CXCR4 and breast cancer: Chemokines play a crucial role in establishing the make-up of the “pre-metastatic niche.” Yang et al. reported that when CXCR2 and CXCR4 are inhibited, recruitment of MDSCs to the pre-metastatic niche of the lung is inhibited and, as a result, breast cancer metastasis to the lung is significantly reduced (37).