CXCL12 and neoplasm: As the key contributor in tumour microenvironment, CAFs secrete a number of factors such as cytokines, chemokines (e.g. IL-6, CXCL12), growth factors (e.g. HGF, transforming growth factor β, fibroblast growth factor) and receptors (e.g. platelet-derived growth factor receptor) [8,9].