Shares of Moderna surged more than 137% on Wednesday, August 19, after the company announced that its personalized mRNA cancer therapy, developed in partnership with Merck, significantly reduced the risk of melanoma recurrence and spread in a late-stage (Phase 3) clinical trial — a landmark result for a treatment approach years in the making.
What the Trial Found
The therapy, known as an individualized neoantigen therapy (INT), is designed to be custom-built for each patient using mRNA technology to train the immune system to recognize and attack cancer cells based on the unique genetic mutations present in that patient's own tumor. In the trial, the treatment — used in combination with Merck's existing immunotherapy drug Keytruda — showed a statistically significant reduction in the risk of melanoma recurring or spreading compared with Keytruda alone. Full detailed results, including specific efficacy percentages and safety data, are expected to be presented at a forthcoming medical conference and published in a peer-reviewed journal.
Market Reaction: A Historic Rally
The news triggered one of the sharper single-day biotech rallies of the year. Moderna shares more than doubled, jumping over 137%. Merck rose 11.2% to 12%, making it the single biggest gainer on the blue-chip Dow. The enthusiasm spilled over into the broader biotech and vaccine sector: Novavax rose 6% to 8%, and US-listed shares of German biotech BioNTech — a Moderna rival in the mRNA space — jumped between 19% and 21%, likely reflecting renewed investor optimism about the broader mRNA cancer-therapy approach rather than company-specific news. The rally helped push the S&P 500 healthcare sector up 2.9% to 3%, a record high and the single biggest contributor to the benchmark index's gains for the day, among all 11 major sectors.
Why This Result Matters
Melanoma is among the most aggressive forms of skin cancer, and reducing recurrence after initial treatment has long been a central challenge in oncology. The personalized nature of this therapy represents a genuinely different approach from traditional cancer treatments: rather than a one-size-fits-all drug, each dose is manufactured specifically for the individual patient based on the genetic signature of their tumor, in principle allowing for a more precisely targeted immune response. A successful Phase 3 result — the final and most rigorous stage of clinical testing before a drug can typically be submitted for regulatory approval — represents a major validation milestone for the entire personalized cancer vaccine field, not just for Moderna and Merck specifically.
Part of a Longer Collaboration
Moderna and Merck have been jointly developing this mRNA-based cancer therapy platform for several years as part of a broader partnership exploring mRNA technology's applications beyond infectious disease, building on the manufacturing and clinical infrastructure Moderna developed during its COVID-19 vaccine program. Wednesday's trial results mark one of the most significant clinical milestones in that partnership to date, and are likely to accelerate the companies' path toward seeking regulatory approval for the combination therapy.
What's Next
With full data still pending presentation and publication, investors and oncologists will be watching closely for the specific efficacy figures, the therapy's safety profile, and any guidance from Moderna and Merck on a potential regulatory filing timeline. Given the scale of Wednesday's market reaction, expectations for the treatment's real-world impact — and its potential to reshape how melanoma and possibly other cancers are treated — have risen sharply. For continuing coverage of the trial results, see Reuters Healthcare & Pharmaceuticals.
If the full data holds up to scrutiny, Wednesday's results could mark a genuine turning point for personalized cancer vaccines — moving the field from a promising concept to a treatment approach with hard clinical evidence behind it.