Moderna and Merck mRNA Cancer Vaccine Meets Goals in Phase 3 Melanoma Trial

Moderna and Merck reported on August 19, 2026, that their personalized mRNA cancer vaccine met its goals in a large Phase 3 clinical trial for melanoma, marking the first successful late-stage study for an individualized neoantigen cancer vaccine.

The vaccine, called intismeran (also known as mRNA-4157), was tested in combination with Merck's immunotherapy Keytruda. The combination reduced the risk of cancer recurrence or spread by 49 percent compared to patients who received Keytruda alone.

The trial enrolled 1,137 patients with surgically removed stage IIB-IV melanoma. Participants were split in a 2:1 ratio, with the larger group receiving both intismeran and Keytruda and the smaller group receiving Keytruda with a placebo. Both groups were treated for approximately one year in a double-blind study.

The combination met its primary goal of extending recurrence-free survival and its secondary endpoint of distant metastasis-free survival. The companies described the improvements as statistically significant and clinically meaningful.

Intismeran works by identifying up to 34 unique mutations in a patient's tumor and using mRNA technology to encode those mutations into a vaccine. This trains the immune system to recognize and attack tumor cells. Keytruda, an established checkpoint inhibitor, enhances that immune response.

Moderna and Merck plan to present the full data at an upcoming international medical conference. They also intend to begin discussions with regulatory agencies about potential approval of the combination treatment.

Beyond melanoma, the companies are studying the vaccine in non-small cell lung cancer, bladder cancer, and renal cell carcinoma.