Other tumors
Well differentiated neuroendocrine tumor

Topic Completed: 1 August 2012

Minor changes: 29 July 2020

Copyright: 2003-2020,, Inc.

PubMed Search: Well differentiated neuroendocrine tumor appendix

Page views in 2019: 7,388
Page views in 2020 to date: 4,685
Cite this page: Mansouri J. Well differentiated neuroendocrine tumor. website. Accessed August 15th, 2020.
Definition / general
  • Most common tumor of appendix, usually incidental (0.02% to 1.5% of all appendectomy specimens) and sporadic
Clinical features
  • Appendix is common site for endocrine tumors, as well as tumors with multiple directional differentiation
  • Incidence peaks at ages 20-39 years, 20 years earlier than intestinal carcinoid
  • 20% of all GI carcinoids arise in appendix
  • Nodal metastases and metastatic spread are rare, even with transmural extension
  • 5 year survival is 85% even with regional metastases
  • Rare liver metastases may be associated with carcinoid syndrome
  • L cell carcinoid:
    • Carcinoid tumor, much less common than classic tumors with insular pattern (EC cell tumors); cell of origin is usually the L cell, which produces enteroglucagons and peptide YY (Arch Pathol Lab Med 2010;134:1612)
    • Minimal metastatic potential
    • Small nodules at tip, often not identified grossly
    • Columns, ribbons, acini or small tubules of small round cells with pale eosinophilic cytoplasm and round/oval nuclei with small nucleoli
    • No/rare mitotic activity
    • No insular masses
    • May have dominant glandular, infiltrative pattern resembling metastatic carcinoma
  • Appendectomy usually is curative if less than 1 cm
  • Right hemicolectomy if > 2 cm or positive surgical margin or extremely pronounced mesoappendiceal spread
  • Perineural or angiolymphatic invasion are not predictive
Prognostic factors
For metastatic disease:
Case reports
  • 28 year old woman with hereditary nonpolyposis colorectal cancer syndrome, colonic adenocarcinoma with microsatellite instability and incidental appendiceal carcinoid tumor without microsatellite instability (Hum Pathol 2004;35:1564)
Gross description
  • 70% at tip, usually < 1 cm
  • Gray or yellow, well-demarcated, firm, intramural nodules that may narrow or obliterate lumen
  • Proximal tumors may cause obstruction
Microscopic (histologic) description
  • Three histologic subtypes including classic, tubular, and goblet cell types, although combined classical carcinoid and goblet cell carcinoid tumor was recently described (Am J Surg Pathol 2010;34:1163)
  • May be diffusely within wall or along lumen
  • Tumors arise in mucosa but bulk is usually within muscularis propria with associated fibrosis and smooth muscle hypertrophy
  • Usually classic carcinoid insular growth pattern of solid islands of uniform polygonal cells with minimal pleomorphism, retraction of peripheral tumor cells from stroma
  • Tumor cells often within intraappendiceal nerves; angiolymphatic invasion is common
  • Cells have granular eosinophilic cytoplasm with either diffusely scattered or peripherally clumped granules
  • Rarely acinar pattern, clear cell/balloon cell pattern or vacuolated cells
  • No/rare mitotic activity
  • May penetrate mesoappendix
  • Two types of well differentiated tumors: EC cell (serotonin producing) and rarely L-cell (enteroglucagon or peptide YY producing, Hum Pathol 1990;21:773)
  • Tumor cells associated with S100+ Schwann-like cells (sustentacular cells)
Molecular / cytogenetics description
  • May have 18q-, less frequently 11q-
  • Usually diploid by flow cytometry
Positive stains
  • Chromogranin, neuron specific enolase, serotonin, substance P
  • L cell carcinoid: positive for CEA, glucagon, peptide YY, pancreatic polypeptide
Negative stains
Back to top