A personalized vaccine developed by Moderna Inc and Merck & Co reduced the recurrence of melanoma in a large, late-stage trial, raising expectations for treating the deadliest form of skin cancer and showing the promise of the embattled mRNA technology.

The trial met its main goal as the vaccine, combined with Merck’s immune drug Keytruda, prevented the cancer’s return after it was surgically removed more often than the immunotherapy alone. It also slowed the spread to new areas of the body, the companies said in a statement Wednesday.

Moderna shares spiked by a record 177 percent on Wednesday, though the stock remains well short of its Covid-era highs. Merck shares climbed nearly 13 percent.

The study, the first positive final-stage trial for any mRNA-based cancer therapy, is a welcome development for both companies. It provides the strongest evidence yet that the technology that made Moderna a household name during the pandemic will have a successful second act. For Merck, facing a patent loss for its best-selling drug Keytruda, it offers a key new market for future growth.

“It is an important step forward for the field of cancer immunotherapy, more specifically for cancer vaccines, which have had a long but relatively unsuccessful track record until now,” said Jedd Wolchok, a melanoma expert and director of the Meyer Cancer Center at Weill Cornell Medicine, in an email. It shows that training the immune system to recognize specific cancer targets can enhance the benefits of existing immune drugs, he said.

Details on how much the shot improved recurrence-free survival — the amount of time a patient lives without their cancer coming back — weren’t released. The trial is still underway to see if patients who get the vaccine live longer.

Melanoma is the most serious form of skin cancer. In the US, roughly 112,000 people are diagnosed and about 8,500 people die from it each year, according to the American Cancer Society.

The companies said they will discuss filing for approval with regulators and plan to present the data at an upcoming medical meeting. In an interview, Moderna Chief Executive Officer Stéphane Bancel said the personalized vaccine could be approved as soon as 2027.

“It is an extraordinary milestone for mRNA science,” Bancel said.

Key Questions

Still, questions remain about the cost and feasibility of producing such bespoke cancer treatments at scale. Keytruda alone can cost more than $200,000 a year for some cancers, depending on how it’s given. Other individualized therapies, such as CAR-T for blood cancers, can exceed half-a-million dollars, though the manufacturing and treatment approaches vary widely from how the melanoma shot would likely be given.

Companies don’t set the prices for new medicines until they clear clinical trials, with details typically given after approval.

Unlike many new cancer treatments, which are tried first in smaller groups of the sickest patients, the melanoma vaccine was given to people whose tumors could be completely removed during surgery, a larger patient pool.

To generate truly substantial sales, the vaccine will need to prove its benefit in tumor types beyond melanoma, analysts said. The worldwide market for all drugs to treat operable melanoma is about $2.3 billion a year now, Bloomberg Intelligence analyst Max Nisen said in an email.

“I am not sure this is a blockbuster indication on its own and if it ever gets there, it’ll be barely,” he said, speaking specifically about its use in melanoma. If it works in other tumor types, like lung cancer, sales could be much larger, he said.

Other analysts were more bullish. The fact that the trial generated favorable results months sooner than Wall Street expected “is a surprisingly positive development” and suggests that the efficacy seen so far in the trial “must have been compelling,” RBC analyst Trung Huynh wrote in a note to clients.

The findings are good news for patients with melanoma, which has long been considered one of the more difficult tumors to treat. The positive trial results come after the US Food and Drug Administration earlier this month approved Replimune Group Inc.’s Tudriqev for patients with advanced melanoma that had stopped responding to immune therapy.

The personalized Moderna-Merck shot works in a different way to stimulate the immune system. The two companies have been focused on the science behind the vaccine, called intismeran autogene, for more than a decade. Developed using the messenger RNA technology that powered Moderna’s Covid immunization, the companies customize the vaccines based on the patient’s specific tumor mutations.

Each one takes about six weeks to make. Scientists take a sample of the patient’s tumor, either from existing tissue or a new biopsy, and analyze it for mutations.

An algorithm identifies which are most likely to provoke an immune response, and as many as 34 of them are used to produce a personalized vaccine, said Jane Healy, head of oncology early development at Merck. During that waiting period, patients get Keytruda.

Study Design

In the trial, which enrolled more than 1,100 patients, the mRNA vaccine was given in combination with Keytruda after the tumors were surgically removed. A control group was given Keytruda alone, a standard treatment to prevent recurrence in patients at risk. The mRNA vaccine was given every three weeks for as many as nine doses, while patients got Keytruda every six weeks for as long as a year.

The goal is for the two drugs to work together to train the body’s immune system to attack any remaining cancer cells.

Moderna’s stock had shot up 113 percent from the beginning of the year through Tuesday’s close on the prospects of the cancer shot. The melanoma trial was seen as a crucial early test of how well the approach would work. Merck and Moderna are testing it in other types of cancer, including lung cancer, bladder cancer, and kidney cancer, but the melanoma studies are the furthest along.

Scientists have long chased the idea of a vaccine that could turn the body’s own defenses against cancer, teaching the immune system to recognize a tumor’s molecular fingerprints and destroy the cells that remain. But it’s proven very difficult.

“Therapeutic vaccines have been something of a holy grail in cancer. People have been trying to do this for, you know, over 100 years in one way or another,” Healy said in an interview before the results were released. One potential benefit of such a shot would be extending survival without adding many more side effects, she said.

The companies said earlier this year that skin cancer patients in a mid-stage trial who got the mRNA shot with Keytruda were 49 percent less likely to die or have their cancer return after five years than those who received Keytruda alone.