| Domain | Key knowledge-base facts |
|---|---|
| Definition / classification | Digestive-system NENs are classified into well-differentiated NET and poorly differentiated NEC; WHO/consensus grading uses Ki-67 and mitotic count. NET grades: G1 **<3%**, G2 **3–20%**, G3 **>20%**; NECs are biologically high-grade and typically G3. WHO 2022/current framework also recognizes MiNEN and separates **NET G3** from NEC (pqac-00000007, pqac-00000008, pqac-00000011, pqac-00000013) |
| Epidemiology | GEP-NEN incidence reported at **3.56/100,000**; prevalence increased from **0.006% (1993)** to **0.048% (2012)**. In NCDB, annual GEP-NEN cases increased from **4,010 to 9,379 (2004–2016)**; **86,324** patients represented **6.33%** of all GEP malignancies. U.S. SEER data cited a **6.4-fold** rise in NEN incidence from 1973–2012 (pqac-00000011, pqac-00000009, pqac-00000013) |
| Hereditary syndromes / risk | About **~5%** of NETs are associated with hereditary syndromes in guideline summaries; broader reviews estimate hereditary syndromes in **~5–10%** of PanNETs / **~10%** of NENs overall. Key syndromes: **MEN1, VHL, NF1**; pooled sequencing of G1/G2 PanNETs found **13.3% hereditary** tumors (30/225) (pqac-00000011, pqac-00000013, pqac-00000014) |
| Key molecular alterations | In pooled G1/G2 PanNET sequencing, **MEN1 42% (95/225)**, **DAXX 16% (37/225)**, **ATRX 12% (27/225)**; nonfunctioning PanNETs showed recurrent PI3K/Wnt/NOTCH/RTK-Ras pathway alterations. High-grade GEP-NENs: **TP53 26%**, **APC 20%**, **KRAS 11%**, **MEN1 11%**; NET G3 enriched for **MEN1**, NEC enriched for **TP53/APC/KRAS**; Rb1 loss independently prognostic. Pancreatic WDNETs commonly harbor **DAXX/ATRX, MEN1, mTOR-pathway** alterations, whereas pancreatic NECs show **RB1, TP53, CDKN2A** changes (pqac-00000014, pqac-00000009, pqac-00000008, pqac-00000018) |
| Core diagnostics | Histopathology should demonstrate neuroendocrine phenotype with at minimum **synaptophysin** and **chromogranin A**; **INSM1** is highlighted as a sensitive/specific nuclear marker. Site-of-origin IHC may include **CDX2** (intestinal), **Islet-1/PAX6** (pancreas), **TTF-1** (lung). Ki-67 grading cutoffs: **<3%, 3–20%, >20%**; WHO 2022 guidance recommends counting **500–2,000** cells in hotspot areas (pqac-00000011, pqac-00000008, pqac-00000013) |
| Imaging | Morphologic workup: contrast-enhanced **CT** recommended; contrast-enhanced **MRI with DWI** used for liver/pancreas/brain/bone. Functional imaging: **SSTR PET** for receptor-positive disease and **FDG PET-CT** for more aggressive/nonfunctioning lesions; heterogeneity of SSTR expression helps treatment selection. In prospective comparison of **18F-AlF-NOTA-octreotide vs 68Ga-DOTATATE**, unique lesions **193 vs 167**, detection ratio **99.1% vs 91.4%**, and **33** incremental 18F lesions with **91%** MRI confirmation; trial **NCT04552847** (pqac-00000004, pqac-00000023, pqac-00000025) |
| Prognosis | Five-year OS by stage for GEP-NENs: localized **83–97%**, regional **67–84%**, metastatic **28–50%**; for NECs, localized **25–60%**, regional **9.2–28.5%**, metastatic about **10%**. In NORDIC NEC 2 high-grade digestive NENs, first-line palliative therapy showed immediate progression **41% NEC vs 24% NET G3**, median PFS **3.4 vs 7.4 mo**, OS **7.4 vs 21.8 mo**; adverse prognostic factors included **Ki-67 >55%**, PS, ALP, age (pqac-00000011, pqac-00000019) |
| Treatments | Surgery remains main curative option; most NCDB patients underwent surgery (**72.9%** alone). SSAs: PROMID TTP **14.3 vs 6 mo**; CLARINET median PFS **NR/32.8 vs 18 mo**. PRRT: NETTER-1 median PFS **NR vs 8.4 mo**, ORR **18% vs 3%**; NETTER-2 PFS **22.8 vs 8.5 mo**. Everolimus: RADIANT-3 PFS **11.0 vs 4.6 mo**; sunitinib: **11.4 vs 5.5 mo**. Temozolomide-based therapy meta-analysis: ORR **41.2%**, DCR **85.3%**. Platinum-etoposide remains first-line backbone for NEC, but immediate progression can be **~30–41%**. CABINET phase 3: cabozantinib improved PFS in epNET **8.4 vs 3.9 mo (HR 0.38)** and pNET **13.8 vs 4.4 mo (HR 0.23)**; ORR **5% epNET / 19% pNET** (pqac-00000009, pqac-00000021, pqac-00000022, pqac-00000018, pqac-00000020) |
| Liquid biopsy | Liquid biopsy review analyzed **65** articles. **ctDNA** appears more informative in **high-grade** tumors; **CTCs** are limited by low shedding. **NETest**/other mRNA-miRNA assays are described as having high sensitivity/specificity and may outperform chromogranin A; one review cites about **~91%** diagnostic accuracy for NETest, but standardization and prospective validation remain limiting (pqac-00000017, pqac-00000012) |


*Table: This table condenses high-yield disease characteristics, diagnostics, molecular features, prognosis, and treatment outcomes for gastroenteropancreatic neuroendocrine neoplasms. It is designed for rapid knowledge-base population using evidence-backed quantitative facts and context citations.*