A personalized cancer vaccine developed by Moderna and Merck is showing remarkable promise against one of the deadliest forms of skin cancer. Researchers reported that when the experimental mRNA vaccine intismeran is combined with the immunotherapy drug Keytruda, the risk of melanoma recurrence falls by nearly half. The findings, presented at the 2026 American Society of Clinical Oncology meeting, are generating excitement among cancer specialists who believe this approach could transform treatment for melanoma and potentially other cancers as well.
What Is Melanoma and Why Is It So Dangerous?
Melanoma is a form of skin cancer that develops in the cells that produce pigment in the skin. Although it is less common than other skin cancers, it is considered the most dangerous because of its ability to spread rapidly to other organs if not detected and treated early. Once melanoma spreads to the lungs, liver, brain, or other distant sites, treatment becomes far more difficult.
The disease remains a major health concern in the United States. Approximately 112,000 new melanoma cases are diagnosed each year, and about 8,500 Americans die from the disease annually. Researchers also estimate that nearly 235,000 new melanoma cases could be diagnosed in 2026 alone. Even after successful surgery, patients with advanced melanoma often face a significant risk that the cancer will return.
A Vaccine Designed for Each Individual Patient
Unlike traditional vaccines that prevent disease before it occurs, this treatment is given after a cancer diagnosis. The goal is to help the immune system hunt down and destroy any cancer cells that may remain after surgery.
The vaccine, known as intismeran autogene, is highly personalized. Researchers begin by analyzing a patient’s tumor and identifying unique genetic mutations. These mutations produce abnormal proteins called neoantigens that are found only on that individual’s cancer cells.
Scientists then create a custom mRNA vaccine containing instructions that teach the immune system to recognize those specific neoantigens. When injected, the vaccine essentially gives the body’s T cells a blueprint for finding and attacking any remaining cancer cells carrying those markers. Each patient’s vaccine is unique because each person’s tumor has a different genetic fingerprint.
As Dr. Janice Mehnert of NYU Grossman School of Medicine explained, “It is a personalized immunotherapy strategy” tailored specifically to each patient’s tumor.
How the Combination Therapy Works
The vaccine is paired with pembrolizumab, better known by its brand name Keytruda.
Cancer cells often evade the immune system by activating biological signals that effectively tell immune cells, “Don’t attack me.” Keytruda blocks one of these escape mechanisms, allowing T cells to recognize cancer cells once again.
The vaccine then amplifies this effect. After researchers identify up to 34 unique neoantigens from a patient’s tumor, the vaccine trains T cells to target those specific markers. In simple terms, Keytruda removes the cancer’s disguise, while the vaccine provides a detailed target list.
Dr. Sarah Arron, a dermatologist and skin cancer surgeon who was not involved in the study, described the process this way: “By matching this RNA treatment to the patient’s melanoma, we can really boost the immunotherapy by driving it toward the patient’s tumor.”
Researchers also found evidence that the treatment increases the number and diversity of cancer-fighting T cells, providing a biological explanation for the improved outcomes seen in patients.
The Results After Five Years
The findings come from the Phase 2b KEYNOTE-942 clinical trial, which enrolled 157 patients with high-risk stage III or stage IV melanoma that had been surgically removed.
Of those patients, 107 received the personalized vaccine plus Keytruda, while 50 received Keytruda alone, which is currently a standard treatment.
After five years, the differences between the two groups were striking.
Researchers found that 68.8 percent of patients receiving the combination therapy remained cancer-free, compared with 49.1 percent of those receiving Keytruda alone. This translated into a 49 percent reduction in the risk of recurrence or death. The benefit was consistent with earlier results reported after three years, suggesting the effect remains durable over time.
The combination therapy also reduced the risk of distant metastasis, meaning the spread of cancer to other organs, by 59 percent over five years.
Perhaps most impressive were the survival figures. Five years after treatment, 92.2 percent of patients who received the vaccine combination were still alive, compared with 71.3 percent of patients who received Keytruda alone.
Dr. Mehnert called the results “strong evidence that this therapy, when used in combination with immunotherapy, can demonstrably reduce the risk of dying from this disease.”
Experts Call It a Landmark Advance
Cancer specialists are responding enthusiastically to the findings.
“Our study offers strong evidence to melanoma patients that intismeran vaccine therapy, when used in combination with immunotherapy, can demonstrably reduce their risk of having their cancer return and improve clinical outcomes,” Mehnert said.
She also noted that the success of the vaccine could have implications beyond melanoma. “Our findings also serve as encouragement to cancer researchers globally that mRNA vaccines like intismeran could work well in combination with immunotherapy for other cancers whose high rates of mutations have proven difficult to target.”
Arron described the results as “a landmark advance in how we treat these very advanced, high-risk melanomas.” She added that the data demonstrate the broader potential of mRNA technology in cancer treatment.
Moderna Chief Development Officer Dr. David Berman was equally enthusiastic, saying, “The degree of benefit was incredible,” while highlighting the substantial reduction in recurrence risk.
While the results are highly encouraging, researchers caution that larger studies are still needed before the treatment can become standard care.
A Phase 3 clinical trial involving nearly 1,000 patients is already underway. If the larger trial confirms the Phase 2 findings, Moderna and Merck are expected to seek approval from the U.S. Food and Drug Administration.
Researchers are also studying the personalized vaccine approach in several other cancers, including lung cancer, bladder cancer, and kidney cancer. If successful, the strategy could open an entirely new chapter in cancer treatment, where vaccines are designed specifically for each patient’s tumor.
For patients like 80-year-old Connie Franciosi, who participated in the trial after being diagnosed with advanced melanoma in 2020, the promise is already very real. Five years later, she remains cancer-free.
“I am cancer-free,” Franciosi said. “Life is good.”