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Moderna shares fell as much as 25% after early-leaked Phase 3 melanoma vaccine data showed a 42% cut in recurrence risk, below Wall Street's lofty expectations.
- Moderna (MRNA) fell as much as 25% on Oct. 22 after Phase 3 melanoma data appeared online two days before its scheduled debut.
- Intismeran autogene plus Keytruda cut recurrence or death risk 42% versus Keytruda alone, short of the Phase 2b result.
- The selloff followed a run that had more than quintupled the stock this year and lifted its valuation to about 52 times forward sales.
Lead
Moderna (NASDAQ: MRNA) plunged as much as 25% on Thursday after detailed results from its Phase 3 melanoma trial with Merck (NYSE: MRK) surfaced online ahead of an embargo. The data showed the personalized mRNA vaccine intismeran autogene, combined with Merck's immunotherapy Keytruda, lowered the risk of recurrence or death by 42%. The shares closed Wednesday at $245.81 and traded near $200 in the afternoon. Merck fell as much as 3.9% intraday.What Happened to Moderna Stock?
Moderna stock fell sharply because the leaked figures landed below the near-best-case outcome priced into the shares. The data appeared on the medical news site Oncology Central around 12:30 p.m. ET and was removed shortly afterward. Moderna shares were halted for volatility minutes later. The full results were scheduled for the Presidential Symposium at the European Society for Medical Oncology congress in Madrid on Oct. 24. Merck and Moderna then released the official figures.
The INTerpath-001 trial enrolled 1,137 patients with high-risk stage IIB to IV melanoma after surgery. Median follow-up was 24.6 months. The vaccine combination also cut the risk of distant metastasis or death by 38%. Two-year recurrence-free survival was 82.2% for the combination versus 70% for Keytruda alone.
Why Did a Positive Trial Trigger a Selloff?
The trial was positive but weaker than the earlier Phase 2b study, and the stock had priced in a stronger result. That study showed a 44% reduction at two years and close to 50% at five years. The Phase 3 hazard ratio of roughly 0.58 marks a step down from those figures.
Valuation magnified the reaction. Moderna had traded at about 52 times forward sales, against a five-year average of 7.7 times. The multiple fell to about 38 after the drop. Revenue declined from $6.85 billion in 2023 to $1.94 billion in 2025, which leaves the company's equity story tied to its oncology pipeline.
The move was a sell-the-news reaction. The consensus view is that commercial success is now less certain, because the margin over Keytruda alone is narrower than hoped.
How Safe Is the Vaccine?
Adverse event rates were similar between the two arms. The vaccine arm saw more fever and injection-site pain. Discontinuations due to adverse events ran 7% with the combination and 5% with Keytruda alone.
Strategic Context for Biotech Cancer Stocks
The episode shows how crowded positioning in biotech cancer stocks can turn a clinical win into a sharp drawdown when results trail the prior trial. Merck's smaller decline reflects its diversified revenue base. Moderna's shares carry far more of the vaccine's expected value. Early leaks of embargoed conference data add a further layer of volatility, as the market must reprice before companies have contextualized the findings.
What Comes Next for the Vaccine Program?
The next catalyst is the ESMO presentation, which will provide subgroup and durability detail. Additional intismeran trials are running in lung, bladder and kidney cancers. Interim kidney cancer results are expected in late 2026 or early 2027. Those readouts will determine whether the Phase 3 melanoma result is an outlier or the template for the platform.
Outlook
The Phase 3 data confirms that the vaccine adds clinical benefit to Keytruda. The magnitude, however, is smaller than in Phase 2b, and Moderna's valuation left little room for any shortfall. ESMO and the 2026-2027 pipeline readouts will drive the next repricing.
