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Neuroendocrine Tumors of Large Bowel

Reviewer(s): Dharam M. Ramnani, MD
The gastrointestinal and pancreatobiliary tracts contain scattered clusters of neuroendocrine cells that form a diffuse endocrine system. The tumors arising from these cells are called neuroendocrine tumors (NETs) that display diverse clinical, biologic, and pathologic features ranging from well-differentiated NETs (Carcinoids) to highly aggressive neuroendocrine carcinomas.

The common underlying thread that connects them is the expression of neuroendocrine markers. They are related to medullary carcinoma of thyroid, pheochromocytoma, and pancreatic endocrine tumors and are seen in about 9% of patients with multiple endocrine neoplasia I.

Pancreatic and gastrointestinal NETs are graded into three tiers - G1, G2, and G3 - based on mitotic counts and/or Ki-67 labeling index. Necrosis, a recognized adverse prognostic indicator, is not taken into account for grading. Neuroendocrine carcinomas are considered high-grade by definition.

Iacobuzio-Donahue, C. A. & Montgomery E. (2012). Gastrointestinal and Liver Pathology; 2nd Edition. Philadelphia, PA. Elsevier Saunders.
Rindi G., et al. A common classification framework for neuroendocrine neoplasms: an International Agency for Cancer Research on Cancer (IARC) and World Health Organization (WHO) expert consensus proposal. Modern Pathology, Aug. 23, 2018.

Well-Differentiated Neuroendocrine Tumor (Carcinoid)

Neuroendocrine Carcinoma