A personalized mRNA cancer vaccine developed by Moderna and Merck — when combined with the immunotherapy drug Keytruda — significantly reduced the risk of melanoma recurrence, new research shows.

The study found a 49% reduction in recurrence among patients with high-risk melanoma whose tumors had been surgically removed. The findings were presented at the 2026 American Society of Clinical Oncology annual meeting.

According to NYU Langone News, the experimental vaccine, called intismeran, is tailored to each patient using genetic information from their own tumor. Researchers identify tumor-specific mutations that produce abnormal proteins, known as neoantigens, and then design an mRNA vaccine to help the immune system’s T cells recognize and attack cancer cells carrying those markers.

In the phase 2b KEYNOTE-942 trial, researchers studied 157 patients with stage III or IV melanoma who had undergone surgery but remained at high risk for recurrence. Of those, 107 received the vaccine plus pembrolizumab (Keytruda), while 50 received pembrolizumab alone, the current standard treatment.

After five years, 68.8% of patients who received the combination therapy remained cancer-free, compared with 49.1% of those treated with pembrolizumab alone.

The combination therapy also reduced the risk of distant metastasis — the spread of cancer to other parts of the body — by 59%. Overall survival was 92.2% in the combination group, compared with 71.3% in the immunotherapy-only group.

Unlike traditional vaccines that prevent disease, this treatment is given after cancer is diagnosed and surgically removed. The goal is to help the immune system eliminate any remaining cancer cells. Pembrolizumab works by blocking a pathway that allows cancer cells to evade immune attack, while the vaccine helps direct the immune system toward specific tumor targets.

“Our study offers strong evidence to melanoma patients that intismeran vaccine therapy, when used in combination with immunotherapy, can demonstrably reduce their risk of having their cancer return and improve clinical outcomes,” said study senior investigator Dr. Janice Mehnert, M.D., a professor at NYU Grossman School of Medicine.

“Our findings also serve as encouragement to cancer researchers globally that mRNA vaccines like intismeran could work well in combination with immunotherapy for other cancers whose high rates of mutations have proven difficult to target,” added Mehnert, who is also director of the melanoma medical oncology program at Perlmutter Cancer Center.

Larger phase 3 trials are now underway to confirm these results and determine which patients are most likely to benefit. Researchers are also studying the personalized mRNA approach in other cancers, including lung, bladder, and kidney.