CXCL1 and breast cancer: Other CXCR2 ligands may play a more important role in breast cancer than CXCL1, for example, CXCL5/epithelial-cell-derived neutrophil activating factor 78 (ENA78) and CXCL8/interleukin-8 (IL-8), whose expression is increased in breast tumors [33].