Kidney tumor

Benign adult tumors

Well differentiated neuroendocrine tumor (carcinoid)

Topic Completed: 1 June 2012

Minor changes: 1 November 2021

Copyright: 2003-2021,, Inc.

PubMed Search: Well differentiated neuroendocrine tumor [title]

Sean R. Williamson, M.D.
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Cite this page: Williamson SR. Well differentiated neuroendocrine tumor (carcinoid). website. Accessed December 8th, 2021.
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 Sleiman Khalil, M.D., Ricardo Drut, M.D.

58 year old man with 7 cm carcinoid tumor

Well differentiated neuroendocrine tumor

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 #204

4 cm lower pole mass

Contributed by Sleiman Khalil, M.D.

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 #204




Contributed by Sleiman Khalil, M.D.







Contributed by Ricardo Drut, M.D.


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 #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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