CXCR4 and neoplasm: CXCR4 is hypoxia-inducible [35] and CXCR4 expression on metastatic tumour cells induces homing of disseminated tumour cells to specific tissues that express high levels of the CXCR4-specific ligand stromal cell-derived factor-1α (SDF-1α/CXCL12) [36].