A new personalized mRNA vaccine for melanoma is being hailed by some oncologists as a major breakthrough after it reduced the risk of cancer recurrence and death by 42% compared with standard treatment in a late-stage clinical trial.

Dr. Robert Vonderheide, director of Penn Medicine’s Abramson Cancer Center and president-elect of the American Association for Cancer Research, said the results are a “game changer.”

“It will be seen as the first step toward using cancer vaccines to their full potential,” said Vonderheide, who was not involved in the trial.

The experimental vaccine, called intismeran, was developed by drugmakers Moderna and Merck. Intismeran is personalized to each patient, using genomic data from the patient’s tumor. The new results will be presented Saturday at the annual meeting of the European Society for Medical Oncology in Madrid.

The trial included 1,137 Stage 3 melanoma patients.…