Melanoma Vaccine Trial Shows 12.2-Point Recurrence-Free Survival Gain

By Tom Whitfield

At two years, 82.2% of adults with resected high-risk stage IIB-IV melanoma receiving personalized mRNA vaccine intismeran autogene plus Keytruda were alive without recurrence, versus 70% receiving placebo plus Keytruda. The company-reported results came from a placebo-controlled international trial of 1,137 adults whose melanoma had been completely removed by surgery.

Two-thirds received intismeran autogene plus Keytruda, while the remaining third received placebo plus Keytruda. The 12.2-percentage-point difference favored the vaccine combination on recurrence-free survival. Across follow-up, the combination reduced the combined risk of recurrence or death by 42%, according to the companies’ disclosure.

That figure does not show a 42% reduction in deaths alone or that 42% of patients were cured. Overall survival remains under follow-up.

The 82.2% figure measures recurrence-free survival at two years, not a cure rate for every recipient. It came from the same study in which all participants had complete surgical removal and received Keytruda.

What did the trial establish?

Intismeran autogene uses information about mutations in each patient’s tumor to create a personalized treatment. Its synthetic messenger RNA gives the immune system instructions for recognizing cancer-specific targets, with the aim of attacking cells that might remain after surgery.

The approach is bespoke because it draws on each patient’s tumor mutation profile. Unlike a preventive vaccine given to healthy people, this treatment is intended for patients who have already had cancer.

The trial covered high-risk stage IIB to IV melanoma, a form of skin cancer, after surgery. That disease-specific result cannot establish that the same approach works against every cancer.

Professor Pippa Corrie, a consultant medical oncologist, helped run the study at Addenbrooke’s Hospital in Cambridge. She said: “The personalised cancer vaccine uses exciting technology to stimulate the patient’s own immune system to recognise and attack any tumour cells remaining after surgery.”

For patients, the two-year result addresses a specific postoperative concern: whether melanoma would return after complete removal. The finding compares adding intismeran autogene to Keytruda against placebo plus Keytruda, because every trial group received that immunotherapy.

What safety findings did the companies report?

According to the companies’ disclosure, severe to fatal treatment-related adverse events, classified as grades three through five, occurred in 14.2% of the combination group and 13.4% of the comparison group. Common side effects with the combination included fever, injection-site pain and fatigue.

The companies reported no new safety signals. The serious-event rates were close between groups in the company-reported figures.

What happens before clinicians can use the vaccine?

Moderna and MSD are engaging with regulators after reporting the positive trial results. A successful trial does not itself provide permission to sell a medicine, leaving intismeran autogene investigational.

The result currently applies to adults with completely resected high-risk stage IIB-IV melanoma who received intismeran autogene plus Keytruda in the study. It does not establish effectiveness in other cancers or in preventive vaccination.

The continuing overall-survival analysis will determine whether better recurrence-free survival translates into longer lives. Until that analysis reports, the 42% figure remains a combined recurrence-or-death result rather than a mortality benefit. Regulatory decisions will determine whether the still-investigational vaccine can be marketed.