CXCR4 and neoplasm: The results presented here demonstrate that targeting the CXCL12/CXCR4 axis in the orthotopic mouse model of spontaneously metastasizing OS by repetitive tail-vein bolus injections of the anti-CXCR4 mAb 12G5 slowed down the osteolytic tumor development and, even more importantly in the context of OS, significantly reduced the number of primary tumor cells that disseminated to the lung where they were recognized as apparently non-growing micrometastases.