Adding an experimental mRNA-based vaccine from Moderna Inc and Merck & Co reduced the risk that the most deadly skin cancer would spread by 65% over treatment with an immunotherapy alone in a midstage trial, the companies reported on Monday. The results, presented at the American Society of Clinical Oncology meeting in Chicago, follow earlier promising data from the trial showing the customized mRNA vaccine given in combination with Merck's Keytruda cut the risk of death or recurrence of melanoma by 44% compared with Keytruda alone. The findings add to a growing body of evidence suggesting that mRNA technology, which rose to prominence during the COVID-19 pandemic, can be used to assemble personalized vaccines that train the immune system to attack the specific type of cancer cells in a patient's tumors.