Moderna stock was up around 58% in premarket trading Wednesday after the company and Merck announced their melanoma vaccine combination beat Keytruda alone in a Phase 3 clinical trial. This is the first time an mRNA-based cancer therapy has cleared a Phase 3 bar.
The trial, called INTerpath-001, enrolled around 1,100 patients with completely resected stage IIB-IV melanoma. It tested intismeran autogene, an investigational mRNA-based individualized neoantigen therapy, paired with Merck’s blockbuster immunotherapy drug Keytruda.
The combination met its primary endpoint of recurrence-free survival and a key secondary endpoint of distant metastasis-free survival. Both results were statistically meaningful compared to Keytruda alone.
MODERNA, MERCK MRNA CANCER VACCINE SUCCEEDS IN PHASE 3$MRNA and $MRK say their personalized mRNA cancer vaccine, intismeran, combined with Keytruda slowed melanoma recurrence and spread in a late-stage trial.
The study was stopped at its first interim analysis after positive… pic.twitter.com/Vk7N1jptd6
— Wall St Engine (@wallstengine) August 19, 2026
This is also the first Phase 3 study to show a clinically meaningful improvement over Keytruda alone in the adjuvant setting for resected melanoma patients who had not received prior systemic therapy.
Merck stock climbed around 6% on the news. The S&P 500 futures were flat at the time of the announcement.
The vaccine is built using Moderna’s mRNA technology, which allows the companies to tailor each dose to dozens of mutations unique to each patient’s tumor. That level of customization is a key part of what sets it apart from previous cancer vaccine attempts.
Moderna has reportedly automated this individualized production process. Analysts believe the approach can scale to support billions of dollars in annual sales.
For Moderna, this is a pivotal moment. The company has faced investor pressure to diversify beyond its COVID-19 vaccine. In June, five-year Phase 2 follow-up data showed cancer recurrence or death was cut in half among patients who received the vaccine-Keytruda combination.
A successful Phase 3 readout now opens the door to a regulatory filing. The companies have said they plan to share results with regulators and discuss the path toward approval.
For Merck, the stakes are equally high. Keytruda, the world’s best-selling drug with $32 billion in sales last year, faces patent expirations in the coming years. A new approved combination therapy would help offset that revenue loss.
The safety profiles for both drugs remained consistent with earlier studies. No new safety signals were observed during the trial.
The study will continue tracking overall survival as a key secondary endpoint.
Beyond melanoma, the two companies are running nine Phase 2 and Phase 3 trials across lung, bladder, kidney, stomach, and pancreatic cancers.
The companies plan to present the full dataset at an upcoming international medical meeting.
“Today’s results represent a landmark moment for adjuvant melanoma treatment,” said Georgina Long, the Phase 3 study’s lead researcher and an oncology professor at the University of Sydney.
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