Neuroendocrine Tumour (NET)
A tumour arising from neuroendocrine cells, most commonly in the GI tract and pancreas. Many NETs overexpress somatostatin receptors, enabling treatment with somatostatin analogues and targeted radiotherapy with lutetium Lu-177 dotatate (peptide receptor radionuclide therapy).
Technical Context
WHO NET classification: well-differentiated NETs (Grade 1: Ki-67 <3%; Grade 2: Ki-67 3-20%; Grade 3: Ki-67 >20% but well-differentiated morphology) and poorly differentiated neuroendocrine carcinomas (NEC: Ki-67 >20%, poorly differentiated, aggressive). Functional NETs secrete hormones causing clinical syndromes: insulinoma (hypoglycaemia), gastrinoma (Zollinger-Ellison syndrome), glucagonoma, VIPoma (watery diarrhoea), carcinoid (serotonin → flushing/diarrhoea). SSTR expression: 70-90% of well-differentiated NETs express SSTR2, enabling: Ga-68 DOTATATE PET diagnostic imaging (identifying tumour location and SSTR status), somatostatin analogue therapy (octreotide LAR, lanreotide — controlling hormone secretion + antiproliferative effect in well-differentiated G1-G2 NETs — PROMID and CLARINET trials), and PRRT with Lu-177 dotatate (NETTER-1 trial: significant PFS improvement in midgut NETs progressing on octreotide LAR). Treatment sequence: surgery (cure for localised disease) → SSA (antiproliferative + symptom control) → PRRT or everolimus/sunitinib for progressive disease.