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A Personalized mRNA Vaccine Cut Melanoma’s Return By 42 Percent In The Largest Trial Yet

Moderna and Merck’s intismeran is brewed from each patient’s own tumor. Added to Keytruda after surgery, it left 82 percent of high-risk patients cancer-free at two years, against 70 percent on Keytruda alone.

By Davies Daily Staff Reports · Friday, October 23, 2026

A vaccine vial and syringe.
A vaccine vial and syringe. Photo: United States Census Bureau, public domain — file photo.

Moderna and Merck released the full results on Thursday of the most advanced study yet of a personalized cancer vaccine, the Associated Press reports — and the numbers are the strongest the field has produced. The vaccine, called intismeran, is custom-brewed from each patient’s own tumor. In a trial of more than 1,100 patients whose high-risk melanoma had been surgically removed, adding nine doses of it to the standard drug Keytruda cut the risk of the cancer returning, or of death, by 42 percent at two years; the risk of the disease spreading fell 38 percent. At the two-year mark, 82 percent of the vaccine group were alive without a recurrence, against 70 percent on Keytruda alone. The side effects were mainly a sore arm and fatigue.

The vaccine uses the same mRNA technology as the COVID-19 vaccines. Scientists sequence the mutations unique to a patient’s tumor and build a vaccine that teaches the immune system to attack the abnormal proteins — neoantigens — those mutations produce. The brewing itself takes days; the full process runs about six weeks.

“The field has been looking for a win and I think this one is a big one,” said Dr. Hussein Tawbi of MD Anderson, one of the study’s researchers. Karen Knudsen of the Parker Institute, who was not involved, called it “a new frontier.” The results were to be presented this Saturday at the ESMO cancer meeting in Madrid; they were released early, on Thursday, after a leak. The companies are now engaging regulators about approval.

The Facts

  • The result: recurrence-or-death risk down 42% at two years; disease-spread risk down 38% (AP; Reuters). 82% recurrence-free on vaccine + Keytruda vs. 70% on Keytruda alone.
  • The trial: more than 1,100 patients with high-risk, surgically removed melanoma; nine custom doses, three weeks apart.
  • The method: mRNA vaccine built from each tumor’s own mutations (neoantigens); full process about six weeks.
  • Next: results were set for Saturday’s ESMO meeting in Madrid and released early after a leak; the companies are engaging regulators on approval.

Sources: The Associated Press; Reuters.

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