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WHO Classification of Tumours
Neuroendocrine tumor G2 (NET G2)
Small intestine


Definition

Intestinal neuroendocrine tumours (NETs) and neuroendocrine carcinomas (NECs) are classified on the basis of criteria common to all gastrointestinal and pancreatic neuroendocrine neoplasms:
A neuroendocrine tumour (NET) is defined as a well-differentiated, neuroendocrine neoplasm composed of cells with features similar to those of the normal gut endocrine cell, expressing general markers of neuroendocrine differentiation (usually diffuse and intense chromogranin A and synaptophysin) and hormones (usually intense but not necessarily diffuse) according to site, with mild- to-moderate nuclear atypia and a low number of mitoses.
The proposed grading based on proliferation with the following definitions of mitotic count and Ki67 index:
G1 (NET G1) : mitotic count, <2 per 10 high power fields (HPF) and/or ≤2% Ki67 index;
G2 (NET G2): mitotic count 220 per 10 HPF and/or 320% Ki67 index

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Bosman FT, Carneiro F, Hruban RH, Theise ND (Eds.)
WHO Classification of Tumours of the Digestive System.
4th Edition
International Agency for Research on Cancer: Lyon 2010



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Commentary: Neuroendocrine tumours of the digestive system

Neuroendocrine neoplasms of the small intestine exhibit site-related differences, depending on their location in the duodenum and proximal jejunum when compared with distal jejunum, ileum and Meckel diverticulum.

> Histological subtypes
Gastrin-producing NET (gastrinoma)
Somatostatin-producing NET (somatostatinoma)
Enterochromaffin cell (EC), serotonin-producing NET
L cell, Glucagon-like peptide-producing and PP/PYY-producing NET
Gangliocytic paraganglioma