CXCL12 and cancer: This system is a substantial advancement over previously described in vitro flow-based assay systems in that it possesses a unique blend of: (i) prolonged, extravascular stimulation of vascular endothelium with CXCL12, modeling both the high levels and directionality of this chemokine in target organs for metastatic breast and other cancers [21] and (ii) region-specific endothelium stimulation with chemokines to enable comparison of cancer cell adhesion to endothelium of differing metastatic potential within the same experiment.