Moderna and Merck say mRNA cancer vaccine succeeded in late-stage melanoma trial

STAT News – Wednesday, August 19, 2026
By Matthew Herper and Angus Chen

A personalized mRNA cancer vaccine, added to an existing treatment, slowed the return of melanoma and its spread to other parts of the body in a late-stage clinical trial, the drugmakers Merck and Moderna announced Wednesday, results that could herald a new, powerful approach in oncology.

So-called “neoantigen” vaccines have long been seen as having potential as cancer treatments, but this is the first randomized Phase 3 clinical trial aimed at definitively proving their benefit. In this case the personalized vaccine, intismeran, was combined with Merck’s Keytruda in adjuvant melanoma, meaning patients’ disease had been surgically removed.

If the results hold up — the drugmakers did not immediately release detailed data — they could deliver new hope and potentially longer lives for patients. They could also be a further testament to the power of mRNA as a platform to develop both traditional vaccines and therapeutics.

“I think this is really an important achievement,” said Jedd Wolchok, the director of the Meyer Cancer Center at Weill Cornell Medicine and an immunotherapy pioneer. “It tells us what might have been considered science fiction 15 or 20 years ago — that we can produce a personalized vaccine based on sequencing from a tumor from a pathology specimen — could be used to delay progression of melanoma.

“It really establishes personalized cancer vaccines as being a new addition to standard cancer therapy,” Wolchok said.

The long-awaited results come from a 1,137-participant trial in which patients were randomly assigned to receive either the cancer vaccine or a placebo; neither they nor their doctors knew who received the treatment. Merck and Moderna said the treatment extended both “recurrence-free survival” (RFS), which is how long patients live without melanoma coming back, and “distant metastasis-free survival” (DMFS), which is how long they go without new lesions appearing in parts of the body other than where the cancer started. The companies also said the results are “clinically meaningful.”This 2016 STAT video explains how cancer vaccines rally the immune system to identify and kill cancerous cells based on genetic information from the patient’s own tumors. Alex Hogan and Hyacinth Empinado/STAT

“While we need to await the final results, this early report is certainly promising and builds on the encouraging results that have been observed across smaller studies over the past decade,” said Catherine Wu, an oncologist at the Dana-Farber Cancer Institute. “It is highly conceivable that this treatment paradigm will be extendable to other cancers as well.”

Approval of the treatment would be a boon for Moderna’s mRNA platform, which has become a political lightning rod. Top officials in the Trump administration stopped funding a great deal of mRNA research but have also seemed open to the potential use of the technology in cancer vaccines. Still, Moderna no longer uses the term “vaccine” to describe its product in development but rather an individualized neoantigen therapy.

Investors have seen the Phase 3 results as pivotal to the future of Moderna, whose stock has struggled since the height of the pandemic, dropping more than 80%. Financial analysts estimate that an approved product could generate more than $6 billion in annual sales in melanoma alone, and much more should the same approach work in lung, kidney, and bladder cancer. 

Merck and Moderna said results would be made available at a future medical meeting. While pharmaceutical companies regularly release detailed information on clinical trial results in press releases, Merck has long insisted that all details be saved for formal publication and presentation.

In Phase 2 results presented at the annual meeting of the American Society of Clinical Oncology in June, the combination of intismeran and Keytruda resulted in a 49% reduction in the risk of disease recurrence and a 49% reduction in distant metastasis compared to Keytruda alone after patients had been followed for five years.

Merck and Moderna began working on cancer vaccines in 2016. Jane Healy, Merck’s head of early oncology development, remembers that the idea originated in the company’s use of DNA sequencing to look at all the mutations in tumors to predict whether Keytruda would be effective. What, they wondered, if that same data could be used to attack tumors on an individual basis?

“I have a picture on my whiteboard from June of 2015 when we drew up how we were going to do it,” said Stephen Hoge, Moderna’s president.

So scientists genetically sequenced patient tumors and then searched for unique mutations that the immune system might be able to use to tell cancer cells apart from healthy ones. Then, they built vaccines by training the immune system to recognize targets specific to patient tumors. That required custom manufacturing for each patient, though, and it wasn’t clear how well the approach would work.

“It’s an algorithm as much as it is a therapy,” Healy said.

“I thought the chances that this is going to work are actually pretty small,” Roger Perlmutter, who spearheaded research at Merck from 2011 to 2020, told STAT in an interview last year. “And there were a variety of fundamental immunological reasons why I thought that was true, but I thought it was important to be tested.”

One of the biggest challenges was developing the manufacturing ability to make every patient and individual mRNA therapy matched to their tumor quickly — in the trial it was done at a “needle to needle” time of six weeks. “The beauty of mRNA technology is the scalability and the adaptability. It lends itself really well to this setting,” Healy said.

Hoge noted that the very same manufacturing facilities developed to make these trials possible had allowed the company to quickly develop its vaccine for Covid-19. Now, he said, the company’s fully robotic manufacturing facility is ready to make enough doses of the cancer vaccine for commercial launch. Hoge said the companies hope to file with the Food and Drug Administration as quickly as possible — in months, not years.

While the Phase 3 trial showed the vaccine slowed the return of melanoma and its spread, it was stopped at the first of several planned interim analyses, meaning the question of whether it also extends overall survival remains unsettled, and could take years to determine.

One challenge in coming up with an answer is that melanoma drugs are now so effective that patients who progress in clinical trials often have another treatment option — meaning people in control groups live longer on existing therapies alone. But Hoge noted that in the earlier study of the therapy, the benefit to patients continued to improve, with what the companies called “an encouraging trend to overall survival.”

That represents a big new hope for patients — and a much-needed win for Merck and, in particular, Moderna.

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