SPP1 and neoplasm: Most of the well-described tumor-promoting functions of CAFs happen in the context of paracrine and juxtracrine signaling via the secretion of multiple growth factors including TGF-β, connective tissue growth factor (CTGF), stromal-derived growth factor (SDF-1) vascular endothelial growth factor (VEGF), osteopontin (OPN) or hepatocyte growth factor (HGF) just to mention some, as well as a myriad of cytokines and chemokines such as IL-6, IL-8, IL-1, CXCL2, CXCL5, CXCL12/SDF-1a, CCL20 and others [18, 20, 50].