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Moderna reports positive Phase 3 results for experimental melanoma vaccine

Moderna reported that its Phase 3 trial for a personalized mRNA melanoma vaccine, used with Merck's Keytruda, helped keep patients cancer-free longer.

Published August 19, 2026 at 10:35 PM EDT

The short answer

Moderna reported that its Phase 3 trial for a personalized mRNA melanoma vaccine, used with Merck's Keytruda, helped keep patients cancer-free longer. Moderna and its partner Merck reported that a Phase 3 clinical trial for an experimental mRNA melanoma vaccine showed a statistically significant improvement in keeping patients cancer-free. The trial involved more than 1,100 participants with advanced-stage melanoma.

Moderna reports positive Phase 3 results for experimental melanoma vaccine

The Facts

Who
Moderna, Merck, and more than 1,100 clinical trial participants.
What
Moderna and Merck announced that a Phase 3 trial of an experimental mRNA melanoma vaccine, combined with the drug Keytruda, showed a statistically significant improvement in helping advanced melanoma patients remain cancer-free.
When
Wednesday morning (stock price reaction); other dates not reported
Where
United States
Why
Melanoma is the fifth most common cancer in the U.S., causing an estimated 8,500 deaths annually; this personalized vaccine marks a potential new application for mRNA technology in cancer treatment.

Moderna and its partner Merck reported that a Phase 3 clinical trial for an experimental mRNA melanoma vaccine showed a statistically significant improvement in keeping patients cancer-free. The trial involved more than 1,100 participants with advanced-stage melanoma. Following the announcement, Moderna's stock value more than doubled on a Wednesday morning.

The treatment process involves removing a piece of a patient's tumor to identify unique genetic mutations. Scientists use artificial intelligence to determine which mutations to include in a personalized vaccine. This synthetic mRNA is then injected into the patient, where it instructs cells to build a protein that trains the immune system to recognize and attack melanoma cells.

In the clinical trial, all participants had their tumors surgically removed and received Keytruda, a standard immunotherapy drug produced by Merck. A portion of the group also received the experimental mRNA vaccine. The results indicated that the group receiving the combination of the vaccine and Keytruda remained cancer-free for a longer period compared to those who did not receive the vaccine.

A patient would experience this treatment as a multi-step medical process: first undergoing surgery to harvest tumor tissue, followed by a waiting period while artificial intelligence and scientists manufacture a custom vaccine specific to their tumor's genetic sequence. The vaccine is designed to work alongside existing drugs like Keytruda, which functions by removing the "cloak of invisibility" cancer uses to hide from the immune system. If successful, this could change the day-to-day management of advanced skin cancer from standard immunotherapy to a combination of immunotherapy and personalized mRNA shots.

The success of this Phase 3 trial establishes a precedent for using mRNA technology—previously best known for its role in COVID-19 vaccines—to treat non-infectious diseases like cancer. This could influence future federal policy regarding how personalized medicines are approved and regulated. The next step for the vaccine is a formal review by the Food and Drug Administration (FDA), which is the final regulatory hurdle before the treatment can be made commercially available to the public. A specific date for the FDA review was not reported.

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Questions readers ask

What happened: Moderna reports positive Phase 3 results for experimental melanoma vaccine?

Moderna and Merck announced that a Phase 3 trial of an experimental mRNA melanoma vaccine, combined with the drug Keytruda, showed a statistically significant improvement in helping advanced melanoma patients remain cancer-free.

Who is involved?

Moderna, Merck, and more than 1,100 clinical trial participants.

When did this happen?

Wednesday morning (stock price reaction); other dates not reported

Where did this happen?

United States

Why does this matter?

Melanoma is the fifth most common cancer in the U.S., causing an estimated 8,500 deaths annually; this personalized vaccine marks a potential new application for mRNA technology in cancer treatment.