الفهرس 
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Abstract
Including a wide range of clinicopathological entities, neuroendocrine tumours (NET) are a group of diverse neoplasms arising from cells of neuroendocrine origin. Recently, significant progress has been observed not only in our understanding of the biology and genetics of NET but also in the diagnosis and treatment.
The incidence of NET is increasing in the last few years . Although some series report slightly higher incidence in men compared to women, there appears no significant difference in terms of gender. 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), neurofi bromatosis type 1, von Hippel-Lindau (VHL) disease and tuberous sclerosis. In patients with these syndromes, the age of diagnosis is 15–20 years lower than those with sporadic NETs.
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. These secreted peptides/ amines can be used as tumour markers, and they may lead to clinical symptoms.
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 % of 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, vasoactive intestinal peptide (VIP), etc.
NETs have some common histopathologic characteristics. They show similar immune reactivity to pan-neuroendocrine markers, chromogranin A and synaptophysin . Neuron-specific enolase (NSE), CD56 and CD57 areless specific markers; they can be used to identify poorly differentiated NETs.
Immunohistochemical assessment of specific hormoneexpression is not routine in pathological evaluation, and positive immune reaction for hormone expression in the tumour tissue does not indicate that the tumour is functional.
NETs are graded based on mitotic count and Ki-67 index . Grading should be combined with organ-specific TNM staging system. Primary localization, size and invasion depth of the tumour and status of surgical margin of the excision resection material are also important.