CXCR1 and breast carcinoma: ER-positive breast cancer cells have been shown to secrete platelet-derived growth factor (PDGF-CC), which binds to platelet-derived growth factor receptor (PDGFR) in CAFs, resulting in increased expression of hepatocyte growth factor (HGF), insulin-like growth factor binding protein 3 (IGFBP3) and stanniocalcin1 (STC1) in charge of endocrine therapy resistance of tumor cells, and targeted inhibition of PDGF-CC restores tumor cell sensitivity to endocrine therapy (86).