Colon tumor
Carcinoid tumors
Carcinoid - rectum

Author: Raul Gonzalez, M.D. (see Authors page)

Revised: 22 May 2018, last major update March 2016

Copyright: (c) 2002-2018,, Inc.

PubMed Search: Carcinoid rectum [title]
Cite this page: Gonzalez, R. Carcinoid - rectum. website. Accessed June 21st, 2018.
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

Images hosted on Pathout server:

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