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Objective: To retrospectively analyze toxicity, progression-free survival (PFS), overall survival (OS) and their determinants in patients with advanced pancreatic neuroendocrine tumors (panNETs), previously pretreated with chemotherapy, undergoing peptide receptor radionuclide therapy (PRRT) with 177Lu-DOTATATE.

Methods: In total, 102 patients with advanced panNETs, previously pretreated with one (67%) or several (33%) lines of chemotherapy were included, of whom 90 % had progressive disease and the majority (74.5%) with grade 2 tumors. 177Lu-DOTATATE, 7.4 GBq per cycle, was administered with 6 to 8 weeks interval, in 88 % of patients utilizing a dosimetry-guided protocol, until an absorbed dose of 23 Gy to the kidneys was reached.

Results: Mean 32±10.9 GBq per patient was administered in 1-10 cycles starting median 36 months after panNET diagnosis. Median follow-up was 34 months. Median PFS was 24 months and median OS was 42 months from start of PRRT. Independent risk factors for both progression and death were liver tumor burden >50%, more than one line of previous chemotherapy and elevated alkaline phosphatase (ALP). Resection of the primary tumor was linked to longer survival. Bone marrow toxicity grade 3-4 occurred in 10.8%. One patient (1.0 %) developed acute myeloid leukemia. Bone marrow toxicity was unrelated to type and length of previous chemotherapy, amount of administered activity and absorbed dose to the bone marrow.

Conclusion: 177Lu-DOTATATE therapy was feasible, highly effective and safe in patients with advanced panNETs heavily pretreated with chemotherapy. More than one line of chemotherapy was a therapy related independent risk factor for shorter PFS and OS.