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
OtherHigh Risk
EndocrineElevated Risk
GastricElevated Risk
PancreaticElevated 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%0.4%
FAP to age 801, 2, 3>99%2.8%
AFAP to age 801, 2, 3>70%2.8%
Other - Desmoid TumorsTo age 802, 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 803, 5, 62.6%-8.5%1.2%
Central Nervous SystemTo age 801, 2, 31%0.5%
PancreaticTo age 801, 2, 3Possibly elevated risk1.1%

APC Cancer Risk Management Table

The overview of medical management options provided is a summary of professional society guidelines. The most recent version of each guideline should be consulted for more detailed 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 colonoscopy110 to 15 yearsAnnually
Colorectal surgical evaluation and counseling.1, 7Based on cancer diagnosis and/or polyp number, size and histologyNA
Consider chemoprevention with NSAIDs to reduce adenoma burden after surgery.1NANA
Other - Desmoid TumorsAbdominal MRI or CT1When symptoms are presentAt least annually
Small Bowel/PeriampullaryUpper endoscopy, with consideration of capsule endoscopy to visualize the entire small bowel120 to 25 years, or earlier if there is a family history of small bowel adenomas or cancerEvery 3 to 5 years
HepatoblastomaConsider liver palpation, abdominal ultrasound, and alpha-fetoprotein (AFP) measurement.1InfancyEvery 3 to 6 months during first 5 years of life
GastricConsider screening for patients with high risk features1, 4IndividualizedIndividualized
ThyroidThyroid ultrasound1Late teensEvery 2 to 5 years, or consider more often if there is a family history of thyroid cancer
Central Nervous SystemPatient education about the importance of quickly seeking attention for signs and symptoms of neurologic cancer1IndividualizedNA
PancreaticConsider screening for patients with a family history of pancreatic cancer1IndividualizedIndividualized

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.

This patient's relatives are at risk for carrying the same mutation(s) and associated cancer risks as this patient. Cancer risks for females and males who have this/these mutation(s) are provided below.

Family members should talk to a healthcare provider about genetic testing. Close relatives such as parents, children, brothers and sisters have the highest chance of having the same mutation(s) as this patient. Other more distant relatives such as cousins, aunts, uncles, and grandparents also have a chance of carrying the same mutation(s). Testing of at-risk relatives can identify those family members with the same mutation(s) who may benefit from surveillance and early intervention.

Children should be tested for APC gene mutations by age 10-12 years, when colon cancer screening should begin. If hepatoblastoma sceening is being performed, APC genetic testing could be done in infancy.1

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.8

References

  1. Gupta S, et al. NCCN Clinical Practice Guidelines in Oncology® Genetic/Familial High-Risk Assessment: Colorectal. V 1.2021. May 11. Available at https://www.nccn.org.
  2. Jasperson KW, et al. APC-Associated Polyposis Conditions. 2017 Feb 2. In: Pagon RA, et al., editors. GeneReviews® [Internet]. PMID: 20301519.
  3. SEER*Explorer: An interactive website for SEER cancer statistics [Internet]. Surveillance Research Program, National Cancer Institute. [Cited 2020 Sep 14]. Available from https://seer.cancer.gov/explorer/.
  4. Ajani JA, et al. NCCN Clinical Practice Guidelines in Oncology®: Gastric Cancer. V 4.2021. Aug 3. Available at https://www.nccn.org.
  5. Uchino S, Age- and Gender-Specific Risk of Thyroid Cancer in Patients With Familial Adenomatous Polyposis. J Clin Endocrinol Metab. 2016 101:4611-4617. PMID: 27623068.
  6. Chenbhanich J, Prevalence of thyroid diseases in familial adenomatous polyposis: a systematic review and meta-analysis. Fam Cancer. 2019 18:53-62. PMID: 29663106.
  7. 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.
  8. 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 21-Apr-2022