Anus & perianal area


Small cell (neuroendocrine) carcinoma

Last author update: 31 March 2021
Last staff update: 21 April 2021

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PubMed Search: small cell carcinoma anus "free full text"[sb]

Raul S. Gonzalez, M.D.
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Cite this page: Gonzalez RS. Small cell (neuroendocrine) carcinoma. website. Accessed December 9th, 2022.
Definition / general
  • Poorly differentiated neuroendocrine carcinoma arising in the anus
Essential features
  • Rare primary neuroendocrine carcinoma of the anus
  • Very aggressive, with early metastatic spread; 5 year survival approximately 10%
  • Similar histology to small cell carcinoma at other sites
Radiology images

Images hosted on other servers:


PET scan

Metastatic disease

Case reports
  • Chemotherapy and radiation
Microscopic (histologic) description
  • Poorly differentiated neuroendocrine tumor composed of solid nests of small cells with minimal cytoplasm, hyperchromatic nuclei with molding, central necrosis and high mitotic activity
  • Resembles pulmonary counterpart
  • May have overlying squamous cell carcinoma in situ (Pathol Int 2012;62:356)
Microscopic (histologic) images

Contributed by Raul S. Gonzalez, M.D.
Small cell carcinoma Small cell carcinoma

Small cell carcinoma

Large cell carcinoma Large cell carcinoma

Large cell carcinoma

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Small cell carcinoma

Small cell carcinoma

Positive stains
Negative stains
  • CDX2 (positive in rectal small cell carcinomas)
Sample pathology report
  • Anus, mass, biopsy:
    • Small cell neuroendocrine carcinoma (see comment)
    • Comment: The carcinoma is positive for synaptophysin and chromogranin by immunohistochemistry. Neuroendocrine carcinomas are high grade by definition.
Differential diagnosis
Board review style question #1

This primary anal lesion is positive for pankeratin. What other stain would be expected to be positive?

  1. CD45
  2. CDX2
  3. Napsin A
  4. Synaptophysin
Board review style answer #1
D. Anal small cell carcinoma, like all neuroendocrine carcinomas, is positive for synaptophysin.

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Reference: Small cell (neuroendocrine) carcinoma
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