CXCL12 and breast cancer: Breast cancer-derived exosomes can promote a myofibroblast-like phenotype in MSCs in vitro, through the activation of the TGF-β pathway, leading to the secretion of tumor-promoting factors such as stromal cell derived factor-1 (SDF-1), vascular endothelial growth factor (VEGF), chemokine (C-C motif) ligand 5 (CCL5) and TGF-β [43].