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WHO Classification of Tumours
Neuroendocrine tumor G1 (NET G1) / Carcinoid
Small intestine


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


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)
Enterochromaffin cell (EC), serotonin-producing NET
L cell, Glucagon-like peptide-producing and PP/PYY-producing NET
Gangliocytic paraganglioma