Familial adenomatous polyposis: risks and monitoring

Familial adenomatous polyposis is a hereditary cancer-associated syndrome in which hundreds or thousands of adenomatous polyps form in the colon, and without preventive treatment, colorectal cancer almost inevitably develops. This is caused by a germline (inherited) pathogenic variant in the APC gene, which controls the growth of mucosal cells. The risk of colorectal cancer without prevention is close to 100% by age 40-50, so early detection and timely preventive surgery radically improve the prognosis. [1]

The classic form of the syndrome manifests in adolescence and young adulthood with dozens or hundreds of polyps, while the "attenuated" form (FAP) has fewer polyps and a later onset, but also carries a high risk of cancer. In addition to the colon, other organs are also involved: the duodenum and major duodenal papilla, stomach, thyroid gland, soft tissues (desmoid tumors), and the liver in children (hepatoblastoma). Management of the syndrome involves not only colonoscopy but a lifelong program of multi-organ monitoring. [2]

In recent years, key approaches have been revised: colonoscopy intervals for children and adults have been clarified, upper endoscopy with assessment according to the Spigelman scale for the duodenum has been standardized, and indications for organ-preserving surgery and drug prophylaxis (adjunctive) have been described. For desmoid tumors (a common extraintestinal manifestation in familial adenomatous polyposis), the first targeted drug (nirogasestat) was approved in 2023, changing the treatment pathway for some patients. [3]

This article outlines current standards for diagnosis, risk stratification, and treatment: when to begin monitoring a child from a high-risk family, how to choose the type of prophylactic surgery, how and why to monitor the duodenum and thyroid gland, what is known about polyp chemoprophylaxis, and how to manage desmoid tumors. All recommendations are consistent with international sources. [4]

Code according to the International Classification of Diseases, 10th revision and 11th revision

In the International Classification of Diseases, Eleventh Revision, familial adenomatous polyposis is coded in the block "Malignant neoplasms of the colon and polyposis," with reference to position 2B90.Y ("familial adenomatous polyposis") and to polyposis syndromes 2E92.40. The International Classification of Diseases, Eleventh Revision supports post-coordination, so that associated features (e.g., dysplasia, duodenal polyposis) can be added. [5]

The International Classification of Diseases, Tenth Revision, historically used "substitute" codes (e.g., Q85.8 "Other phakomatoses" or organ codes for polyps), which was inconvenient. The 2026 version of the International Classification of Diseases, Tenth Revision (US version, ICD-10-CM) introduced a separate code, D13.91 "Familial adenomatous polyposis," which more accurately reflects the diagnosis for billing and registry maintenance. Some reference books contain alternative accompanying codes for specific polyps/tumors, but the underlying diagnosis is familial adenomatous polyposis. [6]

Table 1. Codes for familial adenomatous polyposis

System	Code	How to use
ICD 11	2B90.Y (“Family adenomatous polyposis”)	Primary diagnosis; if necessary, post-coordination of complications
ICD 11	2E92.40 "Polyposis syndrome"	Polyposis group code; reference category
ICD-10 (US version, 2026)	D13.91 "Family adenomatous polyposis"	Primary diagnosis code in the invoice and registers
ICD 10 (historically)	Q85.8 and organ codes (e.g. K63.5)	Used before D13.91; remain as concomitant/organ if needed

Epidemiology

Familial adenomatous polyposis is a rare syndrome that accounts for approximately 1-2% of all cases of colorectal cancer. According to large reviews and registries, familial adenomatous polyposis and Lynch syndrome form the main "hereditary core" of colorectal cancer. [7]

Without surveillance, the absolute risk of colorectal cancer in carriers of the pathogenic APC variant is close to 100% by age 40–50, necessitating early colonoscopy and timely prophylactic colectomy. Thanks to screening and surgery, overall survival in familial adenomatous polyposis has improved significantly compared to the pre-surveillance era. [8]

The extraintestinal burden is significant: the duodenum (including the ampulla) is the second most significant "risk node"; with the correct endoscopic strategy, mortality from the duodenum can be reduced. Of the extracolorectal tumors in adults, duodenal cancer and thyroid cancer are most often discussed; in children, carriers of familial adenomatous polyposis have a higher risk of hepatoblastoma. [9]

Population prevalence is estimated at tens of cases per 100,000 families, depending on the region and the availability of registries. Active family registries increase the proportion of presymptomatic detection and reduce the number of emergency surgeries in adolescents and young adults. [10]

Table 2. Epidemiological landmarks

Indicator	Grade
Share of all colorectal cancers	1-2%
Risk of colorectal cancer without prevention	Close to 100% by 40-50 years
Leading extraintestinal mortality in colon surgery	Duodenal cancer (if unsupervised)
Gain from registers	More presymptomatic findings, fewer emergency interventions

Reasons

The only confirmed cause is germline pathogenic variants in the APC (adenomatous polyposis colorectal) gene, a tumor suppressor gene. The carrier has a "first hit" in APC from birth, and a "second hit" (somatic mutation of the second copy) occurs in the mucosal cells and triggers the adenoma → carcinoma cascade. This explains the multiple polyps and their early development. [11]

A distinction is made between classic familial adenomatous polyposis (hundreds to thousands of polyps, early onset) and an attenuated variant (FAP) with dozens of polyps and later onset. Genotype-phenotype relationships are partially understood: certain mutation loci in APC are associated with a higher risk of desmoid tumors and specific extracolorectal manifestations. [12]

Gardner syndrome and Turcot variant are historical clinical names for phenotypes of familial adenomatous polyposis with a predominance of extraintestinal manifestations (cutaneous/bone osteomas, desmoid tumors; association with central nervous system tumors). Today, they are considered "umbrellas" within the spectrum of familial adenomatous polyposis. [13]

Inheritance is autosomal dominant: the risk of passing the condition to offspring is 50% in each pregnancy. Up to 20-30% of cases may be de novo (no family history), so genetic testing is indicated for all patients with typical clinical features. [14]

Risk factors

The primary and significant risk factor is the presence of a pathogenic APC variant. Lifestyle factors do not negate the genetic risk, but they do influence the overall oncological burden and the tolerability of interventions. Therefore, standard recommendations for diet, activity, and smoking cessation remain important. [15]

The severity of extraintestinal manifestations is influenced by both genetic (locus mutations) and iatrogenic factors (for example, tissue trauma and surgery can "spur" the growth of desmoid tumors). This is taken into account when planning surgery: with a high risk of desmoid tumors, sparing approaches are preferred and, if possible, major reconstructions are postponed. [16]

For children from high-risk families, timely initiation of surveillance is crucial: colonoscopy at 10-15 years of age (often 12-14 years according to European pediatric guidelines), and in some registries, earlier if symptoms appear. Early entry into the program reduces the incidence of urgent presentations. [17]

Long-term observational series emphasize that strict, “protocolized” routes (colonoscopy, upper endoscopy, thyroid, and liver in children) reduce mortality and surgical morbidity in the long term. [18]

Pathogenesis

APC is a key regulator of the WNT/β-catenin pathway. Its loss disrupts β-catenin degradation, increases proliferation, and leads to the formation of adenomas. Because the germline variant is present in all cells, the entire colonic epithelium is primed for adenomatous growth, while a second strike in somatic cells triggers polyp formation at multiple sites simultaneously. [19]

In the duodenum and ampulla of Vater, adenomas develop against a background of the same molecular abnormalities; it is here, after removal of the colon, that the main extraintestinal risk is concentrated. The Spiegelman system (scoring for number, size, histology, and degree of dysplasia) is used to assess the severity of duodenal polyposis, which determines monitoring intervals. [20]

Desmoid tumors are clonal fibroblast/myofibroblast proliferations associated with WNT pathway activation (often due to somatic CTNNB1 mutations or the APC context). They are locally infiltrative, recur after surgery, but do not metastasize. Currently, the standard strategy is "active watchful waiting," with the option of systemic treatment in the event of progression. [21]

Additional "second" mutations (KRAS, TP53, etc.) accelerate the progression of individual lesions to high-grade dysplasia and invasive cancer. This justifies biopsies of suspicious polyps, precise mucosal mapping, and timely surgery. [22]

Symptoms

In adolescence, asymptomatic progression or nonspecific complaints are possible: mucus and blood in the stool, changes in stool frequency, anemia, and abdominal discomfort. As the polyp load increases, blood loss and the risk of intestinal obstruction increase. Often, the diagnosis is first established through family screening before symptoms develop. [23]

Duodenal manifestations include dyspepsia, epigastric pain, iron deficiency anemia, and sometimes pancreatitis involving the ampulla. These are often only detected by targeted endoscopy, so the upper section should not be overlooked. [24]

Desmoid tumors appear as dense, painless masses in the abdominal wall or within the abdomen, and can cause pain and compression of intestinal loops and blood vessels. They are characterized by a fluctuating, unpredictable natural history, ranging from stabilization to slow growth and, rarely, spontaneous regression. [25]

In some patients, “indirect” signs occur: thyroid nodules, elevated tumor markers in case of duodenal lesions, and in children, an enlarged liver/increased alpha-fetoprotein (screening for hepatoblastoma in high-risk families is discussed individually). [26]

Table 3. Clinical clues for early detection

Block	Examples	What to do
Colorectal symptoms	Blood in stool, anemia, change in stool	Colonoscopy + genetics APC
Upper gastrointestinal tract	Dyspepsia, anemia, "silent" duodenal polyposis	Esophagogastroduodenoscopy with examination of the ampulla
Soft tissues	Dense nodes in the abdominal wall, pain	Exclude desmoid (MRI/CT)
Family background	Early cancer/polyposis in relatives	APC Cascade Testing

Classification, forms and stages

A distinction is made between classic familial adenomatous polyposis (hundreds to thousands of polyps) and a more attenuated variant (tens of polyps, later onset). Both require monitoring, but the rate of colonoscopy and surgical time differ. [27]

For the duodenum, the Spigelman staging system is used—a summary scale based on the number of polyps, their size, histology (tubular/tubulovillous/villous), and the degree of dysplasia. The stage determines the frequency of endoscopy and the question of prophylactic duodenectomy in extreme cases. [28]

According to the surgical status of the colon, a distinction is made between “before surgery”, “after collecto-proctectomy with an ileoanal reservoir” and “after colectomy with an ileorectal anastomosis” - the frequency of rectoscopy/reservoir examination and the goals of chemoprophylaxis depend on this. [29]

Based on extraintestinal manifestations, a "desmoid-pron" phenotype (high risk of desmoids), a "thyroid" phenotype (nodules/thyroid cancer), and a "duodenal" phenotype (rapid progression of the Spigelman stage) are noted. This helps personalize the routing. [30]

Table 4. Spiegelman scale (briefly) for the duodenum

Criterion	1 point	2 points	3 points
Number of polyps	1-4	5-20	>20
Size, mm	1-4	5-10	>10
Histology	Tubular	Tubulovillous	villous
Dysplasia	Light	Moderate	Heavy

Sum: 0 - stage 0; 1-4 - I; 5-6 - II; 7-8 - III; 9-12 - IV. Observation intervals are linked to the stage. [31]

Complications and consequences

The main complication without preventive measures is colorectal cancer. After colon removal, duodenal tumors become more prominent: in some patients, they determine long-term risk. Regular upper endoscopy and proper assessment of the ampulla of Vater are critical. [32]

Desmoid tumors can cause pain, intestinal obstruction, and vascular and organ compression. Due to high recurrence and localized aggressiveness, "direct" surgery is not always preferred; today, the algorithm often begins with observation or drug therapy, followed by excision in threatening situations. [33]

Among endocrine complications, an increased risk of thyroid nodules and cancer has been discussed in carriers of familial adenomatous polyposis, particularly in women. A number of guidelines recommend regular thyroid ultrasound screening, beginning in adolescence. [34]

Children from high-risk families may experience rare but serious events such as hepatoblastoma; screening (examination, alpha-fetoprotein, liver ultrasound) at an early age is discussed for individual families; the issue is decided individually with a pediatric oncologist/geneticist. [35]

When to see a doctor

If a child or young adult has a family history of familial adenomatous polyposis, it's important to seek treatment early—before symptoms develop—to initiate genetic testing and a monitoring program. This allows for the detection of polyposis in the preclinical phase and the planning of preventative measures. [36]

Any persistent episodes of blood in the stool, unexplained iron deficiency anemia, or changes in bowel habits are reasons for a targeted colonoscopy. For those with familial adenomatous polyposis, visits and examinations are carried out strictly according to schedule, even if they feel well. [37]

If dyspepsia, weight loss, epigastric pain, or signs of pancreatobiliary obstruction occur, upper endoscopy with mandatory assessment of the ampulla (often with lateral vision) is necessary. This is part of the standard monitoring for familial adenomatous polyposis. [38]

Dense “lumps” in the abdominal wall, increasing abdominal pain, signs of subobstruction are reasons for urgent imaging for a desmoid tumor and consultation with a multidisciplinary team. [39]

Diagnostics

The first step is genetics: testing for pathogenic variants of APC in an individual with multiple adenomas or from a family with a confirmed diagnosis. A positive result confirms the syndrome and initiates cascade testing in first-degree relatives (children – within an ethically agreed-upon timeframe). A negative result does not exclude a clinical diagnosis in a typical presentation. [40]

The second step is colonoscopy: for children at risk, it starts at 10-15 years of age (often 12-14 years according to European pediatric guidelines) and is repeated every 1-2 years (or more often, depending on the "polyp load"). For adults, colonoscopy with a polyp map is performed frequently before surgery; after surgery, examinations of the stump/reservoir/rectum are performed. [41]

The third step is upper endoscopy with a targeted examination of the duodenum and ampulla (a lateral endoscope or a "cap" on a straight endoscope). Intervals depend on the Spigelman stage: from 5 years (stage 0-I) to 6-12 months (III-IV), with a discussion of endotherapy or surgery in severe cases. [42]

Step 4 - extraintestinal referrals: annual thyroid ultrasound (from adolescence), discussion of childhood liver screening in high-risk families, monitoring of soft tissue lesions (suspected desmoid - magnetic resonance imaging). [43]

Table 5. Basic diagnostic route

Direction	When to start	Frequency (guidelines)	Notes
APC Genetics	If suspected/in the family	One time	Cascade testing of relatives
Colonoscopy	10-15 years (often 12-14)	Every 1-2 years before surgery	Accelerate as the load increases
Upper endoscopy	20-25 years old	By Spigelman stage	Inspection of the ampoule is mandatory
Thyroid gland (ultrasound)	Adolescence	Annually/based on findings	Especially in women

Differential diagnosis

Familial adenomatous polyposis is distinguished from other polyposis syndromes: MAP polyposis (biallelic variants in MUTYH), juvenile polyposis, Peutz-Jeghers syndrome, and PTEN-associated hamartomatous syndromes. The number, type, and distribution of polyps, age of onset, and genetics help quickly determine the specifics. [44]

Familial adenomatous polyposis is distinguished from "multiple sporadic adenomas" by its early age and familial occurrence, but de novo cases are possible, so genetics are important even without a family history. When in doubt, molecular verification takes the wheel. [45]

Lynch syndrome typically does not produce thousands of polyps; the underlying mechanism is a mismatch repair defect, and diagnosis relies on immunohistochemistry and microsatellite instability. In familial adenomatous polyposis, such markers are not expected in adenomas before cancer develops. [46]

In cases of severe duodenal polyposis, differentiation is made with syndromes where the upper section is primarily affected; ultimately, the clinical picture of the colon and the genetic test for APC remain decisive. [47]

Table 6. How familial adenomatous polyposis differs from its “neighbors”

Syndrome	Type of polyps	Age/number	Gene
Familial adenomatous polyposis	Adenomas	Early age, hundreds-thousands	APC
MAP polyposis	Adenomas	Later, dozens	MUTYH (biallel)
Peitz-Jeghers	Hamartomas	Early, small intestine	STK11
Juvenile polyposis	Juvenile	Childhood	BMPR1A/SMAD4

Treatment

The basic principle is "monitor while possible and operate promptly": colonoscopy with frequent removal of large polyps slows progression but does not eliminate the need for prophylactic surgery. When the "polyp load" makes endoscopic monitoring ineffective/unsafe, colectomy is considered. The choice of surgery depends on anatomy, age, risk of desmoids, and the willingness to undergo lifelong follow-up visits. [48]

Two main options: total proctocolectomy with an ileoanal reservoir (complete removal of the colon and rectum—minimal risk of cancer in the remainder, but higher surgical complexity) or subtotal colectomy with an ileorectal anastomosis (preservation of the rectum—functionally simpler, but requires frequent rectoscopy and readiness for subsequent proctectomy in case of progression). The decision is individual. [49]

Upper gastrointestinal tract: lifelong esophagogastroduodenoscopy with Spigelman assessment. For stages III-IV, endoscopic removal of large and villous adenomas (including papillectomy for ampullary adenoma) is considered in experienced centers; for extremely severe diffuse polyposis, prophylactic (pan)duodenectomy is discussed in specialized institutions. Even during surgery, stump/anastomosis monitoring is maintained. [50]

Thyroid gland: many guides recommend regular ultrasound examinations (starting in adolescence) and early detection of papillary cancer. If a nodule is detected, a general oncoendocrine algorithm is used (fine-needle aspiration biopsy if indicated). [51]

Desmoid tumors: According to current consensus, the primary management strategy is "watch and wait" for asymptomatic/minor growth. In case of progression or symptoms, systemic therapy is indicated. In 2023, nirogasestat (a gamma-secretase inhibitor) was approved for adults with progressive desmoids, making it a standard option. Other options include low-dose chemotherapy combinations, antiestrogens, and targeted agents, within the framework of protocols/guidelines. Surgery is elective (high risk of recurrence). [52]

Chemoprophylaxis: does not replace surgery, but can reduce the "polyp burden." The best data are for cyclooxygenase inhibitors (celecoxib) and combinations (sulndac + erlotinib) - a reduction in the number and volume of polyps in studies; however, the regulatory status has changed: celecoxib had accelerated approval as an adjunct to usual care, the indication was later revised. In any case, the appointment is strictly individualized, taking into account side effects (cardiovascular and gastrointestinal risks). [53]

Postoperative follow-up includes stump/reservoir examinations (with a preserved rectum or an ileoanal reservoir), upper endoscopy according to Spigelman, thyroid gland, and soft tissues (desmoids). In children, additional routes are determined by the multidisciplinary team. Visits are more frequent in the first few years after surgery. [54]

A team approach: Management of familial adenomatous polyposis requires a center with expertise in hereditary cancers, high-level endoscopy (including lateral ampulla examination), colorectal surgery, sarcomas/desmoids, oncoendocrinology, and genetics. This is not a "luxury" but a factor in reducing complications and mortality. [55]

Patient support: iron and vitamin supplements (correction of anemia/deficiencies), nutritional support, physical activity, training in endoscopy preparation techniques and recognizing "red flags." Post-colectomy: guidance on hydration, dehydration prevention, and bowel management. [56]

Finally, a family strategy: cascade testing of first-degree relatives, a clear "observation passport," and reminders about procedure deadlines. This saves years of life and reduces the incidence of emergency situations. [57]

Table 7. Upper endoscopy intervals according to Spigelman stage (landmarks)

Stage	Observation interval	Tactics
0-I	3-5 years	Biopsies of suspicious lesions, training
II	1-3 years	Removal of large/villous adenomas
III	6-12 months	Aggressive endotherapy, frequent follow-up examinations
IV	Individually; discussion of duodenectomy	Experience Center, Multidisciplinary Council

Table 8. Selecting a colon surgery (simplified cheat sheet)

Situation	Approach	Pros	Cons
Very high polyp load, young patients	Proctocolectomy + ileoanal reservoir	Minimal risk of cancer in the remains	More complex surgery, reservoir risks
Moderate activity, intact rectum, willingness to undergo frequent examinations	Colectomy + ileorectal anastomosis	Better function, simpler operation	Residual risk of rectal cancer, frequent examinations

Table 9. Desmoid tumors in familial adenomatous polyposis: what is important

Stage	Recommendations
Start	Observation in case of oligosymptomatic course
With progression	Systemic therapy (including nirogasestat for adults)
Surgery	Limited - in case of threat to life/organ function
Team	The participation of a center with experience in desmoids is essential.

Prevention

Primary prevention (preventing the onset of the syndrome) is impossible—it is a hereditary condition. However, secondary prevention is extremely effective: early colonoscopy, timely prophylactic surgery, and monitoring of the upper colon significantly reduce mortality and the number of emergency interventions. [58]

Chemoprophylaxis (cyclooxygenase inhibitors, combinations with epidermal growth factor receptor inhibitors) can reduce the polyp burden, facilitating endoscopic tasks, but it does not replace surgery and requires a risk/benefit assessment. The decision is made by a specialist familiar with familial adenomatous polyposis. [59]

Family prevention includes cascade testing and presymptomatic screening of first-degree relatives. For children, this includes the inclusion of pediatric guidelines (ESPGHAN) and gentle psychological support for the family. [60]

Lifestyle (weight control, physical activity, quitting smoking) does not “cancel” the genetic risk, but it helps to tolerate treatment and reduces the overall oncological burden. [61]

Forecast

Without monitoring, familial adenomatous polyposis almost inevitably leads to colorectal cancer in young or middle age. With a program (endoscopy and timely surgery), the prognosis improves significantly, and patients live long, active lives. The primary risks shift to the duodenum and desmoid tumors, where monitoring is focused. [62]

Radical prophylactic surgery reduces the risk of colorectal cancer to virtually zero, but does not eliminate lifelong surveillance of the stump/reservoir and upper sections. The quality of endoscopy and the discipline of visits directly influence long-term outcomes. [63]

The advent of targeted therapy for desmoid tumors (nirogasestat, 2023) has improved the management of advanced cases and reduced the need for invasive interventions. This is important news for the "desmoid-pron" phenotypes of familial adenomatous polyposis. [64]

Result: when routed to an experimental center and protocols are followed, mortality from the syndrome becomes comparable to the population mortality rate for the corresponding ages, with the exception of subgroups with severe duodenal polyposis and aggressive desmoids - they require particularly close monitoring. [65]

FAQ (frequently asked questions)

At what age should colonoscopy begin in children from high-risk families?
Typically at 10-15 years of age (often 12-14 years according to European pediatric guidelines), then every 1-2 years. The decision is individualized based on genetics and clinical findings. [66]

What is the "Spigelman stage" and why is it important?
It is a scale for assessing the severity of duodenal polyposis based on number, size, histology, and dysplasia. The stage determines the intervals for esophagogastroduodenoscopy and the treatment strategy (endoscopy versus prophylactic surgery). [67]

Is it possible to avoid surgery by taking "polyp pills"?
No. Chemoprophylaxis can reduce the "polyp burden" but does not replace prophylactic colectomy for familial adenomatous polyposis. The decision on medication is made by a specialist, taking into account the risks. [68]

How are desmoid tumors treated in familial adenomatous polyposis? Treatment
often begins with observation; if progression occurs, systemic therapy is used (nirogasestat was approved in 2023 for adults with progressive desmoids). Surgery is optional. [69]