A novel mRNA cancer vaccine helps reduce the chances of melanoma
patients' tumors returning
[October 23, 2026]
By LAURAN NEERGAARD
WASHINGTON (AP) — A first-of-its-kind cancer vaccine is significantly
reducing the chances that melanoma patients’ tumors come back, according
to results of a major study released Thursday by drugmakers Moderna and
Merck.
The vaccine was custom-brewed for each patient to match their tumor.
Adding it to a standard post-surgery treatment reduced by 42% the risk
of melanoma returning two years after surgery, according to the most
advanced study to date of this new strategy for fighting cancer.
“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 researchers in the international study.
The vaccine, called intismeran, is made with the same Nobel
Prize-winning mRNA technology that was behind COVID-19 vaccines.
Experimental personalized cancer vaccines made with mRNA and some other
approaches also are being tested against other types of cancer including
lung, kidney and pancreatic.
Experts not involved with the new study say its success bolsters the
field.
“This is a new frontier,” said Karen Knudsen, CEO of the Parker
Institute, which helps fund cancer immunotherapy research.
“It’s a big step forward for science, for oncology, because this vaccine
will apply to many different cancers,” said Dr. Michael Atkins, deputy
director of Georgetown University’s Lombardi Comprehensive Cancer
Center.
Moderna and Merck had announced in August that the late-stage trial of
intismeran was successful but the detailed results were set to be
released Saturday at a meeting of the European Society of Medical
Oncology in Madrid. Some of the data was leaked publicly late Thursday,
prompting a full release ahead of the weekend's scientific presentation.
Most people think of vaccines as preventing an infection, like measles
or whooping cough. There are already two cancer-preventing vaccines, the
HPV and hepatitis B shots that block infection from those tumor-causing
viruses. And research is underway to prevent some types of inherited
cancer such as Lynch syndrome-caused colorectal cancer.
But a personalized vaccine designed to block surgically-removed cancer
from returning is very different. For the intismeran study, scientists
hunted gene mutations unique to each patient’s tumor, mutations that
create proteins which shouldn’t be in the body unless those cancer cells
start to grow again. The custom vaccine — nine doses given three weeks
apart — teaches the patient’s immune system to watch out for and attack
those so-called neoantigens.
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In this image made from video, Tony Hout, left, talks with Dr.
Hussein Tawbi at UT MD Anderson Cancer Center in Houston, Monday,
Oct. 19, 2026. (AP Photo/Lekan Oyekanmi)
 How did it work? The study included
more than 1,100 people with high-risk melanoma that was surgically
removed. Everyone was given the standard follow-up therapy: Merck’s
immunotherapy named Keytruda. The participants were randomly
assigned to also receive custom-brewed vaccine doses or a placebo.
Two years later, 82% of the people in the vaccine group were still
living without a recurrence of their cancer compared to 70% who had
gotten standard Keytruda alone. The trial is continuing to track
participants’ longer-term outcomes.
In 2024, Tony Hout joined the vaccine trial at MD Anderson after
seeking care for a spot on his ear that had been bleeding
intermittently and wouldn’t fully heal. Doctors recognized melanoma
and during surgery discovered it had started to spread.
“I want to make sure I’m doing everything I can to be here for my
family,” said Hout, 62, who has since moved to Cayuga, Indiana, and
travels back to Houston every few months for a study check-up. Scans
this week showed he’s still cancer-free.
The vaccine’s side effects were mainly the sore arm, fatigue and
other reactions typical of mRNA coronavirus vaccination, MD
Anderson's Tawbi said.
Moderna and Merck are talking with regulatory authorities about next
steps for seeking approval of the vaccine.
Customized medicines generally are very expensive. The drugmakers
aren’t discussing what such a cancer vaccine might cost.
But Moderna President Stephen Hoge said the company’s special cancer
vaccine manufacturing facility in Massachusetts is providing doses
for thousands of people enrolled in multiple studies underway
internationally.
Hoge said it takes a few days to brew the vaccine but the whole
process, starting with analyzing the tumor genetics to come up with
what is essentially a recipe for each patient, can take roughly six
weeks, sometimes more. Meanwhile, the melanoma patients had already
started their standard Keytruda, a different kind of immunotherapy.
Moderna shares dropped 18% Thursday after the study’s full results
were made public, but they remained more than 200% higher than they
were in late August before investors were first told of the initial
results.
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