GDF15 and neoplasm: CAFs directly stimulate cancer cell growth and also enhance tumor angiogenesis by paracrine signaling, such as vascular endothelial growth factor (VEGF) [52], hepatocyte growth factor (HGF) [53], growth differentiation factor 15 (GDF15) [54], C-X-C Motif Chemokine Ligand 12 (CXCL12) [55] and CXCL14 [51].