Moderna (NASDAQ: MRNA) shares plunged more than 17% to $202.63 in Thursday’s regular trading session after detailed Phase 3 results for its personalized melanoma vaccine, developed with Merck (NYSE: MRK), emerged earlier than planned despite the treatment meeting key clinical goals.
The experimental vaccine, intismeran autogene, combined with Merck’s immunotherapy Keytruda reduced the risk of cancer recurrence or death by 42% and the risk of distant metastasis (cancer spreading to other parts of the body) or death by 38% compared with Keytruda alone.
The results appeared prematurely on the Oncology Central website before being removed. Merck and Moderna subsequently released the findings ahead of their scheduled conference presentation.
Moderna shares fell more than 25% intraday, temporarily wiping approximately $24 billion from the company’s market value before recovering some losses by the close.
The stock fell a further 6% in Friday’s premarket trading.
Reuters reported that UBS analyst Michael Yee described the recurrence-free survival findings as solid but characterized the decline as an expected “sell-the-news” event after the stock’s substantial advance and elevated expectations.
Melanoma Trial Shows Improved Two-Year Outcomes
The Phase 3 INTerpath-001 trial enrolled 1,137 patients with high-risk stage IIB-IV melanoma whose tumors had been completely removed through surgery. Patients received either intismeran plus Keytruda or placebo plus Keytruda.
The vaccine is designed individually using genetic information from each patient’s tumor to help the immune system recognize and attack cancer cells.
After a median follow-up of 24.6 months, the estimated two-year recurrence-free survival rate was 82.2% for patients receiving the combination, compared with 70% for those receiving Keytruda alone.
Estimated two-year distant metastasis-free survival was 88.5% with the combination versus 80.2% with Keytruda alone.
A separate, prespecified analysis found little difference in treatment effectiveness during the first six months. After six months, following completion of the vaccine dosing regimen, the combination reduced the risk of recurrence or death by 58%. That estimate applies specifically to the later follow-up period, not the trial’s entire observation period.
Grade 3-5 (severe or more serious) treatment-related adverse events occurred in 14.2% of patients receiving the combination and 13.4% of those receiving Keytruda alone. The companies reported no new safety concerns.
Moderna’s Rally Reverses as Analysts Cite High Expectations
Thursday’s decline interrupted a months-long rally that accelerated after Merck and Moderna announced in August that the trial had met its primary and key secondary endpoints without releasing detailed efficacy figures.
Despite the selloff, Moderna remained up approximately 587% in 2026. The stock closed about 20% below its 52-week high of $254.48, reached on Wednesday. Trading volume reached nearly 50 million shares on Thursday, more than three times the previous session’s volume of about 16 million.
Separately, Moderna Tokenized bStocks (MRNAB) was quoted at $191.91, down 20.67% over 24 hours, according to CoinMarketCap. The tokenized instrument trades separately from Moderna’s Nasdaq-listed shares, with its price change measured over a different period.
William Blair analyst Myles Minter viewed the trial results favorably but questioned whether the vaccine could deliver comparable effectiveness in other cancer types to justify Moderna’s valuation.
TD Cowen analysts described the 42% reduction in recurrence or death as compelling and within the range that medical experts consider exceptional, according to Reuters. However, Bloomberg cited TD Cowen analyst Tyler Van Buren as characterizing the distant-metastasis result as “less exceptional” than the recurrence benefit.
Fierce Biotech separately reported that the 38% reduction in distant metastasis or death fell short of expectations shaped by earlier Phase 2 findings. However, the trials involved different patient populations and follow-up periods, limiting direct comparisons.
Merck and Moderna said overall survival data remain immature, although the results show a favorable trend. The companies are discussing the findings with regulatory authorities, but the data have not yet established a definitive overall survival benefit.
The company will present the detailed results on Saturday, October 24, at the European Society for Medical Oncology Congress in Madrid. The findings have also been accepted for publication in The New England Journal of Medicine.