5-HT, serotonin, 5-hydroxytryptamine; Akt, protein kinase B; BRAF, gene encoding serine/threonine-protein kinase B-Raf; Blood; CGH, comparative genomic hybridization; CREB, cAMP response element-binding protein; Carcinoid; CgA, chromogranin A; D cell, somatostatin; DAG, diacylglycerol; EC, enterochromaffin; ECL, enterochromaffin-like; EGFR, epidermal growth factor receptor; ERK, extracellular-signal-regulated kinase; G cell, gastrin; GABA, γ-aminobutyric acid; GEP-NEN, gastroenteropancreatic neuroendocrine neoplasms; GPCR, G-protein coupled receptor; Gastroenteropancreatic Neuroendocrine Neoplasms; IGF-I, insulin-like growth factor-I; ISG, immature secretory vesicles; Ki-67; LOH, loss of heterozygosity; MAPK, mitogen-activated protein kinase; MEN-1/MEN1, multiple endocrine neoplasia type 1; MSI, microsatellite instability; MTA, metastasis associated-1; NEN, neuroendocrine neoplasms; NFκB, nuclear factor κB; PET, positron emission tomography; PI3, phosphoinositide-3; PI3K, phosphoinositide-3 kinase; PKA, protein kinase A; PKC, protein kinase C; PTEN, phosphatase and tensin homolog deleted on chromosome 10; Proliferation; SD-208, 2-(5-chloro-2-fluorophenyl)-4-[(4-pyridyl)amino]p-teridine; SNV, single-nucleotide variant; SSA, somatostatin analog; SST, somatostatin; Somatostatin; TGF, transforming growth factor; TGN, trans-Golgi network; TSC2, tuberous sclerosis complex 2 (tuberin); Transcriptome; VMAT, vesicular monoamine transporters; X/A-like cells, ghrelin; cAMP, adenosine 3',5'-cyclic monophosphate; mTOR, mammalian target of rapamycin; miR/miRNA, micro-RNA