MSD and Moderna reported full Phase III trial results for their personalised cancer vaccine, intismeran autogene, at the ESMO 2026 conference in Madrid, showing patients given the vaccine plus Keytruda had a 42% lower risk of death or recurrence than those on Keytruda alone at 24.6 months. The companies said in their presentation that they have begun discussions with regulatory authorities following the results.
The therapy is an mRNA-based vaccine jointly developed by the two companies for patients diagnosed with completely resected stage IIB-IV melanoma. Two years after treatment, 82% of combination-arm patients remained alive and free of returning melanoma, versus 70% in the Keytruda-only group, CNBC reported.
A separate analysis showed a 58% reduction in the risk of recurrence or death after the six-month vaccine regimen. Each dose is engineered to target mutations specific to an individual patient's tumour, teaching the immune system to identify and destroy those cancer markers while Keytruda amplifies that immune attack.
The full data were scheduled for the conference's first Presidential Symposium on 24 October but a leak forced their release two days ahead of that date. Details from the trial began circulating on X from unverified sources before the official release, with at least one account posting a report detailing the 42% figure. Merck confirmed the results came out early, Yahoo Finance reported.
Moderna shares fell as much as 26% following the announcement before closing down more than 17%, wiping more than $17 billion in market value from the company in what was described as the stock's worst day since 20 August. MSD closed down 2.5%.
BMO Capital Markets analyst Evan Seigerman wrote in a research note that the reduction in recurrence or death is clinically meaningful, and argued that the decline most likely reflects expectations that had been inflated before the full data release rather than any genuine failure of the combination's efficacy. UBS analysts wrote that the data set is overall strong and that it raises confidence in forthcoming vaccine studies in kidney and bladder cancers.
From mid-August to the before the leak, Moderna's stock had nearly quadrupled following the August announcement that the trial had met its primary goals, though the companies released no supporting detail at that time. Dr Dean Li, president of Merck Research Laboratories, said that even adding a therapy on top of something as effective as Keytruda, the combination had no difficulty demonstrating additional benefit, and acknowledged the companies have more work to do to show the product can work across tumour types.
Overall survival data are not yet mature, though there is a favourable trend in the combination group. No new safety signals were observed.
Melanoma patients with completely resected stage IIB-IV disease may gain access to a new adjuvant treatment option if regulators approve the combination, with Moderna's chief executive indicating a full regulatory filing is expected to be completed for submission next year. GlobalData predicts sales of the cancer vaccine will surpass $1 billion in 2031.
Reporting: Yahoo Finance, CNBC
Background: Yahoo Finance
Written by Pick & Scroll News from the reporting and documents linked above.
