Patient Selection and Toxicities of PRRT for Metastatic Neuroendocrine Tumors and Research Opportunities

Targeted radionuclide therapy in endocrine-related cancers: advances in the last decade

Targeted radionuclide therapy plays an increasingly important role in managing endocrine-related tumors and significantly advances the therapeutic landscape for patients with these diseases. With increasing FDA-approved therapies and advances in the field, come an increased knowledge of the potential for long-term toxicities associated with these therapies and the field must develop new strategies to increase potency and efficacy while individualizing the selection of patients to those most likely to respond to treatment. Novel agents and modalities of therapy are also being explored. This review will discuss the current landscape and describe the avenues for growth in the field currently being explored.

Diagnostic Approaches to Neuroendocrine Neoplasms of Unknown Primary Site

ABSTRACT

Neuroendocrine tumors (NETs) are relatively uncommon heterogeneous neoplasms arising from endocrine and neuronal origin cells showing highly variable clinical behavior. By the time these tumors are discovered, up to 14% of patients with histologically proven NETs have metastasis, with the liver as the most frequently affected organ. Sometimes, no known primary site can be identified via routine imaging. Neuroendocrine tumors of unknown origin carry a poorer prognosis (compared with metastatic NETs with a known primary site) because of a lack of tailored surgical intervention and appropriate medical therapy (eg, chemotherapy or targeted therapy). A multimethod approach is frequently used in the trial to accurately determine the primary site for NETs of unknown primary sites and may include clinical, laboratory, radiological, histopathological, and surgical data. New molecular techniques using the genomic approach to identify the molecular signature have shown promising results. Various imaging modalities include ultrasound, computed tomography (CT), dual-energy CT, magnetic resonance imaging, and functional and hybrid imaging (positron emission tomography/CT, positron emission tomography/magnetic resonance imaging); somatostatin receptor imaging with new tracers is frequently used in an attempt for localization of the primary site.

Mechanisms of Resistance in Gastroenteropancreatic Neuroendocrine Tumors

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs), although curable when localized, frequently metastasize and require management with systemic therapies, including somatostatin analogues, peptide receptor radiotherapy, small-molecule targeted therapies, and chemotherapy. Although effective for disease control, these therapies eventually fail as a result of primary or secondary resistance. For small-molecule targeted therapies, the feedback activation of the targeted signaling pathways and activation of alternative pathways are prominent mechanisms, whereas the acquisition of additional genetic alterations only rarely occurs. For somatostatin receptor (SSTR)-targeted therapy, the heterogeneity of tumor SSTR expression and dedifferentiation with a downregulated expression of SSTR likely predominate. Hypoxia in the tumor microenvironment and stromal constituents contribute to resistance to all modalities. Current studies on mechanisms underlying therapeutic resistance and options for management in human GEP-NETs are scant; however, preclinical and early-phase human studies have suggested that combination therapy targeting multiple pathways or novel tyrosine kinase inhibitors with broader kinase inhibition may be promising.

Effect of Neuroendocrine Neoplasm Treatment on Human Reproductive Health and Sexual Function

Neuroendocrine neoplasms (NEN) are characterized by a wide clinical heterogeneity and biological variability, with slow progression and long survival in most cases. Although these tumors can affect young adults, there are few studies that focus on the sexual and reproductive system. The aim of this review was to evaluate the effect of NEN treatment, including somatostatin analogues (SSA), targeted therapy (Everolimus and Sunitinib), radiolabeled-SSA and chemotherapy, on male and female reproductive systems and sexual function. This narrative review was performed for all available prospective and retrospective studies, case reports and review articles published up to March 2022 in PubMed. To date, few data are available on the impact of SSA on human fertility and most of studies come from acromegalic patients. However, SSAs seem to cross the blood–placental barrier; therefore, pregnancy planning is strongly recommended. Furthermore, the effect of targeted therapy on reproductive function is still undefined. Conversely, chemotherapy has a well-known negative impact on male and female fertility. The effect of temozolomide on reproductive function is still undefined, even if changes in semen parameters after the treatment have been described. Finally, very few data are available on the sexual function of NEN treatment.

Differenzierte Therapiestrategie bei Lebermetastasen gastro-entero-pankreatischer Neuroendokriner Neoplasien

Neuroendokrine Neoplasien (NEN) bilden eine heterogene Gruppe maligner Tumoren, die überwiegend dem gastro-entero-pankreatischen System (GEP) zuzuordnen sind. Hierbei sind Dünndarm und Pankreas die häufigsten Organe für Primärtumoren, die Leber stellt den dominanten Metastasierungsort dar. Da viele Patient*innen lange asymptomatisch bleiben, führen oftmals zufällig diagnostizierte Lebermetastasen oder ein Ileus zur Diagnose. Die einzige kurative Therapieoption stellt die komplette Entfernung von Primarius und Metastasen dar. Besonders im Falle der metastasierten Erkrankung sollten die vorhandenen Therapieoptionen immer im interdisziplinären Tumorboard mit Spezialisten*innen aus Gastroenterologie, (Leber-)Chirurgie, Radiologie, Nuklearmedizin, Radiotherapie, Pathologie und Endokrinologie evaluiert werden. Durch die Kombination der verschiedenen Therapieverfahren kann auch für Patient*innen mit fortgeschrittener Erkrankung eine jahrelange Prognose bei guter Lebensqualität erreicht werden. Wichtig für die Therapieentscheidung sind neben patientenindividuellen Faktoren der Differenzierungsgrad des Tumors, dessen hormonelle Sekretion, das Metastasierungsmuster und der Erkrankungsverlauf. Die Behandlung von Lebermetastasen umfasst neben den unterschiedlichen chirurgischen Strategien die lokal-ablativen radiologischen und nuklearmedizinischen Verfahren, die als Ergänzung zu den systemischen Therapien zur Verfügung stehen.

Overview of the 2022 WHO Classification of Neuroendocrine Neoplasms

In this review, we detail the changes and the relevant features that are applied to neuroendocrine neoplasms (NENs) in the 2022 WHO Classification of Endocrine and Neuroendocrine Tumors. Using a question-and-answer approach, we discuss the consolidation of the nomenclature that distinguishes neuronal paragangliomas from epithelial neoplasms, which are divided into well-differentiated neuroendocrine tumors (NETs) and poorly differentiated neuroendocrine carcinomas (NECs). The criteria for these distinctions based on differentiation are outlined. NETs are generally (but not always) graded as G1, G2, and G3 based on proliferation, whereas NECs are by definition high grade; the importance of Ki67 as a tool for classification and grading is emphasized. The clinical relevance of proper classification is explained, and the importance of hormonal function is examined, including eutopic and ectopic hormone production. The tools available to pathologists for accurate classification include the conventional biomarkers of neuroendocrine lineage and differentiation, INSM1, synaptophysin, chromogranins, and somatostatin receptors (SSTRs), but also include transcription factors that can identify the site of origin of a metastatic lesion of unknown primary site, as well as hormones, enzymes, and keratins that play a role in functional and structural correlation. The recognition of highly proliferative, well-differentiated NETs has resulted in the need for biomarkers that can distinguish these G3 NETs from NECs, including stains to determine expression of SSTRs and those that can indicate the unique molecular pathogenetic alterations that underlie the distinction, for example, global loss of RB and aberrant p53 in pancreatic NECs compared with loss of ATRX, DAXX, and menin in pancreatic NETs. Other differential diagnoses are discussed with recommendations for biomarkers that can assist in correct classification, including the distinctions between epithelial and non-epithelial NENs that have allowed reclassification of epithelial NETs in the spine, in the duodenum, and in the middle ear; the first two may be composite tumors with neuronal and glial elements, and as this feature is integral to the duodenal lesion, it is now classified as composite gangliocytoma/neuroma and neuroendocrine tumor (CoGNET). The many other aspects of differential diagnosis are detailed with recommendations for biomarkers that can distinguish NENs from non-neuroendocrine lesions that can mimic their morphology. The concepts of mixed neuroendocrine and non-neuroendocrine (MiNEN) and amphicrine tumors are clarified with information about how to approach such lesions in routine practice. Theranostic biomarkers that assist patient management are reviewed. Given the significant proportion of NENs that are associated with germline mutations that predispose to this disease, we explain the role of the pathologist in identifying precursor lesions and applying molecular immunohistochemistry to guide genetic testing.

Clinical Utility of 18F-FDG PET in Neuroendocrine Tumors Prior to Peptide Receptor Radionuclide Therapy: A Systematic Review and Meta-Analysis

Simple Summary

Functional imaging with ¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET) has evolved into a major clinical tool in cancer diagnosis and management for many malignancies in diverse clinical settings, providing valuable information on tumor behavior and aggressiveness. In the field of neuroendocrine tumors (NETs), recent advances in molecular imaging and targeted treatments with novel theranostic agents favor a more patient-tailored approach. Although peptide receptor radionuclide therapy (PRRT) has recently become an established therapy for progressive NETs, the role of ¹⁸F-FDG PET prior to PRRT in patients with NETs of different origins and grades remains to be determined. Herein, we provide a comprehensive summary of available evidence in contemporary literature by means of a systematic review and meta-analysis, demonstrating that dual-functional imaging with ⁶⁸Ga-DOTA-peptides and ¹⁸F-FDG prior to PRRT appears to be a useful tool in NET management by delineating tumor somatostatin receptor expression and glycolytic metabolic activity, and predicting tumor response and survival outcomes.

Abstract

The role of ¹⁸F-FDG PET in patients with variable grades of neuroendocrine tumors (NETs) prior to peptide receptor radionuclide therapy (PRRT) has not been adequately elucidated. We aimed to evaluate the impact of ¹⁸F-FDG PET status on disease control rate (DCR), progression-free survival (PFS), and overall survival (OS) in neuroendocrine tumor (NET) patients receiving PRRT. We searched the MEDLINE, Embase, Cochrane Library, and Web of Science databases up to July 2020 and used the Newcastle-Ottawa scale (NOS) criteria to assess quality/risk of bias. A total of 5091 articles were screened. In 12 studies, 1492 unique patients with NETs of different origins were included. The DCR for patients with negative ¹⁸F-FDG PET status prior to PRRT initiation was 91.9%, compared to 74.2% in patients with positive ¹⁸F-FDG PET status (random effects odds ratio (OR): 4.85; 95% CI: 2.27–10.36). Adjusted analysis of pooled hazard ratios (HRs) confirmed longer PFS and OS in NET patients receiving PRRT with negative ¹⁸F-FDG PET (random effects HR:2.45; 95%CIs: 1.48–4.04 and HR:2.25; 95% CIs:1.55–3.28, respectively). In conclusion, ¹⁸F-FDG PET imaging prior to PRRT administration appears to be a useful tool in NET patients to predict tumor response and survival outcomes and a negative FDG uptake of the tumor is associated with prolonged PFS and OS.

Laboratory, Clinical, and Survival Outcomes Associated With Peptide Receptor Radionuclide Therapy in Patients With Gastroenteropancreatic Neuroendocrine Tumors

IMPORTANCE

Peptide receptor radionuclide therapy (PRRT) is approved in the US for treatment of gastroenteropancreatic neuroendocrine tumors (NETs), but data on PRRT outcomes within US populations remain scarce.

OBJECTIVE

To analyze the first 2 years of PRRT implementation at a US-based NET referral center.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study was conducted using medical records of patients with metastatic NET receiving PRRT from 2018 through 2020 in a NET program at a tertiary referral center. Included patients were those at the center with metastatic NETs who received at least 1 dose of PRRT over the study period. Laboratory toxic effects were assessed using Common Terminology Criteria for Adverse Events version 5.0. Tumor response was determined using Response Evaluation Criteria in Solid Tumors 1.1. Survival analysis was conducted to identify factors associated with progression-free survival (PFS) and overall survival. Data were analyzed from August 2018 through August 2020.

EXPOSURES

Receiving 4 cycles of lutetium-177-dotatate infusion, separated by 8-week intervals targeted to 7.4 GBq (200 mCi) per dose.

MAIN OUTCOMES AND MEASURES

Data were compared from before and after PRRT to determine hematologic, liver, and kidney toxic effects and to assess tumor progression and patient survival.

RESULTS

Among 78 patients receiving at least 1 dose of PRRT, median (interquartile range) age at PRRT initiation was 59.8 (53.5-69.2) years and 39 (50.0%) were men. The most common primary NET sites included small bowel, occurring in 34 patients (43.6%), and pancreas, occurring in 22 patients (28.2%). World Health Organization grade 1 or 2 tumors occurred in 62 patients (79.5%). Among all patients, 56 patients underwent pretreatment with tumor resection (71.8%), 49 patients received nonsomatostatin analogue systemic therapy (62.8%), and 49 patients received liver-directed therapy (62.8%). At least 1 grade 2 or greater toxic effect was found in 47 patients (60.3%). Median PFS was 21.6 months for the study group, was not reached by 22 months for patients with small bowel primary tumors, and was 13.3 months for patients with pancreatic primary tumors. Having a small bowel primary tumor was associated with a lower rate of progression compared with having a pancreatic primary tumor (hazard ratio, 0.19; 95% CI, 0.07-0.55; P = .01). Median overall survival was not reached.

CONCLUSIONS AND RELEVANCE

This cohort study of patients with metastatic NETs found that PRRT was associated with laboratory-measured toxic effects during treatment for most patients and an overall median PFS of 21.6 months. Patients with small bowel NETs had longer PFS after PRRT compared with patients with pancreatic NETs.

How We Do It: A Multidisciplinary Approach to 177Lu DOTATATE Peptide Receptor Radionuclide Therapy

Lutetium 177 (¹⁷⁷Lu) DOTA-0-Tyr3-Octreotate (DOTATATE) peptide receptor radionuclide therapy (PRRT) is an effective treatment for advanced gastroenteropancreatic neuroendocrine tumors. This review presents a clinical practice workflow that has been successful since ¹⁷⁷Lu DOTATATE PRRT was approved by the U.S. Food and Drug Administration. The workflow relies heavily on the input of a multidisciplinary team and involves a nuclear medicine consultation service, tumor board, and specific preparations in advance of therapy and day-of-therapy procedures. A systematic checklist designed to ensure appropriate selection of treatment candidates and identification of any concerns to address to safely administer PRRT is provided. All patients were evaluated with gallium 68 DOTATATE PET/CT, and in cases of high-grade tumors, they were also evaluated with fluorine 18 fluorodeoxyglucose PET/CT, with imaging findings reviewed as part of the systematic checklist before PRRT. Adverse effects are discussed and imaging follow-up regimens are reviewed, including alternative diagnostic contrast materials. Approaches to multiple challenging patient scenarios are illustrated through case examples. Finally, alternative theranostic radionuclides and treatment strategies are discussed.