Breakthrough Phase 3: Personalized mRNA Vaccine Plus Keytruda Cuts Melanoma Recurrence

Moderna and Merck on Wednesday reported that their personalized mRNA cancer vaccine, intismeran autogene, when given with Merck's anti‑PD‑1 immunotherapy Keytruda (pembrolizumab), met the primary endpoint and a key secondary endpoint in the pivotal Phase 3 INTerpath‑001 trial for patients with completely resected high‑risk melanoma. The companies said this is the first positive Phase 3 result for an individualized neoantigen therapy and the first positive Phase 3 outcome for any mRNA‑based cancer treatment.

The randomized INTerpath‑001 study enrolled 1,137 patients with stage IIB–IV cutaneous melanoma after complete surgical resection. Participants received either intismeran plus Keytruda or Keytruda alone. According to the companies, the combination produced statistically significant and clinically meaningful improvements in recurrence‑free survival (the trial’s primary endpoint) and in distant metastasis‑free survival (a key secondary endpoint) versus Keytruda monotherapy. The trial will continue to follow patients to evaluate overall survival.

Intismeran is manufactured from each patient’s tumor sample: the tumor’s mutational profile is analyzed and a synthetic mRNA is created to encode up to 34 patient‑specific neoantigens. The personalized vaccine is designed to prime the immune system to recognize those tumor markers and enhance the anti‑tumor activity of Keytruda.

"This is the first Phase 3 study to show that intismeran, a treatment designed based on the unique mutational 'fingerprint' of a patient's own tumor, given in combination with pembrolizumab can reduce the risk of recurrence or death in patients with completely resected stage IIB‑IV melanoma compared to KEYTRUDA alone," said Professor Georgina Long, the study's principal investigator and Medical Director of Melanoma Institute Australia.

The companies reported no new safety signals and said adverse events were consistent with prior studies of the combination. These Phase 3 results build on five‑year follow‑up data from a Phase 2b trial presented at the 2026 ASCO Annual Meeting, where the combination demonstrated a 49% reduction in the risk of recurrence or death versus Keytruda alone.

Merck and Moderna plan to present the full dataset at an upcoming international medical conference and will engage regulatory authorities regarding potential approval filings. Intismeran is also being evaluated in nine additional Phase 2 and Phase 3 trials across other tumor types, including non‑small cell lung cancer, bladder cancer and renal cell carcinoma.

Financial markets reacted to the announcement: Moderna shares rose more than 10% in premarket trading and Merck shares gained over 1%. The companies cited U.S. projections for 2026 estimating roughly 112,000 new melanoma cases and more than 8,500 deaths. Keytruda remains a major product for Merck, generating $8.03 billion in sales in the first quarter of 2026.