Surgical removal of a melanoma tumour does not always eliminate the risk of the disease. In many cases, the cancer can recur in the same area, spread to nearby lymph nodes, or even reach distant organs such as the lungs and liver. Although immunotherapy drugs like pembrolizumab are routinely given after surgery to reduce this risk, not all patients respond successfully, and some tumours eventually develop resistance to treatment.
New research suggests that combining pembrolizumab with a personalized mRNA vaccine called intismeran could significantly improve outcomes for patients with advanced melanoma. The vaccine, developed using tissue from a patient’s own tumour, is designed to train the immune system to recognize and attack any remaining cancer cells that could trigger a relapse.
Findings from the Phase 2b KEYNOTE-942 trial were presented at the 2026 annual meeting of the American Society of Clinical Oncology (ASCO) in Chicago and simultaneously published in the Journal of Clinical Oncology.
According to researchers, the study provides strong evidence that adding intismeran to standard immunotherapy can lower the likelihood of melanoma returning and improve long-term survival. Scientists also believe the approach may eventually prove useful against other difficult-to-treat cancers with high mutation rates.
Melanoma develops in melanocytes, the pigment-producing cells of the skin, and is considered the most aggressive form of skin cancer because of its tendency to spread rapidly. While melanoma is common in Western countries, it is less frequently seen in India, largely due to higher melanin levels in darker skin, which offer greater protection against harmful ultraviolet radiation.
Promising Trial Results
The trial included 157 patients from the United States and Australia who had undergone surgery for advanced melanoma that had spread to lymph nodes or other parts of the body. Among them, 107 patients received a combination of intismeran and pembrolizumab, while 50 patients were treated with pembrolizumab alone.
After more than five years of follow-up, nearly 69 percent of patients receiving the combination therapy remained free of cancer, compared with about 49 percent of those treated only with pembrolizumab. The combined treatment also reduced the risk of cancer spreading to distant organs by 59 percent.
At four years, recurrence-free survival reached approximately 72 percent in patients receiving both treatments, compared with 49 percent in the immunotherapy-only group. Distant metastasis-free survival was 83 percent with the combination therapy versus 65 percent with pembrolizumab alone.
Overall survival rates were also higher in the combination group, reaching 92.2 percent compared to 71.3 percent among patients receiving only immunotherapy.
How the Personalized Vaccine Works
Unlike COVID-19 mRNA vaccines, which are designed to prevent infection before exposure to a virus, intismeran is a therapeutic vaccine developed after a patient has already been diagnosed and treated for cancer. Its purpose is not to prevent cancer from occurring but to reduce the risk of it returning.
After a tumour is surgically removed, scientists analyze its genetic makeup to identify unique cancer-specific markers known as neoantigens. These markers are found only on that patient’s cancer cells. Using this information, researchers create a customized mRNA vaccine tailored specifically to the individual.
When injected into the body, the vaccine instructs the immune system to recognize these neoantigens and activate T cells, the white blood cells responsible for detecting and destroying abnormal or cancerous cells.
The vaccine is administered through an intramuscular injection alongside intravenous pembrolizumab. Together, the two treatments enhance the body’s ability to detect and eliminate lingering cancer cells.
Why Combination Therapy Matters
Pembrolizumab works by blocking PD-1, a protein on T cells that cancer cells often exploit to avoid immune attack. By inhibiting this pathway, the drug helps restore the immune system’s ability to recognize and destroy tumour cells.
However, melanoma can develop resistance by finding alternative ways to evade immune detection. Intismeran helps overcome this challenge by teaching the immune system to recognize dozens of tumour-specific neoantigens, creating multiple targets for attack and making it more difficult for cancer cells to escape.
In simple terms, pembrolizumab removes the immune system’s brakes, while intismeran provides a detailed map of the cancer’s unique targets. Together, they create a stronger and more focused anti-cancer response.
Future Potential
Currently, the vaccine is intended for patients with stage III or stage IV melanoma whose tumours have been surgically removed and who show no detectable disease after surgery. It is being used as an additional safeguard against recurrence.
Experts caution that there is not yet enough evidence to determine whether intismeran could eventually replace immunotherapy. For now, its benefits have only been demonstrated when used alongside pembrolizumab.
A larger Phase 3 clinical trial is already underway to confirm these findings. Researchers are also evaluating the vaccine’s potential in lung cancer and other tumour types. If future studies are successful, personalized mRNA vaccines could become an important new strategy for preventing cancer recurrence and improving long-term survival in patients with hard-to-treat cancers.
