Nine of the 10 most common cancer deaths are caused by solid tumours, but in most cases it’s the cancer’s spread to other parts of the body – known as metastasis – that proves fatal.

Now, researchers have uncovered a potential trigger for metastasis: the squeezing of cancer cells by the tiniest of veins that transforms them into a different type of cell now able to form new tumors.

In a study published in Nature Communications, the scientists described how they constructed a biomedical device that simulated blood flow through our narrowest blood veins. They showed that when human melanoma cancer cells are forced through channels narrower than 10 micrometres – about a fifth the width of a human hair – they begin to behave more like stem cells, gaining traits that could help them survive, spread, and form new tumors.