| Syndrome | Causal genes / inheritance | Small bowel cancer risk estimates | Suggested surveillance approach | Key citations |
|---|---|---|---|---|
| Lynch syndrome (LS/HNPCC) | Pathogenic variants in **MLH1, MSH2, MSH6, PMS2** or **EPCAM** deletion; **autosomal dominant** | Lifetime small bowel cancer risk reported at **0.4%–12%** overall; cumulative incidence by age 75 reported as **64.7% for MLH1**, **20.1% for MSH2**, **0% for MSH6/PMS2** in the cited review cohort; **~50%** of LS-associated small bowel cancers arise in the **duodenum** (pqac-00000028) | Routine **jejunal/ileal screening is generally not recommended**; duodenal/distal ileal lesions may be accessible during routine gastroscopy/colonoscopy; consider more tailored surveillance in **MLH1** carriers; capsule endoscopy has low complication rates (**0%–0.5%**) and reported diagnostic yield up to **8.6%** for asymptomatic small-bowel neoplasms (pqac-00000028, pqac-00000027) | (pqac-00000027, pqac-00000028) |
| Familial adenomatous polyposis (FAP) | **APC** pathogenic variants; **autosomal dominant**; de novo cases occur (pqac-00000033) | Elevated small bowel/duodenal cancer risk; duodenal surveillance risk stratified by **Spigelman classification**; jejunal/ileal polyps less well studied (pqac-00000027, pqac-00000028) | **Push enteroscopy** recommended for **Spigelman III–IV** disease; **double-balloon enteroscopy (DAE)** for high polyp burden; surveillance at **3–6 month intervals** for high-burden disease or **12-month intervals** for minimal disease; multimodal care in tertiary centers emphasized (pqac-00000028, pqac-00000027) | (pqac-00000027, pqac-00000028, pqac-00000033) |
| Peutz-Jeghers syndrome (PJS) | **STK11/LKB1** pathogenic variants; typically **autosomal dominant** (syndrome context from screening guidance) | High small bowel polyp/cancer risk; pediatric complication burden notable, with **intussusception >20% by age 10** and **>50% by age 20** (pqac-00000032) | Start GI screening at **age 8 years** with endoscopy/colonoscopy plus small bowel imaging (**video capsule endoscopy or MR enterography**); if polyps are found, repeat every **2–3 years**; some protocols alternate **CE and MRI-E every 1–3 years**; significant polyps **≥15 mm** should undergo **enteroscopy-assisted resection** (pqac-00000031, pqac-00000032) | (pqac-00000027, pqac-00000031, pqac-00000032) |
| Constitutional mismatch repair deficiency (CMMRD) | **Biallelic** mismatch repair gene pathogenic variants; **autosomal recessive** (pqac-00000031) | Small bowel cancer prevalence reported at **10%–16%**; median diagnosis age around **28 years** (pqac-00000031) | Surveillance includes **annual upper endoscopy** from **age 8** and **capsule endoscopy** from **age 10**; concurrent **push enteroscopy** is recommended because lesions are often duodenal (pqac-00000031) | (pqac-00000031) |
| MUTYH-associated polyposis (MAP) | **MUTYH** pathogenic variants; usually **autosomal recessive** (syndrome context reflected in guideline-style review) | Duodenal cancer risk described as **comparable to FAP**; risk focus is mainly **proximal small bowel/duodenum** (pqac-00000031) | Surveillance limited to **proximal small bowel**; **upper endoscopy with duodenoscopy** starting at **age 25–30 years** in American guidance or **35 years** in European guidance; **polypectomy regardless of size** is recommended because Spigelman staging is less reliable in MAP (pqac-00000031) | (pqac-00000031) |


*Table: This table summarizes the major hereditary syndromes linked to small bowel cancer, highlighting causal genes, reported risk estimates, and syndrome-specific surveillance/prevention approaches. It is useful for quickly comparing how surveillance differs across Lynch syndrome, FAP, Peutz-Jeghers syndrome, CMMRD, and MAP.*