CXCR4 and neoplasm: These niches possess immunological privilege and are abundant in signals (e.g., CXCL12-CXCR4, GAS6-AXL, TGF-β2, BMP-7) that promote and sustain dormancy, shielding disseminated tumor cells (DTCs) from immune surveillance and treatment [21,30,113,194,195,196].