# Familial Adenomatous Polyposis

Familial adenomatous polyposis requires early APC-directed family testing, intensive colorectal surveillance, timely risk-reducing colectomy, and lifelong upper gastrointestinal assessment with ampullary visualization to prevent colorectal and duodenal malignancy.

**Clinical question:** How should physicians diagnose, surveil, and select risk-reducing surgery for patients with familial adenomatous polyposis?

Updated: 2026-09-16T00:55:24.613283+00:00

## What matters in practice
- Confirm APC-associated polyposis with germline APC testing and use the familial pathogenic variant for predictive testing of at-risk relatives. [21]
- Begin colorectal surveillance in classic FAP at age 10-15 years; confirmed FAP surveillance intervals can be individualized to colon phenotype, generally every 1-3 years. [21][2]
- Move from endoscopic management to colectomy when adenomas larger than 10 mm cannot be reasonably removed, adenoma burden accelerates, high-grade dysplasia is present, or the colon cannot be adequately surveyed. [21]
- Perform EGD with ampullary visualization by age 20-25 years or before colon surgery; use Spigelman staging for duodenal adenomatous burden and consider complete small-bowel evaluation with advanced disease. [21][11]
- Do not use NSAIDs or erlotinib as substitutes for colectomy: adenoma regression has been observed, but no FDA-approved chemopreventive agent has established prevention of subsequent cancer. [21]

## Establish APC-associated polyposis and identify relatives who need early surveillance

Genotype directs predictive testing and determines whether intensive surveillance should begin in childhood.

Establish an APC-associated polyposis condition by identifying a heterozygous germline pathogenic APC variant. Classic and attenuated FAP are APC-associated phenotypes; gastric adenocarcinoma and proximal polyposis of the stomach is also included in the APC-associated spectrum. [21]

A clinical phenotype of more than 100 colorectal adenomatous polyps supports classic FAP; fewer than 100 adenomas with a family history of FAP also supports the diagnosis. Attenuated FAP generally has fewer than 100 adenomas, later polyp development, and a more proximal colonic distribution. [10][17]

For a known familial APC pathogenic variant, offer predictive molecular testing to at-risk relatives early enough to determine whether childhood surveillance is necessary. In confirmed FAP after predictive testing, colonic surveillance should normally begin at age 12-14 years; GeneReviews recommends colonoscopy every 1-2 years beginning at age 10-15 years for classic FAP. [2][21]

When a patient has multiple colorectal adenomas but no germline APC or MUTYH variant, retain concern for APC mosaicism rather than labeling the condition sporadic without further assessment. Low-level APC mosaicism accounts for a substantial fraction of otherwise unexplained adenomatous polyposis, and first-degree relatives may warrant colonoscopic risk assessment at referral or again at age 50 years, although this latter recommendation lacked guideline consensus. [1][2]
- Use the known familial APC variant for predictive testing rather than relying on serial endoscopy alone when informative testing is available. [21]
- In a patient with 10 or more metachronous adenomas after clearing lesions larger than 5 mm, perform annual colonoscopy; if subsequent examinations show no polyp 10 mm or larger, extend to every 2 years. [2]

*Phenotype and surveillance distinctions in APC-associated polyposis. [2][10][21]*

| Clinical setting | Actionable interpretation | Next surveillance action |
| --- | --- | --- |
| Classic FAP phenotype | More than 100 colorectal adenomatous polyps supports clinical FAP. [10] | Begin colonoscopy at age 10-15 years; repeat every 1-2 years. [21] |
| Attenuated FAP phenotype | Usually fewer than 100 adenomas, often with later onset and proximal predominance. [17] | Begin colorectal surveillance in late adolescence. [21] |
| Confirmed FAP by predictive testing | APC pathogenic variant identifies patients at high colorectal and upper GI risk. [21] | Colonic surveillance may be individualized to phenotype every 1-3 years. [2] |
| Multiple metachronous adenomas after clearance | At least 10 metachronous adenomas indicates substantial recurrent adenoma burden. [2] | Annual colonoscopy; extend to every 2 years only if no subsequent lesion is 10 mm or larger. [2] |

## Use colonoscopic burden and histology to time colectomy

The operative decision is driven by endoscopic controllability and dysplasia, not by a fixed polyp count alone.

Continue colonoscopic surveillance while adenomas remain endoscopically manageable, but refer for colectomy planning when multiple adenomas larger than 10 mm cannot reasonably be removed, adenoma number increases substantially between examinations, high-grade dysplasia is identified, or innumerable diminutive adenomas prevent adequate colonic surveillance. Limited endoscopic access or inability to adhere to surveillance is also a relative indication for colectomy. [21]

Colectomy is the preventive standard for classic FAP because it reduces colorectal cancer risk. The operation should be selected and timed through a colorectal surgery team able to integrate rectal polyp burden, endoscopic feasibility, patient reliability for lifelong surveillance, and competing extracolonic disease. [21]

Surveillance materially changes outcomes. In a systematic review, symptomatic FAP presentation was associated with colorectal cancer in 33.6%-66.2% of patients versus 3.8%-9.4% among those under surveillance; surveillance delayed colorectal cancer development by up to 16 years and improved mean survival by up to 12 years. [9]

Do not defer indicated surgery because pharmacologic polyp regression occurs. NSAIDs and erlotinib have reduced adenoma burden in studies, but no agent is FDA-approved for FAP chemoprevention because reduction in later cancer risk remains unclear. Colectomy or proctocolectomy remains initial standard care. [21][16]
- Escalate to operative planning after high-grade dysplasia, rapid interval increase in adenoma burden, or failure to clear adenomas larger than 10 mm endoscopically. [21]
- Treat inability to maintain adequate colonoscopic surveillance as an oncologic risk factor, not solely a logistical issue. [21]
- Continue surveillance after prophylactic colorectal surgery because adenocarcinoma and pouch neoplasia have been reported after prophylactic operations. [1]

*Colorectal decision triggers for FAP. [21]*

| Finding | Interpretation | Action |
| --- | --- | --- |
| Adenomas controlled by endoscopic resection | Colon remains adequately surveillable. [21] | Continue phenotype-directed colonoscopic surveillance. [2][21] |
| Multiple adenomas larger than 10 mm not reasonably removable | Endoscopic clearance is inadequate. [21] | Refer for risk-reducing colectomy planning. [21] |
| High-grade dysplasia | Advanced neoplastic change raises urgency of definitive colorectal management. [21] | Proceed with colorectal surgical evaluation for colectomy. [21] |
| Innumerable diminutive adenomas, poor access, or inability to comply with surveillance | Adequate cancer surveillance cannot be ensured. [21] | Treat as a relative indication for colectomy. [21] |

## Perform lifelong upper GI surveillance with ampullary assessment

After colorectal risk reduction, duodenal and periampullary neoplasia become central management targets.

Perform esophagogastroduodenoscopy with visualization of the ampulla of Vater by age 20-25 years or before colon surgery. Upper GI surveillance should not omit ampullary inspection, because duodenal and ampullary adenomas can progress independently of the colorectal phenotype. [21][14]

Stage duodenal adenomatosis using the Spigelman classification, which is recommended for risk stratification and has demonstrated excellent interobserver reliability among experienced endoscopists (intraclass correlation coefficient 0.95, 95% CI 0.91-0.98). In advanced Spigelman stage, consider complete small-bowel visualization. [11][21]

The clinical stakes are substantial: duodenal adenomas develop in an estimated 88%-98% of patients with FAP, and estimated duodenal cancer risk reaches 18% by age 75 years. High-risk duodenal adenoma features are reported in 50% of patients by age 70 years. [9]

Endoscopically remove duodenal polyps larger than 10 mm when feasible. Repeated endoscopic resection and ampullectomy can downstage severe disease, but high-grade dysplasia or unresectable lesions should trigger evaluation for radical surgery, including duodenectomy or pancreaticoduodenectomy when malignancy is threatening. [14][12]
- Document the ampullary appearance at each surveillance examination because ampullary abnormalities increased from 18.3% at first EGD to 47.4% by the fourth EGD in one surveillance cohort. [12]
- Do not rely on Spigelman stage alone to exclude cancer risk: ampullary abnormality and patient age were among predictors of high-grade dysplasia in a large surveillance series. [12]
- Continue duodenal surveillance after total gastrectomy when anatomy permits; gastrectomy does not eliminate duodenal cancer risk. [14]

### Gastric polyposis that changes management

During EGD, characterize gastric polyps and obtain histology when dysplasia is suspected. In a 337-patient FAP cohort, the 10-year cumulative gastric cancer incidence was 0% with no polyps, 1% with polyps, 6% with low-grade dysplasia, 11% with polyps 2 cm or larger, and 20% with high-grade dysplasia; high-grade dysplasia and polyps at least 2 cm were strongly associated with gastric cancer. [15]

Refer patients with gastric high-grade dysplasia or cancer for surgical evaluation. Total gastrectomy with Roux-en-Y esophagojejunostomy is indicated when gastric polyps harbor high-grade dysplasia or cancer. [14]

*Upper GI escalation in FAP. [11][12][14][15][21]*

| Endoscopic or histologic finding | Risk interpretation | Next action |
| --- | --- | --- |
| FAP without prior upper GI assessment | Upper GI neoplasia requires dedicated surveillance. [21] | EGD with ampullary visualization by age 20-25 years or before colon surgery. [21] |
| Advanced duodenal adenomatosis | Spigelman staging supports risk stratification; advanced disease may justify complete small-bowel visualization. [11][21] | Increase expert endoscopic assessment and consider complete small-bowel evaluation. [21] |
| Duodenal polyp larger than 10 mm | Larger lesions warrant therapeutic endoscopic consideration. [14] | Remove endoscopically when feasible. [14] |
| High-grade dysplasia or unresectable duodenal/ampullary lesion | Malignancy risk may exceed what iterative endoscopic therapy can control. [12] | Refer for radical surgical evaluation, including duodenectomy or pancreaticoduodenectomy. [12] |
| Gastric high-grade dysplasia or gastric cancer | High-grade dysplasia carries a 20% 10-year cumulative gastric cancer incidence in one cohort. [15] | Obtain surgical evaluation; total gastrectomy is indicated for gastric polyps with high-grade dysplasia or cancer. [14] |

## Recognize desmoid disease and pediatric hepatoblastoma risk

Extraintestinal manifestations can alter surgical timing and prompt targeted evaluation.

Maintain a low threshold to evaluate new abdominal mass symptoms in FAP for intra-abdominal desmoid tumor, particularly after abdominal surgery. Desmoid tumors are locally aggressive and infiltrative but rarely metastasize; reported FAP incidence is 10%-20%, and family history, surgery, and APC mutation are recognized risk factors. [19][18]

For children known to carry an APC pathogenic variant or at 50% familial risk, annual hepatoblastoma screening from birth through age 5 years has been recommended. [10]

Do not automatically infer FAP from an isolated desmoid tumor. Although 5%-15% of desmoids are associated with FAP, reported yield of identifying FAP among patients with intra-abdominal or truncal desmoids without prior history was 4%-5%; a selective colonoscopy or genetic-testing strategy is therefore more appropriate than universal screening. [19]
- In FAP with a new mesenteric or retroperitoneal mass, include desmoid-type fibromatosis in the immediate differential because it can invade adjacent structures without metastatic spread. [19]
- In an isolated desmoid presentation, prioritize FAP assessment when multiple desmoids or other clinical features increase pretest probability. [19]

*Targeted extracolonic actions in FAP. [10][18][19]*

| Clinical scenario | Action | Reason |
| --- | --- | --- |
| Known APC pathogenic variant or 50% FAP risk, birth through age 5 years | Perform annual hepatoblastoma screening. [10] | This is the recommended pediatric surveillance window. [10] |
| FAP with postoperative or new abdominal mass symptoms | Evaluate for intra-abdominal desmoid tumor. [18][19] | FAP-associated desmoids are frequently intra-abdominal and surgery is a risk factor. [18][19] |
| Isolated intra-abdominal or truncal desmoid without known FAP | Use selective, phenotype-driven colonoscopy or genetic testing rather than universal FAP screening. [19] | Detection yield for occult FAP is reported at 4%-5%. [19] |

## Build surveillance around irreversible risk and procedural feasibility

Management requires parallel colorectal, upper GI, surgical, and family-based follow-up.

At each surveillance encounter, document three variables that change management: colorectal adenoma size and removability, interval change in adenoma number, and dysplasia grade. These determine whether continued endoscopic control remains reasonable or colectomy should be advanced. [21]

Coordinate colorectal and upper GI planning rather than treating them as sequential problems. EGD should occur by age 20-25 years or before colon surgery, and advanced duodenal disease may require complete small-bowel visualization or referral for therapeutic endoscopy and surgery. [21][12]

After colorectal surgery, continue surveillance of remaining at-risk gastrointestinal mucosa and maintain upper GI monitoring. Post-prophylactic adenocarcinomas and neoplastic change in ileal pouches have been reported, while duodenal cancer becomes a major malignancy after colectomy. [1][14]
- Refer early to a multidisciplinary hereditary cancer program when colectomy is being considered, when high-grade dysplasia is identified, or when duodenal/ampullary lesions require advanced resection. [12][21]
- Separate adenoma-burden reduction from proven cancer prevention when discussing medication: no chemopreventive agent is FDA-approved for FAP. [21]

*Longitudinal checkpoint framework for FAP. [1][12][21]*

| Checkpoint | Required decision | Escalation trigger |
| --- | --- | --- |
| Colonoscopy | Can the colon still be completely and reliably surveilled? [21] | Unremovable adenomas larger than 10 mm, high-grade dysplasia, accelerating burden, or inadequate surveillance. [21] |
| EGD with ampullary visualization | What is the duodenal and ampullary neoplasia burden? [11][21] | Advanced disease, high-grade dysplasia, or unresectable lesions. [12] |
| After prophylactic colorectal surgery | Which residual mucosa remains at risk? [1] | New neoplasia in retained or pouch mucosa requires continued endoscopic management. [1] |

## References
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## Editorial note

Prepared from cited clinical literature using Astra's research workflow. Verify recommendations against current guidance and patient-specific factors.