Kidney tumor
Other tumors
Well differentiated neuroendocrine tumor (carcinoid)

Topic Completed: 1 June 2012

Minor changes: 1 October 2019

Copyright: 2003-2019,, Inc.

PubMed Search: Well differentiated neuroendocrine tumor [title]

Sean R. Williamson, M.D.
Page views in 2019: 1,849
Page views in 2020 to date: 1,120
Cite this page: Williamson SR. Well differentiated neuroendocrine tumor (carcinoid). website. Accessed July 5th, 2020.
Definition / general
  • Very rare, low grade (well differentiated) neuroendocrine tumor with finely granular cytoplasm, uniform nuclei and stippled chromatin
  • Similar morphology to neuroendocrine tumors of other organs, though without a definitive cell of origin (Hum Pathol 2011;42:1554)
  • Also called low grade neuroendocrine carcinoma
  • Rare, < 100 cases reported; associated with horseshoe kidney, which has an increased risk of renal tumors in general or renal teratoma (Pol J Pathol 2011;62:72)
Clinical features
Radiology images

Contributed by
Dr. Sleiman Khalil, Syria

58 year old man with 7 cm carcinoid tumor

 Contributed by
 Dr. Ricardo Drut, Argentina

Well differentiated neuroendocrine tumor

Images hosted on other servers:

CT scan shows mass with calcifications

Prognostic factors
  • Age > 40 years, size > 4 cm, > 1 mitotic figure / 10 HPF, metastasis at diagnosis, extension through renal capsule (J Urol 2006;176:2359)
Case reports
Gross images

Case of the Week

4 cm lower pole mass

 Contributed by
 Dr. Sleiman Khalil, Syria

58 year old man with 7 cm carcinoid tumor

Microscopic (histologic) description
  • Pure or associated with teratoma
  • Usually well demarcated but may have focal infiltration
  • Extracapsular extension in 52%
  • Tightly packed cords, trabeculae with variable stroma, nests or ribbons; uniform cells with eosinophilic, finely granular cytoplasm and uniform nuclei with stippled chromatin
  • Often calcifications; no / rare mitotic activity, no necrosis
Microscopic (histologic) images

AFIP images

Insular pattern

Organoid pattern with classic nuclear features

Case of the Week #204




Contributed by Dr. Sleiman Khalil, Syria







Contributed by Dr. Ricardo Drut


Images hosted on other servers:

Various images

Cytology description
  • Monotonous plasmacytoid cells arranged singly and in small clusters
  • Occasional cells in acinar pattern resembling glandular differentiation
  • Tumor cells have fine speckled chromatin (Diagn Cytopathol 2007;35:306)
Cytology images

Images hosted on other servers:

Monotonous cells with granular cytoplasm

Clusters with round to oval nuclei

Staining consistent with neuroendocrine differentiation

Positive stains
Negative stains
Electron microscopy description
  • Membrane bound dense core granules
Electron microscopy images

Case of the Week #204

Prominent neurosecretory granules

Differential diagnosis
  • Metanephric adenoma: negative for neuroendocrine markers synaptophysin, chromogranin, CD56
  • Metastatic carcinoid tumor: clinical history of carcinoid tumor elsewhere, renal metastases may be multiple (BMC Urol 2010;10:22)
  • Neuroblastoma: may have neurofibrillary stroma, Homer-Wright pseudorosettes, catecholamine production
  • Papillary renal cell carcinoma: often foamy macrophages, no neuroendocrine nuclear features, negative for neuroendocrine markers synaptophysin, chromogranin, CD56
  • PNET: challenging due to overlap in expression of CD99, positive FISH for EWSR1 rearrangement may be helpful
  • Small cell carcinoma of kidney: high grade atypia with scant cytoplasm, molding, high mitotic / proliferative index
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