Moderna's stock climbed more than 90% in premarket trading on Wednesday after the company and Merck announced that a Phase 3 trial of their personalized mRNA cancer treatment in melanoma had succeeded. Shares of Merck also rose about 7% before the market opened.

The outcome carries particular weight for Moderna, whose revenue has fallen sharply from its pandemic-era peak as demand for its COVID-19 vaccine declined, and which has been working to show that its mRNA platform can succeed beyond its COVID-19 and RSV shots.

The companies' INTerpath-001 trial announcement showed that intismeran autogene — a personalized mRNA cancer vaccine designed to teach the immune system to recognize and target a patient's tumor — delivered noteworthy improvements in both the time patients remained free of cancer and the time they remained free of cancer spread when combined with Merck's KEYTRUDA, Merck's top-selling immunotherapy and one of the world's best-selling medicines, with 2024 sales of roughly $29.5 billion.

At a planned interim analysis, the Phase 3 trial met its primary endpoint of improving recurrence-free survival as well as a key secondary endpoint of improving distant metastasis-free survival. The results were considered statistically significant and clinically meaningful among patients with completely removed stage IIB, IIC, III or IV melanoma who had not previously received systemic therapy. The trial will continue to track patients for additional outcomes, including overall survival.

Melanoma is the most serious form of skin cancer, with roughly 100,000 new cases diagnosed each year in the United States. Even after tumors are completely removed, patients at these stages face a substantial risk of the cancer returning, which is why post-surgery, or adjuvant, treatment is a central part of care.

The readout represents a major milestone for the technology, marking the first successful Phase 3 result for individualized neoantigen therapy and for an mRNA-based cancer treatment. It is also the first Phase 3 trial to demonstrate a meaningful benefit over KEYTRUDA alone for patients receiving treatment after melanoma surgery, according to the companies. KEYTRUDA monotherapy is itself an approved post-surgery option in melanoma, and no individualized neoantigen therapy has yet reached the market, so an approval would make intismeran the first treatment of its kind available to patients.

Intismeran autogene, also known as V940/mRNA-4157, is a cancer vaccine customized to each patient. Researchers identify mutations unique to the patient's tumor and use that information to develop an mRNA treatment intended to train the immune system to recognize those cancer cells and attack them. The treatment is being jointly developed by Moderna and Merck.

Moderna and Merck said they will present the full findings at an upcoming international medical meeting and engage with regulators on potential submissions for the combination. If the detailed data support the topline findings, the treatment could help establish personalized cancer vaccines as a new option for patients after surgery.

The latest results follow positive Phase 2b findings from KEYNOTE-942/mRNA-4157-P201. Five-year data presented at ASCO 2026 showed that the combination reduced the risk of cancer recurrence or death by 49% versus KEYTRUDA alone, and lowered the risk of distant cancer spread or death by 59%, providing earlier evidence for the Phase 3 program.

The companies are now testing intismeran in nine Phase 2 and Phase 3 trials across multiple cancers. The INTerpath program includes studies in melanoma, non-small cell lung cancer, bladder cancer and kidney cancer, with additional clinical work exploring pancreatic cancer, gastric cancer and different uses of the treatment in lung cancer.