A series of proofs by several researchers showed the presence of influence of the CXCR4-SDF-1 (CXCL12) axis on tumors: many kinds of tumors, including breast cancer, ovarian cancer, prostate cancer, rhabdomyosarcoma, and neuroblastoma metastasize to the bones through the bloodstream in a CXCL12-dependent manner (Geminder et al., 2001; Müller et al., 2001; Libura et al., 2002; Dontu et al., 2003; Hall and Korach, 2003; Jankowski et al., 2003; Sun et al., 2003; Porcile et al., 2004). The gene discussed is CXCR4; the disease is prostate cancer.