Researchers at the Mayo Clinic have completed a groundbreaking new test: They knocked widespread blood cancer into remission with a single massive blast of measles vaccine.

Stacy Erholtz, who was suffering from an advanced stage of blood cancer, recovered thanks to an intravenous injection of the measles virus, which was sufficient to overwhelm the cancer’s natural defenses, the StarTribune reports.

As far as clinical trials go, this was a small test because it only had two subjects. But lead researcher Dr. Stephen Russell told StarTribune it’s a promising start.

“It’s a landmark. We’ve known for a long time that we can give a virus intravenously and destroy metastatic cancer in mice. Nobody’s shown that you can do that in people before,” he said.

The viruses bind to cancer cells and use them to replicate. The process destroys the cells, and the body’s immune system attacks what’s left since it’s marked as viral material. This test also gave doctors a benchmark for the virus dose needed to reduce cancer in patients — 100 billion infectious units instead of the standard 10,000 units.

There are still hurdles to overcome — like the body’s own defenses. Once the immune system has experience fighting a virus, it’s not effective a second time. The body attacks it before it can begin taking over cancer cells.

Doctors will also need to do more testing on more patients. They plan to expand their trials by September.