Moderna and Merck's mRNA cancer vaccine reduces melanoma recurrence in late-stage trial

An experimental personalized mRNA cancer vaccine developed by Moderna and Merck, known as Intismeran, successfully met its primary and secondary goals in a Phase 3 trial of 1,137 high-risk melanoma patients. Combined with Merck's immunotherapy Keytruda, the custom-made vaccine significantly reduced the risk of cancer recurrence and slowed its spread to distant organs. Following the landmark announcement on August 19, 2026, Moderna's stock soared 90% as the companies prepare to discuss regulatory approval with officials, aiming for a potential market launch by 2027.

Intismeran phase three trial results

• ▪The Phase 3 clinical trial of the personalized cancer vaccine, known as Intismeran, enrolled 1,137 high-risk patients with stage IIB-IV melanoma whose tumors had been completely removed through surgery.
• ▪Volunteers in the Phase 3 trial were randomized to receive either up to nine doses of Keytruda plus the personalized vaccine, or Keytruda alone, for approximately one year.
• ▪An experimental personalized mRNA cancer vaccine developed by Moderna and Merck met its primary goal of significantly extending the time patients lived without their melanoma returning in a Phase 3 trial.

mRNA cancer vaccine mechanism

• ▪The personalized mRNA cancer vaccine, Intismeran, is designed to target specific mutations in each patient's unique tumor rather than using a one-size-fits-all approach.
• ▪Moderna CEO Stephane Bancel stated that the vaccine does not use patients' own cells, which could allow the manufacturing process to be scaled and the price reduced.
• ▪The vaccine trains the patient's immune system to recognize and kill unique cancer markers, and is paired with Merck's Keytruda to help the body attack the cancer more effectively.

Melanoma recurrence reduction

• ▪The combination of the personalized mRNA vaccine and Keytruda reduced the risk of melanoma recurrence compared to using Keytruda alone in patients whose cancer had been surgically removed.
• ▪In a preceding mid-stage trial, the combination of the personalized vaccine and Keytruda reduced the risk of melanoma recurrence or death by 49% after five years.

Metastasis prevention outcomes

• ▪The combination regimen of the personalized mRNA vaccine and Keytruda met its key secondary study goal of slowing or preventing the cancer from spreading to distant parts of the body.
• ▪The ongoing Phase 3 study will continue to assess other clinical outcomes, including the overall survival benefit of the combination regimen.

Moderna Merck stock surge

• ▪Following the announcement of the trial results on August 19, 2026, Moderna's stock soared approximately 90% in premarket trading.
• ▪Merck shares rose between 7.5% and 8% in premarket trading on August 19, 2026, following the release of the interim clinical trial data.

Regulatory approval pathway

• ▪Dr. Dean Li, president of Merck Research Laboratories, stated that the drugmakers plan to begin discussions with regulatory agencies about the treatment and its safety in the next few months.
• ▪Moderna hopes to have the personalized mRNA cancer vaccine on the market by the year 2027.

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