Merck, Moderna's cancer vaccine succeeds in Phase 3 trial

Doctors took a sample of a melanoma patient's own tumor. They used it to build a custom vaccine, then gave that vaccine back to the same patient. Merck and Moderna said Wednesday that approach worked in a major trial. Patients who got it with Keytruda had fewer cancers return or spread. Patients on Keytruda alone did worse.

This is a bigger deal than one drug trial. It's the first time any cancer vaccine has succeeded this late in testing. This one was custom-built from a patient's own tumor. Cancer vaccines have been a promising idea for decades. They have a long history of failing in trials exactly this size. Merck and Moderna haven't released exact numbers yet. They've only said the vaccine beat Keytruda alone on two measures. Patients stayed cancer-free longer, and it took longer before the cancer spread elsewhere.

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Will this actually become a treatment patients can get? Not soon. Full data still needs to go to regulators. And each vaccine has to be custom-built for every single patient. That's a slower, more expensive process than a normal drug. Merck and Moderna haven't said what it might cost or when it could reach an FDA approval decision. If it works as well as this trial suggests, it could open the door to personalized vaccines for other cancers. Not just melanoma.