Despite the introduction of new targeted therapies and cytotoxic agents, chemotherapy-pretreated metastatic breast cancer (MBC) remains an essentially incurable disease with only moderate median overall survival (OS). over 20 human tumor types overexpress C-X-C chemokine receptor type 4 (CXCR4). CXCR4 levels correlate with aggressive metastatic phenotypes and negative prognosis...