CXCR4 is a G protein-coupled receptor (GPCR) widely expressed in a variety of cell types including leucocytes, where it promotes migration, recruitment and activation (Bonavia et al., 2003; Salcedo and Oppenheim, 2003; Juarez et al., 2004; Choi and An, 2011; Comerford and McColl, 2011), neurons, where it modulates electrical activity (Banisadr et al., 2002; Guyon and Nahon, 2007; Rostene et al., 2011), and various cancers and metastases (Wang et al., 2006) where it is involved in tumor progression (Liu et al., 2006; Gao et al., 2010; Zhao et al., 2010). The gene discussed is ACKR3; the disease is cancer.