label: Appendix Enterochromaffin Cell Serotonin-Producing Neuroendocrine Tumor
label_lc: appendix enterochromaffin cell serotonin-producing neuroendocrine tumor
description: A well-differentiated neuroendocrine tumor arising from the wall of the appendix.  It is characterized by the presence of neoplastic cells forming round solid nests and occasionally glandular structures.  The majority of the cases are asymptomatic, and they are found incidentally in appendectomy specimens.  The majority of the tumors are located in the distal end of the appendix and they are enterochromaffin-cell carcinoid tumors producing serotonin.  Most cases show morphologic evidence of appendiceal wall and lymphatic vessel invasion by tumor cells.  Despite the morphologic evidence of invasion, appendiceal carcinoid tumors only infrequently produce lymph node or distant metastases.