Moderna and Merck cancer vaccine cuts melanoma recurrence or death risk 42%

About 82% of melanoma patients given Moderna and Merck's personalized cancer vaccine with Keytruda were alive without their cancer returning after two years, compared with 70% of patients receiving Keytruda alone, according to CNBC.

What the trial found: The companies said the treatment, called intismeran autogene, reduced the risk of melanoma recurrence or death by 42% compared with Keytruda alone in a Phase 3 trial. STAT described the result as a 42% reduction in the risk of disease recurrence. CNBC also reported that the combination reduced the risk of cancer spreading to distant parts of the body or death by 38%.

Why it matters: Melanoma can return after treatment, and the vaccine is built around mutations unique to each patient's tumor. That means this is not a one-size-fits-all shot pulled from a warehouse. The tumor is analyzed, and the mRNA treatment is designed to target its specific neoantigens, the mutations that can help the immune system identify cancer cells.

The market reaction: Moderna shares fell as much as 25% Thursday after partial trial data reportedly leaked before the companies released fuller results. That drop came after Moderna stock had climbed more than 530% this year, as investors piled into expectations around the cancer program. Merck shares fell about 1% Thursday. Analysts cited by CNBC said the results appeared positive and clinically meaningful, but investor expectations had become unusually high.

The catch: A personalized treatment takes time. CNBC reported that manufacturing a dose can take about six weeks. Merck chief executive Robert Davis said the companies believe they can shorten that process, which matters because a treatment tailored to one person is only useful when it can reach that person quickly enough.

The detailed results are scheduled for presentation at the European Society for Medical Oncology conference in Madrid this weekend, where the practical questions around personalized production and use in other cancers will be closely watched.