Nature Cell Biol. doi:10.1038/ncb1973 (2009)

Motility is crucial for cancer cells to spread and seed new tumours. To learn more about what drives this movement, Erik Sahai of Cancer Research UK's London Research Institute and his colleagues used multiphoton confocal microscopy to follow metastatic breast-cancer cells in live mice.

They found that the cells could travel in groups or individually. Blocking a growth factor called TGFβ meant that cells could only move in a group and by means of the lymphatic system. Cells moving alone exhibited activated TGFβ signalling and were able to enter the bloodstream. However, TGFβ signalling in these cells was transient — although required for single-cell motility, it needed to be shut down to enable the tumour to grow in its new home.