- Early intervention for recurrence has been shown to be of benefit but current methods of localizing recurrence are either insensitive (CT), non-specific (MRI) or both (bone scan) Many prostate cancers express the prostate specific membrane antigen (PSMA) a transmembrane protein with NAALADase (N-acetylated-alphalinked- acidic dipeptidase) and folate hydrolase enzymatic activity. PSMA is also expressed in angiogenesis but otherwise has limited expression in normal tissue.