PRRT neuroendocrine tumor response monitored using circulating transcript analysis: the NETest

The Clinical Utility of the NETest in Patients with Small Intestinal Neuroendocrine Neoplasms (Si-NENs): A "Real-Life" Study

Current biomarkers do not adequately predict the behaviour of neuroendocrine neoplasms (NENs). This study assessed the NETest, a multianalyte blood biomarker, in patients with small intestinal NENs (Si-NENs). We studied two patient groups: Group 1: metastatic Si-NENs (n = 102) and Group 2: post-operatively disease-free according to 68Ga-DOTATATE PET (n = 16). NETest scores were ≤20% (normal), 21-40% (low), 41-79% (intermediate), or ≥80% (high). Overall survival (OS) and progression-free survival (PFS) were assessed using the Kaplan-Meier method. Univariate and multivariate analyses were performed using the Cox proportional hazards model. In Group 1, the median NETest score was 40% (IQR: 33.3-46.7%). The NETest value (HR: 1.032, 95% CI: 1.003-1.062, p = 0.033) and high-risk NETest category (HR: 10.5, 95% CI: 1.35-81.7, p = 0.025) were independent predictors of PFS, along with presence of lung metastases, CgA levels > 10 × ULN, and tumour growth rate (TGR). Independent predictors of OS were the NETest value (HR: 1.035, 95% CI: 1.005-1.066, p = 0.024) and high-risk NETest category (HR: 15.2, 95% CI: 1.52-151, p = 0.02), along with presence of lung metastases and CgA levels > 10 × ULN. In Group 2, ROC analysis identified an AUC of 0.909 (95% CI: 0.75-0.100) for prediction of local or metastatic recurrence. Blood NETest scores were associated with PFS and OS in patients with metastatic Si-NENs, along with TGR, CgA > 10 × ULN, and presence of lung metastases.

NETest in advanced high-grade gastroenteropancreatic neuroendocrine neoplasms

Molecular blood biomarkers are lacking for high-grade (HG) gastroenteropancreatic (GEP) neuroendocrine neoplasms (NEN). To histologically distinguish between neuroendocrine carcinoma (NEC), neuroendocrine tumors G3 (NET G3), adenocarcinoma and MINEN is often challenging. The mRNA-based NETest has diagnostic, prognostic and predictive value in neuroendocrine tumors G1-2 but has not been studied in HG GEP-NEN. Patients with advanced HG GEP-NEN were prospectively included in an observational study. A blood sample was collected before the start of chemotherapy and pseudonymised before NETest was performed. NETest results are expressed as an activity index (NETest score) from 0 to 100. The normal score cut-off is 20. Histological sections were pseudonymised before centralized pathological re-evaluation. Samples from 60 patients were evaluable with the NETest. Main primary tumor sites were colon (14), rectum (12), pancreas (11) and esophagus (7). Re-classification: 30 NEC, 12 NET G3, 3 HG-NEN ambiguous morphology, 8 MiNEN, 3 adenocarcinomas with neuroendocrine differentiation (ADNE), 3 adenocarcinomas and 1 NET G2. Elevated NETest (>20) was seen in 38/45 (84%) HG GEP-NEN, all 17 large-cell NEC (100%), 11/13 (85%) small-cell NEC, all ambiguous cases and 7/12 (64%) NET G3. NETest was elevated in 5/8 (63%) MiNEN, 2/3 ADNE, however not in 3 adenocarcinomas. Median survival was 10.2 months (9.6-10.8 95%CI) for evaluable HG GEP-NEN treated with palliative chemotherapy (n = 39), and survival was significantly shorter in patients with NETest >60 with an OS of only 6.5 months. This is the first study to evaluate use of the NETest in advanced HG GEP-NEN. The NETest was almost always elevated in GEP-NEC and in all large-cell NEC. The NETest was also frequently elevated in NET G3 and MiNEN, however cases were limited. Baseline NETest was not predictive for benefit of chemotherapy, however a NETest >60 was prognostic with a shorter survival for patients receiving chemotherapy.

Biochemical Markers for Neuroendocrine Tumors: Traditional Circulating Markers and Recent Development-A Comprehensive Review

Neuroendocrine neoplasms (NENs) are a heterogeneous group of neoplasms presenting unique challenges in diagnosis and management. Traditional markers such as chromogranin A (CgA), pancreatic polypeptide (PP), and neuron-specific enolase (NSE) have limitations in terms of specificity and sensitivity. Specific circulating markers such as serotonin and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) and various gastrointestinal hormones such as gastrin, glucagon, somatostatin, and vasoactive intestinal peptide (VIP) have a role in identifying functional NENs. Recent advances in molecular and biochemical markers, also accounting for novel genomic and proteomic markers, have significantly improved the landscape for the diagnosis and monitoring of NENs. This review discusses these developments, focusing on both traditional markers such as CgA and NSE, as well as specific hormones like gastrin, insulin, somatostatin, glucagon, and VIP. Additionally, it covers emerging genomic and proteomic markers that are shaping current research. The clinical applicability of these markers is highlighted, and their role in improving diagnostic accuracy, predicting surgical outcomes, and monitoring response to treatment is demonstrated. The review also highlights the need for further research, including validation of these markers in larger studies, development of standardized assays, and integration with imaging techniques. The evolving field of biochemical markers holds promise for improving patient outcomes in the treatment of NENs, although challenges in standardization and validation remain.

Evaluation of a blood miRNA/mRNA signature to follow-up Lu-PRRT therapy for G1/G2 intestinal neuroendocrine tumors

Background

177Lu-oxodotreotide peptide receptor therapy (LuPRRT) is an efficient treatment for midgut neuroendocrine tumors (NETs) of variable radiological response. Several clinical, biological, and imaging parameters may be used to establish a relative disease prognosis but none is able to predict early efficacy or toxicities. We investigated expression levels for mRNA and miRNA involved in radiosensitivity and tumor progression searching for correlations related to patient outcome during LuPRRT therapy.

Methods

Thirty-five patients received LuPRRT for G1/G2 midgut NETs between May 2019 and September 2021. Peripheral blood samples were collected prior to irradiation, before and 48 h after the second and the fourth LuPRRT, and at 6-month follow-up. Multiple regression analyses and Pearson correlations were performed to identify the miRNA/mRNA signature that will best predict response to LuPRRT.

Results

Focusing on four mRNAs and three miRNAs, we identified a miRNA/mRNA signature enabling the early identification of responders to LuPRRT with significant reduced miRNA/mRNA expression after the first LuPRRT administration for patients with progressive disease at 1 year (p < 0.001). The relevance of this signature was reinforced by studying its evolution up to 6 months post-LuPRRT. Moreover, nadir absolute lymphocyte count within the first 2 months after the first LuPRRT administration was significantly related to low miRNA/mRNA expression level (p < 0.05) for patients with progressive disease.

Conclusion

We present a pilot study exploring a miRNA/mRNA signature that correlates with early hematologic toxicity and therapeutic response 12 months following LuPRRT. This signature will be tested prospectively in a larger series of patients.

Absorbed Dose-Response Relationship in Patients with Gastroenteropancreatic Neuroendocrine Tumors Treated with [177Lu]Lu-DOTATATE: One Step Closer to Personalized Medicine

[177Lu]Lu-DOTATATE has been approved for progressive and inoperable gastroenteropancreatic neuroendocrine tumors (GEP-NETs) that overexpress somatostatin receptors. The absorbed doses by limiting organs and tumors can be quantified by serial postinfusion scintigraphy measurements of the γ-emissions from 177Lu. The objective of this work was to explore how postinfusion [177Lu]Lu-DOTATATE dosimetry could influence clinical management by predicting treatment efficacy (tumor shrinkage and survival) and toxicity. Methods: Patients with GEP-NETs treated with [177Lu]Lu-DOTATATE between 2016 and 2022 and who underwent dosimetry were included. Absorbed doses were calculated for healthy organs (liver, kidneys, bone marrow, and spleen) and tumors using PLANET Dose and the local energy deposition method based on serial posttreatment SPECT/CT. Up to 5 lesions per site were selected and measured on images collected at baseline and 3 mo after treatment end (measurement masked to the somatostatin receptor imaging uptake). For toxicity assessment, laboratory parameters were regularly monitored. Clinical data, including time to death or progression, were collected from the patients' health records. Correlations between absorbed doses by organs and toxicity and between absorbed doses by lesions and tumor volume variation were studied using regression models. Results: In total, 35 dosimetric studies were performed in patients with mostly grade 2 (77%) tumors and metastases in liver (89%), lymph nodes (77%), and bone (34%), and 146 lesions were analyzed: 1-9 lesions per patient, mostly liver metastases (65%) and lymph nodes (25%). The median total absorbed dose by tumors was 94.4 Gy. The absorbed doses by tumors significantly decreased between cycles. The absorbed dose by tumors was significantly associated with tumor volume variation (P < 0.001) 3 mo after treatment end, and it was a significant prognostic factor for survival. Toxicity analysis showed a correlation between the decrease of hematologic parameters such as lymphocytes or platelet concentrations and the absorbed doses by the spleen or bone marrow. The mean absorbed dose by the kidneys was not correlated with nephrotoxicity during the studied period. Conclusion: In patients treated with [177Lu]Lu-DOTATATE for GEP-NETs, tumor and healthy organ dosimetry can predict survival and toxicities, thus influencing clinical management.

Models using comprehensive, lesion-level, longitudinal [68Ga]Ga-DOTA-TATE PET-derived features lead to superior outcome prediction in neuroendocrine tumor patients treated with [177Lu]Lu-DOTA-TATE

PURPOSE

Somatostatin receptor (SSTR) imaging features are predictive of treatment outcome for neuroendocrine tumor (NET) patients receiving peptide receptor radionuclide therapy (PRRT). However, comprehensive (all metastatic lesions), longitudinal (temporal variation), and lesion-level measured features have never been explored. Such features allow for capturing the heterogeneity in disease response to treatment. Furthermore, models combining these features are lacking. In this work we evaluated the predictive power of comprehensive, longitudinal, lesion-level 68GA-SSTR-PET features combined with a multivariate linear regression (MLR) model.

METHODS

This retrospective study enrolled NET patients treated with [177Lu]Lu-DOTA-TATE and imaged with [68Ga]Ga-DOTA-TATE at baseline and post-therapy. All lesions were segmented, anatomically labeled, and longitudinally matched. Lesion-level uptake and variation in uptake were measured. Patient-level features were engineered and selected for modeling of progression-free survival (PFS). The model was validated via concordance index, patient classification (ROC analysis), and survival analysis (Kaplan-Meier and Cox proportional hazards). The MLR was benchmarked against single feature predictions.

RESULTS

Thirty-six NET patients were enrolled and stratified into poor and good responders (PFS ≥ 25 months). Four patient-level features were selected, the MLR concordance index was 0.826, and the AUC was 0.88 (0.85 specificity, 0.81 sensitivity). Survival analysis led to significant patient stratification (p<.001) and hazard ratio (3⨯10-5). Lastly, in a benchmark study, the MLR modeling approach outperformed all the single feature predictors.

CONCLUSION

Comprehensive, lesion-level, longitudinal 68GA-SSTR-PET analysis, combined with MLR modeling, leads to excellent predictions of PRRT outcome in NET patients, outperforming non-comprehensive, patient-level, and single time-point feature predictions.

MESSAGE

Neuroendocrine tumor, peptide receptor radionuclide therapy, Somatostatin Receptor Imaging, Outcome Prediction, Treatment Response Assessment.

Plasma Markers for Therapy Response Monitoring in Patients with Neuroendocrine Tumors Undergoing Peptide Receptor Radionuclide Therapy

BACKGROUND

Pretherapeutic chromogranin A, alkaline phosphatase (ALP), or De Ritis ratio (aspartate aminotransferase/alanine aminotransferase) are prognostic factors in patients with metastatic neuroendocrine tumors (NET) undergoing peptide receptor radionuclide therapy (PRRT). However, their value for intratherapeutic monitoring remains unclear. We evaluated if changes in plasma markers during PRRT can help identify patients with unfavorable outcomes.

METHODS

A monocentric retrospective analysis of 141 patients with NET undergoing PRRT with [177Lu]Lu-DOTATOC was conducted. Changes in laboratory parameters were calculated by dividing the values determined immediately before each cycle of PRRT by the pretherapeutic value. Patients with low vs. high PFS were compared with the Wilcoxon rank-sum test.

RESULTS

Progression, relapse, or death after PRRT was observed in 103/141 patients. Patients with low PFS showed a significant relative ALP increase before the third (p = 0.014) and fourth (p = 0.039) cycles of PRRT. Kaplan-Meier analysis revealed a median PFS of 24.3 months (95% CI, 20.7-27.8 months) in patients with decreasing ALP values (Δ > 10%) during treatment, 12.5 months (95% CI, 9.2-15.8 months) in patients with increasing ALP values (Δ > 10%), and 17.7 months (95% CI, 13.6-21.8 months) with stable ALP values (Δ ± 10%).

CONCLUSIONS

Based on these exploratory data, a rise in plasma ALP might indicate disease progression and should be interpreted cautiously during therapy.

The Quest for Circulating Biomarkers in Neuroendocrine Neoplasms: a Clinical Perspective

OPINION STATEMENT

Given the considerable heterogeneity in neuroendocrine neoplasms (NENs), it appears unlikely that a sole biomarker exists capable of fully capturing all useful clinical aspects of these tumors. This is reflected in the abundant number of biomarkers presently available for the diagnosis, prognosis, and monitoring of NEN patients. Although assessment of immunohistochemical and radiological markers remains paramount and often obligatory, there has been a notable surge of interest in circulating biomarkers over the years given the numerous benefits associated with liquid biopsies. Currently, the clinic primarily relies on single-analyte assays such as the chromogranin A assay, but these are far from ideal because of limitations such as compromised sensitivity and specificity as well as a lack of standardization. Consequently, the quest for NEN biomarkers continued with the exploration of multianalyte markers, exemplified by the development of the NETest and ctDNA-based analysis. Here, an extensive panel of markers is simultaneously evaluated to identify distinct signatures that could enhance the accuracy of patient diagnosis, prognosis determination, and response to therapy prediction and monitoring. Given the promising results, the development and implementation of these multianalyte markers are expected to usher in a new era of NEN biomarkers in the clinic. In this review, we will outline both clinically implemented and more experimental circulating markers to provide an update on developments in this rapidly evolving field.

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.

Monitoring and Surveillance of Patients with Gastroenteropancreatic Neuroendocrine Tumors Undergoing Radioligand Therapy

Radioligand therapy (RLT) with [177Lu]Lu-DOTA-TATE is a standard of care for adult patients with somatostatin-receptor (SSTR)-positive gastroenteropancreatic neuroendocrine tumors (GEP-NETs). Taking advantage of this precision nuclear medicine approach requires diligent monitoring and surveillance, from the use of diagnostic SSTR-targeted radioligand imaging for the selection of patients through treatment and assessments of response. Published evidence-based guidelines assist the multidisciplinary healthcare team by providing acceptable approaches to care; however, the sheer heterogeneity of GEP-NETs can make these frameworks difficult to apply in individual clinical circumstances. There are also contradictions in the literature regarding the utility of novel approaches in monitoring and surveilling patients with GEP-NETs receiving RLT. This article discusses the emerging evidence on imaging, clinical biochemistry, and tumor assessment criteria in the management of patients receiving RLT for GEP-NETs; additionally, it documents our own best practices. This allows us to offer practical guidance on how to effectively implement monitoring and surveillance measures to aid patient-tailored clinical decision-making.

Promising targetable biomarkers in pancreatic neuroendocrine tumours

INTRODUCTION

In the treatment scenario of PanNETs-targeted therapies are desired but limited, as rarity and heterogeneity on PanNETs pose limitations to their development.

AREAS COVERED

We performed a literature review searching for promising druggable biomarkers and potential treatments to be implemented in the next future. We focused on treatments which have already reached clinical experimentation, although in early phases. Six targets were identified, namely Hsp90, HIFa, HDACs, CDKs, uPAR, and DDR. Even though biological rational is strong, so far reported efficacy outcomes are quite disappointing. The reason of that should be searched in the patients' heterogeneity, lack of biomarker selection, poor knowledge of interfering mechanisms as well as difficulties in patients accrual. Moreover, different ways to assess treatment efficacy should be considered, other than response rate, in light of the more indolent nature of NETs.

EXPERT OPINION

Development of targeted treatments in PanNETs is still an uncovered area, far behind other more frequent cancers. Rarity of NETs led to accrual of unselected populations, possibly jeopardizing the drug efficacy. Better patients' selection, both in terms of topography, grading and biomarkers is crucial and will help understanding which role targeted therapies can really play in these tumors.

Established and novel circulating neuroendocrine tumor biomarkers for diagnostic, predictive and prognostic use

The management of neuroendocrine tumors (NETs) represents a clinical challenge due to heterogeneity of their clinical behaviour, molecular biology and response to treatment. Over the years, several circulating biomarkers have been developed for the early diagnosis and follow-up of NETs. The specific secretory products of tumors associated with a secretory syndrome (functioning tumors) may be used as diagnostic and/or prognostic biomarkers while the most common non-specific circulating biomarkers, that may be increased in both functioning and non-functioning tumors, are chromogranin A and the neuron specific enolase. However, the diagnostic accuracy as well as the prognostic and predictive value of these biomarkers are limited and novel techniques of multianalyte analysis of regulators of tumor biology have been developed. The NETest has been most extensively studied and proved to be useful in NET diagnosis, early detection of post-operative recurrence and prediction of response to treatment but further investigation establishing higher level of evidence is required for implementation in clinical practice.

An Overview of Circulating Biomarkers in Neuroendocrine Neoplasms: A Clinical Guide

Neuroendocrine neoplasms (NENs) are a heterogeneous group of diseases that are characterized by different behavior and clinical manifestations. The diagnosis and management of this group of tumors are challenging due to tumor complexity and lack of precise and widely validated biomarkers. Indeed, the current circulating mono-analyte biomarkers (such as chromogranin A) are ineffective in describing such complex tumors due to their poor sensitivity and specificity. In contrast, multi-analytical circulating biomarkers (including NETest) are emerging as more effective tools to determine the real-time profile of the disease, both in terms of accurate diagnosis and effective treatment. In this review, we will analyze the capabilities and limitations of different circulating biomarkers focusing on three relevant questions: (1) accurate and early diagnosis; (2) monitoring of disease progression and response to therapy; and (3) detection of early relapse.

Peptide Receptor Radionuclide Therapy (PRRT): Innovations and Improvements

Neuroendocrine neoplasms (NENs) are tumors originating from neuroendocrine cells distributed throughout the human body. With an increasing incidence over the past few decades, they represent a highly heterogeneous group of neoplasms, mostly expressing somatostatin receptors (SSTRs) on their cell surface. Peptide receptor radionuclide therapy (PRRT) has emerged as a crucial strategy for treating advanced, unresectable neuroendocrine tumors by administering radiolabeled somatostatin analogs intravenously to target SSTRs. This article will focus on the multidisciplinary theranostic approach, treatment effectiveness (such as response rates and symptom relief), patient outcomes, and toxicity profile of PRRT for NEN patients. We will review the most significant studies, such as the phase III NETTER-1 trial, and discuss promising new radiopharmaceuticals, including alpha-emitting radionuclide-labeled somatostatin analogs and SSTR antagonists.

Circulating hsa-miR-5096 predicts 18F-FDG PET/CT positivity and modulates somatostatin receptor 2 expression: a novel miR-based assay for pancreatic neuroendocrine tumors

Gastro-entero-pancreatic neuroendocrine tumors (GEP-NETs) are rare diseases encompassing pancreatic (PanNETs) and ileal NETs (SINETs), characterized by heterogeneous somatostatin receptors (SSTRs) expression. Treatments for inoperable GEP-NETs are limited, and SSTR-targeted Peptide Receptor Radionuclide Therapy (PRRT) achieves variable responses. Prognostic biomarkers for the management of GEP-NET patients are required. ¹⁸F-FDG uptake is a prognostic indicator of aggressiveness in GEP-NETs. This study aims to identify circulating and measurable prognostic miRNAs associated with ¹⁸F-FDG-PET/CT status, higher risk and lower response to PRRT.

Methods

Whole miRNOme NGS profiling was conducted on plasma samples obtained from well-differentiated advanced, metastatic, inoperable G1, G2 and G3 GEP-NET patients enrolled in the non-randomized LUX (NCT02736500) and LUNET (NCT02489604) clinical trials prior to PRRT (screening set, n= 24). Differential expression analysis was performed between ¹⁸F-FDG positive (n=12) and negative (n=12) patients. Validation was conducted by Real Time quantitative PCR in two distinct well-differentiated GEP-NET validation cohorts, considering the primary site of origin (PanNETs n=38 and SINETs n=30). The Cox regression was applied to assess independent clinical parameters and imaging for progression-free survival (PFS) in PanNETs. In situ RNA hybridization combined with immunohistochemistry was performed to simultaneously detect miR and protein expression in the same tissue specimens. This novel semi-automated miR-protein protocol was applied in PanNET FFPE specimens (n=9). In vitro functional experiments were performed in PanNET models.

Results

While no miRNAs emerged to be deregulated in SINETs, hsa-miR-5096, hsa-let-7i-3p and hsa-miR-4311 were found to correlate with ¹⁸F-FDG-PET/CT in PanNETs (p-value:<0.005). Statistical analysis has shown that, hsa-miR-5096 can predict 6-month PFS (p-value:<0.001) and 12-month Overall Survival upon PRRT treatment (p-value:<0.05), as well as identify ¹⁸F-FDG-PET/CT positive PanNETs with worse prognosis after PRRT (p-value:<0.005). In addition, hsa-miR-5096 inversely correlated with both SSTR2 expression in PanNET tissue and with the ⁶⁸Gallium-DOTATOC captation values (p-value:<0.05), and accordingly it was able to decrease SSTR2 when ectopically expressed in PanNET cells (p-value:<0.01).

Conclusions

hsa-miR-5096 well performs as a biomarker for ¹⁸F-FDG-PET/CT and as independent predictor of PFS. Moreover, exosome-mediated delivery of hsa-miR-5096 may promote SSTR2 heterogeneity and thus resistance to PRRT.

Neuroendocrine Tumor Therapy Response Assessment

Peptide receptor radionuclide therapy has become an integral part of management of neuroendocrine neoplasms. Gallium-68- and lutetium-177-labeled somatostatin receptor analogues have replaced yttrium-90- and 111-indium-based tracers. Several newer targeted therapies are also being used in clinical and research settings. It is imperative to accurately evaluate the response to these agents. The characteristics of NENs and the response patterns of the targeted therapies make response assessment in this group challenging. This article provides an overview of the strengths and weaknesses of the various biomarkers available for response assessment.

Interim Analysis of a Prospective Validation of 2 Blood-Based Genomic Assessments (PPQ and NETest) to Determine the Clinical Efficacy of 177Lu-DOTATATE in Neuroendocrine Tumors

Reliable biomarkers for neuroendocrine tumor (NET) management during peptide receptor radionuclide therapy (PRRT) are lacking. We validated the role of 2 circulating biomarkers: the PRRT prediction quotient (PPQ) as a predictive marker for response and the NETest as a monitoring biomarker. Furthermore, we evaluated whether tissue-based genetic alterations are effective in predicting progression-free survival (PFS). Methods: Data were prospectively collected on patients at the Memorial Sloan Kettering Cancer Center with 177Lu-DOTATATE-treated somatostatin receptor (SSTR)-positive gastroenteropancreatic and lung NETs (n = 67; median age, 66 y; 52% female; 42% pancreatic, 39% small-bowel; 78% grade 1 or 2). All cases were metastatic (89% liver) and had received 1-8 prior treatments (median, 3), including somatostatin analogs (91%), surgery (55%), or chemotherapy (49%). Treatment response included PFS. According to RECIST, version 1.1, responders had stable disease or a partial response (disease-control rate) and nonresponders had progression. Blood was collected before each cycle and at follow-up. Samples were deidentified and assayed and underwent masked analyses. The gene expression assays included RNA isolation, real-time quantitative polymerase chain reaction, and multialgorithm analyses. The PPQ (positive predicts a responder; negative predicts a nonresponder) at baseline was determined. The NETest (0-100 score) was performed. Statistics were analyzed using Mann-Whitney U testing (2-tailed) or Kaplan-Meier survival testing (PFS). In patients with archival tumor tissue, next-generation sequencing was performed through an institutional platform (Memorial Sloan Kettering-Integrated Mutation Profiling of Actionable Cancer Targets). Results: Forty-one patients (61%) were responders. PPQ accurately predicted 96% (64/67). The hazard ratio for prediction was 24.4 (95% CI, 8.2-72.5). Twelve-month disease control was 97% for PPQ-positive patients versus 26% for PPQ-negative patients (P < 0.0001). Median progression-free survival was not reached in those predicted to respond (PPQ-positive, n = 40) but was 8 mo in those predicted not to respond (PPQ-negative, n = 27). The NETest result in responders was 67 ± 25 at baseline and significantly (P < 0.05) decreased (-37 ± 44%) at follow-up. The NETest result in nonresponders was 44 ± 23 at baseline and significantly (P < 0.05) increased (+76% ± 56%) at progression. Overall, the NETest changes (increases or decreases) were 90% accurate. Thirty patients underwent next-generation sequencing. Tumors were microsatellite-stable, and the median mutational burden was 1.8. Alterations involved mainly the mTOR/PTEN/TSC pathway (30%). No relationship was associated with PRRT response. Conclusion: Our interim analysis confirmed that PPQ is an accurate predictor of 177Lu-DOTATATE responsiveness (radiosensitivity) and that NETest changes accurately correlated with treatment response. Tissue-based molecular genetic information had little value in PRRT prediction. Blood-based gene signatures may improve the management of patients undergoing 177Lu-DOTATATE by providing information on tumor radiosensitivity and disease course, thus allowing individualized strategies.

An Insight on Functioning Pancreatic Neuroendocrine Neoplasms

Pancreatic neuroendocrine neoplasms (PanNENs) are rare neoplasms arising from islets of the Langerhans in the pancreas. They can be divided into two groups, based on peptide hormone secretion, functioning and nonfunctioning PanNENs. The first group is characterized by different secreted peptides causing specific syndromes and is further classified into subgroups: insulinoma, gastrinoma, glucagonoma, somatostatinoma, VIPoma and tumors producing serotonin and adrenocorticotrophic hormone. Conversely, the second group does not release peptides and is usually associated with a worse prognosis. Today, although the efforts to improve the therapeutic approaches, surgery remains the only curative treatment for patients with PanNENs. The development of high-throughput techniques has increased the molecular knowledge of PanNENs, thereby allowing us to understand better the molecular biology and potential therapeutic vulnerabilities of PanNENs. Although enormous advancements in therapeutic and molecular aspects of PanNENs have been achieved, there is poor knowledge about each subgroup of functioning PanNENs.Therefore, we believe that combining high-throughput platforms with new diagnostic tools will allow for the efficient characterization of the main differences among the subgroups of functioning PanNENs. In this narrative review, we summarize the current landscape regarding diagnosis, molecular profiling and treatment, and we discuss the future perspectives of functioning PanNENs.

Diagnostic work-up and advancement in the diagnosis of gastroenteropancreatic neuroendocrine neoplasms

Neuroendocrine neoplasms (NENs) are a heterogeneous group of neoplasms ranging from well-differentiated, slowly growing tumors to poorly differentiated carcinomas. These tumors are generally characterized by indolent course and quite often absence of specific symptoms, thus eluding diagnosis until at an advanced stage. This underscores the importance of establishing a prompt and accurate diagnosis. The gold-standard remains histopathology. This should contain neuroendocrine-specific markers, such as chromogranin A; and also, an estimate of the proliferation by Ki-67 (or MIB-1), which is pivotal for treatment selection and prognostication. Initial work-up involves assessment of serum Chromogranin A and in selected patients gut peptide hormones. More recently, the measurement of multiple NEN-related transcripts, or the detection of circulating tumor cells enhanced our current diagnostic armamentarium and appears to supersede historical serum markers, such as Chromogranin A. Standard imaging procedures include cross-sectional imaging, either computed tomography or magnetic resonance, and are combined with somatostatin receptor scintigraphy. In particular, the advent of ¹¹¹In-DTPA-octreotide and more recently PET/CT and ⁶⁸Ga-DOTA-Octreotate scans revolutionized the diagnostic landscape of NENs. Likewise, FDG PET represents an invaluable asset in the management of high-grade neuroendocrine carcinomas. Lastly, endoscopy, either conventional, or more advanced modalities such as endoscopic ultrasound, capsule endoscopy and enteroscopy, are essential for the diagnosis and staging of gastroenteropancreatic neuroendocrine neoplasms and are routinely integrated in clinical practice. The complexity and variability of NENs necessitate the deep understanding of the current diagnostic strategies, which in turn assists in offering optimal patient-tailored treatment. The current review article presents the diagnostic work-up of GEP-NENs and all the recent advances in the field.

A Clinical Guide to Peptide Receptor Radionuclide Therapy with 177Lu-DOTATATE in Neuroendocrine Tumor Patients

Peptide receptor radionuclide therapy (PRRT) with [¹⁷⁷Lu]Lu-[DOTA⁰,Tyr³]-octreotate (¹⁷⁷Lu-DOTATATE) has become an established second- or third-line treatment option for patients with somatostatin receptor (SSTR)-positive advanced well-differentiated gastroenteropancreatic (GEP) neuroendocrine tumors (NETs). Clinical evidence of the efficacy of PRRT in tumor control has been proven and lower risks of disease progression or death are seen combined with an improved quality of life. When appropriate patient selection is performed, PRRT is accompanied by limited risks for renal and hematological toxicities. Treatment of NET patients with PRRT requires dedicated clinical expertise due to the biological characteristics of PRRT and specific characteristics of NET patients. This review provides an overview for clinicians dealing with NET on the history, molecular characteristics, efficacy, toxicity and relevant clinical specifics of PRRT.

Optimisation of radioligand therapy in neuroendocrine tumours: Current and evolving evidence

Treatment of neuroendocrine tumours (NETs) with radioligand therapy (RLT) for example, ¹⁷⁷ Lu-DOTATATE is generally well-tolerated and prolongs time to progression in most patients. However, approximately 20% of patients are nonresponders. In addition, complete responses are rare (<5% of patients), and durable responses beyond 3-4 years are uncommon. This article will discuss factors which may improve the outcomes of PRRT by using biomarkers to identify patients at high risk to be nonresponders (imaging and liquid biomarkers) and will examine mechanisms to potentially improve/optimise current RLT treatment strategies. These include mechanisms to potentiate the effects of RLT, increase tumour absorbed dose, overcoming radio-resistance and upregulation of somatostatin receptors, although larger studies will be required to demonstrate which techniques are going to be most efficacious in clinical practice.

Pediatric Neuroendocrine Neoplasms: Rare Malignancies with Incredible Variability

Neuroendocrine neoplasms (NENs) encompass a variety of neuroendocrine tumors (NETs) and neuroendocrine carcinomas (NECs) which can arise anywhere in the body. While relatively rare in the pediatric population, the incidence of NENs has increased in the past few decades. These neoplasms can be devastating if not diagnosed and treated early, however, symptoms are variable and can be indolent for many years. There is a reported median of 10 years from the appearance of the first symptoms to time of diagnosis. Considering some of these neoplasms have a mortality rate as high as 90%, it is crucial healthcare providers are aware of NENs and remain vigilant. With better provider education and easily accessible resources for information about these neoplasms, awareness can be improved leading to earlier disease recognition and diagnosis. This manuscript aims to provide an overview of both the most common NENs as well as the rarer NENs with high lethality in the pediatric population. This review provides up to date evidence and recommendations, encompassing recent changes in classification and advances in treatment modalities, including recently completed and ongoing clinical trials.

NETest: serial liquid biopsies in gastroenteropancreatic NET surveillance

Objective

Up to now, serial NETest measurements in individuals assessing the disease course of gastroenteropancreatic neuroendocrine tumors (GEPNETs) at long-term follow-up and treatment response were not studied.

Design

The study was a longitudinal validation study of serial NETest measurements - a blood-based gene expression signature - in 132 patients with GEPNETs on therapy or watch-and-wait strategy.

Methods

Serial samples were collected during 46 (range: 6-71) months of follow-up. NETest scores were compared with Response Evaluation Criteria in Solid Tumors version 1.1-defined treatment response (e.g. no evidence of disease (NED), stable disease (SD) or progressive disease (PD)).

Results

Consecutive NETest scores fluctuated substantially (range: 0-100) over time in individuals with SD (n = 28) and NED (n = 30). Follow-up samples were significantly higher in SD (samples 3-5) and NED subgroups (samples 2-5) compared with baseline results, without changes in imaging. In 82% of untreated patients with PD, consecutive NETest scores consistently remained high. In patients undergoing systemic treatment, the median pre-treatment NETest score in treatment-responders was 76.5 (n = 22) vs 33 (n = 12) in non-responders (P = 0.001). Patients with low pre-treatment scores had 21 months reduced progression-free survival (10 vs 31 months; P = 0.01). The accuracy of the NETest for treatment response prediction was 0.73 (P = 0.009).

Conclusion

In patients not undergoing treatment, consecutive low NETest scores are associated with indolent behavior. Patients who develop PD exhibit elevated scores. Elevated results have important predictive value for treatment responsiveness and could be used for individualizing decisions on systemic therapy. The clinical value of follow-up NETest scores for patients who choose to watch and wait requires further study.

Glucose Metabolism Modification Induced by Radioligand Therapy with [177Lu]Lu/[90Y]Y-DOTATOC in Advanced Neuroendocrine Neoplasms: A Prospective Pilot Study within FENET-2016 Trial

[18F]F-FDG (FDG) PET is emerging as a relevant diagnostic and prognostic tool in neuroendocrine neoplasms (NENs), as a simultaneous decrease in [68Ga]Ga-DOTA peptides and increase in FDG uptake (the “flip-flop” phenomenon) occurs during the natural history of these tumors. The aim of this study was to evaluate the variations on FDG PET in NEN patients treated with two different schemes of radioligand therapy (RLT) and to correlate them with clinical−pathologic variables. A prospective evaluation of 108 lesions in 56 patients (33 males and 23 females; median age, 64.5 years) affected by NENs of various primary origins (28 pancreatic, 13 gastrointestinal, 9 bronchial, 6 unknown primary (CUP-NENs) and 1 pheochromocytoma) and grades (median Ki-67 = 9%) was performed. The patients were treated with RLT within the phase II clinical trial FENET-2016 (CTID: NCT04790708). RLT was offered for 32 patients with the MONO scheme (five cycles of [177Lu]Lu-DOTATOC) and for 24 with the DUO scheme (three cycles of [177Lu]Lu-DOTATOC alternated with two cycles of [90Y]Y-DOTATOC). Variations in terms of the ΔSUVmax of a maximum of three target lesions per patient (58 for MONO and 50 for DUO RLT) were assessed between baseline and 3 months post-RLT FDG PET. In patients with negative baseline FDG PET, the three most relevant lesions on [68Ga]Ga-DOTA-peptide PET were assessed and matched on post-RLT FDG PET, to check for any possible changes in FDG avidity. Thirty-five patients (62.5%) had at least one pathological FDG uptake at the baseline scans, but the number was reduced to 29 (52%) after RLT. In the patients treated with DUO-scheme RLT, 20 out of 50 lesions were FDG positive before therapy, whereas only 14 were confirmed after RLT (p = 0.03). Moreover, none of the 30 FDG-negative lesions showed an increased FDG uptake after RLT. The lesions of patients with pancreatic and CUP-NENs treated with the DUO scheme demonstrated a significant reduction in ΔSUVmax in comparison to those treated with MONO RLT (p = 0.03 and p = 0.04, respectively). Moreover, we found a mild positive correlation between the grading and ΔSUVmax in patients treated with the MONO scheme (r = 0.39, p < 0.02), while no evidence was detected for patients treated with the DUO scheme. Our results suggest that RLT, mostly with the DUO scheme, could be effective in changing NEN lesions’ glycometabolism, in particular, in patients affected by pancreatic and CUP-NENs, regardless of their Ki-67 index. Probably, associating [90Y]Y-labelled peptides, which have high energy emission and a crossfire effect, and [177Lu]Lu ones, characterized by a longer half-life and a safer profile for organs at risk, might represent a valid option in FDG-positive NENs addressed to RLT. Further studies are needed to validate our preliminary findings. In our opinion, FDG PET/CT should represent a potent tool for fully assessing a patient’s disease characteristics, both before and after RLT.

Neuroendocrine Tumors and Peptide Receptor Radionuclide Therapy: When Is the Right Time?

Since its approval in 2018 by the US Food and Drug Administration, peptide receptor radionuclide therapy (PRRT) has become a mainstay in the treatment of neuroendocrine tumors. Lutetium-177-DOTATATE, the only approved agent, is indicated for the treatment of gastroenteropancreatic-neuroendocrine tumors. Although patient selection appears straightforward with somatostatin receptor-positron emission tomography, there is considerable complexity when deciding which patients to treat and when to start PRRT. Herein, we review the many factors that affect patient selection, focusing on the optimal patients to treat. Although significant effort has been expended to determine which patients benefit the most from PRRT, a validated predictive biomarker remains elusive. Although PRRT has been used for more than 2 decades in Europe and standards of care exist for safe treatment, there remain numerous questions regarding when PRRT should be used relative to other treatments. It is important to remember that multidisciplinary discussions are essential. Currently, there are a number of ongoing studies looking to assess the efficacy of PRRT compared with other treatment options and to optimize treatment through combination therapy, different dosing strategies, or use of different radionuclides and radioligands.

Clinical Management of Neuroendocrine Neoplasms in Clinical Practice: A Formal Consensus Exercise

Simple Summary

Well-structured international guidelines are currently available regarding the management of patients with neuroendocrine neoplasms (NENs). However, in relation to the multiplicity of treatments and the relative rarity and heterogeneity of NENs, there are many controversial issues in which clinical evidence is insufficient and for which expert opinion can be of help. A group of experts selected 14 relevant topics and formulated relative statements concerning controversial issues in several areas on diagnosis, prognosis, therapeutic strategies, and patient follow-up. Specific statements have also been formulated regarding patient management on radioligand therapy (RLT), as well as in the presence of co-morbidities or bone metastases. All the statements were drafted, discussed, modified, and then approved. The Nominal Group Technique (NGT) method was used to obtain consensus. The results of this paper can facilitate the clinical approach of patients with NENs in daily practice in areas where there is scarcity or absence of clinical evidence.

Abstract

Many treatment approaches are now available for neuroendocrine neoplasms (NENs). While several societies have issued guidelines for diagnosis and treatment of NENs, there are still areas of controversy for which there is limited guidance. Expert opinion can thus be of support where firm recommendations are lacking. A group of experts met to formulate 14 statements relative to diagnosis and treatment of NENs and presented herein. The nominal group and estimate-talk-estimate techniques were used. The statements covered a broad range of topics from tools for diagnosis to follow-up, evaluation of response, treatment efficacy, therapeutic sequence, and watchful waiting. Initial prognostic characterization should be based on clinical information as well as histopathological analysis and morphological and functional imaging. It is also crucial to optimize RLT for patients with a NEN starting from accurate characterization of the patient and disease. Follow-up should be patient/tumor tailored with a shared plan about timing and type of imaging procedures to use to avoid safety issues. It is also stressed that patient-reported outcomes should receive greater attention, and that a multidisciplinary approach should be mandatory. Due to the clinical heterogeneity and relative lack of definitive evidence for NENs, personalization of diagnostic–therapeutic work-up is crucial.

Current updates and future directions in diagnosis and management of gastroenteropancreatic neuroendocrine neoplasms

Gastroenteropancreatic neuroendocrine neoplasms are a heterogenous group of rare neoplasms that are increasingly being discovered, often incidentally, throughout the gastrointestinal tract with varying degrees of activity and malignant potential. Confusing nomenclature has added to the complexity of managing these lesions. The term carcinoid tumor and embryonic classification have been replaced with gastroenteropancreatic neuroendocrine neoplasm, which includes gastrointestinal neuroendocrine and pancreatic neuroendocrine neoplasms. A comprehensive multidisciplinary approach is important for clinicians to diagnose, stage and manage these lesions. While histological diagnosis is the gold standard, recent advancements in endoscopy, conventional imaging, functional imaging, and serum biomarkers complement histology for tailoring specific treatment options. In light of developing technology, our review sets out to characterize diagnostic and therapeutic advancements for managing gastroenteropancreatic neuroendocrine tumors, including innovations in radiolabeled peptide imaging, circulating biomarkers, and endoscopic treatment approaches adapted to different locations throughout the gastrointestinal system.

In patients with well-differentiated neuroendocrine tumours, there is no apparent benefit of somatostatin analogues after disease control by peptide receptor radionuclide therapy

PURPOSE

Peptide receptor radionuclide therapy (PRRT) and somatostatin analogues (SSAs) are commonly combined as primary treatment for neuroendocrine neoplasms (NEN), and SSAs given as maintenance. We sought to evaluate whether sequential therapy with PRRT followed by SSAs has progression or survival benefits in patients with NEN after disease control by PRRT.

METHODS

This prospective, randomised, single-centre study had as principal eligibility criteria: unresectable, locally advanced, or metastatic, histologically confirmed well-differentiated NEN; no symptoms/biochemical diagnosis of carcinoid syndrome; no SSAs or ≤ 3 months of SSAs before PRRT; and stable disease or partial or complete response after PRRT. Altogether, 115 patients were randomised 2:1 to an SSA group (n = 74) given octreotide acetate LAR every 4 weeks, or a control group (n = 41) receiving only best supportive care. Octreotide treatment was to stop upon intolerable toxicity or patient refusal, or, at physician/patient discretion, upon NEN progression. The primary endpoint was progression-free survival (PFS), the secondary endpoint, and overall survival (OS).

RESULTS

Median (25th-75th percentile) follow-up from the first PRRT activity to death or latest observation was 6.6 (3.18-10.22) years. During that time, 71/115 patients (62%) progressed, 52/74 (70%) in the SSA group, and 19/41 (46%) in the control group (p = 0.01). Eighty-eight/115 patients (76%) died, 58/74 (78%) in the SSA group, and 30/41 (73%) in the control group (p = 0.52). Median (95% CI) PFS was 4.7 (2.8-7.7) years in the SSA group, and 6.4 (4.1-not reached) years in controls. Overall, median OS was 6.6 years. Neither PFS nor OS differed between groups (p = 0.129, p = 0.985, respectively).

CONCLUSIONS

In patients with disease control after PRRT, subsequent SSA treatment appeared not to be associated with better PFS or OS. Whether to continue SSA administration upon progression after PRRT requires evaluation in a prospective, randomised, controlled multicentre study with a relatively homogeneous sample.

Know thy tumour: Biomarkers to improve treatment of molecular radionuclide therapy

Molecular radionuclide therapy (MRT) is an effective treatment for both localised and disseminated tumours. Biomarkers can be used to identify potential subtypes of tumours that are known to respond better to standard MRT protocols. These enrolment-based biomarkers can further be used to develop dose-response relationships using image-based dosimetry within these defined subtypes. However, the biological identity of the cancers treated with MRT are commonly not well-defined, particularly for neuroendocrine neoplasms. The biological heterogeneity of such cancers has hindered the establishment of dose-responses and minimum tumour dose thresholds. Biomarkers could also be used to determine normal tissue MRT dose limits and permit greater injected doses of MRT in patients. An alternative approach is to understand the repair capacity limits of tumours using radiobiology-based biomarkers within and outside patient cohorts currently treated with MRT. It is hoped that by knowing more about tumours and how they respond to MRT, biomarkers can provide needed dimensionality to image-based biodosimetry to improve MRT with optimized protocols and personalised therapies.

Advances in the Diagnosis and Therapeutic Management of Gastroenteropancreatic Neuroendocrine Neoplasms (GEP-NENs)

Neuroendocrine neoplasms (NENs) are an increasingly common cause of neoplastic diseases. One of the largest groups of NENs are neoplasms localized to the gastroenteropancreatic system, which are known as gastroenteropancreatic NENs (GEP-NENs). Because of nonspecific clinical symptoms, GEP-NEN patient diagnosis and, consequently, their treatment, might be difficult and delayed. This situation has forced researchers all over the world to continue progress in the diagnosis and treatment of patients with GEP-NENs. Our review is designed to present the latest reports on the laboratory diagnostic techniques, imaging tests and surgical and nonsurgical treatment strategies used for patients with these rare neoplasms. We paid particular attention to the nuclear approach, the use of which has been applied to GEP-NEN patient diagnosis, and to nonsurgical and radionuclide treatment strategies. Recent publications were reviewed in search of reports on new strategies for effective disease management. Attention was also paid to those studies still in progress, but with successful results. A total of 248 papers were analyzed, from which 141 papers most relevant to the aim of the study were selected. Using these papers, we highlight the progress in the development of diagnostic and treatment strategies for patients with GEP-NENs.

Therapeutic strategies for gastroenteropancreatic neuroendocrine neoplasms: State-of-the-art and future perspectives

Although gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) have always been considered rare tumors, their incidence has risen over the past few decades. They represent a highly heterogeneous group of neoplasms with several prognostic factors, including disease stage, proliferative index (Ki67), and tumor differentiation. Most of these neoplasms express somatostatin receptors on the cell surface, a feature that has important implications in terms of prognosis, diagnosis, and therapy. Although International Guidelines propose algorithms aimed at guiding therapeutic strategies, GEP-NEN patients are still very different from one another, and the need for personalized treatment continues to increase. Radical surgery is always the best option when feasible; however, up to 80% of cases are metastatic upon diagnosis. Regarding medical treatments, as GEP-NENs are characterized by relatively long overall survival, multiple therapy lines are adopted during the lifetime of these patients, but the optimum sequence to be followed has never been clearly defined. Furthermore, although new molecular markers aimed at predicting the response to therapy, as well as prognostic scores, are currently being studied, their application is still far from being part of daily clinical practice. As they represent a complex disease, with therapeutic protocols that are not completely standardized, GEP-NENs require a multidisciplinary approach. This review will provide an overview of the available therapeutic options for GEP-NENs and attempts to clarify the possible approaches for the management of these patients and to discuss future perspectives in this field.

Update on Epidemiology, Diagnosis, and Biomarkers in Gastroenteropancreatic Neuroendocrine Neoplasms

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) are a heterogeneous group of malignancies that originate from the diffuse neuroendocrine cell system of the pancreas and gastrointestinal tract and have increasingly increased in number over the decades. GEP-NENs are roughly classified into well-differentiated neuroendocrine tumors and poorly differentiated neuroendocrine carcinomas; it is essential to understand the pathological classification according to the mitotic count and Ki67 proliferation index. In addition, with the advent of molecular-targeted drugs and somatostatin analogs and advances in endoscopic and surgical treatments, the multidisciplinary treatment of GEP-NENs has made great progress. In the management of GEP-NENs, accurate diagnosis is key for the proper selection among these diversified treatment methods. The evaluation of hormone-producing ability, diagnostic imaging, and histological diagnosis is central. Advances in the study of the genetic landscape have led to deeper understanding of tumor biology; it has also become possible to identify druggable mutations and predict therapeutic effects. Liquid biopsy, based on blood mRNA expression for GEP-NENs, has been developed, and is useful not only for early detection but also for assessing minimal residual disease after surgery and prediction of therapeutic effects. This review outlines the updates and future prospects of the epidemiology, diagnosis, and management of GEP-NENs.

NETest: A Systematic Review Focusing on the Prognostic and Predictive Role

The NETest is a standardized and reproducible liquid biopsy for neuroendocrine tumors (NETs). It evaluates the expression of 51 NET genes by real-time polymerase chain reaction, providing an accurate molecular profile of the neoplasm. Diagnostic utility of NETest has been widely demonstrated, while its role in predicting prognosis and treatment response is less studied. This systematic review aims to collect and discuss the available evidence on the prognostic and predictive role of NETest, trying to answer 3 questions, frequently raised in clinical practice. Is NETest able to differentiate stable from progressive disease? Increased NETest levels (at least >40%) correlate with disease progression. Is NETest able to predict tumor progression and tumor response to treatment? Some studies demonstrated that the baseline NETest score >33-40% could predict tumor progression. Moreover, NETest performed after treatment (as peptide receptor radionuclide therapy) could predict treatment response also before radiological findings, since the decrease or stability of NETest score predicts tumor response to treatment. Is NETest able to evaluate tumor recurrence risk after surgery? NETest can predict surgical treatment outcome detecting minimal residual disease after radical surgery, which is characterized by a lower but positive NETest score (20-40%), while a higher score (>33-40%) is associated with nonradical surgery. In conclusion, in addition to its demonstrated diagnostic role, this systematic review highlights the efficacy of NETest to assess disease status at the moment of the NETest execution and to predict tumor recurrence after surgery. The efficacy for other applications should be proven by additional studies.

Potential value of pre- and post-therapy [68Ga]Ga-DOTA-TATE PET/CT in the prognosis of response to PRRT in disseminated neuroendocrine tumors

BACKGROUND

Peptide receptor radionuclide therapy (PRRT) is one of the most effective therapeutic options for the treatment of metastatic, well-differentiated neuroendocrine tumors (NETs). It improves progressive disease-free survival and enables the control of hormone secretion in functioning tumors.Currently, there are no clearly established predictors of response to PRRT. The main factors hindering such a prediction are the heterogeneity of somatostatin receptor expression within and between lesions, lack of standardized parameters for functional imaging, and the use of different PRRT protocols.The main goal of our study was to quantify SUVmax changes in [68Ga]Ga-DOTA-TATE PET/CT scans as a potential predictor of long-term response to PRRT.

MATERIAL AND METHODS

Out of 20 patients treated with PRRT using [177Lu]Lu and/or [177Lu]Lu/[90Y]Y-DOTA-TATE in 2017-2019 due to dissemination of neuroendocrine neoplasm, 12 patients underwent [68Ga]Ga-DOTA-TATE PET/CT on average 3.1 months before and 4.5 months after PRRT and were eligible for the analysis.In total, 76 NET lesions were evaluated. We measured SUVmax for every lesion in both PET/CT scans (before and after PRRT). Those values were corrected by liver SUVmax and liver SUVmean measured in volumetric analysis and specified as SUVlmax and SUVlmean. As a next step, changes in SUVlmax and SUVlmean were assessed based on both PET/CT scans. Finally, results were correlated with the clinical outcome assessed as progressive disease, disease stabilization, or partial response.

RESULTS

The mean follow-up period was 19.9 months. Progressive disease, partial response, and disease stabilization were found in five, two, and five patients, respectively. Among patients with a partial response, the decrease in mean SUVlmax was 66.3% when compared to baseline. In patients with stable disease, the decrease in SUVlmax was 30.3% when compared to baseline. In patients with progressive disease, the mean increase in SUVlmax was 9.1% when compared to baseline. The changes in SUVlmean were -69,8%, -30.8%, and -3.7%, respectively.

CONCLUSIONS

A decrease in the SUVmax value in NET lesions, corrected by normal liver tissue uptake assessed in [68Ga]Ga-DOTA-TATE PET/CT scans, indicates a lower risk for NET progressive disease within 20 months after PRRT and may constitute an additional and independent parameter for the estimation of overall risk for disease progression.

Theragnostic in neuroendocrine tumors

In the last few decades, the incidence and prevalence of neuroendocrine tumors has been increasing. The theragnostic approach, that allows the diagnosis and treatment of different neoplasms with the same ligand, is a typical nuclear medicine tool. Applied for years, is also pivotal in neuroendocrine tumors (NETs) where it has improved the diagnostic accuracy and the therapeutic efficacy with impact on patient's survival. Theragnostic also allows the identification of important prognostic factors such as tumor location and burden, presence of liver metastases and intensity of somatostatin receptors (SSTR) expression to consider in new and possibly combined studies to ameliorate patient's outcome. Moreover, the possibility to evaluate receptor expression even in non-NET malignancies has de facto widened the possible indications for PRRT. We believe that this innovative therapeutic approach will be implemented in next years by radiomics and biological tumors characterization to better address PRRT applications.

Dosimetry for Radiopharmaceutical Therapy: The European Perspective

This review presents efforts in Europe over the last few years with respect to standardization of quantitative imaging and dosimetry and comprises the results of several European research projects on practices regarding radiopharmaceutical therapies (RPTs). Because the European Union has regulatory requirements concerning dosimetry in RPTs, the European Association of Nuclear Medicine released a position paper in 2021 on the use of dosimetry under these requirements. The importance of radiobiology for RPTs is elucidated in another position paper by the European Association of Nuclear Medicine. Furthermore, how dosimetry interacts with clinical requirements is described, with several clinical examples. In the future, more efforts need to be undertaken to increase teaching and standardization efforts and to incorporate radiobiology for further individualizing patient treatment, with the aim of improving the outcome and safety of RPTs.

Value of Peptide Receptor Radionuclide Therapy as Neoadjuvant Treatment in the Management of Primary Inoperable Neuroendocrine Tumors

INTRODUCTION

Neuroendocrine neoplasms including neuroendocrine tumors (NETs) are often diagnosed as primary disseminated or inoperable. In those cases, systemic extensive therapy is necessary, but radical treatment is unlikely. As described in the literature, in some selected cases, peptide receptor radionuclide therapy (PRRT) may be used as a first-line/neoadjuvant therapy that allows further successful surgery. Such treatment may enable a reduction of total tumor burden or allow a radical treatment which improves the final outcomes.

AIM

This study aims to assess whether neoadjuvant PRRT could be a treatment option for patients with initially unresectable NETs.

METHODS

Among the group of 114 patients treated with PRRT between the years 2005 and 2020, in 32 cases, it was the first-line therapy, mainly due to massive disease burden at the time of diagnosis. Among them, nine patients received PRRT as the first-line treatment due to the primary inoperable tumors with the intention of preoperative reduction of the tumor size in order to allow for a surgical treatment.

RESULTS

Neoadjuvant PRRT enabled surgery in four out of nine (45%) patients. Finally, in two out of four cases, the goal (radical surgery) has been achieved.

CONCLUSION

PRRT may be considered not only as a palliative but also as a neoadjuvant therapy in advanced, somatostatin-positive NETs that were initially inoperable.

A novel liquid biopsy (NETest) identifies paragangliomas and pheochromocytomas with high accuracy

Pheochromocytomas and paragangliomas (PHEOs/PGLs) represent diagnostically challenging and complex neuroendocrine tumors (NETs). Current biomarker tests for PHEOs/PGLs are technically complex or limited. We assessed the diagnostic utility of a NET-specific 51-marker gene blood assay (NETest) in patients with PHEOs/PGLs (n = 81), including ten pediatric patients, and age-/gender-matched controls (n = 142) using a prospective case:control (1:2) analysis. mRNA was measured (qPCR), and results were scaled from 0 to 100 (upper limit of normal < 20). Receiver operating curve (ROC) and non-parametric (Mann-Whitney) tests were used for analyses (two-tailed). All data are presented as mean ± s.e.m. NETest accuracy for PHEO/PGL diagnosis was 100%. PHEO/PGL scores were 70 ± 3 vs 8.5 ± 1 in controls (P < 0.0001), and ROC analysis was 0.99 ± 0.004 (P < 0.0001). Diagnostic metrics were 94% accurate, 100% sensitive, and 92% specific. Imaging correlation with 68Ga-PET-SSA was 100%. NETest levels in PHEOs (n = 26) were significantly (P < 0.0001) elevated (83 ± 4) vs 66 ± 4 in PGLs (n = 40) and mixed PHEOs/PGLs (n = 5: 37 ± 3). Adrenal-derived tumors (n = 30) exhibited higher scores (76 ± 5) than extra-adrenal-derived tumors (66 ± 4, P < 0.05). Cluster 2 tumors exhibited significantly (P = 0.034) elevated NETest levels (n = 4: 92 ± 2) vs cluster 1 tumors (n = 35: 69 ± 4). Regulatory pathway analysis identified elevated RAS-RAF, metastatic, pluripotential, neural and secretory gene cluster levels (P < 0.05) in PHEOs compared to PGLs. Cluster 2 PPGLs exhibited elevated (P = 0.046) levels of growth factor signaling genes compared to cluster 1. The PHEOs/PGLs in the pediatric cohort (n = 10) were all NETest-positive (81 ± 8) and exhibited a gene expression profile spectrum analogous to adults. Circulating NET transcript analysis identifies PHEOs/PGLs with 100% efficacy and is likely to have clinical utility in the diagnosis and management of PHEO/PGL patients.

Somatostatin Receptor Imaging and Theranostics: Current Practice and Future Prospects

A new era of precision diagnostics and therapy for patients with neuroendocrine neoplasms began with the approval of somatostatin receptor (SSTR) radiopharmaceuticals for PET imaging followed by peptide receptor radionuclide therapy (PRRT). With the transition from SSTR-based γ-scintigraphy to PET, the higher sensitivity of the latter raised questions regarding the direct application of the planar scintigraphy-based Krenning score for PRRT eligibility. Also, to date, the role of SSTR PET in response assessment and predicting outcome remains under evaluation. In this comprehensive review article, we discuss the current role of SSTR PET in all aspects of neuroendocrine neoplasms, including its relation to conventional imaging, selection of patients for PRRT, and the current understanding of SSTR PET-based response assessment. We also provide a standardized reporting template for SSTR PET with a brief discussion.

Biomarkers in Small Intestine NETs and Carcinoid Heart Disease: A Comprehensive Review

Simple Summary

Neuroendocrine tumors (NET), a heterogeneous group of tumors arising from neuroendocrine cells, often pose a diagnostic and therapeutic challenge for the clinician. Biomarkers can serve as a useful diagnostic, prognostic, and predictive tool in the management of these rare tumors. For years the field of NET biomarkers was mainly based on products se-creted by neuroendocrine tumor cells, however, during the last decade the development of nov-el multianalyte biomarkers has rapidly evolved the field. The aim of this review is to summa-rize the literature on the use and limitations of available NET biomarkers for the diagnosis and management of small intestine neuroendocrine tumors (SI-NETs) and carcinoid heart disease.

Abstract

Biomarkers remain a valuable tool for the diagnosis and management of Neuroendocrine tumors (NETs). Traditional monoanalyte biomarkers such as Chromogranin A (CgA) and 5-Hydrocyondoleacetic acid (5-HIAA) have been widely used for many years as diagnostic, predictive and prognostic biomarkers in the field of NETs. However, the clinical utility of these molecules often has limitations, mainly inherent to the heterogeneity of NETs and the fact that these tumors can often be non-secretory. The development of new molecular multianalyte biomarkers, especially the mRNA transcript based “NETest”, has rapidly evolve the field and gives the ability for a “liquid biopsy” which can reliably assess disease status in real time. In this review we discuss the use of established and novel biomarkers in the diagnosis and management of small intestine NETs and carcinoid heart disease.

Imaging of neuroendocrine tumors: A pictorial review of the clinical value of different imaging modalities

Neuroendocrine tumors (NETs) are multifaceted tumors occurring in a variety of organs and often present as metastatic at the time of diagnosis. Accurate staging is the most significant factor in therapy planning, but it remains a challenge. Imaging is established as the cornerstone for disease detection/diagnosis, staging, and follow up. To accurately assess and monitor tumor burden in patients with NETs, various imaging techniques have been developed and optimized. Current recommendations for the imaging of patients with NETs include a combination of both morphologic (or anatomic) and molecular imaging, but a final choice can be puzzling for clinicians. Recognizing that there is no uniform sequence consensus on the "best" imaging test, and the heterogeneity of technologic availability at different centers, we hope to provide a pictorial review of the different imaging techniques and their role and utility in management of patients with NETs, aimed to provide a practical guide for all clinicians.

Treatment of advanced gastroenteropancreatic neuroendocrine neoplasia, are we on the way to personalised medicine?

Gastroenteropancreatic neuroendocrine neoplasia (GEPNEN) comprises clinically as well as prognostically diverse tumour entities often diagnosed at late stage. Current classification provides a uniform terminology and a Ki67-based grading system, thereby facilitating management. Advances in the study of genomic and epigenetic landscapes have amplified knowledge of tumour biology and enhanced identification of prognostic and potentially predictive treatment subgroups. Translation of this genomic and mechanistic biology into advanced GEPNEN management is limited. 'Targeted' treatments such as somatostatin analogues, peptide receptor radiotherapy, tyrosine kinase inhibitors and mammalian target of rapamycin inhibitors are treatment options but predictive tools are lacking. The inability to identify clonal heterogeneity and define critical oncoregulatory pathways prior to therapy, restrict therapeutic efficacy as does the inability to monitor disease status in real time. Chemotherapy in the poor prognosis NEN G3 group, though associated with acceptable response rates, only leads to short-term tumour control and their molecular biology requires delineation to provide new and more specific treatment options.The future requires an exploration of the NEN tumour genome, its microenvironment and an identification of critical oncologic checkpoints for precise drug targeting. In the advance to personalised medical treatment of patients with GEPNEN, clinical trials need to be based on mechanistic and multidimensional characterisation of each tumour in order to identify the therapeutic agent effective for the individual tumour.This review surveys advances in NEN research and delineates the current status of translation with a view to laying the basis for a genome-based personalised medicine management of advanced GEPNEN.

Evaluation of 68Ga-PSMA-11 PET-MRI in Patients with Advanced Prostate Cancer Receiving 177Lu-PSMA-617 Therapy: A Radiomics Analysis

¹⁷⁷Lutetium PSMA-617 (Lu-PSMA) therapy in patients with metastatic castration resistant prostate cancer (mCRPC) has gained visibility through the ongoing phase III trial. The data on prediction of therapy outcome and survival out of pretherapeutic imaging parameters is still sparse. In this study, the predictive and prognostic value of radiomic features from ⁶⁸Ga-PSMA-11 PET-MRI are analyzed. In total, 21 patients with mCRPC underwent ⁶⁸Ga-PSMA-11 PET-MRI before Lu-PSMA therapy. The PET-positive tumor volume was defined and transferred to whole-body T2-, T1- and contrast-enhanced T1-weighted MRI-sequences. The radiomic features from PET and MRI sequences were extracted by using a freely available software package. For selecting features that allow differentiation of biochemical response (PSA decrease > 50%), a stepwise dimension reduction was performed. Logistic regression models were fitted, and selected features were tested for their prognostic value (overall survival) in all patients. Eight patients achieved biochemical response after Lu-PSMA therapy. Ten independent radiomic features differentiated well between responders and non-responders. The logistic regression model, including the feature interquartile range from T2-weighted images, revealed the highest accuracy (AUC = 0.83) for the prediction of biochemical response after Lu-PSMA therapy. Within the final model, patients with a biochemical response (p = 0.003) and higher T2 interquartile range values in pre-therapeutic imaging (p = 0.038) survived significantly longer. This proof-of-concept study provides first evidence on a potential predictive and prognostic value of radiomic analysis of pretherapeutic ⁶⁸Ga-PSMA-11 PET-MRI before Lu-PSMA therapy.

Theranostics in oncology: What radiologists want to know

Combination of radioligand imaging and therapy, so called radiotheranostics, is a novel tool of precision oncology with proven clinical value. In-depth knowledge of functional imaging nuances is critically needed for precise prognostication and guidance of management. Here, we review theranostic applications with up to Phase III type evidence for outcome improvement: Imaging and therapy of neuroendocrine neoplasms (NEN) exploiting high levels of somatostatin receptor (SSTR) expression and radiotheranostics of prostate cancer targeting the prostate specific membrane antigen (PSMA). This narrative review focusses on these two applications and elucidates patient selection and response assessment by radioligand scintigraphy and/or positron emission tomography. Furthermore, we provide a brief outlook on future applications for novel targets outside of NEN and prostate cancer.

EANM position paper on the role of radiobiology in nuclear medicine

With an increasing variety of radiopharmaceuticals for diagnostic or therapeutic nuclear medicine as valuable diagnostic or treatment option, radiobiology plays an important role in supporting optimizations. This comprises particularly safety and efficacy of radionuclide therapies, specifically tailored to each patient. As absorbed dose rates and absorbed dose distributions in space and time are very different between external irradiation and systemic radionuclide exposure, distinct radiation-induced biological responses are expected in nuclear medicine, which need to be explored. This calls for a dedicated nuclear medicine radiobiology. Radiobiology findings and absorbed dose measurements will enable an improved estimation and prediction of efficacy and adverse effects. Moreover, a better understanding on the fundamental biological mechanisms underlying tumor and normal tissue responses will help to identify predictive and prognostic biomarkers as well as biomarkers for treatment follow-up. In addition, radiobiology can form the basis for the development of radiosensitizing strategies and radioprotectant agents. Thus, EANM believes that, beyond in vitro and preclinical evaluations, radiobiology will bring important added value to clinical studies and to clinical teams. Therefore, EANM strongly supports active collaboration between radiochemists, radiopharmacists, radiobiologists, medical physicists, and physicians to foster research toward precision nuclear medicine.

Imaging and liquid biopsy in the prediction and evaluation of response to PRRT in neuroendocrine tumors: implications for patient management

Purpose

The aim of this narrative review is to give an overview on current and emerging imaging methods and liquid biopsy for prediction and evaluation of response to PRRT. Current limitations and new perspectives, including artificial intelligence, are discussed.

Methods

A literature review of PubMed/Medline was performed with representative keywords. The search included articles published online through August 31, 2020. All searches were restricted to English language manuscripts.

Results

Peptide radio receptor therapy (PRRT) is a prospectively evaluated and approved therapy option in neuroendocrine tumors (NETs). Different ligands targeting the somatostatin receptor (SSTR) are used as theranostic pairs for imaging NET and for PRRT. Response assessment in prospective trials often relies on the morphological RECIST 1.1 criteria, based on lesion size in CT or MRI. The role of SSTR-PET and quantitative uptake parameters and volumetric data is still not defined. Monoanalyte tumor marker chromogranin A has a limited value for response assessment after PRRT. New emerging liquid biopsy techniques are offering prediction of response to PRRT and prognostic value.

Conclusions

New response criteria for NET patients undergoing PRRT will comprise multiparametric hybrid imaging and blood-based multianalyte markers. This represents tumor biology and heterogeneity.

Evaluation of SSTR2 Expression in SI-NETs and Relation to Overall Survival after PRRT

Simple Summary

Small intestinal neuroendocrine tumors (SI-NETs) are slow growing tumors expressing somatostatin receptors (SSTR), which are targeted in diagnostic and therapeutic methods. A fairly new treatment that targets SSTR2 is peptide receptor radionuclide therapy (PRRT), which prolongs survival for patients with metastasized NETs. However, the treatment is costly, and the effect is variable. Therefore, finding predictors for treatment response is warranted. The aim of this retrospective study was to immunohistochemically analyze the SSTR2 expression in SI-NETs, using a previously constructed tissue microarray, and to investigate if a high SSTR2 expression was correlated to overall survival (OS). Among 42 patients that had received PRRT, 10 had at least one tumor with low SSTR2 expression. The patients were grouped according to the SSTR2 expression (“High SSTR2” and “Low SSTR2”) in previously resected tumors. In contrast to the hypothesis of the study, patients with low SSTR2 expression had significantly longer OS after PRRT, compared with patients with high SSTR2 expression. Hence, the study suggests that low SSTR2 expression in resected tumors should not exclude SI-NET patients from receiving PRRT.

Abstract

(1) Purpose: Small intestinal neuroendocrine tumors (SI-NETs) often present with distant metastases at diagnosis. Peptide receptor radionuclide therapy (PRRT) with radiolabeled somatostatin analogues is a systemic treatment that increases overall survival (OS) in SI-NET patients with stage IV disease. However, the treatment response after PRRT, which targets somatostatin receptor 2 (SSTR2), is variable and predictive factors have not been established. This exploratory study aims to evaluate if SSTR2 expression in SI-NETs could be used to predict OS after PRRT treatment. (2) Methods: Using a previously constructed Tissue Micro Array (TMA) we identified tissue samples from 42 patients that had received PRRT treatment during 2006–2017 at Sahlgrenska University hospital. Immunohistochemical expression of SSTR2, Ki-67 and neuroendocrine markers synaptophysin and Chromogranin A (CgA) were assessed. A retrospective estimation of ¹⁷⁷Lu-DOTATATE uptake in 33 patients was performed. Data regarding OS and non-surgical treatment after PRRT were collected. Another subgroup of 34 patients with paired samples from 3 tumor sites (primary tumor, lymph node and liver metastases) was identified in the TMA. The SSTR2 expression was assessed in corresponding tissue samples (n = 102). (3) Results: The patients were grouped into Low SSTR2 or High SSTR2 groups based upon on levels of SSTR2 expression. There was no significant difference in ¹⁷⁷Lu-DOTATATE uptake between the groups. The patients in the Low SSTR2 group had significantly longer OS after PRRT than the patients in the High SSTR2 group (p = 0.049). PRRT treated patients with low SSTR2 expression received less additional treatment compared with patients with high SSTR2 expression. SSTR2 expression did not vary between tumor sites but correlated within patients. (4) Conclusion: The results from the present study suggest that retrospective evaluation of SSTR2 expression in resected tumors cannot be used to predict OS after PRRT.

Consensus on molecular imaging and theranostics in neuroendocrine neoplasms

Nuclear medicine plays an increasingly important role in the management neuroendocrine neoplasms (NEN). Somatostatin analogue (SSA)-based positron emission tomography/computed tomography (PET/CT) and peptide receptor radionuclide therapy (PRRT) have been used in clinical trials and approved by the European Medicines Agency (EMA) and the US Food and Drug Administration (FDA). European Association of Nuclear Medicine (EANM) Focus 3 performed a multidisciplinary Delphi process to deliver a balanced perspective on molecular imaging and radionuclide therapy in well-differentiated neuroendocrine tumours (NETs). NETs form in cells that interact with the nervous system or in glands that produce hormones. These cells, called neuroendocrine cells, can be found throughout the body, but NETs are most often found in the abdomen, especially in the gastrointestinal tract. These tumours may also be found in the lungs, pancreas and adrenal glands. In addition to being rare, NETs are also complex and may be difficult to diagnose. Most NETs are non-functioning; however, a minority present with symptoms related to hypersecretion of bioactive compounds. NETs often do not cause symptoms early in the disease process. When diagnosed, substantial number of patients are already found to have metastatic disease. Several societies' guidelines address Neuroendocrine neoplasms (NENs) management; however, many issues are still debated, due to both the difficulty in acquiring strong clinical evidence in a rare and heterogeneous disease and the different availability of diagnostic and therapeutic options across countries. EANM Focus 3 reached consensus on employing ⁶⁸gallium-labelled somatostatin analogue ([⁶⁸Ga]Ga-DOTA-SSA)-based PET/CT with diagnostic CT or magnetic resonance imaging (MRI) for unknown primary NET detection, metastatic NET, NET staging/restaging, suspected extra-adrenal pheochromocytoma/paraganglioma and suspected paraganglioma. Consensus was reached on employing ¹⁸fluorine-fluoro-2-deoxyglucose ([¹⁸F]FDG) PET/CT in neuroendocrine carcinoma, G3 NET and in G1-2 NET with mismatched lesions (CT-positive/[⁶⁸Ga]Ga-DOTA-SSA-negative). Peptide receptor radionuclide therapy (PRRT) was recommended for second line treatment for gastrointestinal NET with [⁶⁸Ga]Ga-DOTA-SSA uptake in all lesions, in G1/G2 NET at disease progression, and in a subset of G3 NET provided all lesions are positive at [¹⁸F]FDG and [⁶⁸Ga]Ga-DOTA-SSA. PRRT rechallenge may be used for in patients with stable disease for at least 1 year after therapy completion. An international consensus is not only a prelude to a more standardised management across countries but also serves as a guide for the direction to follow when designing new research studies.