Experimental mRNA vaccine cuts risk melanoma returns by 42%

When the news arrived in August that what could be the first personalized mRNA cancer vaccine had succeeded in a late-stage clinical trial in melanoma, oncologists and the public alike were exhilarated. And that was before its makers had even disclosed just how well the therapy worked.

Now they have. The experimental vaccine, combined with the approved drug Keytruda, reduced the risk that patients' cancer came back after surgery or that they died by 42% compared with Keytruda alone, opening up a path for an entirely new way to treat the disease.

"This new vaccine is something that we've never really seen before in terms of the efficacy that it has demonstrated and the way that it works," Dr. Michael Postow, chief of the melanoma service at Memorial Sloan Kettering Cancer Center, told CNN.

The results are set to be presented Saturday in Madrid at a European Society for Medical Oncology meeting. Merck, the developer of the experimental vaccine along with Moderna, released the data early, on Thursday, after reports that they'd been published online and then taken down.

This is a developing story and will be updated.