CXCR4 and breast carcinoma: The CXCL12-CXCR4 axis in myeloid cells including neutrophils is also responsible for NK cell apoptosis and inactivation by enhancing the Fas signaling pathway and restraining IL-18 production in neutrophils, respectively, in metastatic B16F0 melanoma, PyMT breast carcinoma, and YAC-1 lymphoma (131).