STEAP1 (Six-Transmembrane Epithelial Antigen of the Prostate 1) is a cell surface protein that serves as a promising therapeutic target in cancer, particularly prostate cancer. Unlike other STEAP family members, STEAP1 does not function as a metalloreductase due to the absence of NADPH-binding sites, though it can promote Fe(3+) reduction when fused to NADPH-binding domains from other STEAP proteins [UniProt]. STEAP1 is overexpressed in multiple cancer types, with particularly high expression in metastatic castration-resistant prostate cancer (mCRPC), making it an attractive target for immunotherapy 1. The protein's cell membrane localization suggests a role in intercellular communication between tumor cells 2. STEAP1 demonstrates broad expression relative to other prostate cancer antigens like PSMA in lethal metastatic prostate cancers 3. Clinically, STEAP1-targeted therapies show significant promise, with the T-cell engager xaluritamig (AMG 509) demonstrating encouraging response rates in mCRPC patients (49% PSA50 response, 24% objective response rate) 4. STEAP1 is also being investigated as a target for CAR-T cell therapy and other novel immunotherapeutic approaches 3. However, antigen escape represents a potential resistance mechanism, highlighting the need for combination therapeutic strategies 3.