  Metastasis is a process of cell migration that can be collective and guided
by chemical cues. Viewing metastasis in this way, as a physical phenomenon,
allows one to draw upon insights from other studies of collective sensing and
migration in cell biology. Here we review recent progress in the study of cell
sensing and migration as collective phenomena, including in the context of
metastatic cells. We describe simple physical models that yield the limits to
the precision of cell sensing, and we review experimental evidence that cells
operate near these limits. Models of collective migration are surveyed in order
understand how collective metastatic invasion can occur. We conclude by
contrasting cells' sensory abilities with their sensitivity to drugs, and
suggesting potential alternatives to cell-death-based cancer therapies.
