Most people know someone who has had a mole checked. The wait for a result can feel long. For patients with melanoma, the fear doesn't disappear once the tumor is removed. The cancer can return years later.
A large trial has now shown a way to lower that risk. A personalized mRNA vaccine from Merck and Moderna, added to standard immunotherapy, cut the risk of melanoma coming back or death by 42 percent compared with immunotherapy alone.
The result came from the phase 3 INTerpath-001 trial. It was presented at the European Society for Medical Oncology (ESMO) Congress 2026.
What a personalized vaccine actually means
Each dose is built for one single patient. Doctors first take a sample of the tumor and read its genetic code. A computer picks out the mutations that make the cancer look different from healthy cells. These markers are called neoantigens.
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A synthetic strand of mRNA is then built that codes for up to 34 of those markers. The shot teaches the immune system to recognize and attack cells carrying them. The vaccine, called intismeran autogene (also known as V940 or mRNA-4157), is still experimental.
It is paired with pembrolizumab, the active ingredient in Merck's immunotherapy drug Keytruda. Pembrolizumab removes a brake that cancer cells use to hide from the immune system. The vaccine points the immune cells at the right target. Keytruda helps keep them active.
What the trial actually tested
The INTerpath-001 trial enrolled 1,137 patients whose melanoma had been fully removed by surgery but who had a high risk of it coming back, according to AJMC. The disease ranged from stage 2B to stage 4.
Two out of three patients got the vaccine plus Keytruda. The rest got Keytruda plus a placebo. The vaccine was given once every three weeks for up to nine doses. Treatment ran for about a year.
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Patients were followed for a median of close to 25 months. By two years, roughly 8 in 10 patients on the combination were still cancer free. In the Keytruda-only group, 7 in 10 were.
The risk of the cancer spreading to distant parts of the body or of death fell by 38 percent in the combination group.
Principal investigator Georgina Long, medical director of Melanoma Institute Australia, called the results a potential foundational shift in how doctors treat earlier-stage melanoma.
Side effects and what the vaccine is not
The vaccine added some new side effects on top of Keytruda, but no new safety signals turned up. About half of patients had a fever and half had pain at the injection site. Nearly 4 in 10 felt fatigued.
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More serious side effects were only slightly more common with the combination. The rate was 14 percent, compared with 13 percent for Keytruda alone.
The vaccine is not approved yet. It is also not a prevention shot. The trial tested it only in people who had already been diagnosed and whose tumor had just been surgically removed. Merck and Moderna said they plan to engage with regulators about approval submissions.
Melanoma in the United States
In the United States, melanoma is one of the most serious forms of skin cancer. The American Cancer Society estimates about 112,000 new invasive melanomas will be diagnosed in 2026. Roughly 8,510 people are expected to die from the disease.
Death rates have fallen over the past decade as new immunotherapy drugs reached patients. Doctors say anyone with a mole that is new, changing or looks unusual should book a visit with a dermatologist.
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This article is made and published by Mie Hermansen, who may have used AI in the preparation.