Familial Adenomatous Polyposis syndrome (FAP) or Attenuated Familial Adenomatous Polyposis syndrome (AFAP)



Additional Information

APC gene

Associated Syndrome Name: Familial Adenomatous Polyposis (FAP)/Attenuated Familial Adenomatous Polyposis (AFAP)

APC Summary Cancer Risk Table

Cancer Genetic Cancer Risk
ColorectalHigh Risk
GastricElevated Risk
PancreaticElevated Risk
OtherHigh Risk

APC gene Overview

Familial Adenomatous Polyposis (FAP)/Attenuated Familial Adenomatous Polyposis (AFAP) 1, 2
  • Individuals with APC mutations have either Familial Adenomatous Polyposis syndrome (FAP) or Attenuated Familial Adenomatous Polyposis syndrome (AFAP). The distinction between FAP and AFAP is based on the number of adenomatous polyps found in the patient, as described below.
  • Patients with FAP/AFAP have a greatly increased risk for colorectal cancer, often at very young ages.
  • Patients with FAP/AFAP are likely to develop large numbers of adenomatous polyps in the GI system, particularly in the colon, rectum, stomach and small bowel. Patients with 100 or more polyps are said to have a diagnosis of FAP and patients with less than 100 polyps are said to have a diagnosis of AFAP. These polyps begin to form at an average age of 16, but can be found in individuals as young as age 7.
  • Patients with FAP/AFAP also have a high risk for other cancers, most notably small bowel and periampullary cancer. There are also elevated risks for childhood hepatoblastoma, and cancers of the thyroid, pancreas, and central nervous system (CNS).
  • Gastric polyps are common, but the risk for gastric cancer is not thought to be significantly increased in patients living in Western cultures. A more significantly increased risk for gastric cancer has been observed in Japanese and Korean patients.
  • Patients with FAP, and less commonly, patients with AFAP, can have clinical findings other than cancer, such as osteomas, dental abnormalities, congenital hypertrophy of the retinal pigment epithelium (CHRPE) and benign cutaneous lesions. Desmoid tumors, which occur in some individuals with FAP, are the most serious cause of morbidity among affected individuals outside of cancer, and may be triggered by abdominal surgery.
  • Although there are high risks for cancer in patients with FAP/AFAP, these risks can be greatly reduced with appropriate medical management. Guidelines from the National Comprehensive Cancer Network (NCCN) are listed below. It is recommended that patients with APC mutations and a diagnosis of FAP or AFAP be managed by a multidisciplinary team with experience in the prevention and treatment of the complications associated with hereditary colorectal cancer conditions.

APC gene Cancer Risk Table

Cancer Type Age Range Cancer Risk Risk for General Population
ColorectalFAP to age 211, 2, 37%<0.1%
FAP to age 501, 2, 393%0.3%
FAP to age 801, 2, 3>99%3.0%
AFAP to age 801, 2, 3>70%3.0%
Other - Desmoid TumorsTo age 801, 310%-30%<0.04%
Small Bowel/PeriampullaryTo age 801, 2, 34%-12%0.2%
HepatoblastomaTo age 51, 2, 31%-2%<0.001%
GastricTo age 801, 2, 3, 4Slightly increased risk in Western cultures, but may be significantly increased in cultures with a higher baseline gastric cancer rate.0.6%
ThyroidTo age 801, 2, 31%-2%1.1%
Central Nervous SystemTo age 801, 2, 31%0.5%
PancreaticTo age 801, 2, 3Possibly elevated risk1%

APC Cancer Risk Management Table

The overview of medical management options provided is a summary of professional society guidelines as of the last Myriad update shown on this page. The specific reference provided (e.g., NCCN guidelines) should be consulted for more details and up-to-date information before developing a treatment plan for a particular patient.

This overview is provided for informational purposes only and does not constitute a recommendation. While the medical society guidelines summarized herein provide important and useful information, medical management decisions for any particular patient should be made in consultation between that patient and his or her healthcare provider and may differ from society guidelines based on a complete understanding of the patient’s personal medical history, surgeries and other treatments.

Cancer Type Procedure Age to Begin Frequency
(Unless otherwise indicated by findings)
ColorectalSigmoidoscopy or colonoscopy210 to 15 yearsAnnually
Colorectal surgical evaluation and counseling.2, 5, 6Based on cancer diagnosis and/or polyp number, size and histologyNA
Consider chemoprevention with NSAIDs to reduce adenoma burden after surgery.2NANA
Other - Desmoid TumorsAbdominal palpation with consideration of abdominal MRI or CT.21 to 3 years post-colectomyEvery 5 to 10 years, or with symptoms
Small Bowel/PeriampullaryUpper endoscopy, including complete visualization of the ampulla of Vater220 to 25 years, or earlier if patient had a colectomy before age 20 yearsEvery 4 years
HepatoblastomaConsider liver palpation, abdominal ultrasound, and alpha-fetoprotein (AFP) measurement.2InfancyEvery 3 to 6 months during first 5 years of life
GastricUpper endoscopy2, 420 to 25 years, or earlier if patient had a colectomy before age 20 yearsEvery 4 years
ThyroidThyroid examination and/or consider ultrasound.2Late teensAnnually
Central Nervous SystemPhysical examination2IndividualizedAnnually
PancreaticCurrently there are no specific medical management guidelines for pancreatic cancer risk in mutation carriers.NANA

Information for Family Members

The following information for Family Members will appear as part of the MMT for a patient found to have a mutation in the APC gene.

A major potential benefit of myRisk genetic testing for hereditary cancer risk is the opportunity to prevent cancer in relatives of patients in whom clinically significant mutations are identified. Healthcare providers have an important role in making sure that patients with clinically significant mutations are informed about the risks to relatives, and ways in which genetic testing can guide lifesaving interventions.

Children should be tested for APC gene mutations by age 10 years, when colon cancer screening should begin. If hepatoblastoma sceening is being performed, APC genetic testing could be done in infancy.2

Approximately 20% of individuals with FAP/AFAP have not inherited the APC mutation from a parent. In these cases the mutation has developed spontaneously in that individual (a de novo mutation). Once this occurs, the children of that individual are each at 50% risk of inheriting the mutation.7


  1. Jasperson KW, et al. APC-Associated Polyposis Conditions. 2017 Feb 2. In: Pagon RA, et al., editors. GeneReviews® [Internet]. Available from http://www.ncbi.nlm.nih.gov/books/NBK1345/ PMID: 20301519.
  2. Provenzale D, et al. NCCN Clinical Practice Guidelines in Oncology® Genetic/Familial High-Risk Assessment: Colorectal. V 1.2018. July 12. Available at http://www.nccn.org.
  3. Fast Stats: An interactive tool for access to SEER cancer statistics. Surveillance Research Program, National Cancer Institute. https://seer.cancer.gov/faststats. (Accessed on 1-2-2017)
  4. Ajani JA, et al. NCCN Clinical Practice Guidelines in Oncology®: Gastric Cancer. V 2.2018. May 22. Available at http://www.nccn.org.
  5. Achatz MI, et al. Cancer Screening Recommendations and Clinical Management of Inherited Gastrointestinal Cancer Syndromes in Childhood. Clin Cancer Res. 2017 23:e107-e114. PMID: 28674119.
  6. Syngal S, et al. ACG clinical guideline: Genetic testing and management of hereditary gastrointestinal cancer syndromes. Am J Gastroenterol. 2015 110:223-62. PMID: 25645574.
  7. Aretz S, et al. Somatic APC mosaicism: a frequent cause of familial adenomatous polyposis (FAP). Hum Mutat. 2007 28:985-92. PMID: 17486639.
Last Updated on 09-Jul-2019