The SAUNA trial is a multi-national, multi-centre, open-label, randomised, controlled, pragmatic clinical trial in patients with advanced, non-functional gastroenteropancreatic (GEP) neuroendocrine tumours (NET) with progressive disease on first-line therapy with somatostatine analogues (SSA). Eligible patients will be divided into two substudies according to the second-line therapy of choice (peptide receptor radionuclide therapy (PRRT) or targeted therapy, at the discretion of the local investigator). Patients within each substudy will be randomised 1:1 between continuation or withdrawal from SSA at the start of second-line systemic therapy. Stratification will occur according to study site and according to the Ki67 value (below 10% (grade 1 and low grade 2) and equal to or above 10% (high grade 2)).

Inclusion Criteria:

• Age ≥18 years
• Written informed consent prior to any study-related procedures
• Eastern Cooperative Oncology Group (ECOG) performance status ≤2,
• Histologically-proven diagnosis of locally advanced or metastatic, non-functional, well-differentiated World Health Organisation 2019 grade 1-2 GEP NET
• Documented radiological disease progression on first-line SSA treatment at label dose or higher
• For targeted therapy substudy: indication to start with either sunitinib or everolimus as second-line therapy, according to local investigator
• For PRRT substudy: indication to start with PRRT with Lutetium (177Lu) oxodotreotide as second-line therapy, according to local investigator

Exclusion Criteria:

• Indication for chemotherapy treatment of GEP NET in second-line
• Presence of poorly differentiated grade 3 neuroendocrine carcinoma (NEC), well-differentiated grade 3 NET or rapidly progressive NET
• Prior treatment with everolimus, sunitinib or PRRT
• Contra-indication, proven allergy or other indication than functional NET for the use of a SSA
• Patient showing progressive disease while being on a lower than the registered dose
• Functional NET, defined as the presence of clinical and biochemical evidence of a hormonal NET-related syndrome
• Patient undergoing palliative, systemic oncological treatment for other malignancy than GEP NET
• Concurrent anti-cancer treatment in another investigational trial
• Any abnormal findings at screening, clinical finding, including psychiatric and behavioural problems, or any other medical condition(s) or laboratory findings that, in the opinion of the investigator, might jeopardize the patient's safety or decrease the chance of obtaining satisfactory data needed to achieve the objective(s) of the study
• Pregnant or lactating patient at screening or if the patient wishes to get pregnant during treatment phase of the trial