Nuclear medicine imaging of neuroendocrine tumours

Different tracers have been proposed in nuclear medicine to visualize neuro endocrine tumours; the majority are based on specific uptake mechanisms whi le some are aspecific. Among the most important gamma-emitting tracers, rad iolabelled metaiodobenzylguanidine (I-123 or I-131-MIBG) and In-111-pentetr eotide should be mentioned. In particular, good results can be obtained wit h In-111-pentetreotide scanning, which visualizes more than 70% of all neur oendocrine tumours and in some indications, as in gastro-entero-pancreatic (GEP) tumours, has a diagnostic sensitivity superior to that of conventiona l radiological imaging. Radiolabelled monoclonal antibodies have at present only a storical value, while a series of new peptides represent interestin g subjects in areas currently being regarded. Positron emission tomography (PET) is a successful modality to detect cance r and recent years, has demonstrated a great diagnostic value in a large se ries of tumour types. F-18-deoxy-glucose (FDG)-PET has also been used to di agnose tumours of neuroendocrine origin. Even if F-18-FDG has been successf ully and widely employed in oncology, it has not demonstrated a significant uptake in well differentiated neuroendocrine tissues. On the contrary, oth er positron emitter tracers seem to be more promising. A serotonin precurso r 5-hydroxytryptophan (5-HTP) labelled with C-11 has shown an increased upt ake in carcinoids. This uptake seems to be selective and some clinical evid ence has demonstrated that it allows the detection of more lesions with PET than with CT or octreotide scintigraphy. Another radiopharmaceutical in de velopment for PET is C-11 L- DOPA, which seems to be useful in visualizing endocrine pancreatic tumours. This Review summarizes the potential of sever al nuclear medicine techniques in the diagnosis of neuroendocrine tumours a nd stresses the renewed role of nuclear medicine in the management of this disease.