mRNA vaccine cuts melanoma recurrence risk in Keytruda trial

A personalized mRNA vaccine has now posted its strongest evidence yet in melanoma, cutting the risk of recurrence or death by 49% when paired with Keytruda in a phase 2b trial of patients who had already undergone complete surgery for high-risk stage III or IV cutaneous melanoma.

The treatment, known as mRNA-4157 and later called V940 and intismeran autogene, was tested in KEYNOTE-942, also identified as mRNA-4157-P201. In the randomized study, patients received the vaccine plus pembrolizumab, sold as Keytruda, or pembrolizumab alone. The companies first reported in December 2022 that the combination had met its primary efficacy endpoint, and subsequent updates have shown that the benefit persisted rather than fading with time.

The latest five-year update, announced on Jan. 20, 2026, showed a continued 49% reduction in recurrence or death, with a hazard ratio of 0.510 and a 95% confidence interval of 0.294 to 0.887. A June 3, 2024 analysis had already reported a 49% reduction in recurrence or death and a 62% reduction in distant metastasis or death, along with a 2.5-year recurrence-free survival rate of 74.8% for the combination versus 55.6% for Keytruda alone.

That durability matters because melanoma can return even after surgery and checkpoint inhibitor treatment, especially in patients with the highest-risk disease. The trial enrolled 157 patients in the key randomized analysis, while ClinicalTrials.gov lists 267 actual participants overall. The study began on July 18, 2019.

Safety findings have so far looked manageable, though not trivial. Fatigue was the most common grade 3 adverse event, and there were no grade 4 or 5 vaccine-related events. Immune-related adverse events were similar across treatment groups, but grade 3 or higher treatment-related adverse events were higher with the combination than with pembrolizumab alone.

The Food and Drug Administration granted breakthrough therapy designation to the vaccine-Keytruda combination in February 2023, signaling that regulators saw a substantial improvement over existing therapy. The Lancet concluded that adjuvant mRNA-4157 plus pembrolizumab prolonged recurrence-free survival versus pembrolizumab alone and showed a manageable safety profile.

For Moderna, based in Cambridge, Massachusetts, and Merck, based in Rahway, New Jersey, the result is more than another oncology data point. It is an early test of whether mRNA can become a mainstream cancer platform, not just a pandemic technology. The bigger questions now are how quickly a personalized vaccine can be manufactured, what it will cost, and whether a therapy built for individual tumors can move beyond elite cancer centers to routine care.