For instance, an in vitro study showed that CAFs enhance the adhesion of breast cancer cells to brain microvascular endothelial cells and increase blood-brain barrier permeability, thus facilitating the transmigration of breast cancer cells and the establishment of brain metastases, which may be related to the upregulation of integrin α5β1 and αvβ3, αvβ3, c-MET and α2,6-siayltransferase in tumor cells [49]. Here, MET is linked to breast cancer.