Neuroendocrine tumors of GI Tract.

The World Health Organization (WHO) classifies neuroendocrine neoplasms as well-differentiated neuroendocrine tumors (either the primary tumor or metastasis) and poorly differentiated neuroendocrine carcinomas.

Historically, well-differentiated neuroendocrine tumors have been referred to as “carcinoid tumors,” a term which may cause confusion because clinically a carcinoid tumor is a serotonin-producing tumor associated with functional manifestations of carcinoid syndrome.

The use of the term “carcinoid” for neuroendocrine tumor reporting is therefore discouraged for these reasons.

Immunohistochemistry and other ancillary techniques are generally not required to diagnose well-differentiated neuroendocrine tumors. Specific markers that may be used to establish neuroendocrine differentiation include chromogranin A, synaptophysin, and CD56.
Because of their relative sensitivity and specificity, chromogranin A and synaptophysin are recommended.

Recommended Grading System for Well-Differentiated Gastroenteropancreatic Neuroendocrine Tumors

Because of site-specific similarities in histology, immunohistochemistry, and histochemistry, neuroendocrine tumors of the digestive tract have traditionally been subdivided into those of foregut, midgut, and hindgut origin . In general, the distribution pattern along the gastrointestinal (GI) tract parallels that of the progenitor cell type, and the anatomic site of origin of GI neuroendocrine tumors is an important predictor of clinical behavior.

Tumor Size
For neuroendocrine tumors in any part of the gastrointestinal tract, size greater than 2.0 cm is associated with a higher risk of lymph node metastasis. For jejunoileal tumors, nodal metastases occur in about 12% of patients with tumors smaller than 1.0 cm and in most patients with tumors larger than 1.0 cm. Thus, treatment for small intestine neuroendocrine tumor includes complete resection with regional lymphadenectomy.

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