The FDA Just Rejected This Melanoma Drug Twice. Here's Why It Matters.

The FDA Keeps Moving the Goalposts (or Does It?)

So why did the FDA say no? The core issue is trial design. IGNYTE was a single-arm study, meaning every patient got the drug. There was no comparison group receiving a placebo or standard therapy.

Single-arm trials are like taste-testing a new recipe without trying the old one. The dish might be delicious, but you can't prove it's better without a head-to-head comparison. The FDA's concern: without a control group, you can't be sure the responses weren't partly due to nivolumab alone or some quirk of patient selection.

The first rejection came in July 2025. The FDA issued what's called a Complete Response Letter (basically a formal "try again"), citing insufficient evidence and concerns about patient population heterogeneity, meaning the mix of patients was too varied to draw clean conclusions.

Replimune regrouped. The company met with the FDA in September 2025, and according to Replimune, the agency acknowledged that patient heterogeneity was no longer a concern. The company resubmitted its application with additional analyses, including progression-free survival data showing 30.6 months on RP1 plus nivolumab versus just 4.4 months on patients' prior PD-1 therapy. They also used the FDA's preferred tumor measurement standard (RECIST 1.1) and showed that both injected and non-injected tumors shrank at similar rates.

The FDA assembled a fresh review team to avoid bias from the first round. And then it rejected RP1 again, stating the data were "insufficient to conclude substantial evidence of effectiveness."

Replimune Is Not Happy About It

The company's frustration is palpable. Replimune has pointed out that the FDA originally granted RP1 breakthrough therapy designation, a signal that the agency saw promise in the approach. The company also notes that the FDA didn't object when Replimune proposed submitting its application based primarily on IGNYTE data during a pre-submission meeting.

Replimune has framed this as a matter of life and death, noting that roughly 8,500 Americans die from melanoma each year. The company called the regulatory process "fragmented and slow-moving."

Meanwhile, investors have been living through their own kind of pain. Replimune's stock was trading around $5.91 the day before the rejection. Shares had already been sliding from roughly $7.80 earlier in the week as the market braced for bad news. Piper Sandler downgraded the stock to "Neutral" on the day of the rejection, though Wedbush maintained an "Outperform" rating with a $19 price target.

The Bigger Picture: Single-Arm Trials Are Under Siege

This rejection isn't just Replimune's problem. It's a warning shot for the entire oncology industry.

For years, the FDA accepted single-arm trial data for accelerated approvals in cancer, especially for drugs targeting patients with no other options. The logic was simple: if a drug shows strong responses in a disease with limited treatment, waiting years for a randomized trial could cost lives.

But that era is ending. The FDA's March 2023 draft guidance expressed a strong preference for randomized controlled trials for accelerated approval, even in oncology, while still allowing single-arm trials when appropriate. About half of historical accelerated approvals in cancer were based on single-arm studies; the agency has signaled it wants that number to shrink dramatically. January 2025 guidance further tightened the screws, requiring that confirmatory trials be underway at the time of approval.

Replimune, to its credit, already launched a global Phase 3 randomized trial called IGNYTE-3 with 400 patients. Early data from that trial reportedly showed RP1 plus nivolumab beating standard care. But even that wasn't enough to get the single-arm data across the finish line on its own.

What Comes Next

Replimune now faces a difficult choice. The company can try to resubmit again, wait for mature IGNYTE-3 data, or explore other regulatory pathways. Its cash runway extends to the first quarter of 2027, so the clock is ticking but not yet urgent.

The broader lesson is clear, though. If you're a biotech company developing a cancer drug in 2026, a single-arm trial is no longer your golden ticket. Even breakthrough designation and genuinely impressive efficacy data may not be enough if the FDA doesn't see a randomized comparison.

For patients with advanced melanoma who've run out of standard options, this is the cruelest part of the story. The data suggest RP1 works. The FDA wants more proof. And somewhere between those two truths, thousands of people a year are running out of time.

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