Peptide Receptor Radionuclide Therapy Is Effective for Clinical Control of Symptomatic Metastatic Insulinoma: A Long-Term Retrospective Analysis.

Metastatic insulinoma is a rare malignant neuroendocrine tumor characterized by inappropriate insulin secretion, resulting in life-threatening hypoglycemia, which is often difficult to treat. There is currently very limited information about the efficacy of peptide receptor radionuclide therapy (PRRT) for clinical control of hypoglycemia. The aim of this long-term retrospective study was to evaluate the therapeutic efficacy of PRRT for improving hypoglycemia, to evaluate the change of medication after PRRT, and to calculate progression-free survival (PFS) and overall survival (OS). Methods: Inclusion criteria were histologically proven somatostatin receptor-positive metastatic malignant insulinoma and at least 2 cycles of [90Y]Y-DOTATOC or [177Lu]Lu-DOTATOC therapy from early 2000 to early 2022. A semiquantitative scoring system was used to quantify the severity and frequency of hypoglycemic episodes under background antihypoglycemic therapy (somatostatin analog, diazoxide, everolimus, corticosteroids): score 0, no hypoglycemic episodes; score 1, hypoglycemic events requiring additional conservative treatment with optimization of nutrition; score 2, severe hypoglycemia necessitating hospitalization and combined medication or history of hypoglycemic coma. Hypoglycemic score before and after PRRT was analyzed. Time of benefit was defined as a time range of fewer hypoglycemic episodes in the observation period than at baseline. Information on antihypoglycemic medication before and after therapy, PFS, and OS was recorded. Results: Twenty-six of 32 patients with a total of 106 [90Y]Y-DOTATOC/[177Lu]Lu-DOTATOC cycles were included. The average observation period was 21.5 mo (range, 2.3-107.4 mo). Before therapy, 81% (n = 21) of the patients had a hypoglycemia score of 2 and 19% (n = 5) had a score of 1. After PRRT, 81% of patients (n = 21) had a decreased score, and the remaining 5 patients showed a stable situation. There was temporary worsening of hypoglycemia just after injection of [90Y]Y-DOTATOC/[177Lu]Lu-DOTATOC in 19% of patients. The average time of benefit in the observation period was 17.2 mo (range, 0-70.2 mo). Antihypoglycemic medication reduction was achieved in 58% (n = 15) of patients. The median OS and PFS after the start of PRRT were 19.7 mo (95% CI, 6.5-32.9 mo) and 11.7 mo (95% CI, 4.9-18.5 mo), respectively. Conclusion: To our knowledge, our study included the largest cohort of patients with malignant insulinoma to be evaluated. Long-lasting symptom control and reduction of antihypoglycemic medications were shown in most patients after late-line PRRT.

Control of the antitumour activity and specificity of CAR T cells via organic adapters covalently tethering the CAR to tumour cells.

On-target off-tumour toxicity limits the anticancer applicability of chimaeric antigen receptor (CAR) T cells. Here we show that the tumour-targeting specificity and activity of T cells with a CAR consisting of an antibody with a lysine residue that catalytically forms a reversible covalent bond with a 1,3-diketone hapten can be regulated by the concentration of a small-molecule adapter. This adapter selectively binds to the hapten and to a chosen tumour antigen via a small-molecule binder identified via a DNA-encoded library. The adapter therefore controls the formation of a covalent bond between the catalytic antibody and the hapten, as well as the tethering of the CAR T cells to the tumour cells, and hence the cytotoxicity and specificity of the cytotoxic T cells, as we show in vitro and in mice with prostate cancer xenografts. Such small-molecule switches of T-cell cytotoxicity and specificity via an antigen-independent 'universal' CAR may enhance the control and safety profile of CAR-based cellular immunotherapies.

Consensus report of the 2021 National Cancer Institute neuroendocrine tumor clinical trials planning meeting.

Important progress has been made over the last decade in the classification, imaging, and treatment of neuroendocrine neoplasm (NENs), with several new agents approved for use. Although the treatment options available for patients with well-differentiated neuroendocrine tumors (NETs) have greatly expanded, the rapidly changing landscape has presented several unanswered questions about how best to optimize, sequence, and individualize therapy. Perhaps the most important development over the last decade has been the approval of 177Lu-DOTATATE for treatment of gastroenteropancreatic-NETs, raising questions around optimal sequencing of peptide receptor radionuclide therapy (PRRT) relative to other therapeutic options, the role of re-treatment with PRRT, and whether PRRT can be further optimized through use of dosimetry among other approaches. The NET Task Force of the National Cancer Institute GI Steering Committee convened a clinical trial planning meeting in 2021 with multidisciplinary experts from academia, the federal government, industry, and patient advocates to develop NET clinical trials in the era of PRRT. Key clinical trial recommendations for development included 1) PRRT re-treatment, 2) PRRT and immunotherapy combinations, 3) PRRT and DNA damage repair inhibitor combinations, 4) treatment for liver-dominant disease, 5) treatment for PRRT-resistant disease, and 6) dosimetry-modified PRRT.

ACR-ACNM-ASTRO-SNMMI Practice Parameter for Lutetium-177 (Lu-177) DOTATATE Therapy.

OBJECTIVES: This practice parameter (PP) for Lutetium-177 (Lu-177) DOTATATE peptide receptor radionuclide therapy (PRRT) aims to guide authorized users in selection of appropriate adult candidates with gastroeneropancreatic neuroendocrine tumors (GEP-NETs) from foregut, midgut, and hindgut. The essential selection criteria include somatostatin receptor-positive GEP-NETs, which are usually inoperable and progressed despite standard therapy. Lu-177 DOTATATE is a radiopharmaceutical with high avidity for somatostatin receptors that are overexpressed by these tumors. This document ensures safe handling of Lu-177 DOTATATE by the authorized users and safe management of affected patients. METHODS: The document was developed according to the systematic process developed by the American College of Radiology (ACR) and described on the ACR Web site (https://www.acr.org/Clinical-Resources/Practice-Parameters-and-Technical-Standards). The PP development was led by 2 ACR Committees on Practice Parameters (Nuclear Medicine and Molecular Imaging and Radiation Oncology) collaboratively with the American College of Nuclear Medicine, American Society of Radiation Oncology, and Society of Nuclear Medicine and Molecular Imaging. RESULTS: The Lu-177 DOTATATE PP reviewed pharmacology, indications, adverse effects, personnel qualifications, and required clinical evaluation before starting the treatment, as well as the recommended posttherapy monitoring, quality assurance, documentation, and appropriate radiation safety instructions provided in written form and explained to the patients. CONCLUSIONS: Lu-177 DOTATATE is available for therapy of inoperable and/or advanced GEP-NETs when conventional therapy had failed. It can reduce tumor size, improve symptoms, and increase the progression free survival. The PP document provides clinical guidance for authorized users to assure an appropriate, consistent, and safe practice of Lu-177 DOTATATE.

ACR-ACNM-ASTRO-SNMMI Practice Parameter for Lutetium-177 (Lu-177) DOTATATE Therapy.

OBJECTIVES: This practice parameter (PP) for Lutetium-177 (Lu-177) DOTATATE peptide receptor radionuclide therapy (PRRT) aims to guide authorized users in selection of appropriate adult candidates with gastroeneropancreatic neuroendocrine tumors (GEP-NETs) from foregut, midgut, and hindgut. The essential selection criteria include somatostatin receptor-positive GEP-NETs, which are usually inoperable and progressed despite standard therapy. Lu-177 DOTATATE is a radiopharmaceutical with high avidity for somatostatin receptors that are overexpressed by these tumors. This document ensures safe handling of Lu-177 DOTATATE by the authorized users and safe management of affected patients. METHODS: The document was developed according to the systematic process developed by the American College of Radiology (ACR) and described on the ACR Web site (https://www.acr.org/Clinical-Resources/Practice-Parameters-and-Technical-Standards). The PP development was led by 2 ACR Committees on Practice Parameters (Nuclear Medicine and Molecular Imaging and Radiation Oncology) collaboratively with the American College of Nuclear Medicine, American Society of Radiation Oncology, and Society of Nuclear Medicine and Molecular Imaging. RESULTS: The Lu-177 DOTATATE PP reviewed pharmacology, indications, adverse effects, personnel qualifications, and required clinical evaluation before starting the treatment, as well as the recommended posttherapy monitoring, quality assurance, documentation, and appropriate radiation safety instructions provided in written form and explained to the patients. CONCLUSIONS: Lu-177 DOTATATE is available for therapy of inoperable and/or advanced GEP-NETs when conventional therapy had failed. It can reduce tumor size, improve symptoms, and increase the progression free survival. The PP document provides clinical guidance for authorized users to assure an appropriate, consistent, and safe practice of Lu-177 DOTATATE.

Potential for Increasing Uptake of Radiolabeled 68Ga-DOTATOC and 123I-MIBG in Patients with Midgut Neuroendocrine Tumors Using a Histone Deacetylase Inhibitor Vorinostat.

Background: Histone deacetylase (HDAC) inhibitors have been shown in preclinical studies to upregulate norepinephrine transporters in neuroblastoma and pheochromocytoma, and somatostatin receptors in pulmonary carcinoid, small cell lung cancer, and pancreatic neuroendocrine malignancies. This pilot imaging study in humans focuses on midgut neuroendocrine carcinoma metastatic to the liver, evaluating the effect of pretreatment with the HDAC inhibitor vorinostat on uptake of 123I-MIBG and 68Ga-DOTATOC. Materials and Methods: Multiple midgut neuroendocrine liver metastases in clinically stable subjects were imaged with 123I-MIBG and 68Ga-DOTATOC before and after a 4-d course of vorinostat. Scans were performed with strict attention to detail and timed about 1 month apart occurring just before monthly long-acting octreotide administrations. Uptake changes in tumor and normal liver parenchyma were assessed on positron emission computed tomography (PET/CT) with standardized uptake values and on single photon emission computed tomography (SPECT) with qualitative ratio images. Results: The experimental units were metastatic liver lesions within patients (n = 50). There was no significant difference in administered activity or uptake time between pairs of scans for either radiotracer. Statistically significant increase in maximum standardized uptake values (SUVmax) averaged over all lesions was noted on the 68Ga-DOTATOC PET scans (+11%, p < 0.01). SUVmax in normal liver showed no significant change (p = 0.12). There was no qualitative change in uptake of 123I-MIBG after vorinostat. Conclusions: In this pilot imaging study in patients with midgut neuroendocrine liver metastases, a short course of the HDAC inhibitor vorinostat induced a statistically significant increase in SUVmax on 68Ga-DOTATOC PET/computed tomography (CT) imaging in some hepatic neuroendocrine tumor metastases. There was no significant effect of vorinostat on tumor uptake of 123I-MIBG on SPECT/CT imaging. Given the pilot nature of this trial, the findings merit further investigation with a more rigorous protocol evaluating longer pretreatment and different dosages of vorinostat or other HDAC inhibitors, as well as effects on the therapeutic capability of 177Lu- or 90Y-somatostatin analogs.

Sub-3 Å Cryo-EM Structures of Necrosis Virus Particles via the Use of Multipurpose TEM with Electron Counting Camera.

During this global pandemic, cryo-EM has made a great impact on the structure determination of COVID-19 proteins. However, nearly all high-resolution results are based on data acquired on state-of-the-art microscopes where their availability is restricted to a number of centers across the globe with the studies on infectious viruses being further regulated or forbidden. One potential remedy is to employ multipurpose microscopes. Here, we investigated the capability of 200 kV multipurpose microscopes equipped with a direct electron camera in determining the structures of infectious particles. We used 30 nm particles of the grouper nerve necrosis virus as a test sample and obtained the cryo-EM structure with a resolution as high as ∼2.7 Šfrom a setting that used electron counting. For comparison, we tested a high-end cryo-EM (Talos Arctica) using a similar virus (Macrobrachium rosenbergii nodavirus) to obtain virtually the same resolution. Those results revealed that the resolution is ultimately limited by the depth of field. Our work updates the density maps of these viruses at the sub-3Šlevel to allow for building accurate atomic models from de novo to provide structural insights into the assembly of the capsids. Importantly, this study demonstrated that multipurpose TEMs are capable of the high-resolution cryo-EM structure determination of infectious particles and is thus germane to the research on pandemics.

Gold nanoparticles and tilt pairs to assess protein flexibility by cryo-electron microscopy.

A computational method was developed to recover the three-dimensional coordinates of gold nanoparticles specifically attached to a protein complex from tilt-pair images collected by electron microscopy. The program was tested on a simulated dataset and applied to a real dataset comprising tilt-pair images recorded by cryo electron microscopy of RNA polymerase II in a complex with four gold-labeled single-chain antibody fragments. The positions of the gold nanoparticles were determined, and comparison of the coordinates among the tetrameric particles revealed the range of motion within the protein complexes.

Symptom Diaries of Patients with Midgut Neuroendocrine Tumors Treated with 177Lu-DOTATATE.

We report the impact of 177Lu DOTATATE treatment on abdominal pain, diarrhea, and flushing, symptoms that patients with advanced midgut neuroendocrine tumors (NETs) often find burdensome. Methods: All patients enrolled in the international randomized phase 3 Neuroendocrine Tumors Therapy (NETTER-1) trial (177Lu-DOTATATE plus standard-dose octreotide long-acting repeatable [LAR], n = 117; high-dose octreotide LAR, n = 114) were asked to record the occurrence of predefined symptoms in a daily diary. Change from baseline in symptom scores (mean number of days with a symptom) was analyzed using a mixed model for repeated measures. Results: Patients (intent-to-treat) who received 177Lu-DOTATATE experienced a significantly greater decline from baseline in symptom scores than patients who received high-dose octreotide LAR. For 177Lu-DOTATATE, the mean decline in days with abdominal pain, diarrhea, and flushing was 4.10, 4.55, and 4.52 days per 4 weeks, respectively, compared with 0.99, 1.44, and 2.54 days for high-dose octreotide LAR. The mean differences were 3.11 days (95% confidence interval, 1.35-4.88; P = 0.0007) for abdominal pain, 3.11 days (1.18-5.04; P = 0.0017) for diarrhea, and 1.98 days (0.08-3.88; P = 0.0413) for flushing, favoring 177Lu-DOTATATE. A positive repeated measures correlation was found between diary-recorded symptom scores and questionnaire-recorded pain, diarrhea, and flushing. Conclusion: In addition to efficacy and quality of life benefits, symptom diaries from NETTER-1 demonstrated that treatment with 177Lu DOTATATE was associated with statistically significant reductions in abdominal pain, diarrhea, and flushing, constituting the core symptoms of patients with progressive midgut NETs, compared with high-dose octreotide LAR, supporting a beneficial effect of 177Lu DOTATATE on HRQoL.

Mediator structure and conformation change.

Mediator is a universal adaptor for transcription control. It serves as an interface between gene-specific activator or repressor proteins and the general RNA polymerase II (pol II) transcription machinery. Previous structural studies revealed a relatively small part of Mediator and none of the gene activator-binding regions. We have determined the cryo-EM structure of the Mediator at near-atomic resolution. The structure reveals almost all amino acid residues in ordered regions, including the major targets of activator proteins, the Tail module, and the Med1 subunit of the Middle module. Comparison of Mediator structures with and without pol II reveals conformational changes that propagate across the entire Mediator, from Head to Tail, coupling activator- and pol II-interacting regions.

A Novel AKR1C3 Specific Prodrug TH3424 With Potent Antitumor Activity in Liver Cancer.

Overexpression of AKR1C3, an aldo-keto reductase, was recently discovered in liver cancers. In this study, an inverse correlation between AKR1C3 expression and survival of patients with liver cancer was observed. AKR1C3 inhibitors, however, failed to suppress liver cancer cell growth. The prodrug TH3424, which releases a DNA alkylating reagent upon reduction by AKR1C3, was developed to target tumors with overexpression of AKR1C3. TH3424 showed specific killing of liver cancer cells with AKR1C3 overexpression both in vitro and in vivo. In patient-derived mouse xenograft models, TH3424 at doses as low as 1.5 mg/kg eliminated liver tumors with no apparent toxicity. Therefore, TH3424 is a promising drug candidate for liver cancer and other types of cancers overexpressing AKR1C3.

The N-terminus of varicella-zoster virus glycoprotein B has a functional role in fusion.

Varicella-zoster virus (VZV) is a medically important alphaherpesvirus that induces fusion of the virion envelope and the cell membrane during entry, and between cells to form polykaryocytes within infected tissues during pathogenesis. All members of the Herpesviridae, including VZV, have a conserved core fusion complex composed of glycoproteins, gB, gH and gL. The ectodomain of the primary fusogen, gB, has five domains, DI-V, of which DI contains the fusion loops needed for fusion function. We recently demonstrated that DIV is critical for fusion initiation, which was revealed by a 2.8Å structure of a VZV neutralizing mAb, 93k, bound to gB and mutagenesis of the gB-93k interface. To further assess the mechanism of mAb 93k neutralization, the binding site of a non-neutralizing mAb to gB, SG2, was compared to mAb 93k using single particle cryogenic electron microscopy (cryo-EM). The gB-SG2 interface partially overlapped with that of gB-93k but, unlike mAb 93k, mAb SG2 did not interact with the gB N-terminus, suggesting a potential role for the gB N-terminus in membrane fusion. The gB ectodomain structure in the absence of antibody was defined at near atomic resolution by single particle cryo-EM (3.9Å) of native, full-length gB purified from infected cells and by X-ray crystallography (2.4Å) of the transiently expressed ectodomain. Both structures revealed that the VZV gB N-terminus (aa72-114) was flexible based on the absence of visible structures in the cryo-EM or X-ray crystallography data but the presence of gB N-terminal peptides were confirmed by mass spectrometry. Notably, N-terminal residues 109KSQD112 were predicted to form a small α-helix and alanine substitution of these residues abolished cell-cell fusion in a virus-free assay. Importantly, transferring the 109AAAA112 mutation into the VZV genome significantly impaired viral propagation. These data establish a functional role for the gB N-terminus in membrane fusion broadly relevant to the Herpesviridae.

Addition of 131I-MIBG to PRRT (90Y-DOTATOC) for Personalized Treatment of Selected Patients with Neuroendocrine Tumors.

Peptide receptor radionuclide therapy (PRRT) is an effective treatment for metastatic neuroendocrine tumors. Delivering a sufficient tumor radiation dose remains challenging because of critical-organ dose limitations. Adding 131I-metaiodobenzylguanidine (131I-MIBG) to PRRT may be advantageous in this regard. Methods: A phase 1 clinical trial was initiated for patients with nonoperable progressive neuroendocrine tumors using a combination of 90Y-DOTATOC plus 131I-MIBG. Treatment cohorts were defined by radiation dose limits to the kidneys and the bone marrow. Subject-specific dosimetry was used to determine the administered activity levels. Results: The first cohort treated subjects to a dose limit of 1,900 cGy to the kidneys and 150 cGy to the marrow. No dose-limiting toxicities were observed. Tumor dosimetry estimates demonstrated an expected dose increase of 34%-83% using combination therapy as opposed to 90Y-DOTATOC PRRT alone. Conclusion: These findings demonstrate the feasibility of using organ dose for a phase 1 escalation design and suggest the safety of using 90Y-DOTATOC and 131I-MIBG.

High-specific-activity 131iodine-metaiodobenzylguanidine for therapy of unresectable pheochromocytoma and paraganglioma.

Pheochromocytomas and paragangliomas (PPG) are rare cancers arising from the adrenal medulla (pheochromocytoma) or autonomic ganglia (paraganglioma). They have highly variable biological behavior. Most PPG express high-affinity norepinephrine transporters, allowing active uptake of the norepinephrine analog, 131iodine-metaiodobenzylguanidine (131I-MIBG). Low-specific-activity forms of 131I-MIBG have been used since 1983 for therapy of PPG. High-specific-activity 131I-MIBG therapy improves hypertension management, induces partial radiological response or stable disease, decreases biochemical markers of disease activity and is well tolerated by patients. This drug, approved in the USA in July 2018, is the first approved agent for patients with unresectable, locally advanced or metastatic PPG and imaging evidence of metaiodobenzylguanidine uptake, who require systemic anticancer therapy.

Publisher Correction: A glycoprotein B-neutralizing antibody structure at 2.8 Å uncovers a critical domain for herpesvirus fusion initiation.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

A glycoprotein B-neutralizing antibody structure at 2.8 Å uncovers a critical domain for herpesvirus fusion initiation.

Members of the Herpesviridae, including the medically important alphaherpesvirus varicella-zoster virus (VZV), induce fusion of the virion envelope with cell membranes during entry, and between cells to form polykaryocytes in infected tissues. The conserved glycoproteins, gB, gH and gL, are the core functional proteins of the herpesvirus fusion complex. gB serves as the primary fusogen via its fusion loops, but functions for the remaining gB domains remain unexplained. As a pathway for biological discovery of domain function, our approach used structure-based analysis of the viral fusogen together with a neutralizing antibody. We report here a 2.8 Å cryogenic-electron microscopy structure of native gB recovered from VZV-infected cells, in complex with a human monoclonal antibody, 93k. This high-resolution structure guided targeted mutagenesis at the gB-93k interface, providing compelling evidence that a domain spatially distant from the gB fusion loops is critical for herpesvirus fusion, revealing a potential new target for antiviral therapies.

Impact of liver tumour burden, alkaline phosphatase elevation, and target lesion size on treatment outcomes with 177Lu-Dotatate: an analysis of the NETTER-1 study.

PURPOSE: To assess the impact of baseline liver tumour burden, alkaline phosphatase (ALP) elevation, and target lesion size on treatment outcomes with 177Lu-Dotatate. METHODS: In the phase 3 NETTER-1 trial, patients with advanced, progressive midgut neuroendocrine tumours (NET) were randomised to 177Lu-Dotatate (every 8 weeks, four cycles) plus octreotide long-acting release (LAR) or to octreotide LAR 60 mg. Primary endpoint was progression-free survival (PFS). Analyses of PFS by baseline factors, including liver tumour burden, ALP elevation, and target lesion size, were performed using Kaplan-Meier estimates; hazard ratios (HRs) with corresponding 95% CIs were estimated using Cox regression. RESULTS: Significantly prolonged median PFS occurred with 177Lu-Dotatate versus octreotide LAR 60 mg in patients with low (< 25%), moderate (25-50%), and high (> 50%) liver tumour burden (HR 0.187, 0.216, 0.145), and normal or elevated ALP (HR 0.153, 0.177), and in the presence or absence of a large target lesion (diameter > 30 mm; HR, 0.213, 0.063). Within the 177Lu-Dotatate arm, no significant difference in PFS was observed amongst patients with low/moderate/high liver tumour burden (P = 0.7225) or with normal/elevated baseline ALP (P = 0.3532), but absence of a large target lesion was associated with improved PFS (P = 0.0222). Grade 3 and 4 liver function abnormalities were rare and did not appear to be associated with high baseline liver tumour burden. CONCLUSIONS: 177Lu-Dotatate demonstrated significant prolongation in PFS versus high-dose octreotide LAR in patients with advanced, progressive midgut NET, regardless of baseline liver tumour burden, elevated ALP, or the presence of a large target lesion. Clinicaltrials.gov : NCT01578239, EudraCT: 2011-005049-11.

Overview and Current Status of Peptide Receptor Radionuclide Therapy.

Peptide receptor radionuclide therapy (PRRT) is an effective form of treatment of patients with metastatic neuroendocrine tumors, delivering modest objective tumor response rates but notable survival and symptomatic benefits. The first PRRT approved by the US Food and Drug Administration was lutetium 177-DOTATATE and is for use in adults with somatostatin receptor-positive gastroenteropancreatic neuroendocrine tumors. The treatment paradigm typically leads to significant improvement in symptomology coupled with an extended period of progression-free survival. Side effects are limited, with a small fraction of individuals experiencing clinically significant long-term renal or hematologic toxicity.

NANETS/SNMMI Procedure Standard for Somatostatin Receptor-Based Peptide Receptor Radionuclide Therapy with 177Lu-DOTATATE.

With the recent approval of 177Lu-DOTATATE for use in gastroenteropancreatic neuroendocrine tumors, access to peptide receptor radionuclide therapy is increasing. Representatives from the North American Neuroendocrine Tumor Society and the Society of Nuclear Medicine and Molecular Imaging collaborated to develop a practical consensus guideline for the administration of 177Lu-DOTATATE. In this paper, we discuss patient screening, maintenance somatostatin analog therapy requirements, treatment location and room preparation, drug administration, and patient release as well as strategies for radiation safety, toxicity monitoring, management of potential complications, and follow-up. Controversies regarding the role of radiation dosimetry are discussed as well. This document is designed to provide practical guidance on how to safely treat patients with this therapy.

Health-Related Quality of Life in Patients With Progressive Midgut Neuroendocrine Tumors Treated With 177Lu-Dotatate in the Phase III NETTER-1 Trial.

Purpose Neuroendocrine tumor (NET) progression is associated with deterioration in quality of life (QoL). We assessed the impact of 177Lu-Dotatate treatment on time to deterioration in health-related QoL. Methods The NETTER-1 trial is an international phase III study in patients with midgut NETs. Patients were randomly assigned to treatment with 177Lu-Dotatate versus high-dose octreotide. European Organisation for Research and Treatment of Cancer quality-of-life questionnaires QLQ C-30 and G.I.NET-21 were assessed during the trial to determine the impact of treatment on health-related QoL. Patients completed the questionnaires at baseline and every 12 weeks until tumor progression. QoL scores were converted to a 100-point scale according to European Organisation for Research and Treatment of Cancer instructions, and individual changes from baseline scores were assessed. Time to QoL deterioration (TTD) was defined as the time from random assignment to the first QoL deterioration ≥ 10 points for each patient in the corresponding domain scale. All analyses were conducted on the intention-to-treat population. Patients with no deterioration were censored at the last QoL assessment date. Results TTD was significantly longer in the 177Lu-Dotatate arm (n = 117) versus the control arm (n = 114) for the following domains: global health status (hazard ratio [HR], 0.406), physical functioning (HR, 0.518), role functioning (HR, 0.580), fatigue (HR, 0.621), pain (HR, 0.566), diarrhea (HR, 0.473), disease-related worries (HR, 0.572), and body image (HR, 0.425). Differences in median TTD were clinically significant in several domains: 28.8 months versus 6.1 months for global health status, and 25.2 months versus 11.5 months for physical functioning. Conclusion This analysis from the NETTER-1 phase III study demonstrates that, in addition to improving progression-free survival, 177Lu-Dotatate provides a significant QoL benefit for patients with progressive midgut NETs compared with high-dose octreotide.