STEAP-1: A Potential Biomarker, Promising Target?

Abstract

STEAP1 is one of six-transmembrane epithelial antigen of prostate (STEAP) highly expressed in human prostate cancer and is up-regulated in multiple cancers, including bladder, colon, breast, Ewing and lung cancers. Immunohistochemical analysis demonstrates significant STEAP1 expression at the intercellular communication between adjacent cells suggesting that this antigen must be a channel, or a transport protein indicating its potential role in tumor cell intercellular communication increasing the potential of STEAP1 as a diagnostic, prognostic, prophylactic and/or therapeutic target for new immunotherapeutic strategies. In prostate cancer, overexpression relates adenocarcinoma and prostatic intraepithelial neoplasia scores suggest that STEAP1 could be involved in tumor initiation and progression and may be of clinical usefulness in early disease diagnosis. Also, STEAP1 can serve as a biomarker of worse prognosis because of its association with higher Gleason score, seminal vesicle invasion, biochemical recurrence, and worse outcome. Therapeutically, STEAP1 is one of a few prostate cancer antigens that meet the appropriate criteria and represent an attractive target for antibody cancer therapy. It can be a target of anti-tumor CD8, or serve as a tool for vaccination as shown by xenograft models and phases I/II studies. STEAP1 could also serve as a new marker of tumor angiogenesis in lung cancer, indicate for occult residual tumor cells in patients with Ewing Sarcoma and also be used as a cell surface antigen for the development of breast cancer immunotherapy. The standardization of its evaluation as well as the validation through randomized trials would be necessary.