Theranostics has been part of nuclear medicine for decades, starting from the use of radioactive iodine-131, to the application in neuroendocrine tumors labeling somatostatin analogues with 68Ga-, 177Lu-, or 90Y-labeled somatostatin analogs and, more recently, in prostate cancer targeting the prostate-specific membrane antigen (PSMA). This evidence concerns the gene SST and neuroendocrine neoplasm.