CXCL12 and Ewing sarcoma: Despite accumulating evidence that CXCL12 and CXCR4 affect proliferation and growth of ovarian (27), prostate (28,29) and breast cancer (9,30,31), glioma (32), glioblastoma (33,34), esophageal cancer (35), Ewing’s sarcoma (36) and chondrosarcoma (7), the role of the CXCL12-CXCR4 axis in the survival and growth of OS cells remains to be investigated.