Leaked data sank Moderna's shares despite a promising melanoma result
By Sveva Romano, Carlota Guillamet de Gracia, Lola Theato, Emily Sadaoui · Pharmaceuticals, Biotech & Life Sciences desk
What happened
Moderna’s (MRNA) shares fell by nearly 25% on Thursday after Phase 3 trial data for its melanoma vaccine was leaked on social media ahead of its scheduled ESMO presentation [1]. Moderna’s vaccine, intismeran autogene, uses mRNA to train each patient’s immune system to recognise their own tumour. Combined with Merck’s (MRK) immunotherapy Keytruda, it cut the risk of recurrence or death by 42% compared with Keytruda alone (hazard ratio 0.58) in a trial of 1,137 patients with surgically removed melanoma [2]. Clinically, this is a significant success. However, investors were anchored to earlier Phase 2 results, driving inflated expectations that were reflected in a 177% rise in Moderna’s share price [3]. This sell-off erased around $24bn from Moderna’s market value [4].
What people are missing
Unlike traditional vaccines, which help the body fight infections, intismeran autogene is designed to help the immune system recognise and attack a patient’s own cancer cells [5]. Each vaccine is tailored to the individual patient by identifying specific changes in their tumour and using mRNA instructions to teach the immune system what to look for [5]. It is given alongside Merck’s Keytruda, which helps the immune system keep attacking cancer cells rather than switching off its response [5]. The Phase 3 trial results showed that the combination reduced the risk of melanoma returning or the patient dying by 42% compared with Keytruda alone, while also reducing the risk of cancer spreading (metastasising) to distant parts of the body, or death, by 38% [1][2][5]. However, this does not mean patients were 42% more likely to remain cancer-free, and the study has not yet shown whether the treatment helps patients live longer, as the overall survival data are still incomplete [1][5].
Why it matters
The share moves reflected investor expectations rather than trial results, because in practice this marks the first time an mRNA-based treatment built from a patient’s own tumour has succeeded in a large final-stage trial [6]. Earlier vaccines tested in the same pool of melanoma patients and in the same setting have previously failed to perform better than placebo [7], which is why Moderna and Merck’s results were so highly anticipated before the leak. How many patients eventually benefit will depend on whether each personal batch can be made quickly and affordably enough, a concern experts have already raised [8].
What we are watching next
We are watching for the release of the full peer-reviewed data, as the companies have announced that the results have been accepted for publication in the New England Journal of Medicine [6]. Beyond that, the fate of the treatment is in the hands of US and European regulators: while it has been granted Breakthrough Therapy designation by the FDA [9] and PRIME designation by the EMA [10], neither status guarantees approval, so we will be watching how the filings play out.
Sources
- FierceBiotech — Merck & Co and Moderna Post Phase 3 Cancer Vaccine Data Early
- Reuters — Merck/Moderna Cancer Vaccine Cuts Melanoma Death or Recurrence Risk by 42%, Shares Fall (22 October 2026)
- Yahoo Finance — Moderna’s 177% Surge Has Investors Asking What Comes Next
- Reuters — Moderna Sheds About $24 Billion as Cancer Vaccine Data Triggers ‘Sell-the-News’ Retreat (22 October 2026)
- AJMC — Merck, Moderna Cancer Vaccine Cuts Melanoma Recurrence Risk by 42%
- Merck & Moderna — Joint Press Release: Results From Landmark Phase 3 INTerpath-001 Trial for Intismeran Autogene Plus KEYTRUDA (pembrolizumab)
- The Lancet Oncology — Trial Results
- Life Science Daily — Intismeran Autogene Phase 3 Melanoma
- Clinical Trials Arena — MSD, Moderna Intismeran Autogene Cancer Vaccine Melanoma
- Pearce IP — MSD, Moderna Announce mRNA-4157 (V940) + Keytruda Receives EMA PRIME Scheme Designation
Meridian62 notes explain what is happening and why. They are not investment advice and do not recommend buying or selling anything. Read the disclaimer.