CXCR4 Chemokine receptor; guides cells to CXCL12-rich organs. Binds CXCL12 to direct cancer cell homing/migration to metastatic sites (lung, liver, bone). Endothelial cells produce CXCL12; CXCR4+ tumor cells adhere to the vasculature and extravasate. CXCR4 is expressed on fibroblasts/CAFs; CXCL12 from stroma promotes tumor-CAF interactions. Highly expressed on MSCs; mediates MSC homing and survival. The gene discussed is CXCL12; the disease is cancer.