An mRNA cancer vaccine has cleared a Phase 3 trial for the first time. Moderna and Merck & Co‘s personalized melanoma therapy hit its primary endpoint on Wednesday, sending Moderna (Nasdaq: MRNA) stock up 177% by the close, its best single trading day since going public in 2018.
Doctors build intismeran autogene, also known as V940 or mRNA-4157, by sequencing each patient’s tumor, then manufacturing an mRNA vaccine encoding up to 34 mutations specific to that cancer, aiming to train the immune system to recognize and attack it. In the trial, called INTerpath-001, 1,137 people with surgically removed, high-risk melanoma took part, split two-to-one between an arm that added intismeran to roughly a year of Merck’s Keytruda and a control arm that received Keytruda by itself.
Moderna and @Merck today announced positive topline results from the Phase 3 INTerpath-001 trial evaluating adjuvant treatment with intismeran autogene, a novel investigational mRNA-based individualized neoantigen therapy jointly developed by Merck and Moderna, in combination… pic.twitter.com/v4DjH0r823
— Moderna (@moderna_tx) August 19, 2026
The combination met both the study’s main goal of delaying cancer recurrence and a key secondary goal of delaying the disease’s spread to distant parts of the body, with no new safety signals reported. Merck and Moderna haven’t released the specific trial numbers yet, planning instead to present full results at a future medical conference and begin talks with regulators about approval.
Flashback: Moderna and Merck & Co: mRNA Cancer Vaccine Shows “Highly Encouraging Results,” Shares Rise
Earlier data offer a preview of what those numbers might show. At five years of follow-up in an earlier trial of the same combination, presented at this year’s American Society of Clinical Oncology meeting, patients saw a 49% lower risk of recurrence or death and a 59% lower risk of distant metastasis than those on Keytruda alone.
That data was already strong enough to earn the therapy Breakthrough Therapy status from the FDA and the equivalent PRIME designation from European regulators, before Wednesday’s Phase 3 results even arrived.
Georgina Long, the trial’s principal investigator and medical director of the Melanoma Institute Australia, called the results “a landmark moment for adjuvant melanoma treatment.” Dean Li, president of Merck Research Laboratories, said the findings reinforce the promise of “a more personalized approach to cancer treatment.”

Moderna stock closed at $174.38 on trading volume roughly 19 times its three-month average; the rally spread to other mRNA-linked names, with BioNTech gaining nearly 22% and Merck itself rising more than 12%. JPMorgan analysts called a successful vaccine launch central to Moderna’s path back to profitability.
Moderna's $MRNA 177% gain today was the largest by any S&P 500 stock this century 📈 🤑 🥳 pic.twitter.com/zzvoLPazST
— Barchart (@Barchart) August 20, 2026
Moderna reported a $782 million net loss last quarter, and RBC Capital raised its price target on the stock to $130 from $45. Intismeran remains investigational and unapproved, but it’s now one of eight Moderna cancer therapies in Phase 2 or Phase 3 testing, across tumor types that include lung, bladder, and kidney cancer.