This close proximity promotes activation of latent TGF-β1 by further proteolytic cleavage.99 Similarly, integrin αvβ3 has been proposed to act as a docking point for MMP-9 in metastatic breast cancer cells,100 and for MMP-2 in melanoma cells.101 In addition, integrins can cluster with the TGF-β-RII, thereby improving its availability to locally activate TGF-β1. Here, TGFB1 is linked to breast cancer.