Personalized mRNA vaccine cuts melanoma recurrence or death risk 42% in trial

Two years after treatment, 82% of patients who got a personalized mRNA vaccine alongside Keytruda were alive without their melanoma returning, compared with 70% of patients given Keytruda and a placebo.

That is the central result from an Australian-led phase 3 trial of intismeran, a vaccine developed by Moderna and Merck for people whose melanoma had been removed surgically. The combination reduced the risk of recurrence or death by 42% over about two years compared with Keytruda, the Merck immunotherapy also known as pembrolizumab.

The trial included 1,137 patients with high-risk or Stage 3 melanoma at 157 sites worldwide. All received Keytruda for 12 months. Of those patients, 757 also received intismeran and 380 received a placebo.

What makes it different: This is not a vaccine pulled from a pharmacy shelf. Doctors use genetic information from a patient's removed tumor to identify abnormal proteins, called neoantigens, that may help the immune system recognize the cancer. The vaccine can target up to 34 mutations unique to that person's melanoma.

That manufacturing step takes time. CNBC reported it can take roughly six weeks, while NBC News reported patients received their vaccines in a little over nine weeks on average. Patients began Keytruda while their individual vaccine was being made.

The catch: The trial's headline result is encouraging, but it does not settle the question patients care about most: whether the benefit lasts and improves long-term survival. The companies said it was too early to tell whether the combination improved survival. A separate analysis found a 58% reduction in recurrence or death after the first six months, though one oncologist quoted by CNBC called the explanation for that timing a hypothesis, not proof.

Reported side effects from the vaccine included injection-site pain or reactions and mild fever. But the treatment also has a practical limitation: NBC News reported that 17% of 1,749 people screened for the trial did not have tumor samples large enough to make a vaccine. Personalized medicine still needs enough tumor to personalize.

What happens next: The findings are due to be presented Saturday at the European Society for Medical Oncology meeting in Madrid. The full results have not yet been published in a peer-reviewed journal, and intismeran is not available as standard melanoma treatment while further study and regulatory review continue. The thing to watch is whether longer follow-up shows the early gap between 82% and 70% holds up.