STEAP2 and Ewing sarcoma: STEAP1 and STEAP2, the members of the human six-transmembrane epithelial antigen of the prostate (STEAP) protein family, are highly over-expressed in many different cancer entities including prostate, bladder, breast, colon, and lung carcinoma, Ewing’s sarcoma, anaplastic thyroid carcinoma, and malignant melanoma (Hubert et al., 1999; Valenti et al., 2009; Gomes et al., 2012).