Avelumab in G2-3 NET

Inclusion Criteria: * Adults (males or females), aged 18 years or older with pathologically confirmed, advanced (unresectable or metastatic) neuroendocrine tumour from a gastroenteropancreatic or lung source. Both participants with functional NETs and those with nonfunctional NETs shall be eligible for this study. * Histologically confirmed, WHO Grade 2-3, well-differentiated NETs of gastroenteropancreatic or lung origin. * Has received 0,1 or 2 prior lines of systemic therapy (chemotherapy, PRRT, targeted therapies such as everolimus or sunitinib). Somatostatin analogues are not considered a line of therapy for the purposes of this criterion. * Radiological documentation of disease progression within 24 weeks of study enrolment. Disease progression must be demonstrated on two scans less than one year apart. * Participants previously treated with any systemic therapies are eligible to enroll if disease progression is documented during or after their last treatment. * Measurable disease as assessed by CT scan of the chest, abdomen and pelvis which is suitable for accurate repeated measurements (according to RECIST v1.1). * ECOG performance status 0-2. * Adequate bone marrow function (ANC \> 1.5 x 109/L; Platelets \>100 x109/L; haemoglobin \> 90 g9/L). * Adequate liver function defined by a total bilirubin level ≤1.5xULN and AST and ALT levels ≤2.5xULN for participants (or AST and ALT levels ≤ 5xULN for participants with documented metastatic disease to the liver). * Adequa…