CXCR4 and breast cancer: CXC chemokine receptor 4 (CXCR4), a G protein-coupled receptor spanning cell membranes to covert extracellular chemokine CXCL12 binding into intracellular signaling, is frequently hijacked by breast cancer, exerting multifaceted effects on metastatic seeds, pro-metastatic PMN soils, and their crosstalk4,5.