Moderna shares logged their best session ever on Wednesday, August 19, 2026, jumping about 177% after the announcement that the personalized mRNA melanoma vaccine developed with Merck met its primary endpoint in a Phase 3 trial. The stock nearly tripled in a single session, adding roughly $30 billion in market value.
What is intismeran
The product, called intismeran (intismeran autogene, formerly mRNA-4157/V940), is a personalized mRNA neoantigen therapy: it encodes up to 34 mutations unique to each patient's tumor and trains the immune system to recognize and attack cancer cells. It uses the same mRNA platform behind Moderna's COVID-19 vaccine. In the clinical program the treatment is given in combination with Keytruda (pembrolizumab), Merck's immunotherapy.
The INTerpath-001 study
The Phase 3 trial enrolled 1,137 patients with stage IIB-IV melanoma that had been surgically removed, randomized 2-1 to receive either intismeran plus Keytruda or Keytruda alone. Interim results showed the combination extended recurrence-free survival (the primary endpoint) and distant metastasis-free survival, with data that were statistically significant and clinically meaningful. Detailed results have not yet been released and will be presented at an international medical conference, scheduled for Madrid from October 23 to 27.
This is the first positive randomized Phase 3 trial for a neoantigen vaccine and the first late-stage success for an mRNA cancer vaccine. Five-year data from the earlier Phase 2, presented in June, showed a 49% reduction in the risk of recurrence or spread.
Market and executive reaction
Moderna's market value went from roughly $25 billion before the announcement to more than $56 billion after the rally, while Merck, which already holds the established blockbuster Keytruda, saw a more contained gain of about 12%. On Thursday, August 20, Moderna shares corrected around 18%, settling near $142 and giving back part of the historic surge; BioNTech fell 4%.
Georgina Long, who led the trial, called the result a landmark moment with the potential to establish a new treatment paradigm. Dean Li, president of Merck Research Laboratories, said the findings reinforce the promise of a more personalized approach to cancer care, while Moderna CEO Stéphane Bancel highlighted the role of mRNA technology. Experts echoed the enthusiasm: Lennard Lee of the University of Oxford called it the first positive Phase 3 result for an individualized neoantigen therapy, and Karen Knudsen of the Parker Institute described it as the start of a new era in immunotherapy.
Next steps and caveats
The companies have already begun talks with regulators about a potential approval application. Moderna president Stephen Hoge estimated that thousands of high-risk patients could benefit as early as next year if the drug is approved. It is important to note that the treatment is experimental, targets adjuvant melanoma (after surgical removal of the tumor) and is used in combination with Keytruda: it is not a preventive vaccine nor a universal cure for cancer, and the size of the benefit will only be defined once the full dataset is published.
Against a backdrop in which the companies chose to avoid the word vaccine in their communications, following federal funding cuts for mRNA research decided by the Trump administration, the result nonetheless represents a significant turning point for the mRNA platform in treating solid tumors.
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