The prostate-specific membrane antigen (PSMA), also known as Glutamate carboxypeptidase II (GCPII) or N-acetyl –L-aspartyl-L-glutamate peptidase I (NAALDAse I), is an integral type II cell-surface zinc-metalloprotease of 750 amino acids. PSMA is predominantly expressed in epithelial cells of prostate tissue, and also found in the brain, kidney tubules, small bowel, and in endothelial cells in certain solid tumor neovasculature. Its expression in normal and malignant prostate correlates with tumor aggressiveness, with highest levels in hormone refractory and metastatic disease.