Current and Future Radiopharmaceuticals in Neuroendocrine Tumor Imaging

Abstract

Neuroendocrine tumors (NETs) comprise a heterogeneous group of hormonally active and nonactive neoplasms. NET cells are characterized by the presence of peptide receptors at the cell membrane and by neuroamine uptake mechanisms. These features constitute the basis of the clinically used radiopharmaceuticals in NET imaging. Along with the noradrenaline analog 123I-MIBG, somatostatin receptor scintigraphy and single photon emission (computed) tomography (SPE(C)T) using 111In- or 99mTc-labeled somatostatin analogs were, until recently, the main imaging technique for NETs. Significant improvements have been made during the past few years with the development of highly specific positron emission tomography (PET) radiopharmaceuticals for metabolic imaging of NETs, such as the glucose metabolism (18F-FDG) or the uptake of amine precursors (18F-DOPA or 11C-5-HTP). However, somatostatin receptor imaging is by far the most advanced imaging technique for NETs. PET/CT with gallium-68-labeled somatostatin analogs, such as 68Ga-DOTA-TOC, 68Ga-DOTA-TATE, and 68Ga-DOTA-NOC, is the new gold standard with sensitivity and specificity well beyond 90 %. The radiolabeled somatostatin receptor antagonists represent the recent most promising innovation in molecular imaging of NETs. The success of somatostatin receptor imaging has paved the way for the development of other peptide-based radiopharmaceuticals, including exendin and gastrin that are also discussed herein. The chapter is authored, more particularly, from the perspective of the radiopharmaceutical design and development.