Introduction to Neuroendocrine Tumours

Abstract

Neuroendocrine tumours (NETs) are a group of diverse neoplasms arising from cells of neuroendocrine origin. Newer classification and staging systems have been adapted and guidelines published to help to establish a more standardised approach. The estimated incidence of 5.25/100,000 in 2004 is expected to reach to 8/100,000. Although NETs may occur at any age, it is more common after the age of 50. NETs may be associated with familial genetic neuroendocrine tumour syndromes such as multiple endocrine neoplasia (MEN) syndromes (MEN-1 and MEN-2), neurofibromatosis type 1, von Hippel-Lindau (VHL) disease, tuberous sclerosis and Carney complex. NETs are usually slow-growing tumours. They can arise from many organs but commonly from GI tract and pancreas, lung, thymus and other endocrine organs. NETs may synthesise and secrete peptides and/or amines. About 67 % of NETs are located in the GI system; these NETS are sometimes also called carcinoids or GI NETs. Carcinoids secrete numerous peptides, including serotonin (5-HT) and tachykinins. About 10 % GI NETs metastasize to liver and release 5-HT into the blood resulting in carcinoid syndrome characterised by cutaneous flushing, diarrhoea and abdominal pain. Pancreatic NETs comprise the second common group of NETs. These tumours may be functional (~40 %) or non-functional (~60 %). Functional pancreatic NETs are usually defined by the predominant, clinically relevant hormone secretion such as insulin, gastrin, glucagon and vasoactive intestinal peptide (VIP). NETs are graded based on mitotic count and Ki-67 index. Grading should be combined with organ-specific TNM staging system. NETs usually express somatostatin receptors; therefore, somatostatin expression can be used both diagnostically and therapeutically. Somatostatin receptor imaging (111In-DTPA-octreotide or preferably 68Ga-DOTATATE) can be used for initial staging, follow-up and selecting patients for peptide receptor radionuclide therapy (PRRT). Surgery is the only potentially curative treatment modality. Surgery should be considered for patients with early-stage disease, in patients with locoregional and resectable metastatic disease and in some selected symptomatic patients. Somatostatin analogues, interferon and systemic combination chemotherapy are the options for neuroendocrine carcinoma or advanced, inoperable, metastatic disease.