Mechanisms of therapy resistance in pancreatic cancer orchestrated by cancer -associated fibroblasts (CAFs): Schematic illustration on how CAFs diminish the effect of chemotherapy and radiotherapy in pancreatic cancer. c-MET, tyrosine-protein kinase Met CXCR4, C-X-C chemokine receptor type 4; CYR61, cysteine-rich angiogenic inducer 61; deoxyC, deoxycytidine; EMT, epithelial–mesenchymal transition; FAK, focal adhesion kinase; hCNT3, human concentrative nucleoside transporter-3; hENT1, human equilibrative nucleoside transporter-1; HGF, hepatocyte growth factor; IGF, insulin-like growth factor; P, phosphorylated; PER, periostin; P-GP, P-glycoprotein; SDF-1, stromal cell-derived factor-1.