Both β1 and αVβ3 integrins appear to be constitutively active, and do not need any chemokine for their activation.136 The α6β4 integrin is essential for the firm adhesion of CTCs to endothelial cells following the initial binding of E-selectin to the CTCs.137 Integrinβ1 deletion in cancer cells has been shown to decrease the interaction between cancer cells and endothelial cells in vitro.138 Although integrins are clearly involved in cancer cell extravasation, the function of α-integrin in this regard has not been elucidated yet. Here, SELE is linked to cancer.