ECs in the tumor microenvironment overexpress CXCR4 in response to hypoxia (Schioppa et al., 2003) and the secretion of CXCL12 by tumor cells and cells in the tumor microenvironment, recruits ECs into the tumor (Salcedo and Oppenheim, 2003). The gene discussed is CXCL12; the disease is neoplasm.