Personalized mRNA vaccine keeps pancreatic cancer at bay six years after treatment

Story: 2025 C.E.  |  Last updated: June 12, 2025

Six years after receiving a personalized mRNA vaccine in a small clinical trial, Donna Gustafson is cancer-free — and she’s not alone. New data from a Phase 1 trial led by researchers at Memorial Sloan Kettering Cancer Center shows that seven of eight patients who mounted an immune response to the vaccine are still alive six years later, with most showing no sign of cancer recurrence. For a disease with a five-year survival rate below 13%, that’s a result oncologists are treating with serious attention.

At a glance

• Pancreatic cancer vaccine: The investigational mRNA vaccine is custom-built for each patient using genetic mutations unique to their tumor, triggering the immune system to hunt down any cancer cells remaining after surgery.
• Trial results: Eight of 16 patients in the Phase 1 trial produced a strong immune response; six years on, seven of those eight are still alive, compared to two of the eight who did not respond.
• T-cell durability: New findings show that “killer T cells” produced by the vaccine appear to be sustained by “helper T cells” — a two-part immune response that researchers believe may be key to long-term survival.

Why this cancer has resisted everything else

Pancreatic cancer is diagnosed late in most patients, spreads quickly, and responds poorly to standard chemotherapy and radiation. There is no routine screening for it — no equivalent of a colonoscopy or mammogram — so symptoms often don’t appear until the disease is already advanced. Only about 20% of cases are even operable.

For decades, treatment has focused more on slowing the disease than stopping it. Even after successful surgery, cancer frequently returns. That’s the exact problem this vaccine was designed to address — not to shrink existing tumors, but to stop the ones that hide after surgery before they can grow back.

Experts had long believed that pancreatic cancer was simply too “cold” for immunotherapy to work — meaning the immune system couldn’t be provoked into attacking it. This trial is challenging that assumption.

How the personalized vaccine works

After a patient undergoes surgery to remove their tumor, scientists sequence the tumor’s genome and identify mutations specific to that individual’s cancer. Those mutations — called neoantigens — become the blueprint for a custom-built mRNA vaccine. No two patients receive the same formulation.

The vaccine trains the immune system to recognize cancer-specific markers and dispatch T cells to destroy any lingering cancer cells. It uses the same mRNA delivery mechanism that powered COVID-19 vaccines, now redirected at a different target. Crucially, patients in the trial also received standard chemotherapy after vaccination — and the T cells remained active anyway, which is significant because chemotherapy typically suppresses immune function.

The new six-year data, presented at the American Association for Cancer Research’s annual meeting in San Diego, adds a layer of understanding about why the response lasts. Killer T cells — the ones that directly attack cancer — appear to be replenished and sustained by helper T cells that the vaccine also prompts. That tandem effect may be what makes the immune response durable rather than temporary.

The scientists behind the results

The trial was led by Dr. Vinod Balachandran, director of the Olayan Center for Cancer Vaccines at Memorial Sloan Kettering Cancer Center in New York City. The Phase 1 results were published in Nature in 2023 C.E., and the six-year follow-up data represents the longest look yet at whether the immune response holds.

Dr. William Freed-Pastor of Dana-Farber Cancer Institute, who was not involved in the trial, called the central finding clear: people who mounted a response to the vaccine lived longer than those who did not. He and others emphasize, however, that the trial enrolled just 16 patients, and results at this scale can’t yet tell us how the vaccine will perform across a broader population.

Balachandran has already launched a larger Phase 2 trial. Researchers are also exploring whether the approach — which showed disappointing results in advanced cancer in earlier studies — might eventually be adapted to work earlier in the disease process for other cancer types.

What still needs to happen

The trial was small, and larger studies are needed before this treatment could be approved or widely available. Building a custom vaccine for each patient requires significant manufacturing resources, and questions about cost and equitable access — particularly for patients outside major research centers — remain genuinely unresolved. Roughly 66,000 Americans are diagnosed with pancreatic cancer each year, and scaling personalized treatment to that volume will require deliberate planning.

Still, the durability of the immune response — six years of measurable benefit in responders — is not something researchers expected to see from a Phase 1 trial. The conversation in oncology has shifted from whether mRNA cancer vaccines can work to what it will take to make them widely available.

Gustafson, now 72, put it simply when she joined the trial in February 2020 C.E., before mRNA vaccines were a household concept: “I knew that statistically, the odds were against me.” Six years later, the odds look different — at least for her, and for the field.

Read more

For more on this story, see: NBC New York

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