CXCR4 and neoplasm: Consistent with the fact that both CXCR4 and CXCL12 are highly expressed in tumor tissues where their interaction plays a major role in the formation of new vessels, the CXCR4 antagonist AMD3100, which is employed in anti-HIV therapies, can counteract angiogenesis either in vitro or in animal models of human tumors (64–67).