| Topic | Key finding (with numbers) | Source (author/year/journal) | URL/DOI | Evidence type |
|---|---|---|---|---|
| Definition / classification | Appendiceal neuroendocrine neoplasms include well-differentiated NETs (formerly “carcinoid tumors”), poorly differentiated NECs, and MiNENs; ~70–75% are well-differentiated NETs graded G1–G3 by Ki-67 and/or mitotic index. (pqac-00000002, pqac-00000006) | Mohamed et al., 2022, *Cancers* | https://doi.org/10.3390/cancers15010295 | Review/guideline synthesis |
| Epidemiology / incidence | aNET annual incidence reported at ~0.15–0.6 per 100,000; peak age 38–51 years; female predominance ~2:1; found in ~3–5 per 1,000 appendectomies; most arise at the appendix tip (~70%). (pqac-00000001) | Andrini et al., 2023, *Current Treatment Options in Oncology* | https://doi.org/10.1007/s11864-023-01093-0 | Review |
| Epidemiology / incidence trends | In SEER 2000–2017, appendiceal NET incidence increased from 0.03 to 0.90 per 100,000 person-years, with the largest increase in localized disease; survival also improved over time. (pqac-00000007) | Wang et al., 2023, *PLOS ONE* | https://doi.org/10.1371/journal.pone.0294153 | Population-based registry study |
| Stage at diagnosis | SEER (1973–2004) distribution: 60% localized, 28% regional, 12% distant at presentation. (pqac-00000002, pqac-00000011) | Mohamed et al., 2022, *Cancers* | https://doi.org/10.3390/cancers15010295 | Review of registry data |
| Nodal metastasis by size | Reported nodal metastasis rates rise with size: ~2.5% for <1 cm, 31% for 1–2 cm, and 64% for ≥2 cm. (pqac-00000001) | Andrini et al., 2023, *Current Treatment Options in Oncology* | https://doi.org/10.1007/s11864-023-01093-0 | Review |
| Nodal metastasis by size (alternative dataset) | SEER analyses summarized rates of 15% (<1 cm), 47% (1.0–1.9 cm), and 86% (>2 cm); another series reported 31% for 1.1–2 cm and 64% for >2 cm. (pqac-00000000) | Mohamed et al., 2022, *Cancers* | https://doi.org/10.3390/cancers15010295 | Review of registry studies |
| Distant metastasis / carcinoid syndrome | Carcinoid syndrome is very rare (<1%) and generally occurs only with metastases. (pqac-00000001) | Andrini et al., 2023, *Current Treatment Options in Oncology* | https://doi.org/10.1007/s11864-023-01093-0 | Review |
| Surgery threshold: appendectomy | Consensus summarized by guidelines supports appendectomy for tumors <1 cm, and for 1.0–1.9 cm tumors without high-risk features. (pqac-00000000) | Mohamed et al., 2022, *Cancers* | https://doi.org/10.3390/cancers15010295 | Review/guideline synthesis |
| Surgery threshold: right hemicolectomy | Most guidelines recommend right hemicolectomy for tumors >2 cm; high-risk features include deep mesoappendiceal invasion >3 mm, positive/unclear margins, lymphovascular invasion, and higher proliferative rate. (pqac-00000000) | Mohamed et al., 2022, *Cancers* | https://doi.org/10.3390/cancers15010295 | Review/guideline synthesis |
| Intermediate tumors (1–2 cm) | Authors suggest considering right hemicolectomy when tumor size is >15 mm and/or G2 and/or lymphovascular invasion, ideally after multidisciplinary review. (pqac-00000001, pqac-00000020) | Andrini et al., 2023, *Current Treatment Options in Oncology* | https://doi.org/10.1007/s11864-023-01093-0 | Expert review/opinion |
| Hemicolectomy vs appendectomy outcomes (1–2 cm) | Europe-wide pooled cohort of 278 patients: 163 appendectomy vs 115 hemicolectomy; median follow-up 13.0 years; regional nodal metastases in 22/115 (19.6%); estimated occult nodal disease after appendectomy 12.8% (95% CI 6.5–21.1%); no new metastases during >10 years follow-up; adjusted OS HR 0.88 (95% CI 0.36–2.17; p=0.71), supporting no routine hemicolectomy after complete appendectomy for 1–2 cm aNETs. (pqac-00000018, pqac-00000019, pqac-00000022) | Nesti et al., 2023, *The Lancet Oncology* | https://doi.org/10.1016/S1470-2045(22)00750-1 | Multicenter pooled retrospective cohort |
| Recent metastasis study | In an institutional series of 124 appendiceal NETs, only 10 had stage IV disease; 8/10 were synchronous, and among 114 early-stage patients none developed distant metastases during follow-up; authors concluded surveillance after resection is unlikely to help and tumors <2 cm should not receive completion hemicolectomy. (pqac-00000025, pqac-00000026, pqac-00000027) | Al-Toubah et al., 2025, *JNCCN* | https://doi.org/10.6004/jnccn.2024.7069 | Institutional retrospective cohort |
| Recent completion-surgery study | Single-center cohort of 82 patients: lymph-node metastases in 7/82 (8.5%), distant metastases in 3/82 (3.6%); 27/82 (33%) underwent completion hemicolectomy, but only 6/27 (22%) had nodal metastases and none had distant metastases, implying overtreatment in 21/27 (75%); tumor size >2 cm was the only significant predictor of nodal metastasis. (pqac-00000023, pqac-00000024) | Wächter et al., 2025, *Langenbeck's Archives of Surgery* | https://doi.org/10.1007/s00423-024-03603-6 | Single-center retrospective cohort |
| Imaging recommendations | For NETs >2 cm, incomplete resection, or positive nodes/margins, recommend contrast-enhanced triple-phase CT or MRI; somatostatin-receptor PET with Ga-68 or Cu-64 DOTATATE is preferred and considered the diagnostic/surveillance gold standard for SSTR-positive disease. (pqac-00000000) | Mohamed et al., 2022, *Cancers* | https://doi.org/10.3390/cancers15010295 | Review/guideline synthesis |
| Imaging in high-grade disease | Poorly differentiated/high-grade NECs are better evaluated with 18F-FDG PET plus CT/MRI rather than SSTR-based imaging. (pqac-00000000) | Mohamed et al., 2022, *Cancers* | https://doi.org/10.3390/cancers15010295 | Review/guideline synthesis |
| Biomarkers | Chromogranin A may be elevated but is nonspecific; 5-HIAA (plasma or 24-h urine) is mainly useful in serotonin-producing tumors with carcinoid features or liver metastases. (pqac-00000006, pqac-00000000) | Mohamed et al., 2022, *Cancers* | https://doi.org/10.3390/cancers15010295 | Review/guideline synthesis |
| Survival / prognosis | Localized well-differentiated NETs have median OS >20 years; NCDB 5-year survival for ANETs was 86.3% (95% CI 81.4–89.9); 5-year survival by size was 89.9% (≤2 cm), 70.6% (2–4 cm), and 58.2% (>4 cm). (pqac-00000006) | Mohamed et al., 2022, *Cancers* | https://doi.org/10.3390/cancers15010295 | Review of registry data |
| Follow-up / surveillance | Most well-differentiated appendiceal NETs <2 cm with negative margins and mesoappendiceal invasion <3 mm have low recurrence risk and often need no surveillance; postoperative surveillance is unlikely to benefit resected small tumors in recent retrospective data. (pqac-00000000, pqac-00000025, pqac-00000027) | Mohamed et al., 2022, *Cancers*; Al-Toubah et al., 2025, *JNCCN* | https://doi.org/10.3390/cancers15010295; https://doi.org/10.6004/jnccn.2024.7069 | Review/guideline synthesis; retrospective cohort |


*Table: This table compiles key evidence-backed facts about appendiceal neuroendocrine tumors/neoplasms from the retrieved literature, emphasizing incidence, metastatic risk by tumor size, management thresholds, diagnostics, and recent outcome studies. It is designed as a compact reference for evidence-supported knowledge base population.*