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Gastrointestinal System
Polyposis syndromes (FAP, Peutz-Jeghers)
Core Principle of Polyposis Syndromes
Polyposis syndromes are inherited conditions characterized by multiple polyps throughout the gastrointestinal tract, each with distinct genetic mutations, polyp histology, cancer risk, and extraintestinal manifestations.
The key to differentiation lies in polyp type (adenomatous vs hamartomatous), distribution pattern, number of polyps, and associated clinical features.
Understanding the underlying genetic defect explains both the mechanism of polyp formation and the spectrum of associated malignancies.
Board pearl: Always consider hereditary syndromes when polyps appear before age 40 or when >10 polyps are found on colonoscopy.
Familial Adenomatous Polyposis (FAP) Genetics and Mechanism
FAP results from germline mutations in the APC gene (chromosome 5q), a tumor suppressor that regulates β-catenin in the Wnt signaling pathway.
Loss of APC function → uncontrolled cell proliferation → inevitable adenoma formation throughout the colon.
Inheritance is autosomal dominant with nearly 100% penetrance; 25% of cases arise from de novo mutations.
By age 35, virtually all untreated patients develop colorectal adenocarcinoma — making prophylactic colectomy mandatory.
Board pearl: FAP = hundreds to thousands of adenomatous polyps + 100% cancer risk if untreated.
FAP Clinical Presentation and Diagnosis
Classic FAP: >100 adenomatous polyps develop during adolescence, with symptoms (bleeding, diarrhea) typically appearing in the third decade.
Attenuated FAP: 10–100 polyps with later onset and lower (but still elevated) cancer risk.
Diagnosis requires either: (1) >100 adenomatous polyps, (2) >10 adenomatous polyps with family history, or (3) APC mutation on genetic testing.
Screening begins at age 10–12 with annual flexible sigmoidoscopy; if polyps are found, proceed to colonoscopy.
Board distinction: Number matters — FAP has hundreds to thousands of polyps, while Lynch syndrome typically has <10.
FAP Extracolonic Manifestations
Duodenal adenomas (>90% of patients) → periampullary carcinoma risk; upper endoscopy surveillance required.
Desmoid tumors: locally aggressive fibromatoses, often intra-abdominal, that can cause bowel obstruction or vascular compression.
Congenital hypertrophy of retinal pigment epithelium (CHRPE): benign pigmented fundus lesions, present from birth.
Osteomas (skull, mandible), epidermoid cysts, supernumerary teeth.
Gardner syndrome variant: FAP + prominent extraintestinal features (desmoids, osteomas, dental anomalies).
Board pearl: Duodenal cancer is the leading cause of death in FAP patients after prophylactic colectomy.
FAP Management Principles
Prophylactic colectomy is mandatory, typically performed between ages 15–25 depending on polyp burden and symptoms.
Surgical options: total proctocolectomy with ileal pouch-anal anastomosis (preferred) vs colectomy with ileorectal anastomosis (requires rectal surveillance).
Post-colectomy surveillance: annual pouchoscopy/proctoscopy, upper endoscopy every 1–3 years for duodenal polyps.
Chemoprevention with NSAIDs (sulindac, celecoxib) can reduce polyp burden but does not eliminate cancer risk.
Family screening: genetic testing for at-risk relatives; begin surveillance in mutation carriers by age 10.
Peutz-Jeghers Syndrome Genetics and Pathophysiology
Caused by germline mutations in STK11/LKB1 gene (chromosome 19p), encoding a serine/threonine kinase tumor suppressor.
STK11 regulates cell polarity and metabolism through the mTOR pathway; loss leads to hamartomatous polyp formation.
Autosomal dominant inheritance with variable expressivity; 25% of cases are de novo mutations.
Unlike FAP's adenomas, PJS polyps are hamartomas — disorganized overgrowth of normal tissue elements with smooth muscle arborization.
Board pearl: Hamartomatous polyps have low malignant potential themselves but PJS carries high cancer risk via different mechanisms.
Peutz-Jeghers Clinical Features
Mucocutaneous pigmentation: dark blue to brown macules on lips, buccal mucosa, fingers, toes — present in >95% of patients.
Pigmentation typically appears in infancy/early childhood and may fade after puberty, but buccal lesions persist.
Hamartomatous polyps throughout GI tract: small bowel > colon > stomach; typically 10–100 polyps total.
Polyps cause intussusception (most common presentation), bleeding, obstruction, or chronic anemia.
Board clue: Child with perioral pigmentation + intussusception = Peutz-Jeghers syndrome until proven otherwise.
Peutz-Jeghers Cancer Risk
Lifetime cancer risk approaches 90% by age 70, affecting both GI and non-GI organs.
GI cancers: colorectal (39%), gastric (29%), pancreatic (36%), small bowel (13%) — note the high pancreatic cancer risk.
Non-GI cancers: breast (54% in women), ovarian (21%), cervical adenoma malignum, testicular Sertoli cell tumors.
Cancer develops through the "hamartoma-carcinoma sequence" and independent dysplastic foci, not malignant transformation of hamartomas.
Board pearl: PJS has the highest pancreatic cancer risk of all hereditary cancer syndromes.
Peutz-Jeghers Surveillance Strategy
Begin GI surveillance at age 8–10: baseline upper endoscopy and colonoscopy, video capsule endoscopy or MR enterography for small bowel.
Repeat endoscopy every 2–3 years; small bowel imaging every 2–3 years starting in late teens.
Pancreatic surveillance: MRI/MRCP or EUS starting at age 30–35, repeated every 1–2 years.
Breast cancer screening: annual MRI starting at age 25, mammography at age 30.
Gynecologic surveillance: annual pelvic exam and transvaginal ultrasound starting at age 18–20.
Board distinction: PJS requires multi-organ cancer surveillance, while FAP surveillance focuses primarily on GI tract.
Juvenile Polyposis Syndrome
Characterized by multiple juvenile polyps (hamartomas with prominent stroma and dilated, mucus-filled cysts) throughout GI tract.
Caused by mutations in SMAD4 or BMPR1A genes → disrupted TGF-β/BMP signaling → hamartoma formation.
Diagnostic criteria: ≥5 juvenile polyps in colon/rectum, juvenile polyps throughout GI tract, or any juvenile polyps with family history.
Combined syndrome: SMAD4 mutations can cause juvenile polyposis + hereditary hemorrhagic telangiectasia (HHT).
Cancer risk: 40–50% lifetime risk of colorectal cancer; also increased gastric and small bowel cancer risk.
Board pearl: Juvenile polyps are hamartomas but carry significant cancer risk, unlike sporadic juvenile polyps in children.
PTEN Hamartoma Tumor Syndromes
Includes Cowden syndrome and Bannayan-Riley-Ruvalcaba syndrome, caused by PTEN mutations → loss of PI3K/AKT pathway inhibition.
GI features: hamartomatous polyps throughout tract, ganglioneuromas, glycogenic acanthosis (esophageal).
Pathognomonic features: trichilemmomas (facial papules), oral papillomas, acral keratoses, macrocephaly.
Major cancer risks: breast (85% lifetime risk), thyroid (35%, often follicular), endometrial (28%).
Board clue: Macrocephaly + mucocutaneous lesions + GI polyps = PTEN hamartoma syndrome.
Surveillance focuses on breast, thyroid, and endometrial cancer screening rather than GI malignancy.
Serrated Polyposis Syndrome
Characterized by multiple serrated polyps (hyperplastic polyps and sessile serrated adenomas) in the colon.
Diagnostic criteria: (1) ≥5 serrated polyps proximal to sigmoid with ≥2 being >10mm, (2) >20 serrated polyps throughout colon, or (3) any serrated polyps with family history.
Molecular pathway: BRAF mutations → CpG island methylator phenotype (CIMP) → microsatellite instability.
Increased risk of colorectal cancer, particularly right-sided tumors with MSI-high phenotype.
Board pearl: Unlike other polyposis syndromes, no identified germline mutation — likely polygenic inheritance.
Management: colonoscopy every 1–3 years with removal of all polyps >5mm; consider surgery if polyp burden uncontrollable.
Comparative Polyp Histology
Adenomatous polyps (FAP, Lynch): dysplastic epithelium with hyperchromatic nuclei, loss of mucin — these are pre-malignant.
Hamartomatous polyps (PJS, JPS): disorganized but non-dysplastic tissue; PJS shows smooth muscle arborization, JPS shows stromal expansion.
Inflammatory polyps: granulation tissue and inflammation, seen in IBD — not associated with polyposis syndromes.
Hyperplastic/serrated polyps: saw-tooth crypt architecture; traditionally benign but sessile serrated adenomas have malignant potential.
Board distinction: Polyp histology drives syndrome identification — adenomas suggest FAP/Lynch, hamartomas suggest PJS/JPS.
Genetic Testing Approach
Test symptomatic individuals first to identify the familial mutation, then test at-risk relatives for that specific mutation.
Multi-gene panel testing increasingly preferred over sequential single-gene testing due to phenotypic overlap.
Consider genetic counseling before testing to discuss implications for family members, insurance, and reproductive planning.
Negative genetic testing doesn't exclude diagnosis if clinical criteria are met — 20–30% of cases have unidentified mutations.
Board pearl: Genetic testing is indicated for any patient with ≥10 adenomatous polyps, regardless of age or family history.
Surveillance vs Prophylactic Surgery Decisions
FAP: prophylactic colectomy is mandatory due to 100% cancer risk; timing depends on polyp burden and symptoms.
PJS: endoscopic polyp removal when possible; surgery only for complications (intussusception, obstruction) or unresectable polyps.
JPS: individualized — consider colectomy if polyp burden uncontrollable or dysplasia develops.
Lynch syndrome: prophylactic surgery controversial; intensive surveillance often preferred given later onset and fewer polyps.
Board principle: Surgery timing balances cancer risk, quality of life, and patient age/preferences — except in FAP where it's mandatory.
Pregnancy and Reproductive Considerations
All autosomal dominant syndromes have 50% transmission risk to offspring; offer genetic counseling and prenatal/preimplantation testing.
FAP: pregnancy after colectomy requires monitoring for adhesions, bowel obstruction; desmoids may grow during pregnancy.
PJS: increased risk of ovarian and cervical malignancies requires enhanced gynecologic surveillance.
Fertility may be reduced after pelvic surgery (especially ileal pouch procedures) due to adhesions.
Board pearl: Reproductive counseling should address both transmission risk and syndrome-specific pregnancy complications.
Chemoprevention Strategies
FAP: NSAIDs (sulindac 150mg BID, celecoxib 400mg BID) reduce polyp number and size but don't eliminate cancer risk.
Mechanism: COX-2 inhibition → reduced prostaglandin synthesis → decreased epithelial proliferation.
NSAIDs cannot replace surgery in FAP but may delay colectomy timing or reduce duodenal polyp burden.
Limited evidence for chemoprevention in hamartomatous polyposis syndromes.
Board caveat: Chemoprevention is adjunctive only — surveillance and surgery remain the primary management strategies.
Differential Diagnosis of Multiple Polyps
>100 adenomas: FAP (APC mutation) or MUTYH-associated polyposis (biallelic MUTYH mutations, autosomal recessive).
10–100 adenomas: attenuated FAP, MUTYH-associated polyposis, Lynch syndrome, or polymerase proofreading-associated polyposis.
Hamartomatous polyps + mucocutaneous features: PJS (pigmentation) vs PTEN syndromes (trichilemmomas).
Mixed polyp types: consider hereditary mixed polyposis syndrome or serrated polyposis syndrome.
Board approach: Polyp number + histology + associated features → specific syndrome → confirmatory genetic testing.
Board Question Stem Patterns
Teenager with >100 adenomatous polyps → FAP, recommend genetic testing and family screening.
Child with lip pigmentation and intussusception → Peutz-Jeghers syndrome.
Multiple polyps + macrocephaly + facial papules → PTEN hamartoma syndrome.
FAP patient with abdominal mass after colectomy → desmoid tumor.
Young woman with PJS seeking contraception → avoid estrogen due to increased gynecologic cancer risk.
Patient with FAP and new visual symptoms → screen for brain tumors (Turcot syndrome variant).
Multiple juvenile polyps + telangiectasias → combined JPS-HHT from SMAD4 mutation.
One-Line Recap
Polyposis syndromes divide by polyp histology — adenomatous (FAP with mandatory colectomy) vs hamartomatous (PJS with multi-organ cancer surveillance) — each driven by specific genetic defects that explain their distinct cancer risks, extraintestinal manifestations, and management strategies centered on early detection and prophylactic intervention.
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