Role of PET/CT in the functional imaging of endocrine pancreatic tumors

Endocrine pancreatic tumors (EPTs) are a heterogeneous group of neoplasms with variable clinical and biological features and prognosis, ranging from very slow-growing tumors to highly aggressive and very malignant ones. As other neuroendocrine tumors, EPTs are characterized by the presence of neuroamine uptake mechanisms and/or peptide receptors at the cell membrane and these features constitute the basis of the clinical use of specific radiolabeled ligands, both for imaging and therapy. The more widespread use of hybrid machines, i.e., positron emission tomography/computed tomography (PET/CT), allows to perform imaging with high resolution and high diagnostic accuracy especially for small lesions, and to correlate anatomic location with function. The recent WHO recommendations for classification and prognostic factors help the selection of tracers likely to show a positive image on PET; therefore, tracers exploiting specific metabolic patterns (18F-DOPA and 11C-5-HTP) or specific receptor expression (68Ga-DOTA-peptides) are suited to well-differentiated tumors, while the use of 18F-FDG is preferred for poorly-differentiated neoplasms with high proliferative activity and loss of neuroendocrine features. In differentiated EPTs, 11C-5-HTP performs better than 18F-DOPA even though its use is hampered by its complex production and limited availability and experience; 68Ga-peptides are indicated for all type of gastroenteropancreatic (GEP) neuroendocrine tumors, regardless of their functional activity. In addition, 68Ga-DOTA-peptides play a distinctive role in planning peptide receptor radionuclide therapy.