On 19 August 2026, Moderna and Merck announced results showing that their personalized mRNA cancer vaccine, intesmeran, reduced the risk of melanoma recurrence and spread in a phase 3 clinical trial. This represents a major success in a new field of cancer treatment.

The companies tested the vaccine ⁠alongside Merck’s immunotherapy drug Keytruda (pembrolizumab), a PD-1 inhibitor used to treat many cancers and widely used for melanoma.

This post will review the clinical trial for the mRNA-based melanoma vaccine and its results.

About the melanoma mRNA vaccine

Melanoma, one of the deadliest forms of skin cancer, is characterized by the uncontrolled growth of pigment-producing cells. The rates of melanoma have been rising over the past few decades, with more than 330,000 new cases diagnosed worldwide in 2022. In the U.S., skin cancer is one of the most common types of cancer diagnosed, and melanoma accounts for a large majority of skin cancer deaths. It is estimated there will be about 112,000 new cases of melanoma diagnosed and over 8,500 deaths resulting from the disease in the U.S. in 2026 alone.

The intismeran (formerly V940 or mRNA-4157) vaccine approach aims to strengthen existing T-cell activity and create new antitumor T-cell responses. The vaccine can encode up to 34 personalized neoantigens encapsulated within a lipid nanoparticle and, for manufacturing, requires a 1 mm3 tumor sample from patients for neoantigen identification via next-generation sequencing.

The mRNA vaccine for melanoma is individualized; that is, each person receives an mRNA vaccine engineered to match their unique cancer cells. The mRNA melanoma vaccine developed for person X will probably not work in person Y.

I need to make an important point — cancer “vaccine” is a bit of a misnomer. These vaccines induce an immune response for treating melanoma, but they do not prevent the disease. Although we call them “vaccines,” they act more like immunotherapy.

This mRNA vaccine is individualized, meaning it codes for antigenic proteins on each person’s melanoma cells. Every person has slightly different antigens, even if they have the same cancer type. However, this vaccine may provide immunity to melanoma recurrence, so, in a sense, it is also preventative.

So, how does this “vaccine” work? The mRNA cancer vaccine trains the immune system to attack cancer cells missed by surgery or chemotherapy, or that have metastasized. But, and this is important, it probably would not affect another type of tumor. For example, this melanoma mRNA vaccine will probably be useless against colorectal cancer.

This new mRNA-based melanoma vaccine is given after surgery and during Keytruda chemotherapy.

Melanoma vaccine phase 3 clinical trial results

I have previously discussed the phase 2 clinical trial results, which were also positive. This phase 3 clinical trial enrolled 1,137 patients with resected stage IIB-IV high-risk melanoma. The double-blind, randomized trial compared patients who received Keytruda plus personalized intismeran versus patients who received Keytruda alone.

Here is the key result:

• Intismeran, in combination with Keytruda, as adjuvant therapy, showed statistically significant and clinically meaningful improvements in recurrence-free survival (RFS) and distant metastasis-free survival (DMFS) compared with Keytruda alone in patients with completely resected stage IIB, IIC, III, or IV cutaneous melanoma who had not previously received systemic therapy.
• The safety profiles of intismeran and Keytruda in this trial were consistent with those observed in previously reported studies for the combination. No new safety signals were observed.

Professor Georgina Long, the study’s principal investigator and medical director of Melanoma Institute Australia, Chair of Melanoma Medical Oncology and Translational Research at the University of Sydney, concluded:

Today’s results represent a landmark moment for adjuvant melanoma treatment. 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. Intismeran in combination with pembrolizumab has the potential to establish a new treatment paradigm in the adjuvant melanoma setting, helping patients remain cancer-free for longer.

Summary

This mRNA-based vaccine, intismeran, is a game-changer in the treatment and prevention of melanoma recurrence.

Despite HHS Secretary Robert F Kennedy Jr’s antipathy toward mRNA vaccines, research on the vaccines continues unabated. This vaccine, which can reduce the spread and recurrence of melanoma, is one of the great advances in cancer treatment.

If you’re wondering, mRNA vaccines are in development that may treat and prevent recurrence of pancreatic, lung, and colorectal cancers.

I think this is exciting research. But there are still large numbers of anti-vaxxers who make all kinds of specious claims about the “dangers” of mRNA vaccines based on no evidence whatsoever.

I wonder if an anti-vaccine activist who has stage IV melanoma will reject the melanoma vaccine just because it uses mRNA technology.

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