Gastroenteropancreatic neuroendocrine tumours: the current incidence and staging based on the WHO and European Neuroendocrine Tumour Society classification: an analysis based on prospectively collected parameters.

As incidence data on gastroenteropancreatic neuroendocrine tumours (GEP-NETs) have so far only been retrospectively obtained and based on inhomogeneous material, we conducted a prospective study in Austria collecting all newly diagnosed GEP-NETs during 1 year. Using the current WHO classification, the tumor, nodes, metastases (TNM) staging and Ki67 grading and the standard diagnostic procedure proposed by the European Neuroendocrine Tumor Society (ENETS), GEP-NETs from 285 patients (male: 148; female: 137) were recorded. The annual incidence rates were 2.51 per 100,000 inhabitants for men, 2.36 per 100,000 for women. The stomach (23%) was the main site, followed by appendix (21%), small intestine (15%) and rectum (14%). Patients with appendiceal tumours were significantly younger than patients with tumours in any other site. About 46.0% were classified as benign, 15.4% as uncertain, 31.9% as well differentiated malignant and 6.7% as poorly differentiated malignant. Patients with benign or uncertain tumours were significantly younger than patients with malignant tumours. Among the malignant tumours of the digestive tract, 1.49% arose from neuroendocrine cells. For malignant gastrointestinal NETs, the incidence was 0.80 per 100,000: 40.9% were ENETS stage I, 23.8% stage II, 11.6% stage III and 23.8% stage IV. The majority (59.7%) were grade 1, 31.2% grade 2 and 9.1% grade 3. NETs of the digestive tract are more common than previously reported; the majority show benign behaviour, are located in the stomach and are well differentiated. G3 tumours are very rare.