A combination of a personalized cancer vaccine and the immunotherapy drug pembrolizumab reduced the risk of melanoma recurrence by nearly half in patients with high-risk skin cancer, according to five-year follow-up data presented at the American Society of Clinical Oncology Annual Meeting. The findings suggest that tailoring treatment to each patient's unique tumor may offer durable protection against one of the most aggressive forms of skin cancer.

How Does This Personalized Vaccine Approach Work?

The vaccine, called intismeran, is custom-made for each patient based on their individual tumor's genetic fingerprint. Researchers use next-generation sequencing to identify up to 34 unique mutations, called neoantigens, that are specific to that person's cancer. The vaccine then trains the immune system to recognize and attack cancer cells carrying those exact mutations.

When combined with pembrolizumab, a checkpoint inhibitor that removes the brakes on immune cells, the approach becomes even more powerful. Pembrolizumab helps T cells (immune cells) stay active longer and engage more effectively with cancer cells. The vaccine generates new T cell clones, while pembrolizumab amplifies their tumor-fighting ability.

What Did the Five-Year Study Show?

The KEYNOTE-942 trial enrolled 157 patients with high-risk melanoma that had been surgically removed. Researchers randomly assigned participants to receive either the vaccine plus pembrolizumab or pembrolizumab alone. The results were striking:

• Recurrence Risk: The combination reduced the risk of cancer returning by 49%, meaning patients were significantly less likely to experience a melanoma recurrence during the follow-up period.
• Distant Metastasis Risk: The vaccine plus immunotherapy reduced the risk of cancer spreading to distant sites by 59%, a particularly important finding since metastatic melanoma is much harder to treat.
• Overall Survival Trend: While the study was not powered to definitively measure overall survival, there was a trend toward improved survival in the combination group, suggesting potential long-term benefits.
• Safety Profile: The combination was well-tolerated, with no new safety concerns emerging over five years. Side effects from the vaccine itself were mostly mild, including fatigue, injection-site pain, fever, and chills.

"This study confirms that intismeran plus pembrolizumab demonstrates a durable benefit over pembrolizumab alone in resected high-risk melanoma," said Matteo S. Carlino, a medical oncologist at Westmead and Blacktown Hospitals and faculty member at Melanoma Institute Australia.

Matteo S. Carlino, Medical Oncologist at Westmead and Blacktown Hospitals

Why Is This Finding Important for Melanoma Patients?

Melanoma is one of the deadliest forms of skin cancer, and high-risk patients face a significant chance of recurrence even after surgery. The five-year follow-up data is particularly meaningful because it shows the benefits persist long after treatment ends. Patients who received the vaccine plus pembrolizumab maintained their protective advantage years later, suggesting the immune system "remembers" how to fight the cancer.

The research also revealed something encouraging about how the vaccine works at the cellular level. Patients treated with the combination showed an increase in T cell clonality, meaning their immune systems generated more diverse and specialized cancer-fighting cells. Importantly, patients who developed more novel T cell clones were less likely to experience recurrence, providing a biological explanation for why the combination works.

What Happens Next?

The KEYNOTE-942 trial was a phase 2 study, which means it tested the approach in a relatively small group to confirm safety and effectiveness. A larger phase 3 trial called INTerpath-001 is now underway, evaluating the vaccine plus pembrolizumab in a broader population of patients with resected stage II to IV melanoma. This larger study has completed enrollment, and results are anticipated.

Researchers are also exploring whether this personalized vaccine approach works for other cancer types beyond melanoma. The combination of a custom-designed vaccine with checkpoint inhibitors represents a shift toward precision medicine in cancer treatment, where therapy is tailored to each patient's unique tumor biology rather than using a one-size-fits-all approach.

For patients with high-risk melanoma, these findings offer genuine hope. The durable benefits seen over five years suggest that a personalized vaccine combined with immunotherapy could become a standard treatment option, potentially preventing recurrence and improving long-term survival for thousands of patients facing this serious diagnosis.