Melanoma is the most dangerous type of skin cancer, and these initial late-stage results from Moderna and Merck suggest the two companies' approach could become another option for patients who have already had their detectable disease removed.
On Wednesday, the partners said their jointly developed mRNA shot had produced encouraging early results in the first Phase 3 trial of a personalized cancer vaccine. The shot, given alongside Keytruda, hit the study's main goals in more than 1,100 people at high risk or with advanced melanoma who had gone through surgery to remove all noticeable cancer.
The combination also made it less likely the cancer would spread to other parts of the body. This outcome follows earlier positive Phase 2 results for the same combination reported earlier this year.
"It's a big moment for medicine, a big moment for patients," Moderna CEO Stephane Bancel said during an appearance on CNBC's "Squawk Box."
Investors reacted immediately. Moderna's stock soared more than 120% in morning trading, while Merck's shares climbed more than 10%. The different sizes of those moves partly reflected the two companies' market values before the news: Merck was worth about $333 billion, while Moderna was valued at roughly $25 billion.
This trial is the first late-stage test of a personalized mRNA cancer vaccine. The vaccine is built on mRNA and is customized for each patient, while Keytruda is an established immunotherapy. The study included people who had their melanoma surgically removed but remained at elevated risk for the disease returning.
Because all detectable tumor tissue was already removed, the treatment is being tested as an adjuvant therapy, designed to be given after surgery to help prevent the disease from coming back. By combining the two, researchers hope to give patients more powerful protection against the cancer returning.
Adjuvant therapies are given after initial treatment to reduce the risk of recurrence, and this approach has become a key area of research in oncology. The success of this trial could pave the way for similar personalized vaccines in other cancer types. The rationale is straightforward: after the primary tumor is removed, microscopic cancer cells may remain undetectable, and a vaccine that trains the immune system to recognize the patient's unique tumor mutations could eliminate those lingering cells before they grow into new lesions.
In the trial, more than 1,100 patients with high-risk or advanced melanoma who had surgery to remove all visible tumors received the vaccine together with Keytruda, and the treatment met its primary endpoints. This marks a major step in personalized medicine, where treatments are tailored to an individual's genetic profile.
The idea of using mRNA to instruct cells to produce proteins that trigger an immune response against cancer has gained momentum in recent years.
For melanoma, which accounts for the vast majority of skin cancer deaths, the need for effective adjuvant options is urgent. Current standard-of-care for high-risk patients often includes immunotherapy alone, but recurrence rates remain substantial. The combination of a personalized vaccine with an established checkpoint inhibitor like Keytruda may offer a more robust defense by both activating and sustaining the immune system's attack on any residual cancer cells.
Researchers will continue to track the Phase 3 study for further results, including whether the treatment improves overall survival.
The early findings point to the possibility that this personalized shot plus Keytruda could provide a new therapeutic option for the most fatal skin cancer and support a wider move toward individualized mRNA therapies.