Colon (tumor & nontumor)
Neuroendocrine tumors
Neuroendocrine carcinoma

Topic Completed: 29 October 2019

Minor changes: 31 July 2020

Copyright: 2019,, Inc.

PubMed Search: Neuroendocrine carcinoma [title] colon

Raul S. Gonzalez, M.D.
Page views in 2019: 754
Page views in 2020 to date: 4,545
Cite this page: Gonzalez R. Neuroendocrine carcinoma. website. Accessed August 15th, 2020.
Definition / general
  • Full proper term is "poorly differentiated neuroendocrine carcinoma"
  • Two subtypes, based on morphology: large cell neuroendocrine carcinoma and small cell carcinoma
  • Usually in cecum or right colon but can arise anywhere
  • Disease typically presents at advanced stage
Clinical features
Prognostic factors
  • Good prognostic factors include peritumoral lymphocytes, microsatellite instability and pure large cell features; poor prognostic factors include CD117 positivity and vascular invasion (Am J Surg Pathol 2012;36:601)
  • Slightly improved prognosis if disease is not metastatic or patient responds to chemotherapy (Ann Surg Oncol 2014;21:2956)
Case reports
Radiology images

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Rectal mass

Noncontrast CT scans of abdomen

Gross images

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Resected bowel

Microscopic (histologic) description
  • Large cell: organoid arrangement of cells larger than those in small cell carcinoma, with nuclear pleomorphism and hyperchromasia, prominent nucleoli, numerous mitoses and tumor necrosis
  • Small cell: resembles pulmonary small cell carcinoma, with sheets and nests of small ovoid cells with minimal cytoplasm, hyperchromatic nuclei with stippled chromatin, nuclear molding with peripheral palisading, brisk mitotic activity, apoptotic cells, necrosis and vascular invasion; no prominent nucleoli or pleomorphism; may have Azzopardi effect (encrustation of nuclear material around blood vessels)
Positive stains
Electron microscopy description
  • Dense core secretory granules
Sample pathology report
  • Sigmoid colon, resection:
    • Poorly differentiated neuroendocrine carcinoma, see synoptic report and note.
      • NOTE: The tumor demonstrates large cell neuroendocrine carcinoma morphology. Immunostains show the tumor is positive for synaptophysin and chromogranin, with a Ki67 index of 85%. By definition, neuroendocrine carcinomas are WHO grade 3.
Differential diagnosis
Board review style question #1
    Which of the following is true about neuroendocrine carcinomas of the colorectum?

  1. Large cell and small cell subtypes have differences in prognosis and clinical management
  2. They are positive for synaptophysin but negative for chromogranin
  3. They can be any WHO grade
  4. They present at a younger average age than colorectal adenocarcinoma
Board review answer #1
D. They present at a younger average age than colorectal adenocarcinoma

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Reference: Neuroendocrine carcinoma
Board review style question #2
    A colorectal tumor is resected and appears to be a poorly differentiated adenocarcinoma, with focal but convincing gland formation. A synaptophysin immunostain is performed and shows patchy scattered positive staining in about 5% of cells. How should this tumor be diagnosed?

  1. Mixed neuroendocrine-nonneuroendocrine neoplasm
  2. Poorly differentiated adenocarcinoma
  3. Poorly differentiated neuroendocrine carcinoma (large cell neuroendocrine carcinoma)
  4. Poorly differentiated neuroendocrine carcinoma (small cell carcinoma)
Board review answer #2
B. Poorly differentiated adenocarcinoma

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Reference: Neuroendocrine carcinoma
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