On August 19, 2026, Moderna, Inc. (NASDAQ:MRNA) and Merck & Co., Inc. (NYSE:MRK) said that their personalized mRNA cancer vaccine, combined with Merck’s Keytruda, met its main goals in a first-ever Phase 3 trial for melanoma. The news sent Moderna shares up as much as 177%, adding $44 billion to its market value, while Merck shares rose more than 12% to an all-time high.
Why This Matters
This is the first personalized cancer vaccine to succeed at the late-stage trial level, a milestone Moderna has pursued for years after its Covid-19 vaccine business faded. The stock became the most shorted in the S&P 500.
Does this trial genuinely validate personalized cancer vaccines as a new class of medicine, or is the market’s reaction running ahead of data the companies haven’t even fully released yet?
Breakthrough Results vs. Unreleased Data: The Moderna Debate
The combination, involving Moderna, Inc. (NASDAQ:MRNA)’s vaccine intismeran autogene and Merck & Co., Inc. (NYSE:MRK)’s Keytruda, extended the time patients lived without their melanoma returning. It reduced the risk of cancer spreading, building on earlier data showing a 49% reduction in recurrence or death risk and a 59% reduction in distant metastasis risk compared with Keytruda alone. Moderna CEO Stéphane Bancel called it validation of “an entirely new class of medicine.” TD Cowen analysts called it “a landmark moment” and expect regulatory approval as soon as next year. Even after the surge, Moderna trades at less than a third of its 2021 peak. Rezilient Health’s Dr. Danish Nagda argued the platform remains undervalued given the potential to extend the approach to other cancers.
The companies haven’t released the exact numerical improvement behind the results yet, saying only that they were “statistically significant and clinically meaningful.” It means investors bid the stock up 177% on a press release rather than full data. Moderna, Inc. (NASDAQ:MRNA) became the most shorted stock in the S&P 500 last year. The firm still faces the underlying reality that its COVID vaccine business has structurally declined, with this single trial now carrying enormous weight for the turnaround story.
Keytruda Extended: Merck Gains Stability, Not Volatility
Keytruda, already the standard of care for melanoma, gets a validated new use as a combination partner rather than facing displacement. Dr. Dean Li, president of Merck Research Laboratories, said the results support treating cancer earlier, when it’s most treatable, a strategy that could extend Keytruda’s relevance well beyond its current use cases.
Merck & Co., Inc. (NYSE:MRK)’s smaller relative stock move, 12% versus Moderna, Inc. (NASDAQ:MRNA)’s 177%, shows the fact that Merck’s $333 billion market cap makes any single drug combination less transformative to its overall business. Barclays estimates the therapy could reach only about $3 billion in melanoma sales by 2035, a modest figure against Merck’s overall scale.
Conclusion
The trial result is genuinely significant medically, but Moderna’s stock move already prices in a lot of hope for future cancer types the vaccine hasn’t even been tested against yet.
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Disclosure: None. This article is originally published at Insider Monkey.
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