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A cancer diagnosis can be devastating, but confirmed metastasis of that cancer—when tumors caused by the original cancer appear in new places in the body—can be even worse. Metastases are responsible for around 90% of cancer deaths , so stopping cancer cells from spreading would be a huge boon for doctors and patients alike.

Enter nanoparticles. The tiny structures

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Lung cancer cells dividing.

show great promise in treating cancers , and now they could also play a role in seeking out and destroying tumorigenic cells in the blood stream, halting their spread.

To accomplish this latest feat, biomedical engineers from Cornell University used nanoparticles to put a new twist on an old tactic. Previously, researchers had attempted to kill mobile cancer cells by injecting TRAIL, a cancer-killing protein, directly into the blood stream. It worked, but not well. The molecule quickly degraded in the blood, drastically reducing its effectiveness.

For the new approach, the researchers tacked TRAIL onto nanoparticles, which then glommed onto white blood cells. This turned out to be a key development.

Akshat Rathi, writing at Ars Technica:

Red blood cells tend to travel in the center of a blood vessel, and white blood cells stick to the edges. This is because red blood cells are lower density and can be easily deformed to slide around obstacles. Cancer cells have a similar density to white blood cells and remain close to the walls, too. As a result, these nanoparticles are more likely to bump into cancer cells and bind their TRAIL receptors.

The researchers tested their nanoparticle-coated white blood cell treatment in mice injected with cancer cells. In their paper , they report a 65-fold reduction in blood-borne cancer cells in treated mice in just a matter of hours.

There’s still no evidence that the treatment reduces actual metastasis—after all, just a handful of cells landing in the right place could be problematic—so there’s lots more work to be done. But for early results, they are promising.