Endocrine Abstracts

Neuroendocrine tumors (NET) comprise a wide variety of neoplasms that have certain characteristics in common. However, they are defined not by site but by molecular characteristics. The most common forms arise in the gastrointestinal tract, but there are NET which are not directly related to this site, such as medullary cell carcinoma or small-cell lung cancer. Different secretory syndromes have also resulted in certain subtypes receiving names as carcinoid if they produce serotonin or insulinoma if they produce insulin, etc. It has to be realized however, that 50% are described as non-secretors. With respect to nuclear medicine techniques available, many reports have focussed on the use of meta-Iodobenzylguanidine (MIBG) and radiolabelled somatostatin analogs, such as Indium-111-octreotide. Especially In-111-octreotide has a reported sensitivity ranging from 65% for medullary thyroid cancer to almost 100% in small-cell lung cancers and pancreatic neuroendocriene tumors. Many other potential receptors other than the somatostatin receptors, such as GRP-R, CCK2, GLP-1-R, NK1 and VPAC1, have been developed and studied over the past years. It has been suggested that the simultaneous expression of multiple of these peptide receptors in NET provide the molecular basis for in vivo multireceptor targeting, thus improving the efficacy of radiolabelled peptides for diagnosing, staging and treating NET. Most of the peptides under study directed against the previously mentioned receptors were labelled with Indium-111 or Technetium-99m, both easily applicable in clinical practice. Despite optimal results of positron emission tomography (PET) using F18-deoxyglucose in many malignant tumors, its role in NET is still limited. In contrast, PET using F18-DOPA and Ga-68-DOTA octreotate has shown promise. C11-5-hyroxytryptophan (C11-5-HTP) has demonstrated specific and irreversibly entrapment by serotonin-producing tumors, but it has been shown that non-functioning or poorly differentiated tumors or necrotic ones cannot be detected accurately. Highly important improvements have been made by the introduction of hybrid cameras such as SPECT/CT or PET/CT. The combination of both techniques allows whole body imaging quickly providing functional and anatomic information. A close clinical relation between imaging and treatment with radiolabelled peptides has been established over the past decades. Many studies have reported good and/or promising results with respect to Lutetium-177 (Lu-177) and Yttrium-90 (Y-90) labelled peptides, such as Y-90 DOTATOC or Lu-177-lanreotide. In current presentation, an overview is given on the nuclear medicine diagnostic and therapeutic options and developments in neuroendocrine tumors.