Multiagent targeting of neuroendocrine neoplasms

Abstract

In the field of nuclear medicine, multiagent imaging can disclose enhanced expression of specific target molecules of neoplastic cells. This molecular information can be combined with the information provided by anatomical imaging. Over the past 20 years the use of radiolabeled somatostatin analogs as high-affinity tracers binding specifically to somatostatin receptors has allowed successful molecular imaging of neuroendocrine neoplasms (NENs), initially with single-photon-emitting radiopharmaceuticals, and subsequently also with positron-emitting radiopharmaceuticals. In this context, whole-body somatostatin receptor scintigraphy has changed the diagnostic and therapeutic approach to patients with NENs; moreover, somatostatin analog positron emission tomography (PET) tracers that allow higher spatial resolution imaging have recently been introduced. Nevertheless, several NENs can also be successfully imaged with radioagents that target the catecholamine pathway. Although radioiodinated meta-iodobenzylguanidine (MIBG) is traditionally the first option for radionuclide imaging and treatment of these NENs, the use of PET with 18F-l-dihydroxyphenylalanine is being increasingly reported, this approach showing several advantages over conventional imaging. Moreover, changes in tumor biology can be characterized by modifications in receptor or transporter expression on the cell membrane, and evidence has recently emerged that NENs expressing glucose transporters are more aggressive than tumors with low expression of glucose transporters. Therefore, [18F]FDG PET could provide prognostic information useful for stratifying patients according to their risk and for planning the correct therapy. The identification of new radiopharmaceuticals specific for different targets will constitute the basis not only of new diagnostic imaging approaches, but also of new therapeutic applications in NENs, besides radiolabeled peptide receptor radionuclide and 131I-MIBG therapy.