The six-transmembrane epithelial antigen of prostate 4 (STEAP4) is a member of a family of metalloreductases identified as cell-surface antigens in prostate tissue. Similar to two other members of the STEAP family (STEAP 2 and STEAP3), STEAP4 promotes both iron and copper reduction. STEAP4 is highly expressed in placenta, lung, heart and prostate tissues, and overexpressed in prostate cancer cells compared to normal prostate cells. Overexpression of STEAP4 in prostate cells significantly increases cell growth and colony formation, suggesting STEAP4 may have a role in cell proliferation and prostate cancer progression. At least two isoforms are known to exist for this protein. This STEAP4 antibody does not cross-react with other STEAP proteins.