 The present study was designed to investigate epidemiologic data of patients with GEP-NEN and to answer following questions using proteomic analysis MALDI-MS applied to existing pathology specimens paraffin-embedded specimens, FFPE: is it possible to explore protein signatures in this type of tumors? Is the response to therapy predictable using specific protein signatures? Is the tumors tendency to metastasize related to specific protein signatures? The present investigation explores the GEP-NEN databaseregister of following institutions: University Hospital Schleswig Holstein, University hospital of Freiburg, Agaplesion Hospital Rotenburg. The pathology specimens of the studied register-population, were identified in the biobank and pathology-institutes of the participating hospitals and investigated using MALDI-MS technique. 