The potential of STEAP1 and STEAP2 as prognostic biomarkers has previously been demonstrated in many other cancers [28]; furthermore, STEAP1 and STEAP2 are reported to be excellent markers for identifying mesenchymal stem cells, which may be by far the most likely Ewing tumor origin cells and are highly sensitive markers [15]. This evidence concerns the gene STEAP1 and Ewing sarcoma.