A band of ~ 45 kDa corresponded to the glycosylated CXCR4 monomer and was present in all cell lines including HL-60, whereas a 55 kDa isoform was restricted to Ewing sarcoma lines and thus dispensable for the proliferative plerixafor-response of HL-60 cells. Here, CXCR4 is linked to Ewing sarcoma.