For nearly a decade, the idea seemed like science fiction: a vaccine built from a single patient's own tumor to train their immune system to hunt down and destroy skin cancer. Now, after 1,137 people took part in a late-stage trial, drugmakers Moderna and Merck say that vision is one step closer to reality.
The two companies announced Wednesday that their personalized mRNA cancer vaccine appears to slow or stop melanoma from returning in high-risk patients who'd already had surgery to remove the deadly skin cancer. Melanoma is the most dangerous form of skin cancer, but it is also "exquisitely vulnerable to the immune system," said Dr. Janice Mehnert, who directs the melanoma program at NYU Langone Health. That makes it a perfect first test for this approach.
The treatment combines two elements. The first is a vaccine called Intismeran, custom-built for each patient using genetic material from their own tumor. It targets abnormal proteins called neoantigens that sit on the surface of cancer cells — helping the immune system recognize and kill them. The second is Keytruda, an existing immunotherapy from Merck that unleashes the immune system's brakes. Together, they give the body a personalized hit list and the firepower to act on it.
In the trial, patients were randomly assigned to receive either the vaccine-immunotherapy combo or Keytruda alone for about a year. Early results suggest the combo stretched the time before cancer returned in high-risk patients, though the companies haven't said exactly how long. Behind the scenes, a smaller study of 157 patients made headlines in June: after five years, the vaccine combo cut the risk of melanoma returning in half, findings published in the Journal of Clinical Oncology.
"We're just excited to see science win on this one," said Mehnert, the lead investigator of that smaller trial. She described the idea of such a novel treatment "panning out after years of work and literally over 1,000 patients" as exceeding her hopes. Moderna's CEO, Stéphane Bancel, called the Phase 3 findings "a pivotal moment for the field of cancer research," noting that creating an mRNA treatment for an individual patient's cancer was once purely aspirational.
The technology itself is not new. mRNA made its debut in COVID-19 vaccines, and the FDA recently approved the first mRNA flu shot, also from Moderna. But scientists originally dreamed of using it to fight cancer decades before the pandemic. Side effects in the trial were mostly mild or moderate, with some patients needing to pause or stop treatment, and no new safety concerns emerged. The study will keep tracking overall survival.
Wal Street took notice — Moderna shares jumped as much as 147% on Wednesday, while Merck rose about 13%. Yet the road ahead isn't entirely smooth. The future of mRNA research has grown uncertain under the Trump administration, with Health Secretary Robert F. Kennedy Jr. criticizing the technology and cutting $500 million in mRNA research contracts last year. Still, for patients facing the deadliest form of skin cancer, the promise of a vaccine tailored to their own tumor is a reason for hope that no headline can erase.