Moderna Sells Off on Leaked Melanoma Vaccine Data That Oncologists Praised
Moderna shares fell as much as 25% on Thursday, October 22, after partial data from its personalized cancer vaccine study with Merck leaked. CNBC and Forbes both reported the 25% figure. The Wall Street Journal put the decline at nearly 18%, and attributed it to study details that circulated on social media. The WSJ also reported that the study had been closely guarded before the leak.
Merck stock moved far less. According to BioSpace, Merck shares fell by just over 1% to $147.93. Bloomberg described the joint program as a personalized melanoma vaccine that the two companies were developing together, and reported that investors viewed the leaked data as insufficient to prove its value.
The clinical program behind the leak is INTerpath-001, a Phase 3 trial that tested intismeran autogene plus Keytruda (pembrolizumab) in patients with resected stage IIB-IV melanoma. Merck and Moderna announced on August 19 that the trial met its primary endpoints of recurrence-free survival (RFS), the time a patient lives without the cancer returning, and distant metastasis-free survival (DMFS), the time without spread to distant sites. Merck described the readout as the first positive Phase 3 result for an individualized neoantigen therapy and for an mRNA-based cancer therapy. AJMC reported on October 23 that the personalized mRNA vaccine plus standard treatment reduced the risk of recurrence by 42%. That is a relative reduction in hazard, not an absolute gain in survival, and the distinction matters when reading any single headline percentage.
The market and the clinic came to opposite conclusions on the same data. Bloomberg reported on October 23 that oncologists cheered the leaked melanoma results even as Moderna's shares fell. The gap is not a contradiction so much as a question of what each audience was pricing. Oncologists read the magnitude of the effect against the unmet need in resected melanoma. Equity holders were pricing a binary regulatory and commercial outcome, and a partial, unofficial disclosure gave them no way to judge how the result would hold up once the full dataset was released and reviewed.
In my view, the sharper lesson concerns disclosure, not the drug. A leak transfers the timing and the framing of a clinical readout from the sponsor to whoever holds the document. Investors then trade on fragments, and the fragments tend to get reinterpreted in whichever direction the next post points. That dynamic explains why the two sources reporting the same day disagree by seven percentage points on Moderna's decline. Intraday figures from a fast-moving name can differ depending on when and how they were measured, and a leak-driven move offers little anchor for either number.
For savers and fund holders, the practical point is narrower than the headlines suggest. Moderna and Merck are both exposed to this program, but Merck's roughly 1% move indicates that the market treated the melanoma readout as a relatively small part of the larger company. Moderna's larger reaction reflects a higher share of value tied to a smaller set of assets. Whether the 42% figure translates into commercial value depends on data that were not part of the leak, and on regulatory steps that remain ahead of the companies.
The episode also illustrates how much of a clinical story can move before the sponsor has said anything. The trial results were announced in August, the detailed melanoma data surfaced in October, and the price response came before the companies had presented the full picture. For anyone tracking this name, the signal worth watching is the official disclosure, not the first copy of a slide deck.
