Tumour metastasis is a significant contributor to death in cancer patients. Eight metastasis-suppressor genes that reduce the metastatic propensity of a cancer cell line in vivo without affecting its tumorigenicity have been identified. These affect important signal-transduction pathways, including mitogen-activated protein kinases, RHO, RAC and G-protein-coupled and tyrosine-kinase receptors. So how might we use this knowledge to improve the treatment of patients with cancer?