In a study published online on 23 October inCancer Cell, researchers show that when human breast-cancer exosomes can cause tumours when mixed with normal cells then injected into mice. The results could pave the way to finding markers to monitor the progression of cancer, and possibly even point to targets for therapies.

The team also collected exosomes from the blood of 8 healthy individuals and 11 people with breast cancer. Five of the 11 exosome samples from the patients induced tumour growth when mixed with normal cells and injected into mice; none of the exosome samples from healthy people did so.

It is unclear how far exosomes can travel in the body, says Kalluri, but the fact that the team could isolate them from blood suggests that they could be quite mobile. And even if their effect is only local, they could still make nearby cancer cells more aggressive, or transform healthy cells into cancerous ones, he says.

But trying to slow cancer by blocking exosomes is a difficult proposition, says Al-Nedawii. It is unclear how that would affect normal cells, he notes, and some exosomes from healthy cells have been shown to contain proteins that prevent cancer.

A more imminent application might be to use exosomes as a way to detect and monitor cancer, he adds. Kalluri notes that exosomes are more abundant and easier to isolate than tumour cells floating in the blood, which have also been used to track disease. “There are millions of exosomes being made by each cell,” he says. “That’s very powerful.”

Reference

Cancer cells can ‘infect’ normal neighbours, Nature ︱ doi:10.1038/nature.2014.1621