Inclusion Criteria:  Patients diagnosed with a gastroenteropancreatic neuroendocrine tumor by histopathological study. Legally capable patients ≥ 18 and ≤ 80 years of age. Patients who have signed the informed consent for this study as specified in section 10.3. Patients in active treatment: active treatment is considered to be those patients in an advanced stage and in any type of medical treatment (somatostatin analogues, molecular therapies, chemotherapy, radionuclides...), or locoregional therapies.  Note: Decision was taken to treat the patient with an specific treatment prior and independently of patient inclusion in this non interventional study.  Exclusion Criteria:  Patients <18 or > 80 years of age. Female patients that are currently pregnant. Patients with a gastroenteropancreatic neuroendocrine tumor lacking an histopathological diagnosis. Patients in palliative treatment or terminal stage. Patients who have not signed the informed consent or any situation or condition that compromises the giving of patient voluntary informed consent.