New vaccine slashes chance of melanoma patients’ tumors returning, study shows

A personalized mRNA cancer vaccine from Moderna and Merck reduced the risk of melanoma recurrence by 42% in a late-stage trial of over 1,100 high-risk patients. The vaccine, intismeran, is custom-made for each patient's tumor. Two years after surgery, 82% of vaccine recipients were cancer-free versus 70% on Keytruda alone. Side effects were mild. The results were presented at ESMO 2026. Moderna shares dropped 18% on the day of the full data release.

A personalized mRNA cancer vaccine developed by Moderna and Merck has shown a significant reduction in the risk of melanoma recurrence. In a late-stage study of over 1,100 patients with high-risk melanoma that was surgically removed, adding the custom vaccine to standard immunotherapy with Keytruda reduced the risk of the cancer returning by 42% two years after surgery. The vaccine, called intismeran, is made using the same mRNA technology as COVID-19 vaccines and is tailored to each patient's tumor by targeting specific genetic mutations. Two years after treatment, 82% of patients who received the vaccine were still cancer-free, compared to 70% who received only Keytruda. Side effects were mainly mild, including sore arm and fatigue. The results were presented at the European Society of Medical Oncology meeting in Madrid. Moderna and Merck are in discussions with regulators about next steps for approval. The vaccine is also being tested against other cancers, including lung, kidney, and pancreatic cancer. The article notes that Moderna's stock dropped 18% on the day of the full data release, though it remains significantly higher than before the initial results were announced in August.