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PubMed This is a summary of 19 peer-reviewed journal articles Updated
Gastroenterology

FAP Beyond the Colon: Other Organs at Risk

At a Glance

Familial Adenomatous Polyposis (FAP) is a multisystem condition that affects organs beyond the colon. Because the APC gene mutation is present throughout the body, patients require lifelong screening for duodenal polyps, desmoid tumors, and thyroid cancer.

While the “Polyposis” in FAP refers to the colon, FAP is actually a multisystem condition. Because the APC gene mutation is present in almost every cell of your body, polyps and other growths can occur in several different organs. Understanding these “extracolonic” (outside the colon) manifestations is a key part of long-term health management.

The Duodenum and Stomach

After the colon is managed, the duodenum (the first part of the small intestine) becomes the most important area to monitor.

  • Duodenal Polyps: Almost everyone with FAP will eventually develop polyps in the duodenum [1]. Doctors use the Spigelman Staging System to grade these polyps based on their number, size, and appearance [2][3].
  • The Ampulla: A specialized area called the ampulla of Vater (where digestive juices enter the intestine) is a high-risk spot for polyps and requires careful inspection with a side-viewing endoscope [4].
  • Gastric Polyps: Many patients develop fundic gland polyps in the stomach. These are usually harmless, but they still require regular monitoring as gastric cancer risk is an emerging concern in FAP [5][6].

Desmoid Tumors: A Unique Challenge

Desmoid tumors are one of the most significant complications of FAP. They are not “cancer” because they do not spread to distant organs, but they are “locally aggressive,” meaning they can grow into nearby tissues like a vine [7][8].

  • Location: In FAP, they most commonly occur inside the abdomen or in the abdominal wall [1].
  • Triggers: They often appear after a “trigger” event, such as abdominal surgery or pregnancy [1].
  • Management: Because they can grow back frequently after surgery, doctors often prefer active surveillance (closely watching the tumor) or systemic medications instead of immediate removal [9][10].

Thyroid Cancer (Cribriform-Morular Variant)

Patients with FAP have an increased risk of a very specific type of thyroid cancer called the cribriform-morular variant (CMV-PTC) [11].

  • Who is at risk: This most commonly affects women under the age of 35 [12].
  • Prognosis: While it sounds intimidating, this variant generally has an excellent prognosis and tends to be less aggressive than other forms of thyroid cancer [13][14].
  • Screening: Annual physical neck exams (palpation) and ultrasounds are often recommended starting in the teens, though doctors may balance ultrasounds against the risk of over-biopsying harmless nodules [4].

CHRPE: The Eye as a Window

Congenital Hypertrophy of the Retinal Pigment Epithelium (CHRPE) are flat, dark spots on the retina at the back of the eye [15].

  • Diagnostic Clue: These spots do not affect vision, but they are a “tell-tale sign” of FAP. If an eye doctor sees multiple, bilateral (in both eyes) lesions, it is a strong indicator that the person has FAP [16][17].
  • Early Marker: Because these spots are present at birth, an eye exam can be one of the earliest ways to screen children in families with a history of FAP [15][18].

Summary of Surveillance Beyond the Colon

Current guidelines (such as those from the NCCN) recommend a structured approach to monitoring these areas:

Organ Screening Method Starting Age
Duodenum/Stomach Upper Endoscopy (EGD) Age 20–25 [4]
Thyroid Physical Exam & Annual Ultrasound Late teens [4]
Liver (Children) AFP Blood Test & Ultrasound Birth to Age 5 [4]
Eyes Baseline Eye Exam At Diagnosis [19]
Desmoids Physical Exam & Imaging Ongoing [4]

Common questions in this guide

What are extracolonic manifestations of FAP?
Extracolonic manifestations are polyps, tumors, and other growths that occur outside the colon due to the APC gene mutation. In FAP, this commonly includes the duodenum, stomach, thyroid, and eyes.
What is the Spigelman Staging System?
The Spigelman Staging System is a grading method doctors use to evaluate polyps in the duodenum. It looks at the number, size, and appearance of the polyps to determine your risk level and guide how often you need an upper endoscopy.
Are desmoid tumors in FAP considered cancer?
No, desmoid tumors are not considered cancer because they do not spread to distant organs. However, they are locally aggressive and can grow into nearby tissues like a vine, which is why doctors often monitor them closely with active surveillance.
Why do I need an eye exam for a colon condition?
Eye doctors look for flat, dark spots on the retina known as CHRPE. While these spots are completely harmless and do not affect your vision, they are present at birth and serve as a strong early diagnostic clue that a person has FAP.
Does FAP increase the risk of thyroid cancer?
Yes, FAP increases the risk of a specific, highly treatable type called the cribriform-morular variant of thyroid cancer, particularly in women under 35. Regular physical neck exams and annual ultrasounds are recommended starting in the late teens to monitor this risk.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.What is my current Spigelman stage, and how does it change my screening schedule for the duodenum?
  2. 2.Is a side-viewing endoscope being used during my EGD to properly check the ampulla?
  3. 3.Should I have a baseline thyroid ultrasound, and how often should it be repeated?
  4. 4.Based on my specific APC mutation and family history, what is my risk for developing desmoid tumors?
  5. 5.If I need surgery in the future, how will the care team monitor for desmoid development afterward?
  6. 6.Can an eye exam help confirm the diagnosis for other family members who haven't had genetic testing yet?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (19)
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    Targeted next-generation sequencing approach for molecular genetic diagnosis of hereditary colorectal cancer: Identification of a novel single nucleotide germline insertion in adenomatous polyposis coli gene causes familial adenomatous polyposis.

    Wang D, Liang S, Zhang X, et al.

    Molecular genetics & genomic medicine 2019; (7(1)):e00505 doi:10.1002/mgg3.505.

    PMID: 30523670
  2. 2

    The impact of chromoendoscopy for surveillance of the duodenum in patients with MUTYH-associated polyposis and familial adenomatous polyposis.

    Hurley JJ, Thomas LE, Walton SJ, et al.

    Gastrointestinal endoscopy 2018; (88(4)):665-673 doi:10.1016/j.gie.2018.04.2347.

    PMID: 29702101
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    Spigelman stage IV duodenal polyposis does not precede most duodenal cancer cases in patients with familial adenomatous polyposis.

    Thiruvengadam SS, Lopez R, O'Malley M, et al.

    Gastrointestinal endoscopy 2019; (89(2)):345-354.e2 doi:10.1016/j.gie.2018.07.033.

    PMID: 30081000
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    Updated European guidelines for clinical management of familial adenomatous polyposis (FAP), MUTYH-associated polyposis (MAP), gastric adenocarcinoma, proximal polyposis of the stomach (GAPPS) and other rare adenomatous polyposis syndromes: a joint EHTG-ESCP revision.

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    The British journal of surgery 2024; (111(5)) doi:10.1093/bjs/znae070.

    PMID: 38722804
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    Endoscopic Surveillance of Duodenal Polyposis After Total Gastrectomy in Familial Adenomatous Polyposis.

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    ACG case reports journal 2020; (7(8)):e00445 doi:10.14309/crj.0000000000000445.

    PMID: 32903873
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    Endoscopic scoring indices for assessing disease severity in familial adenomatous polyposis: Systematic review.

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    Endoscopy international open 2024; (12(6)):E799-E809 doi:10.1055/a-2330-8037.

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    Desmoid fibromatosis of the cruris: A rare case report.

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    Current management of familial adenomatous polyposis.

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    Evaluating Management of Extra-Abdominal Desmoid Fibromatosis: A Retrospective Analysis of Treatments, Outcomes and Recurrence Patterns.

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    Desmoid-type fibromatosis: toward a holistic management.

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    Current opinion in oncology 2021; (33(4)):309-314 doi:10.1097/CCO.0000000000000743.

    PMID: 33973549
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    Clinicopathological and molecular mechanisms of cribriform morular thyroid carcinoma: a case report and a literature review.

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    Age- and Gender-Specific Risk of Thyroid Cancer in Patients With Familial Adenomatous Polyposis.

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    The Journal of clinical endocrinology and metabolism 2016; (101(12)):4611-4617 doi:10.1210/jc.2016-2043.

    PMID: 27623068
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    Cribriform-Morular Variant of Papillary Thyroid Carcinoma: Clinical and Pathological Features of 30 Cases.

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    Use of congenital hypertrophy of the retinal pigment epithelium as a clinical sign of familial adenomatous polyposis.

    Carvalho AA, Crespo TS, Násser LS, et al.

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    Retinal Pigment Epithelial Hamartomas in Familial Adenomatous Polyposis: New Insights Based on Multimodal Imaging of 233 Lesions.

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    Congenital Hypertrophy of Retinal Pigment Epithelium for Diagnosis of Familial Adenomatous Polyposis - the First FAP registry in Iran

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    Congenital Hypertrophy of the Retinal Pigment Epithelium (CHRPE) as a Screening Marker for Familial Adenomatous Polyposis (FAP): Systematic Literature Review and Screening Recommendations.

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This page is for informational purposes only and does not replace professional medical advice. Always consult your gastroenterologist or genetic counselor about your specific FAP screening schedule.

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