mRNA Cancer Vaccine Cuts Risk of Melanoma Returning by 42%
An experimental, personalized mRNA vaccine cut the risk of melanoma coming back by 42% when added to standard treatment, according to new results from a large study by Moderna and Merck.
Researchers say it is a major step forward for cancer vaccines, which have struggled for years to show they work. "The field has been looking for a win and I think this one is a big one," said Dr. Hussein Tawbi of MD Anderson Cancer Center in Houston, one of the study's researchers, according to The Associated Press.
What the Study Found
The late-stage trial included more than 1,100 people with high-risk melanoma, the deadliest form of skin cancer, that had been surgically removed. All of them received the immunotherapy drug Keytruda, which is standard follow-up care. They were randomly assigned to also get either the vaccine, called intismeran, or a placebo.
Two years after surgery, 82% of patients who got the vaccine were still free of cancer, compared with 70% of those who received Keytruda alone.
The vaccine combination also lowered the risk of the cancer spreading to distant parts of the body by 38%, according to AJMC. Data on overall survival is not yet mature, but the companies reported a favorable trend. The results have been accepted for publication in The New England Journal of Medicine and are being presented at a major European cancer meeting in Madrid.
How the Vaccine Works
Unlike traditional vaccines, intismeran is custom-made for each patient using the same mRNA technology behind COVID-19 vaccines.
Scientists analyze a patient's tumor to find gene mutations unique to that cancer. Those mutations create proteins called neoantigens, which should only show up if cancer cells start to grow again. The vaccine then trains the immune system to hunt down and attack cells carrying those markers.
Patients receive nine doses, given three weeks apart. While each dose takes only a few days to make, the full process, from analyzing the tumor to producing the finished vaccine, can take about six weeks or more.
Side effects were mostly a sore arm, fatigue and other reactions similar to what people experience after a COVID-19 shot. Fever and injection site pain were more common in patients who got the vaccine.
A Patient's Story
Tony Hout, 62, joined the trial at MD Anderson in 2024 after a spot on his ear that bled on and off and would not fully heal turned out to be melanoma. Surgery found it had already begun to spread.
Hout now lives in Cayuga, Indiana, and returns to Houston every few months for checkups. His latest scans showed he is still cancer-free. "I want to make sure I'm doing everything I can to be here for my family," he said.
If you have a mole or spot that is changing or will not heal, it is worth knowing the early signs of melanoma and checking with a doctor.
What Comes Next
Experts say the approach could reach far beyond melanoma. "It's a big step forward for science, for oncology, because this vaccine will apply to many different cancers," said Dr. Michael Atkins of Georgetown University's Lombardi Comprehensive Cancer Center. Merck and Moderna are already testing the vaccine against other cancers, including lung cancer.
"This is a new frontier," said Karen Knudsen, CEO of the Parker Institute.
The companies say they are talking with regulators about next steps, but they have not announced a timeline for approval or a price. That path could be uncertain. Earlier this year, the FDA refused to review Moderna's application for an mRNA flu vaccine.
Despite the strong results, Moderna's stock fell sharply after the full data were released. Some analysts said the 42% figure landed at the low end of what investors had hoped for after an earlier, smaller study, BioPharma Dive reported.
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