Colon tumor
Neuroendocrine neoplasms
Carcinoid - rectum

Topic Completed: 1 March 2016

Minor changes: 23 May 2020

Copyright: 2002-2019,, Inc.

PubMed Search: Carcinoid rectum [title]

Raul S. Gonzalez, M.D.
Page views in 2019: 4,800
Page views in 2020 to date: 1,629
Cite this page: Gonzalez R. Carcinoid - rectum. website. Accessed June 1st, 2020.
Definition / general
Essential features
  • Most common carcinoid of colorectum
  • Good prognosis overall, but larger tumors can behave aggressively
  • Positive for neuroendocrine markers but also PSAP (a potential pitfall)
  • Proper term is "rectal well differentiated neuroendocrine tumor"
  • Rectum is most common site of well differentiated neuroendocrine tumor of colorectum; colon is less common
Prognostic factors
Case reports
Clinical images

Images hosted on other servers:

Small rectal carcinoids on colonoscopy

Gross description
  • Usually < 1 cm, round / polypoid, no ulceration
  • May appear yellow or pale
Microscopic (histologic) description
  • Islands, trabeculae, gland-like structures or sheets of monotonous neuroendocrine cells with amphophilic granular cytoplasm and round nuclei with "salt and pepper" chromatin
  • Usually minimal pleomorphism and little to no mitotic activity
  • Rarely mucin secretion or anaplasia; no necrosis
Microscopic (histologic) images

Contributed by Yuri Tachibana, M.D., Nagasaki University

Rectal WD-NET

Nested pattern


 Contributed by Dr. Raul Gonzalez

Small neuroendocrine tumor of the rectum

Synaptophysin positivity

Images hosted on other servers:

Small submucosal tumor

Rectal carcinoid and liver metastasis

Various images

Atypical carcinoid

Missing Image

Nested rectal carcinoid tumor

Chromogranin+ tumor

Negative stains
Electron microscopy description
  • Cytoplasmic, well formed membrane bound secretory granules with dense (osmophilic) cores
Molecular / cytogenetics description
  • Diploid if nonmetastasizing, aneuploid if metastatic
Differential diagnosis
  • Prostatic adenocarcinoma: positive for PSA, negative for neuroendocrine markers
  • Metastasis from other location: PAX8 is negative in ileal and pulmonary carcinoids but positive in rectal carcinoid tumors
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