Merck's melanoma vaccine shows 42% reduction in cancer recurrence in trials

Merck said its experimental mRNA vaccine cut the risk of melanoma returning or causing death by 42 percent over two years when given together with an immunotherapy drug, data presented at the European Cancer Congress in Madrid on Saturday. The trial involved more than 1,100 patients with high‑risk melanoma who had already undergone surgery.

The study marks the first large‑scale test of a cancer vaccine that uses messenger‑RNA technology first deployed against COVID‑19. Researchers harvested tumor samples from each participant, identified unique mutant proteins, and built a personalized mRNA shot to teach the immune system to recognize those targets. Investors had been watching closely; a leak of early figures on social media prompted a brief dip in Merck and Moderna shares after weeks of strong gains.

Melanoma specialist Antoni Ribas, the trial’s lead investigator, said the packed conference hall and overflow rooms reflected excitement that extended beyond oncologists. He noted the vaccine prompted immune cells to attack the mutated proteins before the cancer could spread. Merck’s chief medical officer Eliav Barr added that the success opens a “very large landscape” of cancers that could be tackled with similar personalized vaccines, and that trials for kidney and bladder cancers are already under way. The company plans to file an FDA application for the melanoma vaccine next year, though it declined to discuss pricing, which is expected to be high given the bespoke manufacturing process.

If regulatory approval follows, the therapy could reshape treatment for patients with aggressive skin cancers and set a precedent for mRNA‑based vaccines in oncology. The data also fuels a broader debate about the cost and accessibility of personalized medicine, while investors watch to see whether Merck can translate the scientific breakthrough into a commercial product. The next steps will include larger confirmatory studies and discussions with health‑care payers about how to fund such individualized treatments.