Six-transmembrane epithelial antigen of the prostate (STEAP) is expressed predominantly in human prostate tissue and in other common malignancies including prostate, bladder, colon, and ovarian carcinomas, and in Ewing's sarcoma, suggesting that it could function as an almost universal tumor antigen. Immunohistochemical analysis indicated STEAP-1 localization at cell-cell junctions of the secretory epithelium of prostate and prostate cancer cells. The favorable expression profiling of STEAP-1 in normal and cancer tissues suggested its potential use as a target for immunotherapy.