Anatomopathological classification of Neuroendocrine tumors (NETs), today, covers a pivotal role in correctly identifying the disease and establish the right diagnostic and therapeutic approach it is needed in order to manage the patient. Depending on its grading and staging, NENs can have very different prognostic perspectives. Basing on WHO 2017 classification, in this paper will be explored their main characteristics, diving into main histotypes, dividing them into functional and non-functional tumors, keeping in mind their main locations: gastroenteropancreatic tract and lungs. Their typical clinical presentation and diagnostic strategies will be explained, mainly focusing on nuclear medicine and the importance of receptor overexpression (especially represented by somatostatin receptors, or SSTRs). This is the knowledge on which is based the diagnostic and therapeutic approach with peptide radiopharmaceuticals, especially 68Ga-DOTA-peptides (today, the gold standard in well-differentiated neuroendocrine neoplasms, only with the exception of insulinoma, that shows a low density of these molecules on its cellular surface)
