Moderna and Merck said their personalized mRNA cancer vaccine reduced the risk of melanoma recurrence or death by 44% when paired with Keytruda, compared with Keytruda alone, in a phase 3 trial reported at ASCO 2026.

The vaccine, known as mRNA-4157, is designed to train the immune system to recognize unique markers in each patient’s tumor. Researchers said the result strengthens the case for individualized cancer immunotherapy, an area that has attracted intense attention from drugmakers and oncologists.

The latest data were measured after three years of follow-up, a period that offers a more meaningful look at whether the treatment can help keep the disease from returning. While the findings are encouraging, the companies will still need to navigate regulatory review before any broader use.

If confirmed in additional studies and real-world settings, the approach could mark an important step toward more precise cancer treatment. For patients with melanoma, a disease that can return aggressively, even a modest improvement in recurrence rates can have major consequences.