CXCL12 and Ewing sarcoma: Interestingly, Hamdan and colleagues recently demonstrated that Ewing sarcoma cell lines up-regulated PDGFB ligand in response to stromal-derived CXCL12 in vitro and in vivo; and that PDGFB promoted maturation of bone marrow-derived pericyte progenitor cells and thereby tumor vasculogenesis; whereas plerixafor diminished PDGFB expression and resulted in compromised tumor vasculature and apoptosis in vivo [49, 52].