Key Takeaways
- Moderna Inc. (NASDAQ:MRNA) sank as much as roughly 25% intraday after apparent Phase 3 results for its personalized melanoma vaccine surfaced online ahead of an embargoed medical-conference presentation.
- The reported data showed a 42% cut in the risk of recurrence or death versus Keytruda alone: a clear win, but no improvement on earlier Phase 2b results.
- After a run that had more than quintupled the share price this year, the selloff suggests investors were positioned for a near-best-case outcome.
Moderna Inc. (NASDAQ:MRNA) shares tumbled on Thursday, Oct. 22, after what appeared to be detailed late-stage results for its experimental melanoma vaccine were published online two days early. Trading was briefly halted for volatility with the stock down about 12%, and losses later deepened, leaving shares near $185 in afternoon trading versus Wednesday’s $245.81 close. Development partner Merck & Co. (NYSE:MRK) fell as much as 3.9% intraday.
What Happened
The figures appeared on medical news site Oncology Central around 12:30 p.m. ET and were removed shortly afterward. They had been embargoed for a late-breaking presentation at the European Society for Medical Oncology (ESMO) Congress in Madrid on Saturday, Oct. 24. Neither company has confirmed the numbers, and Moderna declined to comment to Investing.com.
According to the briefly posted report, adding intismeran autogene to Merck’s immunotherapy Keytruda reduced the risk of melanoma returning or death by 42% versus Keytruda alone in the 1,137-patient INTerpath-001 trial. At two years, 82.2% of combination patients were alive and cancer-free, compared with 70% on Keytruda alone.
Intismeran is designed from a genetic analysis of each patient’s tumor, coding for up to 34 mutations unique to that cancer so the immune system can target cells left behind after surgery. The trial tested it as adjuvant therapy, meaning treatment given after high-risk stage IIB to IV melanoma is surgically removed, to prevent relapse.
Why Good Data Sank the Stock
Success itself was not news. On Aug. 19, the partners said the study met its primary goal of recurrence-free survival and a key secondary goal of distant metastasis-free survival, without disclosing figures. The open question was the size of the benefit.
On that measure, the leaked data are solid rather than spectacular. A 42% risk reduction implies a hazard ratio of about 0.58; below 1.0 favors the new treatment, and lower is better. The earlier Phase 2b study posted 0.56 at two years, improving to 0.51 by five years. UBS Group AG (NYSE:UBS) said last month it believed the market wanted roughly 0.65 or better, a bar the reported result clears.
That points to positioning and valuation as much as the data. Moderna shares had more than quintupled in 2026 before Thursday, and even after the drop they sit far above the roughly $124 average analyst price target compiled by StockAnalysis.
What It Means for Moderna and Merck
For Moderna, intismeran is the centerpiece of its growth story as COVID-19 vaccine sales have shrunk from their pandemic peak. The company does not own it outright, however. Merck paid $250 million in 2022 to exercise its option, and the partners split costs and profits equally.
Execution is a separate hurdle. A therapy made for one patient at a time requires tumor sequencing, custom manufacturing and fast turnaround, raising questions about cost, capacity and insurer reimbursement.
For Merck, the program is strategically useful rather than financially decisive in the near term. A combination that keeps Keytruda central to post-surgery melanoma care could help defend the franchise as the drug’s key U.S. patents begin expiring later this decade. Relative to Merck’s size, though, intismeran is a modest contributor, which fits the far smaller move in its shares.
Why Investors Should Care
The leak turns Saturday’s ESMO presentation from a reveal into a confirmation event. Investors will look for whether the full dataset matches the posted figures, how consistent the benefit is across patient subgroups, the size of the distant-metastasis benefit, safety and early overall survival trends.
These are also interim results. UBS noted the hazard ratio could improve with longer follow-up, as it did in Phase 2b. Beyond ESMO, the next markers are regulatory submission timing and readouts from the wider INTerpath program, which spans nine Phase 2 and Phase 3 trials across melanoma, lung, bladder and kidney cancer.
For Moderna shareholders, the episode underscores that the stock now trades largely on one shared asset. Whether the vaccine works is no longer the main debate; the size of its benefit, the pace of approval and the economics of a bespoke cancer therapy are.