Peptide Receptor Radionuclide Therapy (PRRT) with 177Lu-DOTATATE in Advanced Gastro-entero Pancreatic Neuroendocrine Tumors

Inclusion Criteria: * Patients must have histologically or cytologically confirmation of GEP -NETand Ki 67 index \<= 20%. * Measurable disease according to Response Evaluation Criteria in Solid Tumors (RECIST 1.1.criteria) * Advanced GEP-NET are eligible; patients must have progressive disease based on RECIST 1.1. criteria * Diagnostic OctreoScan and/or PET/CT 68Ga-peptide images demonstrate a significant uptake in the tumour * FDG PET negative (SUV less than 2.5) * Concomitant somatostatin analogs assumption is allowed * Life expectancy greater than 6 months. * ECOG performance status \<2 * Adequate haematological, liver and renal function: haemoglobin \>= 9 g/dL, absolute neutrophil count (ANC) \>= 1.5 x 109 /L, platelets \>= 100 x 109 /L, bilirubin ≤1.5 X upper normal limit (UNL) , Alanine transaminase (ALT) \<2.5 X UNL (\< 5 X UNL in presence of liver metastases), creatinine \< 2 mg/dL. * If female of childbearing potential, agreement to use adequate contraceptive methods (e.g., oral contraceptives, condoms, or other adequate barrier controls, intrauterine contraceptive devices, or sterilization) beginning at the screening visit and continuing until 3 months following last treatment with study drug. Negative serum pregnancy test for females of childbearing potential within 14 days of starting treatment. * Participant is willing and able to give informed consent for participation in the study. Exclusion Criteria: * Ki 67 index \> 20 % * FDG PET positive at least in one documented lesion with a SUV more than 2.5 * Patients treated with chemotherapy and therapeutic radiotherapy within 4 weeks and treated within 2 weeks with palliative radiotherapy, hormonal or biological therapy). * Patients treated with previous radiometabolic therapy with an adsorbed dose to the kidney more than 25 Gy and 1,5 Gy for the bone marrow. * All acute toxic effects of any prior therapy (including surgery radiation therapy, chemotherapy) must have resolved to a grade \<= 1 according to National Cancer Institute Common Terminology Criteria for Adverse Events Version 4.0 (CTCAE) * Participation in another clinical trial with any investigational agents within 30 days prior to study screening. * Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements. * History of allergic reactions attributed to compounds of similar chemical or biologic composition