JUNE 1, 2026

Five-year trial data show personalized mRNA melanoma vaccine significantly reduced recurrence and death risk

A Phase 2 clinical trial of 157 patients found that a personalized mRNA vaccine called intismeran, combined with the immunotherapy drug Keytruda, reduced the risk of melanoma recurrence by 49% compared to Keytruda alone after five years. The results were presented at the American Society of Clinical Oncology conference on June 1, 2026, and published in the Journal of Clinical Oncology. Moderna developed the vaccine in collaboration with Merck, the maker of Keytruda.

A personalized mRNA cancer vaccine developed by Moderna showed strong five-year results in a clinical trial targeting high-risk melanoma patients, according to a paper published Monday in the Journal of Clinical Oncology and presented at the American Society of Clinical Oncology annual conference.

The trial enrolled 157 patients in the United States and Australia who had surgery to remove melanoma tumors and faced a high risk of recurrence. After five years, 68.8% of patients who received the combination of intismeran and Keytruda remained cancer-free, compared with 49.1% of those who received Keytruda alone — a 49% reduction in recurrence risk, according to NPR's reporting. Survival rates also diverged: 92% of patients in the combination group were alive at five years, versus 71% in the Keytruda-only group.

The vaccine works by sequencing each patient's tumor to identify up to 34 unique molecular markers called neoantigens, which are then encoded into a custom mRNA vaccine. When injected, the vaccine trains the patient's T cells to recognize and attack those specific markers. Keytruda complements this by removing molecular "shields" that cancer cells use to hide from the immune system, according to NPR's description of the mechanism. Side effects reported in the trial were mild, including chills and minor injection-site pain.