CXCL1 and breast cancer: To determine whether exogenous CXCL1 could promote breast cancer metastasis, we added the CXCL1 cytokine to cells, and found that 0–50 ng/mL CXCL1 had little influence on the cell proliferation of the 4T1, MDA-MB-231 and MCF-7 breast cancer cells (Fig. 2a).