HBEGF and cancer: The cancer cells secrete platelet-derived growth factor (PDGF)-D and TGF-β1, both of which activate CAFs, whereas CAFs secrete PDGF-B, heparin-binding EGF-like growth factor (HB-EGF), and stromal cell-derived factor-1 (SDF-1, also known as CXCL12), and thereby promote tumor growth and invasion [26].