Merck and Moderna have announced that their personalised mRNA vaccine, given alongside the immunotherapy drug Keytruda, cut the risk of melanoma death or recurrence by 42 percent in a large late-stage trial. The companies said on Thursday that the Phase 3 study of more than 1,100 patients produced the first data showing a vaccine built from a patient’s own tumour mutations can keep the disease at bay.
Melanoma is the deadliest form of skin cancer. The trial randomised surgically treated patients roughly two to one to receive either the vaccine combination or Keytruda alone. After two years, 82.2 percent of the combination group were still cancer free, against 70 percent on Keytruda alone.
How the personalised vaccine works
The vaccine, known as intismeran, carries synthetic mRNA encoding up to 34 mutations found in the patient’s own cancer cells. Researchers compare the genetic sequences of cancerous and healthy tissue so the immune system can seek and destroy the cancer-specific mutations. Keytruda removes a natural brake cancer cells use to hide from immune attack, which is why the pairing matters.
The trial measured recurrence-free survival and distant metastasis-free survival, the time without the cancer returning or spreading to a new part of the body. On the second measure the combination cut the risk of spread by 38 percent. The CDC has drawn sharp criticism over a plan to revive a hepatitis B study in Guinea-Bissau, showing how closely clinical research is being watched.
From embargo break to market jitters
The road to publication was messy. The companies first announced in August that the trial had succeeded but held back details for a presentation at the European Society for Medical Oncology meeting in Madrid. After an oncology news site broke the embargo, the companies rushed out the top-line results. The full data has been accepted for publication in the New England Journal of Medicine, and the companies are preparing a United States filing.
Markets were unimpressed. Moderna shares closed more than 17 percent lower, despite nearly quadrupling since August on anticipation of the data, while Merck shares slipped about 1.8 percent. The drop echoed the recent AI selloff that rattled chip stocks. Analysts questioned how broadly the technology will extend beyond melanoma, even though the combination is already being tested in kidney, bladder and lung cancers.
The caution is a reminder that trial data and market verdicts rarely move in the same direction. For patients, the numbers are the first solid signal that a vaccine designed around a single person’s tumour can change the odds. Moderna’s chief executive said the companies expect a launch in 2027, calling the results a new chapter in cancer treatment. Whether regulators and insurers agree will decide how fast that chapter reaches clinics.
