Colon tumor
Familial polyposis syndromes of colon
Familial adenomatous polyposis of colon, Attenuated FAP (AFAP)

Author: Jennifer Findeis-Hosey, M.D. (see Authors page)
Editorial board review: Raul Gonzalez, M.D.

Revised: 3 March 2016, last major update February 2016

Copyright: (c) 2002-2016, PathologyOutlines.com, Inc.

PubMed Search: Familial adenomatous polyposis [title] attenuated
Cite this page: Familial adenomatous polyposis of colon, Attenuated FAP (AFAP). PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/colontumorafap.html. Accessed December 10th, 2016.
Definition / General
  • Subtype of familial adenomatous polyposis (FAP) characterized by fewer than 100 adenomatous colorectal polyps
  • Colonic adenomatous polyps have high risk for progression to colorectal adenocarcinoma (69% cumulative risk by age 80) (Gastroenterology 2004;127:444)
Essential Features
  • FAP variant characterized by markedly fewer polyps
  • Due to a defect in APC (5q21)
  • Patients might not require colectomy
Terminology
Epidemiology
  • Phenotypically and genetically heterogeneous (Gut 2006;55:1440)
  • Cancers usually develop at age 50 - 55 years, 15 years later than classic FAP
Sites
  • Patients may develop gastric fundic gland polyps, gastric or small bowel flat adenomas, and gastric / duodenal carcinomas (Cancer 1993;71:2709)
  • Extracolonic manifestations of classical FAP are less common in attenuated FAP
Diagnosis
  • Classically reserved for patients with fewer than 100 colonic adenomatous polyps, but exact diagnostic criteria have not been firmly established
Case Reports
Treatment
  • Patients with fewer than 20 - 30 polyps may not require total colectomy if they have frequent surveillance colonscopies with polypectomies
Gross Description
  • Polyps are usually more proximal (i.e., right sided) than in classic FAP
    • Rectum often spared
  • Polyps are flat, slightly raised, or plaque-like
  • May have minute central depression or umbilication
Micro Description
  • Adenomatous polyps are microscopically similar to sporadic-type adenomas
Micro Images

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Colonic tubular adenoma

Molecular / Cytogenetics Description
  • Associated with pathogenic variants in the 5' and distal 3' end of APC, as well as interstitial deletions of 5q22, which include the APC gene
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Differential Diagnosis