Moderna melanoma mRNA vaccine shows benefit in Phase 3 trial

Moderna and Merck reported positive results from a Phase 3 clinical trial testing an experimental personalized mRNA vaccine for advanced melanoma. The study enrolled more than 1,100 patients whose tumors had been surgically removed but who remained at high risk of recurrence.

Each vaccine dose was manufactured from a sample of the patient's own tumor. Researchers sequenced the tumor to identify its unique mutations and used artificial intelligence to select which mutations to encode in the synthetic mRNA.

The vaccine was given in combination with Keytruda (pembrolizumab), Merck's approved PD-1 inhibitor. Keytruda blocks a pathway that tumors use to evade immune detection, while the mRNA vaccine instructs the patient's cells to produce tumor-specific proteins that train the immune system to recognize and attack residual cancer cells.

Patients who received the vaccine plus Keytruda experienced a statistically significant and clinically meaningful improvement in recurrence-free survival compared with those who received Keytruda alone. The companies described the finding as a landmark moment for mRNA cancer vaccines.

Melanoma is the fifth most commonly diagnosed cancer in the United States, with approximately 112,000 new cases each year. The American Cancer Society estimates about 8,500 U.S. deaths from melanoma in 2026.

The Phase 3 trial represents the final stage of clinical testing before the companies can submit data to the Food and Drug Administration for regulatory review. No approval decision has been announced.

Researchers emphasized that the vaccine is personalized for each patient, which adds manufacturing complexity. Long-term follow-up data on overall survival and durability of response are still being collected.

Moderna's stock price more than doubled following the announcement, reflecting investor enthusiasm for the mRNA platform's expansion beyond infectious disease.