Moderna shares closed up nearly 177 percent after the first mRNA cancer vaccine succeeded in a late-stage trial, slowing the return and spread of high-risk melanoma when paired with Keytruda.
Moderna shares closed up nearly 177 percent on Wednesday after the company and its partner Merck announced the first successful late-stage trial of an mRNA cancer vaccine, a breakthrough that marks a historic turning point in the fight against cancer. The personalized treatment, called intismeran autogene, slowed the return and spread of high-risk melanoma when combined with the immunotherapy Keytruda, and Wall Street responded with one of the largest single-day surges in biotech history.
Moderna closed at $174.38 a share, up $111.42, on volume of roughly 185 million shares -- about 1,800 percent above its three-month average. The company's market value roughly tripled in a single session, jumping from about $25 billion to about $69 billion, and shares have now climbed more than 400 percent since the start of the year.
The results come from the Phase 3 INTerpath-001 trial, which enrolled 1,137 patients with stage IIB through IV melanoma that had been completely removed by surgery. Patients were randomized two-to-one to receive the personalized vaccine alongside Keytruda, or Keytruda alone, for about a year.
The combination met the trial's primary endpoint of recurrence-free survival, the length of time patients stay free of cancer after treatment, and a key secondary endpoint of distant metastasis-free survival, the time before the disease spreads to other parts of the body. The companies described the improvements as statistically significant and clinically meaningful, with no new safety signals observed.
Those results make intismeran the first individualized neoantigen therapy -- and the first mRNA-based cancer treatment of any kind -- to succeed in a Phase 3 trial. It is also the first late-stage study to show a meaningful improvement over Keytruda alone, the standard-of-care immunotherapy for this patient group, in the adjuvant setting, where the goal is preventing a return of disease after surgery.
Intismeran is designed around the unique mutational fingerprint of each patient's own tumor. After surgery, the tumor is analyzed to identify the specific mutations that make the cancer recognizable, and a custom mRNA vaccine is manufactured to teach the immune system to hunt down and destroy cells carrying those markers.
The approach has been studied for decades but never proven at the late-stage level until now. The treatment builds on earlier data: five-year follow-up from the Phase 2b KEYNOTE-942 trial, presented at the American Society of Clinical Oncology annual meeting in June, showed the combination cut the risk of recurrence or death by 49 percent and the risk of distant metastasis or death by 59 percent compared with Keytruda alone.
Experts have called the result significant precisely because it validates the underlying platform. If an mRNA vaccine can be built against melanoma, the same manufacturing approach can potentially be adapted to other tumor types, opening a new front in cancer treatment that goes beyond chemotherapy and checkpoint inhibitors.
The market reaction was swift and enormous. Moderna's surge came with trading volume roughly 1,819 percent above its recent average, a level of activity rarely seen outside of major index events. The stock set a new 52-week high during the session before closing at $174.38.
Merck shares also climbed about 11 percent on the news. Analysts at JPMorgan highlighted the vaccine's eventual launch as crucial to Moderna's return to profitability, noting that a successful cancer franchise would diversify the company well beyond its COVID-era respiratory products.
Moderna also added regulatory momentum this week when the Food and Drug Administration (FDA) cleared mFLUSIVA, its mRNA seasonal flu vaccine for adults 50 and older, with a U.S. launch targeted for the 2026-27 flu season. The approval gives Moderna its fourth U.S.-approved product and strengthens its respiratory vaccine lineup just as the cancer program moves toward the finish line.
The companies have not announced a submission date, approval timeline, or commercial availability for intismeran, and the treatment remains investigational. Detailed Phase 3 data, including the size of the benefit for different patient subgroups, will be presented at an upcoming international medical meeting, and the trial will continue to track overall survival.
Regulatory discussions are already underway, and a full data release is the next major milestone to watch. If the results hold up under scrutiny, intismeran could become the first approved mRNA cancer therapy, a distinction that would reshape both oncology treatment and the economics of the two companies behind it.
For patients with high-risk melanoma, the practical question is how quickly the therapy can move from the trial setting into routine care. For investors, the question is what the same platform can do for other cancers next. Either way, Wednesday's readout gave both groups something neither had seen before: proof that an mRNA vaccine can beat back cancer, not just prevent a virus.
Moderna shares closed up nearly 177 percent after the first mRNA cancer vaccine succeeded in a late-stage trial, slowing the return and spread of high-risk melanoma when paired with Keytruda.
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