FOLH1 and cancer: Several PCa-targeted PET tracers have emerged that bind specifically to cancer-specific membrane proteins or receptors: PSMA, gastrin-releasing peptide receptor (GRPR), AR, urokinase plasminogen activator (uPA), prostate stem cell antigen (PSCA), the six-transmembrane epithelial antigen of the prostate (STEAP1–4), and CD46 have been investigated extensively within the last few decades.