions shaped the outcome.
Makary also promoted ambitious changes — ending animal testing requirements for certain biologics, accelerating adoption of artificial intelligence in FDA review processes, and reducing the standard number of clinical trials needed for approval — proposals that some experts view as premature or impractical. Aaron Kesselheim, a Harvard Medical School professor, noted that while the agency has signaled an interest in lowering evidence thresholds for some drugs, it has simultaneously made vaccine approvals more stringent.
Staffing and morale have been affected as well. The FDA cut thousands of employees at the start of the prior administration; Makary pledged to rebuild staffing but faced skepticism about how quickly that could happen amid upheaval at HHS and the agency.
For patients and clinicians who saw clear benefits from RP1 in the single-arm study, the denial is a painful example of how regulatory, scientific and political factors can collide. Replimune maintains a randomized trial under way, but the company’s near-term prospects and its ability to complete confirmatory studies are now uncertain after the FDA decision, which prompted significant layoffs.
The debate over RP1 highlights tensions at the heart of the accelerated approval pathway: how to balance early access to promising therapies against the need for robust evidence that a new drug is effective and safe compared with existing treatments. That balance, critics say, has been harder to discern while confidence in the agency’s processes has been shaken by leadership changes and high-profile interventions.
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