GRPR and prostate cancer: Among the cellular mechanisms and molecular targets that can be used for diagnostic imaging in prostate cancer patients are cell division, including upregulated metabolic activity and the synthesis of cell components; osteoblastic activity in bone metastases; and numerous extracellular antigens and receptors, e.g., androgen receptor, prostate-specific membrane antigen (PSMA), gastrin-releasing peptide receptor (GRPR), urokinase-type plasminogen activator (uPA), prostate stem cell antigen (PSCA), six transmembrane epithelial antigen of prostate (STEAP1), and CD46 [4].