A first-of-its-kind cancer vaccine is significantly reducing the chances that melanoma patients’ tumors come back, according to results of a major study released Thursday by drugmakers Moderna and Merck .

The vaccine was custom-brewed for each patient to match their tumor. Adding it to a standard post-surgery treatment reduced by 42% the risk of melanoma returning two years after surgery, according to the most advanced study to date of this new strategy for fighting cancer.

“The field has been looking for a win and I think this one is a big one,” said Dr. Hussein Tawbi of MD Anderson Cancer Center in Houston , one of the researchers in the international study.

The vaccine, called intismeran, is made with the same Nobel Prize-winning mRNA technology that was behind COVID-19 vaccines.…