177Lu-Dotatate plus long-acting octreotide versus high‑dose long-acting octreotide in patients with midgut neuroendocrine tumours (NETTER-1): final overall survival and long-term safety results from an open-label, randomised, controlled, phase 3 trial

Background The primary analysis of the phase 3 NETTER-1 trial showed significant improvement in progression-free survival with Lu-177-Dotatate plus long-acting octreotide versus high-dose long-acting octreotide alone in patients with advanced midgut neuroendocrine tumours. Here, we report the prespecified final analysis of overall survival and long-term safety results. Methods This open-label, randomised, phase 3 trial enrolled patients from 41 sites in eight countries across Europe and the USA. Patients were 18 years and older with locally advanced or metastatic, well differentiated, somatostatin receptor-positive midgut neuroendocrine tumours (Karnofsky performance status score >= 60) and disease progression on fixed-dose long-acting octreotide. Patients were randomly assigned (1:1) via an interactive web-based response system to intravenous Lu-177-Dotatate 7.4 G Bq (200 mCi) every 8 weeks (four cycles) plus intramuscular long-acting octreotide 30 mg (Lu-177-Dotatate group) or high-dose long-acting octreotide 60 mg every 4 weeks (control group). The primary endpoint of progression-free survival has been previously reported; here, we report the key secondary endpoint of overall survival in the intention-to-treat population. Final overall survival analysis was prespecified to occur either after 158 deaths or 5 years after the last patient was randomised, whichever occurred first. During long-term follow-up, adverse events of special interest were reported in the Lu-177-Dotatate group only. This trial is registered with ClinicalTrials.gov, NCT01578239. Findings From Sept 6, 2012, to Jan 14, 2016, 231 patients were enrolled and randomly assigned for treatment. The prespecified final analysis occurred 5 years after the last patient was randomly assigned (when 142 deaths had occurred); median follow-up was 76.3 months (range 0.4-95.0) in the Lu-177-Dotatate group and 76.5 months (0.1-92.3) in the control group. The secondary endpoint of overall survival was not met: median overall survival was 48.0 months (95% CI 37.4-55.2) in the Lu-177-Dotatate group and 36.3 months (25.9-51.7) in the control group (HR 0.84 [950/0 CI 0.60-1.171; two-sided p=0.30). During long-term follow-up, treatment-related serious adverse events of grade 3 or worse were recorded in three (3%) of 111 patients in the Lu-177-Dotatate group, but no new treatment-related serious adverse events were reported after the safety analysis cutoff. Two (2%) of 111 patients given Lu-177-Dotatate developed myelodysplastic syndrome, one of whom died 33 months after randomisation (this person was the only the only reported Lu-177-Dotatate treatment-related death). No new cases of myelodysplastic syndrome or acute myeloid leukaemia were reported during long-term follow-up. Interpretation Lu-177-Dotatate treatment did not significantly improve median overall survival versus high-dose long-acting octreotide. Despite final overall survival not reaching statistical significance, the 11.7 month difference in median overall survival with Lu-177-Dotatate treatment versus high-dose long-acting octreotide alone might be considered clinically relevant. No new safety signals were reported during long-term follow-up. Copyright (C) 2021 Elsevier Ltd. All rights reserved.