Peptide receptor imaging and therapy

Abstract

This article reviews the results of somatostatin receptor imaging (SRI) in patients with somatostatin receptor-positive neuroendocrine tumors, such as pituitary tumors, endocrine pancreatic tumors, carcinoids, gastrinomas, and paragangliomas, or other diseases in which somatostatin receptors may also be expressed, like sarcoidosis and autoimmune diseases. [(111)In-DTPA0]octreotide is a radiopharmaceutical that has great potential for helping visualize whether somatostatin receptor-positive tumors have recurred. The overall sensitivity of SRI to localize neuroendocrine tumors is high. In several neuroendocrine tumor types, inclusion of SRI in the localization or staging procedure may be very rewarding in terms of cost effectiveness, patient management, or quality of life. The value of SRI in patients with other tumors, such as breast cancer or malignant lymphomas, or in patients with granulomatous diseases has to be established. The application of radiolabeled peptides may be clinically useful in another way: after the injection of [(111)In-DTPA0]octreotide, surgeons can detect tumor localizations by a probe that is used during the operation. This may be of particular value if small tumors with a high receptor density are present (e.g., gastrinomas). As the success of peptide receptor scintigraphy for tumor visualization became clear, the next logical step was to try to label these peptides with radionuclides emitting alpha or beta particles, or Auger or conversion electrons, and to perform radiotherapy with these radiolabeled peptides. The results of the described studies with 90Y- and (111)In-labeled octreotide show that peptide receptor radionuclide therapy using radionuclides with appropriate particle ranges may become a new treatment modality. One might consider the use of radiolabeled somatostatin analogs first in an adjuvant setting after surgery of somatostatin receptor-positive tumors to eradicate occult metastases and second for cancer treatment at a later stage.