Position of nuclear medicine techniques in the diagnostic work-up of neuroendocrine tumors

In recent years nuclear medicine has contributed to the impressive development of the knowledge of neuroendocrine tumors in terms of biology (receptor scintigraphy), pharmacology (development of new tracers), and therapy (radiometabolic therapy). At present, it is impossible to plan the management of a patient affected by a neuroendocrine tumor without performing nuclear medicine examinations. The contribution of nuclear medicine had affected and improved the management of these patients by offering various important options that are part of the modern diagnosis and treatment protocols. The clinical experience and the literature confirm that, among the wide variety of tracers and nuclear medicine modalities available today, metaiodobenzylguanidine (MIBG) and DTPA-D-Phe-octreotide (pentetreotide) are the radiopharmaceuticals of current clinical use. Several new somatostatin analogues are under investigation. Positron emission tomography (PET) supplies a range of labelled compounds to be used for the visualization of tumor biochemistry. In addition to the first routinely used PET tracer in oncology, 18F-labelled deoxyglucose (FDG), a number of radiopharmaceuticals based on different precursors such as fluorodopamine and 5-hydroxytryptophan (5-HTP) are going to gain a clinical role. Of course, the diagnosis of neuroendocrine tumors has to be based on integrated information derived from different examinations including nuclear medicine studies. The clinical presentation of neuroendocrine tumors is highly variable: sometimes they manifest typical or atypical symptoms but they may also be detected by chance during an X-ray or ultrasound examination carried out for other reasons. At disease presentation nuclear medicine modalities are sometimes able to direct physicians towards the clinical diagnosis thanks to the specificity of their imaging mechanisms. They also play a role in disease staging and restaging, patient follow-up and treatment monitoring. In addition, the biological characterisation of neuroendocrine tissues (receptor status, glucose metabolism, differentiation, etc.) allows the interpretation of radiopharmaceutical uptake as a prognostic parameter and sometimes as a predictor of the response to treatment.