Background: Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) are rare neoplasms and data on peritoneal metastases (PM) from these tumors are scarce. Objective: The aim of this study was to present population-based data on the incidence, risk factors, and survival of synchronous PM in GEP-NETs.
Methods: Data from all patients diagnosed with a GEP-NET during 2007–2013 were collected from the Netherlands Cancer Registry. Age-standardized incidence rates were calculated and risk factors for developing PM were determined using multivariable logistic regression analysis. Survival was investigated using Kaplan–Meier and Cox regression analyses.
Results: A total of 4114 patients were diagnosed with a GEP-NET. PM were diagnosed in 234 patients (19% of patients with metastasized disease, representing 6% of all GEP-NETs). The incidence of patients diagnosed with PM was 1.6:1,000,000 persons per year. Risk factors for developing PM were higher age (odds ratio [OR] 1.4, 95% CI 1.0–2.0) and primary tumor location in the small intestine (OR 3.5, 95% CI 2.1–5.7) or colon (OR 2.5, 95% CI 1.4–4.4). Small intestinal NETs with PM had the best survival, while appendiceal NETs with PM had the poorest survival (5-year survival rates of 67 and 7%, respectively). Multivariate analysis showed that survival in patients with PM was worse compared with patients without metastases; however, the presence of PM among all metastasized patients was not associated with worse survival.
Conclusions: This nationwide population-based study provides relevant insight into the incidence and risk factors of PM in GEP-NETs, and reveals detailed site-specific data on the presence of PM and survival data that may contribute to develop individualized treatment strategies in patients with these heterogeneous neoplasms.

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Journal Annals of Surgical Oncology
Madani, A, Thomassen, I, van Gestel, Y.R.B.M, van der Bilt, J.D.W, Haak, H.R, de Hingh, I.H.J.T, & Lemmens, V.E.P.P. (2017). Peritoneal Metastases from Gastroenteropancreatic Neuroendocrine Tumors: Incidence, Risk Factors and Prognosis. Annals of Surgical Oncology, 24(8), 2199–2205. doi:10.1245/s10434-016-5734-x