Colon tumor
Carcinoid tumors
Carcinoid - Rectum

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

Revised: 23 May 2016, last major update March 2016

Copyright: (c) 2002-2015,, Inc.

PubMed Search: PubMed Search: Carcinoid rectum[title]
Cite this page: Carcinoid - rectum. website. Accessed October 25th, 2016.
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

Small rectal carcinoids on colonoscopy

Gross Description
  • Usually < 1 cm, round / polypoid, no ulceration
  • May appear yellow or pale
Micro 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
Micro Images

Images hosted on Pathout server - Contributed by Dr. Raul Gonzalez:

Small neuroendocrine tumor of the rectum

Synaptophysin positivity

Images hosted on other servers:

Rectal lesion

Small submucosal tumor

Rectal carcinoid and liver metastasis

Various images

Atypical carcinoid (left to right): H&E, angiolymphatic and perineural invasion, synaptophysin

Images hosted on Flickr:
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 non metastasizing, 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
Additional References