Personalized melanoma vaccine cuts recurrence or death risk by 42%

By Tom Whitfield

A personalized melanoma vaccine reduced the composite risk of recurrence or death by 42% when added to pembrolizumab in an international study of 1,137 surgically treated patients. The study enrolled patients whose melanoma had been removed through surgery and who remained at risk of recurrence.

Melanoma is a skin cancer that can spread elsewhere in the body, and some tumors recur even after surgical removal. Researchers therefore tested whether adding a tumor-specific vaccine to an established immune treatment could reduce recurrence or death after surgery.

What did the international study compare?

Researchers at 157 sites worldwide compared patients who received the experimental vaccine, intismeran, alongside pembrolizumab with patients who received pembrolizumab alone. The combination produced the 42% reduction in the combined risk of recurrence or death.

Both groups received pembrolizumab, so the comparison isolated the added contribution of intismeran. The vaccine was intended to supply information about the patient’s cancer that the drug did not provide on its own.

For patients who remained free of cancer for more than six months after starting treatment, the risk of recurrence or death was 58% lower with the combination. These figures describe a composite outcome, rather than separate reductions in recurrence and mortality.

Professor Georgina Long, medical director at Melanoma Institute Australia, said: “These findings are a foundational shift in our approach to cancer: harnessing the immune system in a more personalised way to reduce the risk of melanoma recurrence or death.”

How did the vaccine work with pembrolizumab?

Intismeran was made to match each patient’s cancer. Researchers analyzed a sample of the removed tumor, identifying features that distinguish its cancer cells. That information helps the immune system recognize and attack cancer cells left behind after surgery.

Pembrolizumab already helps the body’s defense system attack cancer. Long described their roles: “Cancer can fool the immune system with a fake friendly handshake, so the immune system thinks the cancer cell is normal. Pembrolizumab blocks the handshake, allowing immune cells to recognise the cancer and attack it, but it is the same drug for everyone.”

The components addressed different parts of that process. Pembrolizumab unblocked immune recognition of cancer, while intismeran supplied tumor-specific information about the cells to target.

In combination, the vaccine helped immune cells identify residual cells from the removed cancer, while pembrolizumab helped the defense system attack them. The study did not test the vaccine without pembrolizumab.

What safety findings were reported?

Researchers said adding intismeran did not increase the side effects associated with pembrolizumab. Reported effects included:

• Temporary pain at the injection site
• Headaches
• Chills

These effects were generally mild. The reported combination therefore did not show a higher side-effect burden than pembrolizumab alone.

What does the result mean for other cancers?

Researchers said the findings could help guide development of similar treatments for other cancers. The study did not test that possibility outside melanoma; the combination was evaluated only in the melanoma cohort.

Moderna and MSD, known as Merck in the United States, are developing the treatment. It pairs a personalized vaccine with pembrolizumab, the same drug for every patient in this study.

When could the vaccine become available?

The vaccine is not yet available for routine treatment. It must undergo regulatory review before approval, and that process could take several years depending on the country.

Until that review is complete, intismeran remains investigational rather than routine postoperative melanoma care. The next milestone is country-by-country regulatory assessment; beyond melanoma, researchers can use the findings to design trials of similar personalized treatments, although their efficacy in other cancers remains unproven.