A pair of U.S. pharmaceutical companies announced Wednesday that an experimental personalized cancer vaccine showed positive initial results in a late-stage trial.

Moderna and Merck said the drug uses messenger RNA technology to prevent the recurrence of skin cancer.

“For many years, the idea of creating an mRNA treatment designed specifically for an individual patient’s cancer was aspirational,” Moderna CEO Stéphane Bancel said in a statement. “We are now helping turn that vision into a reality.”

The vaccine, known as intismeran autogene, is a customized treatment for individual patients that uses their own tumor tissue to train their immune systems to target and destroy specific cancer cells, the companies said. The vaccine is used to treat advanced and high-risk stages of melanoma that were completely removed through surgery but had a high chance of recurrence.

The companies said their late-stage trial using intismeran in combination with the Merck medication Keytruda met their primary goal of recurrence-free survival, as well as a secondary goal of a patient living without the cancer spreading to distant organs or far-away parts of the body.

On the market since 2014, Keytruda is an immunotherapy medication that is used to treat different types of cancer by helping the body’s immune system find and fight cancer cells.

The companies said the combination regimen of Keytruda and intismeran is the first and only treatment that demonstrates more meaningful improvements than taking Keytruda alone.

"These are very exciting results," Dr. Christina M. Annunziata, the American Cancer Society's senior vice president of extramural discovery, told Spectrum News in a statement. "The people who received the Intismeran mRNA vaccine with Keytruda had half the chance of their cancer recurring compared to those who received just the Keytruda alone.

"It is important to note that this clinical trial was focused on patients whose cancer was completely removed by surgery, and they had no visible cancer remaining at the start of treatment," she added. "This drug was not tested in people with active cancer visible on examination or imaging scans."

Messenger RNA vaccines were first available to the public when Pfizer and Moderna developed the COVID-19 vaccine in 2020. Scientists Drew Weissman and Katalin Kariko won the Nobel Prize for their research leading to the mRNA COVID vaccine. Earlier this month, the Food and Drug Administration approved the first mRNA flu shot for use this year.

Merck and Moderna are evaluating the new combination melanoma treatment through a program that is also evaluating its safety and efficacy for other tumor types and stages of disease, including non-small cell lung cancer, bladder cancer, renal cell carcinoma, pancreatic ductal adenocarcinoma and perioperative gastric carcinoma.

The melanoma study is ongoing to evaluate overall survival and other metrics.

Melanoma is one of the deadliest types of skin cancer. More than 90,000 new cases are diagnosed each year, and at least 8,000 people die from it, according to the U.S. Centers for Disease Control and Prevention. The CDC said the number of melanoma cases has doubled in 30 years.

The companies said their Phase 3 trial results build on earlier findings that the combination treatment demonstrated a 49% reduction in the risk of recurrence or death compared with Keytruda on its own.

Merck and Moderna plan to present the late-stage clinical trial results at an upcoming international medical meeting and to share it with regulatory authorities, they said.