Growth factors secreted by CAFs in the breast cancer microenvironment encompass basic fibroblast growth factor 2 (FGF2) [37], platelet-derived growth factor (PDGF) [38], insulin growth factor 1 (IGF1), and large amounts of C-X-C motif chemokine ligand 12 (CXCL12), also known as stromal cell-derived factor (SDF-1). This evidence concerns the gene CXCL12 and breast cancer.