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

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

Novel therapeutic approaches in GEP-NETs based on genetic and epigenetic alterations

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) are heterogeneous malignancies with distinct prognosis based on primary tumor localization, grade, stage and functionality. Surgery remains the only curative option in localized tumors, but systemic therapy is the mainstay of treatment for patients with advanced disease. For decades, the therapeutic landscape of GEP-NETs was limited to chemotherapy regimens with low response rates. The arrival of novel agents such as somatostatin analogues, peptide receptor radionuclide therapy, tyrosine kinase inhibitors or mTOR-targeted drugs, has changed the therapeutic paradigm of GEP-NETs. However, the efficacy of these agents is limited in time and there is scarce knowledge of optimal treatment sequencing. In recent years, massive parallel sequencing techniques have started to unravel the genomic intricacies of these tumors, allowing us to better understand the mechanisms of resistance to current treatments and to develop new targeted agents that will hopefully start an era for personalized treatment in NETs. In this review we aim to summarize the most relevant genomic aberrations and signaling pathways underlying GEP-NET tumorigenesis and potential therapeutic strategies derived from them.

Efficacy and toxicity of surufatinib in neuroendocrine tumors: A systematic review and meta-analysis

The incidence and prevalence of neuroendocrine neoplasms (NENs) has increased in the US in recent decades. These are well-vascularized tumors, but no antiangiogenic drug has been approved for treatment of extra-pancreatic NENs. The aim is to assess efficacy and safety of surufatinib in pancreatic and extra-pancreatic NETs. We searched PubMed, Embase, Cochrane Library, Web of Science and Clinicaltrials.gov. Clinical trials and observational studies that provided safety and efficacy data in clinical terms were included. Characteristics of the study, baseline characteristics of participants, treatment drugs, measures of efficacy, and toxicity (≥grade 3 adverse effects) were extracted. The meta-analysis was performed using the "R" programming language. Risk ratio (RR) of objective response (OR)/partial response (PR) was 8.55 (95% CI: 1.68-43.66, I2  = 0) in favor of surufatinib. The hazard ratio (HR) of progression-free survival (PFS) was 0.48 (95% CI: 0.25-0.92, I2  = 77%) in favor of surufatinib. The risk of ≥grade 3 adverse effects: diarrhea, hypertension, hypertriglyceridemia, proteinuria, and vomiting were high with the use of surufatinib. Quality of life (QoL) was similar in surufatinib and placebo groups except for the diarrhea that was high with surufatinib. Lack of randomized clinical trials in non-Chinese population. Surufatinib is well tolerated and is more effective than placebo in both pancreatic and extra-pancreatic NETs. More multicenter randomized, double-blinded clinical trials are needed to confirm these results.

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.

Lenvatinib in Patients With Advanced Grade 1/2 Pancreatic and Gastrointestinal Neuroendocrine Tumors: Results of the Phase II TALENT Trial (GETNE1509)

PURPOSE

Approved systemic therapies for advanced gastroenteropancreatic neuroendocrine tumors (GEP-NETs) have shown limited capacity to reduce tumor burden and no antitumor activity after progression to targeted agents (TAs). We investigated the efficacy and safety of lenvatinib in patients with previously treated advanced GEP-NETs.

PATIENTS AND METHODS

This was a multicenter, single-arm, open-label, phase II trial with two parallel cohorts (ClinicalTrials.gov identifier: NCT02678780) involving 21 institutions in 4 European countries. Eligible patients had histologically confirmed advanced grade 1-2 pancreatic (panNET) or GI (GI-NET) NETs with documented tumor progression after treatment with a TA (panNET) or somatostatin analogs (GI-NET). Patients were treated with lenvatinib 24 mg once daily until disease progression or treatment intolerance. The primary end point was overall response rate by central radiology review. Secondary end points included progression-free survival, overall survival, duration of response, and safety.

RESULTS

Between September 2015 and March 2017, a total of 111 patients were enrolled, with 55 (panNET) and 56 (GI-NET) patients in each cohort. The median follow-up was 23 months. The overall response rate was 29.9% (95% CI, 21.6 to 39.6): 44.2% (panNET) and 16.4% (GI-NET). The median (range) duration of response was 19.9 (8.4-30.8) and 33.9 (10.6-38.3) months in the panNET and GI-NET groups, respectively. The median progression-free survival was 15.7 months (95% CI, 14.1 to 19.5). The most common adverse events were fatigue, hypertension, and diarrhea; 93.7% of patients required dose reductions or interruptions.

CONCLUSION

We report the highest centrally confirmed response reported to date with a multikinase inhibitor in advanced GEP-NETs, with a particularly strong response in the panNET cohort. This study provides novel evidence for the efficacy of lenvatinib in patients with disease progression following treatment with other TAs, suggesting the potential value of lenvatinib in the treatment of advanced GEP-NETs.

Advanced Pancreatic Neuroendocrine Neoplasms: Which Systemic Treatment Should I Start With?

PURPOSE OF REVIEW

Pancreatic neuroendocrine neoplasms (panNENs) often present as advanced disease and there is little data to guide treatment sequencing in the advance disease setting. Therefore, we aim to provide a comprehensive summary of the current evidence supporting the use of systemic treatment for patients with diagnosis of advanced and metastatic panNENs, as well as to provide strategies for treatment selection and address challenges for treatment selection and sequencing of therapy.

RECENT FINDINGS

Substantial advances have been made and many clinical trials have been performed over the past two decades expanding therapeutic options available for patients with advanced panNETs. Available systemic treatments for patients with well-differentiated pancreatic neuroendocrine tumors include somatostatin receptors ligands (SRLs), traditional cytotoxic chemotherapy regimens, peptide receptor radiotherapy (PRRT), and biologically targeted therapies, whereas patients with poorly differentiated neurodocrine carcinomas have more limited treatment options. Despite these advances, no clear guidelines exist to support the best sequence of treatments, not only the first-line, but also subsequent lines of therapy in patients with panNENs. Advances in molecular research and discovery of biomarkers for response allowing a more personalized approach to the multimodality therapy of panNENs are still limited. Understanding the impact of previous therapies on subsequent treatment efficacy and toxicity is also an ongoing research question. In the absence of definite predictive markers and paucity of comparative randomized trials, along with the heterogeneity of this patient population, systemic therapy selection in advanced non-resectable disease should be patient centered and often require evaluation within a multidisciplinary setting. The specific clinical context of the patient, with assessment of individual patient clinical and pathological features, somatostatin receptors imaging, and goals of treatment must all be considered when deciding on systemic therapy in the patient. Additional research is needed to address the gap in knowledge regarding optimal sequencing and timing of therapies and to provide individual care.

Targeted Cancer Therapy: What's New in the Field of Neuroendocrine Neoplasms?

Neuroendocrine tumors (NETs) are a heterogeneous family of neoplasms of increasing incidence and high prevalence due to their relatively indolent nature. Their wide anatomic distribution and their characteristic ability to secrete hormonally active substances pose unique challenges for clinical management. They are also characterized by the common expression of somatostatin receptors, a target that has been extremely useful for diagnosis and treatment (i.e., somatostatin analogues (SSAs) and peptide-receptor radionuclide therapy (PRRT)). Chemotherapy is of limited use for NETs of non-pancreatic origin, and the only approved targeted agents for advanced progressive NETs are sunitinib for those of pancreatic origin, and everolimus for lung, gastrointestinal and pancreatic primaries. Despite recent therapeutic achievements, thus, systemic treatment options remain limited. In this review we will discuss the state-of-the-art targeted therapies in the field of NETs, and also future perspectives of novel therapeutic drugs or strategies in clinical development, including recently presented results from randomized trials of yet unapproved antiangiogenic agents (i.e., pazopanib, surufatinib and axitinib), PRRT including both approved radiopharmaceuticals (177Lu-Oxodotreotide) and others in development (177Lu-Edotreotide, 177Lu-Satoreotide Tetraxetan), immunotherapy and other innovative targeted strategies (antibody-drug conjugates, bites,…) that shall soon improve the landscape of personalized treatment options in NET patients.

Targeted Therapies in the Management of Well-Differentiated Digestive and Lung Neuroendocrine Neoplasms

OPINION STATEMENT

Ongoing advances in our understanding of neuroendocrine tumor (NET) biology, genetics, and immunology, will continue to expand the availability of targeted therapies, thus improving the outcomes of patients. Well-differentiated neuroendocrine tumors (NETs) are grouped into pancreatic and non-pancreatic NETs (includes GI and thoracic NETs) for treatment considerations (Fig. 1). For panNETs, initial therapy is driven by the need of radiographic response, and targeted agents are typically reserved for second and third line based on the toxicity profile. Treatment options for non-pancreatic NETs are also expanding and while SSAs are the typical first-line option, everolimus and PRRT both remain approved therapies for future lines, and VEGF TKIs are showing promising results in research settings. Sequencing these agents and best time to incorporate peptide receptor radio therapy into the management algorithm remains an unmet need.

Medical Management of Gastroenteropancreatic Neuroendocrine Tumors

The increased incidence and prevalence of neuroendocrine tumors (NETs) over the past few decades has been accompanied by an improvement in overall survival. There are differences in the management of small bowel NETs versus pNETs. The management of all patients with NETs must be individualized based on patient characteristics as well tumor-related factors. This article reviews the role of somatostatin analogues, historical results with chemotherapy in gastroenteropancreatic NETs (GEPNETs), and more recent evidence for the use of cytotoxic chemotherapy in GEPNETs. The article also discusses molecular targeted therapies approved for use in GEPNETs and some ongoing clinical trials.

Single-Arm Phase II Trials of Combination Therapies: A Review of the CTEP Experience 2008-2017

Designing and interpreting single-arm phase II trials of combinations of agents is challenging because it can be difficult, based on historical data, to identify levels of activity for which the combination would be worth pursuing. We identified Cancer Therapy Evaluation Program single-arm combination trials that were activated in 2008-2017 and tabulated their design characteristics and results. Positive trials were evaluated as to whether they provided credible evidence that the combination was better than its constituents. A total of 125 trials were identified, and 120 trials had results available. Twelve had designs where eligible patients were required to be resistant or refractory to all but one element of the combination. Only 17.8% of the 45 positive trials were deemed to provide credible evidence that the combination was better than its constituents. Of the 10 positive trials with observed rates 10 percentage points higher than their upper (alternative hypothesis) targets, only five were deemed to provide such credible evidence. Many trials were definitively negative, with observed clinical activity at or below their lower (null hypothesis) targets. Ideally, use of single-arm combination trials should be restricted to settings where each agent is known to have minimal monotherapy activity (and a randomized trial is infeasible). In these settings, an observed signal is attributable to synergy and thus could be used to decide whether the combination is worth pursuing. In other settings, credible evidence can still be obtained if the observed activity is much higher than expected, but experience suggests that this is a rare occurrence.

mTOR Pathway in Gastroenteropancreatic Neuroendocrine Tumor (GEP-NETs)

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) originate from neuroendocrine cells in the gastrointestinal tract. They are heterogeneous, and though initially considered rare tumors, the incidence of GEP-NENs has increased in the last few decades. Therapeutic approaches for the metastatic disease include surgery, radiological intervention by chemoembolisation, radiofrequency ablation, biological therapy in addition to somatostatin analogs, and PRRT therapy (177Lu-DOTATATE). The PI3K-AKT-mTOR pathway is essential in the regulation of protein translation, cell growth, and metabolism. Evidence suggests that the mTOR pathway is involved in malignant progression and resistance to treatment through over-activation of several mechanisms. PI3K, one of the main downstream of the Akt-mTOR axis, is mainly involved in the neoplastic process. This pathway is frequently deregulated in human tumors, making it a central target in the development of new anti-cancer treatments. Recent molecular studies identify potential targets within the PI3K/Akt/mTOR pathway in GEP-NENs. However, the use of target therapy has been known to lead to resistance due to several mechanisms such as feedback activation of alternative pathways, inactivation of protein kinases, and deregulation of the downstream mTOR components. Therefore, the specific role of targeted drugs for the management of GEP-NENs is yet to be well-defined. The variable clinical presentation of advanced neuroendocrine tumors is a significant challenge for designing studies. This review aims to highlight the role of the PI3K/Akt/mTOR pathway in the development of neuroendocrine tumors and further specify its potential as a therapeutic target in advanced stages.

Targeted Systemic Treatment of Neuroendocrine Tumors: Current Options and Future Perspectives

Neuroendocrine tumors (NETs) originate from the neuroendocrine cell system in the bronchial and gastrointestinal tract and can produce hormones leading to distinct clinical syndromes. Systemic treatment of patients with unresectable NETs aims to control symptoms related to hormonal overproduction and tumor growth. In the last decades prognosis has improved as a result of increased detection of early stage disease and the introduction of somatostatin analogs (SSAs) as well as several new therapeutic options. SSAs are the first-line medical treatment of NETs and can control hormonal production and tumor growth. The development of next-generation multireceptor targeted and radiolabelled somatostatin analogs, as well as target-directed therapies (as second-line treatment options) further improve progression-free survival in NET patients. To date, however, a significant prolongation of overall survival with systemic treatment in NET has not been convincingly demonstrated. Several new medical options and treatment combinations will become available in the upcoming years, and although preliminary results of preclinical and clinical trials are encouraging, large, preferrably randomized clinical studies are required to provide definitive evidence of their effect on survival and symptom control.

Systemic treatment for lung carcinoids: from bench to bedside

In the huge spectrum of lung neuroendocrine neoplasms, typical and atypical carcinoids should be considered as a separate biological entity from poorly differentiated forms, harboring peculiar molecular alterations. Despite their indolent behavior, lung carcinoids correlate with a worse survival. To date, only limited therapeutic options are available and novel drugs are strongly needed. In this work, we extensively reviewed scientific literature exploring available therapeutic options, new molecular targets and future perspectives in the management of well differentiated neoplasms of bronchopulmonary tree. Systemic therapy represents the main option in advanced and unresectable disease; accepted choices are somatostatin analogs, peptide receptor radionuclide therapy, everolimus and chemotherapy. To date, an univocal treatment strategy has not been identified yet, thus tailored therapeutic algorithms should consider treatment efficacy as well as safety profiles. Several molecular alterations found in carcinoid tumors might act as molecular targets leading to development of new therapeutic options. Further studies are necessary to identify new potential "druggable" molecular targets in the selected subset of low-grade lung carcinoids. Furthermore, evaluating the available therapies in more homogeneous population might improve their efficacy through a perfect tailoring of treatment options.

Treatments for patients with advanced neuroendocrine tumors: a network meta-analysis

Background

It remains unknown which is the most effective regimen among the available therapies for advanced well-differentiated neuroendocrine tumors (NETs). We performed a network meta-analysis to address this important issue.

Methods

PubMed, Embase, Web of Science, Cochrane Library, and major international scientific meetings were searched for relevant randomized controlled trials (RCTs). Progression-free survival (PFS) data was the primary outcome of interest, and overall survival (OS) and serious adverse events (SAEs) were the secondary outcomes of interests, reported as hazard ratio (HR), or odds ratio (OR) and 95% confidence intervals (CIs).

Results

Included in the meta-analysis were 21 eligible articles reporting 15 RCTs with a total of 2922 patients randomized to receive 11 treatments. Peptide receptor radionuclide therapy (PRRT) showed significant PFS advantage over somatostatin analogs (SSA) (HR = 0.21, 95% CI: 0.11-0.41), everolimus (HR = 0.25, 95% CI: 0.11-0.53), sunitinib (HR = 0.29, 95% CI: 0.10-0.82), everolimus+SSA (HR = 0.26, 95% CI: 0.12-0.54), and everolimus+bevacizumab (HR = 0.31, 95% CI: 0.11-0.82). OS findings were not significantly different between treatments. In terms of treatment rankings of PFS, PRRT had the highest probability (96%) of being the most effective treatment, followed by SSA+bevacizumab (86%) and SSA+interferon-α (IFN-α) (78%). As for toxicity, risk of SAEs was similar between the three treatments. Based on the benefit-risk ratio, PRRT, SSA+bevacizumab, and SSA+IFN-α seemed to be the best, second-, and third-best treatment, respectively.

Conclusions

PRRT is likely to be the most preferable treatment for patients with advanced well-differentiated NETs. SSA+bevacizumab and SSA+IFN-α also seem to be more effective regimens with limited risk of SAEs.

Genetics and Epigenetics of Gastroenteropancreatic Neuroendocrine Neoplasms

Gastroenteropancreatic (GEP) neuroendocrine neoplasms (NENs) are heterogeneous regarding site of origin, biological behavior, and malignant potential. There has been a rapid increase in data publication during the last 10 years, mainly driven by high-throughput studies on pancreatic and small intestinal neuroendocrine tumors (NETs). This review summarizes the present knowledge on genetic and epigenetic alterations. We integrated the available information from each compartment to give a pathway-based overview. This provided a summary of the critical alterations sustaining neoplastic cells. It also highlighted similarities and differences across anatomical locations and points that need further investigation. GEP-NENs include well-differentiated NETs and poorly differentiated neuroendocrine carcinomas (NECs). NENs are graded as G1, G2, or G3 based on mitotic count and/or Ki-67 labeling index, NECs are G3 by definition. The distinction between NETs and NECs is also linked to their genetic background, as TP53 and RB1 inactivation in NECs set them apart from NETs. A large number of genetic and epigenetic alterations have been reported. Recurrent changes have been traced back to a reduced number of core pathways, including DNA damage repair, cell cycle regulation, and phosphatidylinositol 3-kinase/mammalian target of rapamycin signaling. In pancreatic tumors, chromatin remodeling/histone methylation and telomere alteration are also affected. However, also owing to the paucity of disease models, further research is necessary to fully integrate and functionalize data on deregulated pathways to recapitulate the large heterogeneity of behaviors displayed by these tumors. This is expected to impact diagnostics, prognostic stratification, and planning of personalized therapy.

Surufatinib in Advanced Well-Differentiated Neuroendocrine Tumors: A Multicenter, Single-Arm, Open-Label, Phase Ib/II Trial

PURPOSE

No antiangiogenic treatment is yet approved for extrapancreatic neuroendocrine tumors (NET). Surufatinib (HMPL-012, previously named sulfatinib) is a small-molecule inhibitor targeting vascular endothelial growth factor receptors, fibroblast growth factor receptor 1 and colony-stimulating factor 1 receptor. We conducted a single-arm phase Ib/II study of surufatinib in advanced NETs.

PATIENTS AND METHODS

Patients with histologically well-differentiated, low or intermittent grade, inoperable or metastatic NETs were enrolled into a pancreatic or extrapancreatic NET cohort. Patients were treated with surufatinib 300 mg orally, once daily. The primary endpoints were safety and objective response rate (ORR) according to Response Evaluation Criteria in Solid Tumors (version 1.1).

RESULTS

Of the 81 patients enrolled, 42 had pancreatic NETs and 39 had extrapancreatic NETs. Most patients had radiologic progression within 1 year prior to enrollment (32 patients in each cohort). In the pancreatic and extrapancreatic NET cohorts, ORRs were 19% [95% confidence intervals (CI), 9-34] and 15% (95% CI, 6-31), disease control rates were 91% (95% CI, 77-97) and 92% (95% CI, 79-98), and median progression-free survival was 21.2 months (95% CI, 15.9-24.8) and 13.4 months (95% CI, 7.6-19.3), respectively. The most common grade ≥3 treatment-related adverse events were hypertension (33%), proteinuria (12%), hyperuricemia (10%), hypertriglyceridemia, and diarrhea (6% for each), and increased alanine aminotransferase (5%).

CONCLUSIONS

Surufatinib showed encouraging antitumor activity and manageable toxicities in patients with advanced NETs. Two ongoing phase III studies, validating the efficacy of surufatinib in patients with NETs, will contribute to the clinical evidence.

Effect of Endostar combined with chemotherapy in advanced well-differentiated pancreatic neuroendocrine tumors

The aim of the present study was to assess the effect of Endostar and temozolomide or dacarbazine plus 5-fluorouracil (5-FU) in patients with advanced pancreatic neuroendocrine tumors (pNETs).Phase II study of 14 patients with locally advanced or metastatic well-differentiated pNETs treated between April 2013 and September 2016. Patients received temozolomide or dacarbazine plus 5-FU, and Endostar. The primary outcome was the radiographic response rate.All 14 patients had nonfunctional pNETs. Six patients received temozolomide and 8 received dacarbazine + 5-FU, combined with Endostar. Thirteen patients were assessable for treatment response: 1(7%) with complete response, 5 (39%) with partial response, 5 (39%) with stable disease, and 2 (15%) with progression. The median progression-free survival was 12 months. The most common grade 1/2 toxicities were neutropenia (43%) and leucopenia (21%).Endostar combined with temozolomide or dacarbazine + 5-FU was effective in the treatment of advanced pNETs. The combinations were well tolerated.

Alternate Endpoints for Phase II Trials in Advanced Neuroendocrine Tumors

BACKGROUND

In phase II trials for neuroendocrine tumors (NETs), the objective response rate (ORR) is traditionally used as a primary endpoint. However, the validity of the ORR as a primary endpoint has never been systematically examined. Therefore, a literature-based analysis of phase II trials for NETs was performed to identify valid alternative endpoints for predicting median progression-free survival (PFS) in clinical trials for NETs.

MATERIALS AND METHODS

Phase II trials of medical treatment for advanced NETs were identified based on a systematic search using MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials.

RESULTS

A total of 22 trials were identified, and 1,310 patients and 27 treatment arms were included in the analysis. There was no significant relationship between the ORR and median PFS (r = .374; 95% confidence interval [CI], -0.051 to 0.800; p = .085). Conversely, 12-month PFS rates showed very strong correlations with median PFS (r = .929; 95% CI, 0.831-1.027; p < .001).

CONCLUSION

The results of the present analysis indicate that the ORR is not significantly correlated with median PFS and suggest that 12-month PFS rates are good alternate endpoints for screening phase II trials for NETs.

IMPLICATIONS FOR PRACTICE

Phase II trials are screening trials that seek to identify agents with sufficient activity to continue development. Thus, earlier endpoints are preferable, and the objective response rate (ORR) has been traditionally used as a surrogate endpoint in phase II trials for neuroendocrine tumors (NETs). However, the present study showed that the ORR was not significantly correlated with median progression-free survival (PFS). On the other hand, the 12-month PFS rate showed very strong correlation with median PFS and is considered a good alternate endpoint for screening phase II trials for NETs.

The Treatment Landscape and New Opportunities of Molecular Targeted Therapies in Gastroenteropancreatic Neuroendocrine Tumors

Neuroendocrine neoplasms (NENs) are a heterogeneous group of neoplasms that originate from neuroendocrine stem cells and express both neural and endocrine markers. They are found in almost every organ, and while NENs are mostly associated with slow growth, complications due to the uncontrolled secretion of active peptides, and metastatic disease, may significantly impair the quality of life and can ultimately lead to the death of affected individuals. Expanding knowledge of the genetic, epigenetic, and proteomic landscapes of NENs has led to a better understanding of their molecular pathology and consequently increased treatment options for patients. Here, we review the principal breakthroughs in NEN treatment management, owing largely to omics technologies over the last few years, current recommendations of systemic treatment, and ongoing research into the identification of predictive and response biomarkers based on molecular targeted therapies.

Diabetes and pancreatic neuroendocrine tumours: Which interplays, if any?

Pancreatic neuroendocrine tumours (PanNETs) represent an uncommon type of pancreatic neoplasm, whose incidence is increasing worldwide. As per exocrine pancreatic cancer, a relationship seems to exist between PanNETs and glycaemic alterations. Diabetes mellitus (DM) or impaired glucose tolerance often occurs in PanNET patients as a consequence of hormonal hypersecretion by the tumour, specifically affecting glucose metabolism, or due to tumour mass effects. On the other hand, pre-existing DM may represent a risk factor for developing PanNETs and is likely to worsen the prognosis of such patients. Moreover, the surgical and/or pharmacological treatment of the tumour itself may impair glucose tolerance, as well as antidiabetic therapies may impact tumour behaviour and patients outcome. Differently from exocrine pancreatic tumours, few data are available for PanNETs as yet on this issue. In the present review, the bidirectional association between glycaemic disorders and PanNETs has been extensively examined, since the co-existence of both diseases in the same individual represents a further challenge for the clinical management of PanNETs.

Current and emerging therapies for PNETs in patients with or without MEN1

Pancreatic neuroendocrine tumours (PNETs) might occur as a non-familial isolated endocrinopathy or as part of a complex hereditary syndrome, such as multiple endocrine neoplasia type 1 (MEN1). MEN1 is an autosomal dominant disorder characterized by the combined occurrence of PNETs with tumours of the parathyroids and anterior pituitary. Treatments for primary PNETs include surgery. Treatments for non-resectable PNETs and metastases include biotherapy (for example, somatostatin analogues, inhibitors of receptors and monoclonal antibodies), chemotherapy and radiological therapy. All these treatments are effective for PNETs in patients without MEN1; however, there is a scarcity of clinical trials reporting the efficacy of the same treatments of PNETs in patients with MEN1. Treatment of PNETs in patients with MEN1 is challenging owing to the concomitant development of other tumours, which might have metastasized. In recent years, preclinical studies have identified potential new therapeutic targets for treating MEN1-associated neuroendocrine tumours (including PNETs), and these include epigenetic modification, the β-catenin-wingless (WNT) pathway, Hedgehog signalling, somatostatin receptors and MEN1 gene replacement therapy. This Review discusses these advances.

Update in the Therapy of Advanced Neuroendocrine Tumors

OPINION STATEMENT

Neuroendocrine tumors (NETs) are rare neoplasms, with an estimated annual incidence of ~ 6.9/100,000. NETs arise throughout the body from cells of the diffuse endocrine system. More than half originate from endocrine cells of the gastrointestinal tract and the pancreas, thus being referred to as gastroenteropancreatic NETs (GEP-NETs). The only treatment that offers a cure is surgery; however, most patients are diagnosed with metastatic disease, and curative surgery is usually not an option. These patients can be offered long-term systemic treatment, for both symptomatic relief and tumor growth suppression. Evidence-based treatment options include somatostatin analogs, everolimus (a mTOR inhibitor), sunitinib (a tyrosine kinase inhibitor), and peptide receptor radionuclide therapy, alone or combined with cytoreductive procedures (surgery or liver-directed procedures). Other treatment options being investigated are immunotherapy and epigenetic assessment that may lead to more personalized interventions. We believe that each patient should be thoroughly evaluated and their case discussed by a multidisciplinary team that is up-to-date with all treatment modalities including ongoing clinical trials, before selecting the proper treatment option.

Treatment Strategies for Metastatic Neuroendocrine Tumors of the Gastrointestinal Tract

OPINION STATEMENT

The therapeutic landscape of gastroenteropancreatic-neuroendocrine tumors (GEP-NETs) has evolved significantly in recent years. Current and emerging treatment options include somatostatin analogs, radiolabeled somatostatin analogs, the mTOR inhibitor everolimus, and the tyrosine kinase inhibitor sunitinib. Although high-quality data from phase III trials are lacking, cytotoxic agents are commonly used for the treatment of poorly differentiated neuroendocrine carcinomas and well-differentiated NETs originating in the pancreas. Hepatic-directed therapies are recommended for patients with slow-growing, liver-predominant disease but have never been compared to systemic agents. Telotristat ethyl, a novel serotonin synthesis inhibitor, has recently demonstrated efficacy in palliating diarrhea in patients with poorly controlled carcinoid syndrome. In the absence of definite predictive biomarkers, therapeutic decisions in most cases rely on clinical and pathological criteria. However, navigating the current therapeutic algorithm may be challenging, and future trials need to address several important questions: what is the best sequence of treatment? Is there a role for combination therapies in GEP-NETs? Are neoadjuvant, adjuvant, or maintenance strategies safe and effective? Do all NET patients require active treatment? What new molecular targets can be clinically exploited? A tight integration between basic and clinical research is needed to further advance the field of NETs.

Translational research in neuroendocrine tumors: pitfalls and opportunities

Interest in research on neuroendocrine tumors (NETs) has grown in the past 10 years, coinciding with improvements in our understanding of the molecular pathogenesis of NETs. In addition, NETs have become one of the most exciting settings for drug development. Two targeted agents for the management of advanced pancreatic NETs have been approved, but the development of targeted agents for NETs is limited by problems with both patient selection and demonstration of activity. In this review, we analyze these limitations and discuss ways to increase the predictive value of preclinical models for target discovery and drug development. The role of translational research and 'omics' methodologies is emphasized, with the final aim of developing personalized medicine. Because NETs usually grow slowly and metastatic tumors are found at easily accessible locations, and owing to improvements in techniques for liquid biopsies, NETs provide a unique opportunity to obtain tumor samples at all stages of the evolution of the disease and to adapt treatment to changes in tumor biology. Combining clinical and translational research is essential to achieve progress in the NET field. Slow growth and genetic stability limit and challenge both the availability and further development of preclinical models of NETs, one of the most crucial unmet research needs in the field. Finally, we suggest some useful approaches for improving clinical drug development for NETs: moving from classical RECIST-based response end points to survival parameters; searching for different criteria to define response rates (for example, antiangiogenic effects and metabolic responses); implementing randomized phase II studies to avoid single-arm phase II studies that produce limited data on drug efficacy; and using predictive biomarkers for patient selection.

Vascular hyperpermeability as a hallmark of phacomatoses: is the etiology angiogenesis related to or comparable with mechanisms seen in inflammatory pathways? Part II: angiogenesis- and inflammation-related molecular pathways, tumor-associated macrophages, and possible therapeutic implications: a comprehensive review

Phacomatoses are a special group of familial hamartomatous syndromes with unique neurocutaneous manifestations as well as characteristic tumors. Neurofibromatosis type 2 (NF2) and tuberous sclerosis complex (TSC) are representatives of this family. A vestibular schwannoma (VS) and subependymal giant cell tumor (SGCT) are two of the most common intracranial tumors associated with these syndromes, related to NF2 and TSC, respectively. These tumors can present with an obstructive hydrocephalus due to their location adjacent to or in the ventricles. Remarkably, both tumors are also known to have a unique association with elevated protein concentrations in the cerebrospinal fluid (CSF), sometimes in association with a non-obstructive (communicating) hydrocephalus. Of the two, SGCT has been shown to be associated with a predisposition to CSF clotting, causing a debilitating recurrent shunt obstruction. However, the exact relationship between high protein levels and clotting of CSF remains unclear, nor do we understand the precise mechanism of CSF clotting observed in SGCT. Elevated protein levels in the CSF are thought to be caused by increased vascular permeability and dysregulation of the blood-brain barrier. The two presumed underlying pathophysiological processes for that in the context of tumorigenesis are angiogenesis and inflammation. Both these processes are correlated to the phosphatidylinositol-3-kinase/Akt/mammalian target of rapamycin pathway which is tumorigenesis related in many neoplasms and nearly all phacomatoses. In this review, we discuss the influence of angiogenesis and inflammation pathways on vascular permeability in VSs and SGCTs at the phenotypic level as well as their possible genetic and molecular determinants. Part I described the historical perspectives and clinical aspects of the relationship between vascular permeability, abnormal CSF protein levels, clotting of the CSF, and communicating hydrocephalus. Part II hereafter describes the different cellular and molecular pathways involved in angiogenesis and inflammation observed in both tumors and explores the existing metabolic overlap between inflammation and coagulation. Interestingly, while increased angiogenesis can be observed in both tumors, inflammatory processes seem significantly more prominent in SGCT. Both SGCT and VS are characterized by different subgroups of tumor-associated macrophages (TAMs): the pro-inflammatory M1 type is predominating in SGCTs, while the pro-angiogenetic M2 type is predominating in VSs. We suggest that a lack of NF2 protein in VS and a lack of TSC1/TSC2 proteins in SGCT significantly influence this fundamental difference between the two tumor types by changing the dominant TAM type. Since inflammatory reactions and coagulation processes are tightly connected, the pro-inflammatory state of SGCT may also explain the associated tendency for CSF clotting. The underlying cellular and molecular differences observed can potentially serve as an access point for direct therapeutic interventions for tumors that are specific to certain phacomatoses or others that also carry such genetic changes.

Pancreatic Neuroendocrine Neoplasms: Basic Biology, Current Treatment Strategies and Prospects for the Future

Pancreatic neuroendocrine neoplasms (pNENs) are rare tumors accounting for only 1%–2% of all pancreatic tumors. pNENs are pathologically heterogeneous and are categorized into three groups (neuroendocrine tumor: NET G1, NET G2; and neuroendocrine carcinoma: NEC) on the basis of the Ki-67 proliferation index and the mitotic count according to the 2010 World Health Organization (WHO) classification of gastroenteropancreatic NENs. NEC in this classification includes both histologically well-differentiated and poorly differentiated subtypes, and modification of the WHO 2010 classification is under discussion based on genetic and clinical data. Genomic analysis has revealed NETs G1/G2 have genetic alterations in chromatin remodeling genes such as MEN1, DAXX and ATRX, whereas NECs have an inactivation of TP53 and RB1, and these data suggest that different treatment approaches would be required for NET G1/G2 and NEC. While there are promising molecular targeted drugs, such as everolimus or sunitinib, for advanced NET G1/G2, treatment stratification based on appropriate predictive and prognostic biomarkers is becoming an important issue. The clinical outcome of NEC is still dismal, and a more detailed understanding of the genetic background together with preclinical studies to develop new agents, including those already under investigation for small cell lung cancer (SCLC), will be needed to improve the prognosis.

Everolimus in the management of metastatic neuroendocrine tumours

Neuroendocrine tumours are increasing in incidence and cause a variety of symptoms. The mammalian target of rapamycin (mTOR) pathway plays a key role in neuroendocrine tumour (NET) pathogenesis, leading to increased lipid synthesis, protein synthesis and cellular growth. Upregulation of this pathway is noted in both hereditary and sporadic NETs. This understanding has led to investigations of mTOR inhibitors as therapy for metastatic NETs. After promising preclinical findings, everolimus, an mTOR inhibitor, was trialled in the RADIANT-1-4 studies on patients with advanced, well differentiated NETs. RADIANT-3 and RADIANT-4 established the efficacy of everolimus in improving progression-free survival (PFS) for metastatic NET of pancreatic, lung and gastrointestinal origin, leading to the US Food and Drug Administration (FDA) approval for its use in tumour control in those settings. Everolimus treatment is generally well tolerated; common adverse events include stomatitis, diarrhoea, rash and hyperglycaemia. Although discontinuation rates are low, many patients may require dose modification to successfully continue therapy. The combination of everolimus with somatostatin analogues (SSAs) (such as octreotide or pasireotide) or other targeted agents such as bevacizumab has not produced additional incremental benefit, and dual biologic therapy is not used widely. Ongoing trials are investigating everolimus compared with chemotherapy, optimal sequencing of therapy and combination of everolimus with radiotherapy. Future research should concentrate on identification of predictive biomarkers for benefit from mTOR therapy and include quality of life as a measure.

WOMEN IN CANCER THEMATIC REVIEW: Systemic therapies in neuroendocrine tumors and novel approaches toward personalized medicine

Neuroendocrine tumors (NETs) are a group of heterogenous neoplasms. Evidence-based treatment options for antiproliferative therapy include somatostatin analogues, the mTOR inhibitor everolimus, the multiple tyrosine kinase inhibitor sunitinib and peptide receptor radionuclide therapy with 177-Lu-octreotate. In the absence of definite predictive markers, therapeutic decision making follows clinical and pathological criteria. As objective response rates with targeted drugs are rather low, and response duration is limited in most patients, numerous combination therapies targeting multiple pathways have been explored in the field. Upfront combination of drugs, however, is associated with increasing toxicity and has shown little benefit. Major advancements in the molecular understanding of NET based on genomic, epigenomic and transcriptomic analysis have been achieved with prognostic and therapeutic impact. New insight into molecular alterations has paved the way to biomarker-driven clinical trials and may facilitate treatment stratification toward personalized medicine in the near future. However, an improved understanding of the complexity of pathway interactions is required for successful treatment. A systems biology approach is one of the tools that may help to achieve this endeavor.

The pivotal role of mammalian target of rapamycin inhibition in the treatment of patients with neuroendocrine tumors

Significant advances have been made toward understanding the biology of neuroendocrine tumors (NET) in terms of defining prognosis and improving clinical management; however, many unmet needs remain. The treatment landscape for NET has evolved, with the approval of the targeted agents everolimus and sunitinib for the treatment of advanced pancreatic NET in 2011 followed by the approval of everolimus for the treatment of advanced nonfunctional gastrointestinal and lung NET in 2016. Mammalian target of rapamycin (mTOR) and components of the mTOR pathway play pivotal roles in NET pathogenesis. Effects of the mTOR inhibitor everolimus have been well documented in preclinical and clinical studies, both as monotherapy and combination therapy. mTOR inhibition as backbone therapy within the NET treatment landscape is a focus of continuing research, which includes evaluation of the growing armamentarium of approved and investigational agents as potential combination partners. Data evaluating the clinical benefits of agents targeting mTOR and related pathways (alone and in combination) in the treatment of patients with NET continue to increase. Many of the findings to date are encouraging.

Pancreatic neuroendocrine tumors: Challenges in an underestimated disease

Pancreatic neuroendocrine tumours (PanNETs) are considered a relatively unusual oncologic entity. Due to its relative good prognosis, surgery remains the goal standard therapy not only in localized disease but also in the setting of locally or metastatic disease. Most of the patients are diagnosed in metastatic scenario, where multidisciplinary approach based on surgery, chemotherapies, liver-directed and/or molecular targeted therapies are commonly used. Owing to a deeper molecular knowledge of this disease, these targeted therapies are nowadays widely implemented, being the likely discovery of predictive biomarkers that would allow its use in other settings. This review is focused on describing the different classifications, etiology, prognostic biomarkers and multidisciplinary approaches that are typically used in PanNET.

Dual inhibition of mTOR pathway and VEGF signalling in neuroendocrine neoplasms: from bench to bedside

After years of limited progress in the treatment of neuroendocrine neoplasms (NENs), an increasing number of therapeutic targets have recently emerged as potential tools to improve disease outcome. The mammalian target of rapamycin (mTOR) pathway and vascular endothelial growth factor (VEGF) signalling are implicated in the regulation of cell growth, proliferation, neo-angiogenesis and tumour cell spread. Their combined blockade, in a simultaneous or sequential strategy, represents an intriguing biological rationale to overcome the onset of resistance mechanisms. However, is becoming increasingly imperative to find the optimal sequential strategy according to the best toxicity profile, and also to identify predictive biomarkers. We will provide an overview of the pre-clinical and clinical data relating to mTOR pathway/VEGF signalling as a potential targets of treatment in NENs.