Figure 1: Adhesion cascade for leukocytes and circulatory metastatic cancer cells. In the first step, the circulatory cells attach and roll along the vascular endothelial cells (rolling and adhesion) through interaction between E-selectin and its ligand. In the second step (arrest), the cells tightly adhere to the endothelial cells and spread over the endothelium and actively transmigrate through the endothelial lining. Chemokines are crucial mediator for the second step arrest and displayed to leukocytes for activation of integrins, and facilitate firm adhesion via ICAM and VCAM for subsequent transmigration across the endothelial lining.