Phase 3 trial results released on October 22, 2026 show that Moderna and Merck's personalized mRNA cancer vaccine Intismeran, combined with Keytruda, cut the risk of death or melanoma recurrence by 42% and disease spread by 38% compared to Keytruda alone. Despite strong clinical efficacy in preventing recurrence post-surgery, Moderna shares fell up to 25% following an online data leak as results met but failed to exceed elevated Wall Street expectations.
Phase 3 trial efficacy results
- ▪A phase 3 trial released on October 22, 2026 showed that combining Intismeran with Keytruda reduced the risk of melanoma spreading or metastasizing across the body by 38% over two years compared to Keytruda alone
- ▪A phase 3 clinical trial involving 1,137 melanoma patients demonstrated that Intismeran combined with Keytruda reduced the risk of death or disease recurrence by 42% compared to Keytruda alone
- ▪Six months after starting treatment with Intismeran and Keytruda, the combination reduced the risk of melanoma recurrence or death by 58% compared to Keytruda alone
- ▪Two years after treatment in a phase 3 trial released on October 22, 2026, 82.2% of melanoma patients receiving Intismeran with Keytruda remained cancer-free, compared to 70% receiving Keytruda alone
How Intismeran works and is administered
- ▪Intismeran is administered in nine doses starting 13 weeks after surgical removal of melanoma lesions, alongside Merck's immunotherapy drug Keytruda
- ▪Intismeran is an experimental personalized mRNA cancer vaccine that uses genetic sequencing of a patient's surgically removed tumor to train the immune system to target cancer cell neoantigens
- ▪Intismeran is designed for post-surgery melanoma patients to prevent cancer from returning or spreading, rather than preventing initial melanoma development
Trial monitoring and safety
- ▪Trial leader Georgina Long stated that participants in the Intismeran trial have been monitored for approximately 25 months and will continue long-term follow-up to evaluate overall survival impacts
- ▪Trial leader Georgina Long stated that the combination therapy of Intismeran and pembrolizumab did not cause any major harmful side effects among participants
Trial disclosures and leaks
- ▪Moderna and Merck announced in August 2026 that the Intismeran and Keytruda combination therapy had succeeded, but they did not provide detailed trial results at that time
- ▪Moderna and Merck released phase 3 trial results for Intismeran on October 22, 2026 after the data leaked online ahead of a planned presentation at the European Society for Medical Oncology meeting in Madrid on October 24, 2026
Stock market reaction to results
- ▪Moderna shares fell between 18% and 25% on October 22, 2026 after leaked phase 3 trial data for Intismeran failed to surpass elevated Wall Street expectations, despite stock gains since August 2026
- ▪BMO Capital Markets analyst Evan Seigerman stated that Moderna's stock price drop reflected inflated market expectations rather than a true indictment of the Intismeran and Keytruda combination therapy's efficacy
Regulatory approval and healthcare adoption
- ▪Moderna and Merck stated on October 22, 2026 that they are engaging with regulatory authorities and expect to file for approval of their melanoma vaccine Intismeran in 2027
- ▪Widespread NHS adoption of Intismeran will depend on cost, as each patient requires individual tumor genetic analysis and custom vaccine manufacturing
Testing in other cancer types
- ▪Independent cancer researchers noted that while the Intismeran melanoma trial provides a proof of principle, efficacy cannot be assumed across other cancer types without longer-term follow-up
- ▪Moderna and Merck are testing the Intismeran personalized mRNA vaccine approach in clinical trials for other solid tumors, including kidney, bladder, and lung cancer
Melanoma survival and patient selection
- ▪Oncologist Georgina Long stated that her team will conduct a statistical analysis to determine which patients are most likely to benefit from the Intismeran and Keytruda treatment
- ▪Oncologist Georgina Long noted that nearly 55% of people with advanced melanoma are now cured with targeted drugs or immunotherapies, compared to survival measured in months 15 years ago
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