CXCL12 and cancer: Not only do the CAFs provide physical support for epithelial cells, but they also secrete a variety of cell growth factors, inflammatory ligands, numerous chemokines and cytokines, and ECM proteins, such as HGF, CXCL12, insulin-like growth factor (IGF), epidermal growth factor (EGF), IL-8, IL-6, and IL-11, which are carried by exosome to influence EMT; interact with cancer cells to increase cancer proliferation, migration, invasion; induce immunosuppression and chemotherapy resistance; and remold ECM [42].