CXCR4 and breast cancer: HER2 could upregulate the expression of the chemokine receptor CXCR4 and therefore promoted liver metastasis via the CXCL12/CXCR4 pathway, while elevated expression of the fibroblast growth factor homologous factor (FGF13) could mediate the formation of liver metastases in the triple negative breast cancer, resulting in molecular subtype-based liver metastasis of breast cancer [24–26].