Data on the incidence of gastroenteropancreatic neuroendocrine tumors (GEP-NETs) have so far only been obtained retrospectively and are based on inhomogeneous material. In the first part of this thesis a prospective study collecting all newly diagnosed GEP-NETs in Austria during one year was performed. Using the current WHO classification, the TNM staging and Ki67-grading, and the standard diagnostic procedure proposed by the European Neuroendocrine Tumor Society, GEP-NETs from 285 patients (male: 148; female: 137) were recorded. The aim of the second phase of this analysis was to describe "unmasked" clinical symptoms, methods of diagnosis, treatment, and short-term follow-up of gastroenteropancreatic neuroendocrine tumors (GEP-NETs) diagnosed during one year in Austria. 277 patients (excluding those with tumours in the esophagus, gallbladder, a Meckel diverticulum and liver metastasis) were included in the second phase. A standardized questionnaire comprising 50 clinical and biochemical parameters (clinical symptoms, mode of diagnosis, treatment, follow-up) was completed by attending physicians.
The annual incidence rates were 2.51 per 100,000 inhabitants for men, 2.36 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 at any other site. 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 neuroendocrine tumours 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.
The most common initial symptoms were episodes of abdominal-pain (29.5%), diarrhea (8.7%), weight-loss (7.5%), gastrointestinal-bleeding (5.4%), flushing (3.7%), and bowel-obstruction (3.3%). Overall 48.1% of tumors were diagnosed by endoscopy, 43.7% during surgery, 5% by fine-needle aspiration of the primary or metastases, and 2.5% during autopsy; 44.5% of tumors were not suspected clinically and were diagnosed incidentally during various surgical procedures. Overall 18.7% were removed endoscopically and 67.6% surgically; 13.7% were followed without interventional treatment. Endoscopic/surgical intervention was curative in 81.4% of patients, palliative in 18.6%. At the time of diagnosis, information on metastasis was available in 83.7% with malignant NETs. Lymph node or distant metastases were documented in 74.7%. In 34/176 (19.3%) patients 41 secondary tumors were documented, 78.0% being classified histologically as adenocarcinomas. During a 1-year follow-up 61.5% showed no evidence of disease, 13.5% had stable disease, 16.7% showed progression of disease, and in 8.3% the NET was the cause of death.