Background: As demonstrated in the primary analysis of the phase 3 NETTER-1 trial, ¹⁷⁷Lu-DOTATATE significantly prolonged progression-free survival (PFS) versus high-dose long-acting octreotide, with a HR of 0.18 (95% CI: 0.11, 0.29; p< 0.0001), in patients with advanced, progressive, well-differentiated, somatostatin receptor-positive midgut neuroendocrine tumors (NETs). Here we report final overall survival (OS) for NETTER-1. Methods: In this international open-label trial, eligible patients were randomized to receive either four cycles of ¹⁷⁷Lu-DOTATATE 7.4 GBq (200 mCi) every 8 ± 1 weeks plus long-acting octreotide 30 mg or high-dose long-acting octreotide 60 mg every 4 weeks (control arm), both on top of best supportive care. After disease progression on randomized treatment or completion of an 18-month treatment period, patients in both arms entered long-term follow-up and could receive further anti-cancer treatment as recommended by their physicians. The primary endpoint was PFS per RECIST 1.1 and OS was a key secondary endpoint. Primary intention-to-treat analysis of OS was prespecified to take place after 158 deaths or 5 years after the last patient was randomized, whichever occurred first. Results: Of 231 randomized patients, 101/117 (86.3%) in the ¹⁷⁷Lu-DOTATATE arm and 99/114 (86.8%) in the control arm entered long-term follow-up. Final analysis occurred 5 years after the last patient was randomized, following 142 deaths, with a median follow-up of more than 76 months. During long-term follow-up, 41/114 (36%) of patients in the control arm received subsequent radioligand therapy (“cross-over”), the majority (22.8%) within 24 months. Median OS was 48.0 months (95% CI: 37.4, 55.2) in the ¹⁷⁷Lu-DOTATATE arm and 36.3 months (95% CI: 25.9, 51.7) in the control arm. HR was 0.84 (95% CI: 0.60, 1.17) with p = 0.30 (unstratified 2-sided log-rank test). A total of 2/112 (1.8%) ¹⁷⁷Lu-DOTATATE treated patients in the study developed myelodysplastic syndrome (MDS). No new cases of MDS or acute leukemia were reported in the long-term follow-up. Overall, no new safety signals emerged during long-term follow-up. Conclusions: Median OS was 48.0 months in the ¹⁷⁷Lu-DOTATATE arm of the NETTER-1 trial and 36.3 months in the control arm. This difference was not statistically significant, potentially impacted by a high rate (36%) of cross-over of patients in the control arm to radioligand therapy after progression. In overall conclusion, the NETTER-1 study demonstrated that ¹⁷⁷Lu-DOTATATE yielded a clinically and statistically significant improvement in PFS as a primary endpoint (HR: 0.18, p< 0.0001) as well as a clinically meaningful trend towards improvement in median OS of 11.7 months. No new safety signals emerged during the 5-year long-term follow-up. Clinical trial information: NCT01578239