CXCR4 and cancer: Previous anti-CXCR4 agents either eliminate all (cancer and normal) CXCR4+ cells due to high affinity coupled to inhibition of survival signalling downstream CXCR4 blockade and/or active antibody Fc-mediated effector function or cause tumour and leucocyte mobilization, due to antagonism of CXCR4-mediated retention in bone marrow15,29,35,36,60.