GEP- NETS UPDATE: Genetics of neuroendocrine tumors

Mixed neuroendocrine and adenocarcinoma of gastrointestinal tract: A complex diagnosis and therapeutic challenge

In this editorial we comment on the manuscript describing a case of adenocarcinoma mixed with a neuroendocrine carcinoma of the gastroesophageal junction. Mixed neuroendocrine and non-neuroendocrine neoplasms of the gastrointestinal system are rare heterogeneous group of tumors characterized by a high malignant potential, rapid growth, and poor prognosis. Due to the rarity of these cancers, the standard therapy is poorly defined. The diagnosis of these tumors is based on combination of morphological features, immunohistochemical and neuroendocrine and epithelial cell markers. Both endocrine and epithelial cell components can act independently of each other and thus, careful grading of each component separately is required. These cancers are aggressive in nature and the potential of each component has paramount importance in the choice of treatment and response. Regardless of the organ of origin, these tumors portend poor prognosis with increased proportion of neuroendocrine component. Multidisciplinary services and strategies are required for the management of these mixed malignancies to provide the best oncological outcomes. The etiopathogenesis of these mixed tumors remains obscure but poses interesting question. We briefly discuss a few salient points in this editorial.

The Evolutionary History of Metastatic Pancreatic Neuroendocrine Tumours Reveals a Therapy Driven Route to High-Grade Transformation

Tumour evolution with acquisition of more aggressive disease characteristics is a hallmark of disseminated cancer. Metastatic pancreatic neuroendocrine tumours (PanNETs) in particular, show frequent progression from a low/intermediate to a high-grade disease. To understand the molecular mechanisms underlying this phenomenon, we performed multi-omics analysis of 32 longitudinal samples from six metastatic PanNET patients. Following MEN1 inactivation, PanNETs exhibit genetic heterogeneity on both spatial and temporal dimensions with parallel and convergent tumuor evolution involving the ATRX/DAXX and mTOR pathways. Following alkylating chemotherapy treatment, some PanNETs develop mismatch repair deficiency and acquire a hypermutator phenotype. This DNA hypermutation phenotype was only found in cases that also showed transformation into a high-grade PanNET. Overall, our findings contribute to broaden the understanding of metastatic PanNET, and suggests that therapy driven disease evolution is an important hallmark of this disease.

PET/MRI imaging in neuroendocrine neoplasm

Molecular imaging plays a vital role in the management of neuroendocrine neoplasms (NENs). Somatostatin receptor (SSTR) PET is critical for evaluating NENs, ascertaining peptide receptor radionuclide therapy (PRRT) eligibility, and treatment response. SSTR-PET/MRI can provide a one-stop-shop multiparametric evaluation of NENs. The acquisition of complementary imaging information in PET/MRI has distinct advantages over PET/CT and MR imaging acquisitions. The purpose of this manuscript is to provide a comprehensive overview of PET/MRI and a current review of recent PET/MRI advances in the diagnosis, staging, treatment, and surveillance of NENs.

Multiomic sequencing of paired primary and metastatic small bowel carcinoids

Background: Small bowel carcinoids are insidious tumors that are often metastatic when diagnosed. Limited mutation landscape studies of carcinoids indicate that these tumors have a relatively low mutational burden. The development of targeted therapies will depend upon the identification of mutations that drive the pathogenesis and metastasis of carcinoid tumors. Methods: Whole exome and RNA sequencing of 5 matched sets of normal tissue, primary small intestine carcinoid tumors, and liver metastases were investigated. Germline and somatic variants included: single nucleotide variants (SNVs), insertions/deletions (indels), structural variants, and copy number alterations (CNAs). The functional impact of mutations was predicted using Ensembl Variant Effect Predictor. Results: Large-scale CNAs were observed including the loss of chromosome 18 in all 5 metastases and 3/5 primary tumors. Certain somatic SNVs were metastasis-specific; including mutations in ATRX, CDKN1B, MXRA5 (leading to the activation of a cryptic splice site and loss of mRNA), SMARCA2, and the loss of UBE4B. Additional mutations in ATRX, and splice site loss of PYGL, leading to intron retention observed in primary and metastatic tumors. Conclusions: We observed novel mutations in primary/metastatic carcinoid tumor pairs, and some have been observed in other types of neuroendocrine tumors. We confirmed a previously observed loss of chromosome 18 and CDKN1B. Transcriptome sequencing added relevant information that would not have been appreciated with DNA sequencing alone. The detection of several splicing mutations on the DNA level and their consequences at the RNA level suggests that RNA splicing aberrations may be an important mechanism underlying carcinoid tumors.

Global challenges in access to diagnostics and treatment for neuroendocrine tumor (NET) patients

SCAN, an online survey, measured access to diagnosis, treatments and monitoring of neuroendocrine tumor (NET) patients globally. Between September and November 2019, NET patients and healthcare professionals (HCPs) completed an online, semi-standardized survey with 54 patient questions and 33 HCP questions. A total of 2359 patients with NETs and 436 HCPs responded. Misdiagnosis was common (44% [1043/2359]). Mean time to diagnosis was 4.8 years (standard deviation [SD], 6.2). Compared with global figures (60% [1407/2359]), the availability of 68 Ga-DOTA positron emission tomography (PET)/computed tomography (CT) was significantly lower in Asia (45% [126/280]) and higher in Oceania (86% [171/200]). HCPs reported that 68 Ga-DOTA PET/CT was free/affordable to fewer patients in Emerging and Developing Economies (EDE) than Advanced Economies (AE; 17% [26/150] and 59% [84/142], respectively). Compared with global data (52% [1234/2359]), patient-reported availability of peptide receptor radionuclide therapy (PRRT) was significantly lower in Asia (31% [88/280]) and higher in Oceania (61% [122/200]). Significant differences were observed in average annual NET specialist costs between AE and EDE ($1081 and $2915, respectively). Compared with AE, patients in EDE traveled further for NET specialists (1032 [SD, 1578] and 181 [SD, 496] km, respectively). Patients and HCPs both recommended referral to HCPs that were more knowledgeable in the field of NETs and had better access to NET experts/specialist centers. National care pathways, enhancing HCP NET knowledge and ensuring effective diagnostics and access to appropriate treatments are crucial to improving patient survival and NET care worldwide.

Hybrid imaging of neuroendocrine tumors in the heart: Union is strength

Cardiac neuroendocrine tumors (NETs) are particularly rare tumors that can lead to a very poor clinical outcome, partly because of metastases but mainly because of manifestations of the hormonal activity they exhibit. Prompt diagnosis is important in order to start the most effective treatment for their removal or management, with the fewest complications. They are often difficult to diagnose, especially in their early stages. One of the reasons for this is that the heart is an organ with a high rate of metabolism and is located in close proximity to other high-metabolism organs. In addition, the anatomic location and their small size render their diagnosis extremely challenging. In recent years, hybrid imaging methods have revolutionized the diagnostic approach to oncology patients and have established a place in the diagnosis of cardiac NETs, because they provide both anatomical and functional information at the same time. Positron emission tomography/computed tomography (PET/CT), PET/magnetic resonance imaging (PET/MRI) and single-photon emission computed tomography/CT (SPECT/CT) are widely used in clinical practice because of the very important metabolic information, the high sensitivity and specificity. However, prospective studies are needed to confirm the true clinical and prognostic value of various hybrid imaging diagnostic techniques in cardiac NETs.

Neuroendocrine neoplasms of the lung and gastrointestinal system: convergent biology and a path to better therapies

Neuroendocrine neoplasms (NENs) can develop in almost any organ and span a spectrum from well-differentiated and indolent neuroendocrine tumours (NETs) to poorly differentiated and highly aggressive neuroendocrine carcinomas (NECs), including small-cell lung cancer (SCLC). These neoplasms are thought to primarily derive from neuroendocrine precursor cells located throughout the body and can also arise through neuroendocrine transdifferentiation of organ-specific epithelial cell types. Hence, NENs constitute a group of tumour types that share key genomic and phenotypic characteristics irrespective of their site of origin, albeit with some organ-specific differences. The establishment of representative preclinical models for several of these disease entities together with analyses of human tumour specimens has provided important insights into crucial aspects of their biology with therapeutic implications. In this Review, we provide a comprehensive overview of the current understanding of NENs of the gastrointestinal system and lung from clinical and biological perspectives. Research on NENs has typically been siloed by the tumour site of origin, and a cross-cutting view might enable advances in one area to accelerate research in others. Therefore, we aim to emphasize that a better understanding of the commonalities and differences of NENs arising in different organs might more effectively inform clinical research to define therapeutic targets and ultimately optimize patient care.

Rectal neuroendocrine neoplasms: what the radiologists should know

Neuroendocrine neoplasms of the rectum (R-NENs) are rare; however, their incidence has increased almost threefold in the last few decades. Imaging of R-NENs includes two primary categories: anatomic/morphologic imaging comprised of endoscopic ultrasound (EUS), computed tomography (CT), magnetic resonance imaging (MRI), and functional/molecular imaging comprising of planar scintigraphy, single-photon emission computed tomography (SPECT), and positron emission tomography (PET). The management depends on stage, dimension, atypical features, histological grade, and lymphovascular invasion (LVI). Low-risk local R-NENs can be resected endoscopically, and high-risk or locally advanced neoplasms can be treated with radical surgery and lymphadenectomy and/or chemoradiation. The review article focuses on imaging illustrations and discusses applications of different imaging modalities in diagnosing and managing R-NENs.

PET/CT and PET/MRI in neuroendocrine neoplasms

Advanced molecular imaging has come to play an integral role in the management of gastro-entero-pancreatic neuroendocrine neoplasms (GEP-NENs). Somatostatin receptor (SSTR) PET has now emerged as the reference standard for the evaluation of NENs and is particularly critical in the context of peptide receptor radionuclide therapy (PRRT) eligibility. SSTR PET/MRI with liver-specific contrast agent has a strong potential for one-stop-shop multiparametric evaluation of GEP-NENs. 18F-FDG is a complementary radiotracer to SSTR, especially in the context of high-grade neuroendocrine neoplasms. Knowledge gaps in quantitative evaluation of molecular imaging studies and their role in assessment of response to PRRT and combination therapies are active research areas. Novel radiotracers have the potential to overcome existing limitations in the molecular imaging of GEP-NENs. The purpose of this article is to provide an overview of the current trends, pitfalls, and recent advancements of molecular imaging for GEP-NENs.

Preclinical Models of Neuroendocrine Neoplasia

Neuroendocrine neoplasia (NENs) are a complex and heterogeneous group of cancers that can arise from neuroendocrine tissues throughout the body and differentiate them from other tumors. Their low incidence and high diversity make many of them orphan conditions characterized by a low incidence and few dedicated clinical trials. Study of the molecular and genetic nature of these diseases is limited in comparison to more common cancers and more dependent on preclinical models, including both in vitro models (such as cell lines and 3D models) and in vivo models (such as patient derived xenografts (PDXs) and genetically-engineered mouse models (GEMMs)). While preclinical models do not fully recapitulate the nature of these cancers in patients, they are useful tools in investigation of the basic biology and early-stage investigation for evaluation of treatments for these cancers. We review available preclinical models for each type of NEN and discuss their history as well as their current use and translation.

Inflammation Related to Obesity in the Etiopathogenesis of Gastroenteropancreatic Neuroendocrine Neoplasms

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) are rare neoplasms, which, due to their heterogeneous nature, non-specific symptoms, and lack of specific tumor markers pose many diagnostic and clinical challenges. In recent years, the effectiveness of GEP-NEN diagnosis has increased, which is probably associated with the greater availability of diagnostic tests and the cooperation of many experienced specialists in various scientific disciplines. In addition to the possible genetic etiology, the cause of GEP-NET development is not fully understood. Inflammation and obesity are known risks that contribute to the development of many diseases. Chronic inflammation accompanying obesity affects the hormonal balance and cell proliferation and causes the impairment of the immune system function, leading to neoplastic transformation. This review explores the role of inflammation and obesity in GEP-NETs. The exact mechanisms inducing tumor growth are unknown; however, the profile of inflammatory factors released in the GEP-NET tumor microenvironment is responsible for the progression or inhibition of tumor growth. Both the excess of adipose tissue and the impaired function of the immune system affect not only the initiation of cancer but also reduce the comfort and lifetime of patients.

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.

Insights into Mechanisms of Tumorigenesis in Neuroendocrine Neoplasms

Genomic studies have identified some of the most relevant genetic players in Neuroendocrine Neoplasm (NEN) tumorigenesis. However, we are still far from being able to draw a model that encompasses their heterogeneity, elucidates the different biological effects consequent to the identified molecular events, or incorporates extensive knowledge of molecular biomarkers and therapeutic targets. Here, we reviewed recent insights in NEN tumorigenesis from selected basic research studies on animal models, highlighting novel players in the intergenic cooperation and peculiar mechanisms including splicing dysregulation, chromatin stability, or cell dedifferentiation. Furthermore, models of tumorigenesis based on composite interactions other than a linear progression of events are proposed, exemplified by the involvement in NEN tumorigenesis of genes regulating complex functions, such as MEN1 or DAXX. Although limited by interspecies differences, animal models have proved helpful for the more in-depth study of every facet of tumorigenesis, showing that the identification of driver mutations is only one of the many necessary steps and that other mechanisms are worth investigating.

The new WHO classification of gastrointestinal neuroendocrine tumors and immunohistochemical expression of somatostatin receptor 2 and 5

The 2019 World Health Organization (WHO) classification of gastrointestinal tumors defines well-differentiated grade 3 neuroendocrine tumors, the mixed neuroendocrine-non-neuroendocrine tumors (MiNENs) and classifies goblet cell carcinoid as goblet cell adenocarcinoma. The expression of somatostatin receptors (SSTRs) is the foundation for somatostatin analogue therapy. At present, there are only a few studies that have analyzed the immunohistochemical reactivity of SSTRs in gastrointestinal neuroendocrine neoplasms (NENs). The aim of the present study was to evaluate the immunohistochemical expression of SSTR2 and SSTR5 in gastrointestinal NENs and goblet cell adenocarcinomas and the correlation of these markers with clinical and morphological factors. The study included 67 patients with NENs and 4 patients with adenocarcinoma ex-goblet cell carcinoid diagnosed between January 2008 and December 2018. Tumors were reclassified according to the 2019 WHO classification. Immunohistochemical staining for chromogranin A, synaptophysin, Ki-67, p53, SSTR2, and SSTR5 were performed in all the cases. The results showed that, G1 and G2 neuroendocrine tumors were more common SSTR2-positive in comparison with G3 carcinomas (P<0.0001). In addition, 33.3% of neuroendocrine carcinomas and 2 cases of low-grade adenocarcinoma ex-goblet cell carcinoid were SSTR2-positive. Neuroendocrine carcinomas had significantly lower SSTR2 and SSTR5 expression compared with well-differentiated neuroendocrine tumors (P=0.0130; P=0.0437, respectively). The SSTR2 expression in the early tumor stages was 100%, more often than in advanced stages (55.6%; P=0.0011). The results demonstrated the decrease in SSTR2 expression with increasing malignancy and tumor stage. The SSTR2-positive expression in neuroendocrine carcinomas and adenocarcinoma ex-goblet cell carcinoid provides evidence for the benefits of somatostatin analog treatment associated with surgery and chemotherapy.

Phakomatoses and Endocrine Gland Tumors: Noteworthy and (Not so) Rare Associations

Phakomatoses encompass a group of rare genetic diseases, such as von Hippel-Lindau syndrome (VHL), neurofibromatosis type 1 (NF1), tuberous sclerosis complex (TSC) and Cowden syndrome (CS). These disorders are due to molecular abnormalities on the RAS-PI3K-Akt-mTOR pathway for NF1, TSC and CS, and to hypoxia sensing for VHL. Phakomatoses share some phenotypic traits such as neurological, ophthalmological and cutaneous features. Patients with these diseases are also predisposed to developing multiple endocrine tissue tumors, e.g., pheochromocytomas/paragangliomas are frequent in VHL and NF1. All forms of phakomatoses except CS may be associated with digestive neuroendocrine tumors. More rarely, thyroid cancer and pituitary or parathyroid adenomas have been reported. These susceptibilities are noteworthy, because their occurrence rate, prognosis and management differ slightly from the sporadic forms. The aim of this review is to summarize current knowledge on endocrine glands tumors associated with VHL, NF1, TSC, and CS, especially neuroendocrine tumors and pheochromocytomas/paragangliomas. We particularly detail recent advances concerning prognosis and management, especially parenchyma-sparing surgery and medical targeted therapies such as mTOR, MEK and HIF-2 α inhibitors, which have shown truly encouraging results.

Multiple endocrine neoplasia type 1 (MEN-1) and neuroendocrine neoplasms (NENs)

Neuroendocrine neoplasms (NENs) are relatively rare neoplasms with 6.4-times increasing age-adjusted annual incidence during the last four decades. NENs arise from neuroendocrine cells, which release hormones in response to neuronal stimuli and they are distributed into organs and tissues. The presentation and biological behaviour of the NENs are highly heterogeneous, depending on the organ. The increased incidence is mainly due to increased awareness and improved detection methods both in the majority of sporadic NENs (non-inherited), but also the inherited groups of neoplasms appearing in at least ten genetic syndromes. The most important one is multiple endocrine neoplasia type 1 (MEN-1), caused by mutations in the tumour suppressor gene MEN1. MEN-1 has been associated with different tumour manifestations of NENs e.g. pancreas, gastrointestinal tract, lungs, thymus and pituitary. Pancreatic NENs tend to be less aggressive when arising in the setting of MEN-1 compared to sporadic pancreatic NENs. There have been very important improvements over the past years in both genotyping, genetic counselling and family screening, introduction and validation of various relevant biomarkers, as well as newer imaging modalities. Alongside this development, both medical, surgical and radionuclide treatments have also advanced and improved morbidity, quality of life and mortality in many of these patients. Despite this progress, there is still space for improving insight into the genetic and epigenetic factors in relation to the biological mechanisms determining NENs as part of MEN-1. This review gives a comprehensive update of current evidence for co-occurrence, diagnosis and treatment of MEN-1 and neuroendocrine neoplasms and highlight the important progress now finding its way to international guidelines in order to improve the global management of these patients.

The Role of Patient Support Groups in Neuroendocrine Neoplasms

PURPOSE OF REVIEW

The purpose of this review is to establish the role patient support groups play in NENs.

RECENT FINDINGS

Published data on the role and work done by these groups is extremely sparse, so the review references publications in the wider cancer advocacy context. For the purposes of the review, a survey was carried out among the members of a global umbrella organization to ascertain the level of activities undertaken in support of the NEN patient community. The concept of "support groups" has changed significantly, as these groups have evolved from patient peer-to-peer support provision to a strategic focus on improving awareness and education among all stakeholders, generating patient evidence to influence policies for access to optimal diagnostics, treatment, and care, and setting the research agenda. Today, NEN patient organizations have an instrumental role of catalysts of change across the healthcare spectrum-especially relevant in a setting of less common and not well-understood diseases, where clear pathways and guidelines are still a challenge.

Models of Gastroenteropancreatic Neuroendocrine Neoplasms: Current Status and Future Directions

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) are a rare, heterogeneous group of tumors that originate from the endocrine system of the gastrointestinal tract and pancreas. GEP-NENs are subdivided according to their differentiation into well-differentiated neuroendocrine tumors (NETs) and poorly differentiated neuroendocrine carcinomas (NECs). Since GEP-NENs represent rare diseases, only limited data from large prospective, randomized clinical trials are available, and recommendations for treatment of GEP-NEN are in part based on data from retrospective analyses or case series. In this context, tractable disease models that reflect the situation in humans and that allow to recapitulate the different clinical aspects and disease stages of GEP-NET or GEP-NEC are urgently needed. In this review, we highlight available data on mouse models for GEP-NEN. We discuss how these models reflect tumor biology of human disease and whether these models could serve as a tool for understanding the pathogenesis of GEP-NEN and for disease modeling and pharmacosensitivity assays, facilitating prediction of treatment response in patients. In addition, open issues applicable for future developments will be discussed.

LAT-1 and GLUT-1 Carrier Expression and Its Prognostic Value in Gastroenteropancreatic Neuroendocrine Tumors

Simple Summary

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) represent about 70% of all NETs; however, improvement in their outcomes has yet to be achieved. Here, we aimed to analyze the role of metabolic players such as the amino acid transporter 1 (LAT-1) and glucose transporter 1 (GLUT-1), regulated by the oxygen-sensing mechanism Von Hippel Lindau-hypoxia-inducible factor (VHL-HIF), in gastroenteropancreatic neuroendocrine tumors (GEP-NET). We also aimed to correlate them with tumor malignancy and progression. We confirmed that specific mechanisms that increase nutrient uptake, such as LAT-1 and GLUT-1, are increased in GEP-NETs, whereas pVHL is decreased. Our results suggest that these biomarkers could have a potential role in NET pathophysiology which might be related to their proliferation and metastatic capacity.

Abstract

Cancer cells develop mechanisms that increase nutrient uptake, including key nutrient carriers, such as amino acid transporter 1 (LAT-1) and glucose transporter 1 (GLUT-1), regulated by the oxygen-sensing Von Hippel Lindau-hypoxia-inducible factor (VHL-HIF) transcriptional pathway. We aimed to analyze these metabolic players in gastroenteropancreatic neuroendocrine tumors (GEP-NET) and correlate them with tumor malignancy and progression. LAT-1, GLUT-1, and pVHL expression was analyzed in 116 GEP-NETs and 48 peritumoral tissue samples by immunohistochemistry. LAT-1 was stably silenced using specific shRNA in the human NET BON cell line. LAT-1 expression was significantly increased in tumor tissue compared to non-tumor tissue in both gastrointestinal (67% vs. 44%) and pancreatic NETs (54% vs. 31%). Similarly, GLUT-1 was substantially elevated in gastrointestinal (74% vs. 19%) and pancreatic (58% vs. 4%) NETs. In contrast, pVHL expression was decreased (85% vs. 58%) in pancreatic NETs. Tumors with metastases at diagnosis displayed increased LAT-1 and GLUT-1 and decreased pVHL expression (p < 0.001). In accordance with these data, silencing LAT-1 curtailed cell proliferation in BON cells. These findings suggest that specific mechanisms that increase nutrient uptake, such as LAT-1 and GLUT-1, are increased in GEP-NETs, whereas pVHL is decreased. These markers might be related to the proliferation and metastatic capacity of these tumors.

Elevated miR-16-5p induces somatostatin receptor 2 expression in neuroendocrine tumor cells

Somatostatin analogs, which are used to treat neuroendocrine tumors, inhibit hormone secretion or promote tumor shrinkage; however, their efficacy varies between patients, possibly because of differential expression of somatostatin receptors (SSTRs) in tumors. In this study, we evaluated the regulatory mechanism underlying the expression of SSTR2, the main octreotide target. Thirty miRNAs were found to be dysregulated in neuroendocrine cells (INS-1 cells) incubated with octreotide compared to that in placebo-treated cells. Among the upregulated miRNAs, miR-16-5p was elevated after short-term octreotide treatment. We conducted in vitro experiments to determine whether the expression of miR-16-5p was associated with the regulation of SSTR2 expression and affected octreotide sensitivity in INS-1 cells. Overexpression of miR-16-5p by transfected mimics induced upregulation of SSTR2 expression. Additionally, the expression of miR-16-5p further enhanced octreotide-induced reduction in cell proliferation in both two- and three-dimensional culture of INS-1 cells. Thus, our results reveal the mechanism underlying SSTR2 expression regulation and may aid in developing therapeutic approaches for enhancing the response to octreotide, particularly in patients unresponsive to SSTR2-targeted somatostatin analog treatment.

Neuroendocrine neoplasia of the gastrointestinal tract revisited: towards precision medicine

Over the past 5 years, a number of notable research advances have been made in the field of neuroendocrine cancer, specifically with regard to neuroendocrine cancer of the gastrointestinal tract. The aim of this Review is to provide an update on current knowledge that has proven effective for the clinical management of patients with these tumours. For example, for the first time in the tubular gastrointestinal tract, well-differentiated high-grade (grade 3) tumours and mixed neuroendocrine-non-neuroendocrine neoplasms (MiNENs) are defined in the WHO classification. This novel classification enables efficient identification of the most aggressive well-differentiated neuroendocrine tumours and helps in defining the degree of aggressiveness of MiNENs. The Review also discusses updates to epidemiology, cell biology (including vesicle-specific components) and the as-yet-unresolved complex genetic background that varies according to site and differentiation status. The Review summarizes novel diagnostic instruments, including molecules associated with the secretory machinery, novel radiological approaches (including pattern recognition techniques), novel PET tracers and liquid biopsy combined with DNA or RNA assays. Surgery remains the treatment mainstay; however, peptide receptor radionuclide therapy with novel radioligands and new emerging medical therapies (including vaccination and immunotherapy) are evolving and being tested in clinical trials, which are summarized and critically reviewed here.

Pancreatic neuroendocrine tumors: Therapeutic challenges and research limitations

Pancreatic neuroendocrine tumors (PNETs) are known to be the second most common epithelial malignancy of the pancreas. PNETs can be listed among the slowest growing as well as the fastest growing human cancers. The prevalence of PNETs is deceptively low; however, its incidence has significantly increased over the past decades. According to the American Cancer Society’s estimate, about 4032 (> 7% of all pancreatic malignancies) individuals will be diagnosed with PNETs in 2020. PNETs often cause severe morbidity due to excessive secretion of hormones (such as serotonin) and/or overall tumor mass. Patients can live for many years (except for those patients with poorly differentiated G3 neuroendocrine tumors); thus, the prevalence of the tumors that is the number of patients actually dealing with the disease at any given time is fairly high because the survival is much longer than pancreatic ductal adenocarcinoma. Due to significant heterogeneity, the management of PNETs is very complex and remains an unmet clinical challenge. In terms of research studies, modest improvements have been made over the past decades in the identification of potential oncogenic drivers in order to enhance the quality of life and increase survival for this growing population of patients. Unfortunately, the majority of systematic therapies approved for the management of advanced stage PNETs lack objective response or at most result in modest benefits in survival. In this review, we aim to discuss the broad challenges associated with the management and the study of PNETs.

Genetic and epigenetic alterations in pancreatic neuroendocrine tumors

Neuroendocrine tumors (NETs) are a heterogenous group of tumors that originate from neuroendocrine cells, mainly in the pancreas and the gastrointestinal and bronchopulmonary tracts. There has been considerable progress in our understanding of the genetic and epigenetic changes associated with pancreatic NETs (PNETs). The main genetic alterations that drive PNETs include genetic alterations in MEN1, VHL and genes involved in the mTOR pathway, DAXX and/or ATRX mutations and their association with alternative telomere lengthening, and genes involved in DNA damage repair and chromatin modification. The epigenetic alterations in PNETs are also common based on genome-wide DNA methylation profiling studies, with a high rate of CpG hypermethylation in MEN1-associated PNETs compared to sporadic and VHL-associated PNETs. Moreover, the dysregulated DNA methylation status is associated with distinct gene expression profiles. This article reviews the commonly and recently discovered genetic and epigenetic changes that are associated with PNETs, inherited PNETs, and genotype-phenotype associations, and it discusses their clinical relevance.

Biomarkers for Pancreatic Neuroendocrine Neoplasms (PanNENs) Management-An Updated Review

Pancreatic neuroendocrine tumors (PanNENs) are rare sporadic cancers or develop as part of hereditary syndromes. PanNENs can be both functioning and non-functioning based on whether they produce bioactive peptides. Some PanNENs are well differentiated while others-poorly. Symptoms, thus, depend on both oncological and hormonal causes. PanNEN diagnosis and treatment benefit from and in some instances are guided by biomarker monitoring. However, plasmatic monoanalytes are only suggestive of PanNEN pathological status and their positivity is typically followed by deepen diagnostic analyses through imaging techniques. There is a strong need for new biomarkers and follow-up modalities aimed to improve the outcome of PanNEN patients. Liquid biopsy follow-up, i.e., sequential analysis on tumor biomarkers in body fluids offers a great potential, that need to be substantiated by additional studies focusing on the specific markers and the timing of the analyses. This review provides the most updated panorama on PanNEN biomarkers.

High-Grade Progression Confers Poor Survival in Pancreatic Neuroendocrine Tumors

INTRODUCTION

Little is known about how pancreatic neuroendocrine tumors (PanNETs) evolve over time and if changes toward a more aggressive biology correlate with prognosis. The purpose of this study was to characterize changes in PanNET differentiation and proliferation over time and to correlate findings to overall survival (OS).

PATIENTS AND METHODS

In this retrospective cohort study, we screened 475 PanNET patients treated at Uppsala University Hospital, Sweden. Sporadic patients with baseline and follow-up tumor samples were included. Pathology reports and available tissue sections were reevaluated with regard to tumor histopathology and Ki-67 index.

RESULTS

Forty-six patients with 106 tumor samples (56 available for pathology reevaluation) were included. Median Ki-67 index at diagnosis was 7% (range 1-38%), grade 1 n = 8, grade 2 n = 36, and grade 3 n = 2. The median change in Ki-67 index (absolute value; follow-up - baseline) was +14% (range -11 to +80%). Increase in tumor grade occurred in 28 patients (63.6%), the majority from grade 1/2 to grade 3 (n = 24, 54.5%). The patients with a high-grade progression had a median OS of 50.2 months compared to 115.1 months in patients without such progression (hazard ratio 3.89, 95% CI 1.91-7.94, p < 0.001).

CONCLUSIONS

A longitudinal increase in Ki-67 index and increase in tumor grade were observed in a majority of PanNETs included in this study. We propose that increase in Ki-67 index and high-grade progression should be investigated further as important biomarkers in PanNET.

Unmet needs in the international neuroendocrine tumor (NET) community: Assessment of major gaps from the perspective of patients, patient advocates and NET health care professionals

Due to the increasing incidence and prevalence of neuroendocrine tumors (NETs), there is a need to assess any gaps in awareness and care. A survey was undertaken in 2017 to identify perceived unmet needs from the perspectives of patients/families, patient advocates and health care professionals (HCPs). The survey consisted of 33–37 questions (depending on type of respondent) across four areas: information, care, treatments and research. In total, 443 participants from 26 countries responded: 338 patients/families, 35 advocates and 70 HCPs. Perceived unmet needs regarding provision of information at diagnosis differed between groups. While 59% of HCPs believed they provided sufficient information, informational needs were mostly/fully met for only 30% of patients and 18% of advocates. Additionally, 91% of patients and 97% of advocates felt that patients had to search for information themselves. Availability of Gallium‐68‐Dotatate PET/CT scan was limited for the majority of patients (patients: 73%; advocates: 85%; HCP: 86%), as was access to treatments, particularly peptide receptor radionuclide therapy (patients: 42%; advocates: 95%; HCPs: 77%). All groups felt that standards of care, including psychological needs and diagnosis of mental health, were not fully met. Although about two‐thirds of patients were managed by a multidisciplinary team, 14% of patients reportedly did not have enough contact. All groups supported more patient involvement in research; patients and advocates prioritized improvement in diagnosis and HCPs focused on clinical trials. This survey revealed significant unmet needs but differing perceptions regarding these among the groups. There is a need for investigation and collaboration to improve standards of care for NET patients.

What's new?

Even though the incidence of neuroendocrine tumors (NETs) has been rising worldwide, the current management of patients varies considerably, potentially leaving many with suboptimal care. An international survey was carried out in 2017 to investigate unmet needs in the NET patient community. The survey revealed that patients perceive numerous unmet needs in key areas including provision of information, diagnostics and treatment access, care standards, and research involvement. While healthcare professionals were aware of these gaps, they generally underestimated their magnitude. Patients and healthcare professionals need to work together to improve the lives and prospects of the increasing numbers of patients.

Management of Gastrointestinal Neuroendocrine Tumors

Neuroendocrine neoplasms (NENs) are derived from neuroendocrine cell system and can have benign or malignant characteristics. They are rare tumors, but have been increasing in incidence over the past 40 years. Patients with NENs may develop symptoms due to primary tumor invasion, metastasis, or from secretion of hormonally active tumor substances. Multiple imaging modalities are used for diagnosis and staging, including specialty scans such as ¹¹¹In pentetreotide (Octreoscan) and ⁶⁸Gallium-DOTATATE, along with endoscopy, endoscopic ultrasound, and biochemical marker testing. Treatment involves both surgical approach, for both primary and metastatic lesions, as well as medical management for symptom management and disease progression. This article will review the current clinical knowledge regarding the diagnosis, treatment, and prognosis of these fascinating neoplasms and the associated hormonal syndromes.

Therapy of Patients with Neuroendocrine Neoplasia-Evidence-Based Approaches and New Horizons

Neuroendocrine tumors (NETs) show low but increasing incidence and originate in multiple organs, including the pancreas, midgut, caecum, rectum, appendix, colon, and lungs. Due to their stunning genetic, histological, and clinical variability, diagnosis and treatment of NETs are challenging. In addition, low incidence and high variability hamper the implementation of high evidence trials. Therefore, guidelines do not cover the complexity of NETs and, frequently, treatment decisions are taken by interdisciplinary tumor conferences at comprehensive cancer centers. Treatment aims are (i) control of tumor growth, (ii) symptom control, as well as (iii) the improvement of progression-free survival (PFS) and overall survival (OS). Here, we discuss high evidence trials facilitating the achievement of these treatment aims. The majority of the evidence exists for treatment with somatostatin analogue, everolimus, peptide receptor radionuclide therapy (PRRT) with 177Lu-DOTATATE, sunitinib, and telotristat. Among those, PRRT is the only treatment option that has the potential to control symptoms, stop tumor growth, and to improve PFS and OS. In contrast, only a low level of evidence exists for treatment with cytotoxic drugs such as streptozotocin and doxorubicine. Finally, we discuss novel treatment options by a combination of cytotoxic drugs, 177Lu-DOTATATE, and tyrosine kinase inhibitors to be tested in randomized prospective trials in the future. In addition, the application of innovative isotopes, such as 225Ac, for PRRT is discussed.

Updates on the Role of Molecular Alterations and NOTCH Signalling in the Development of Neuroendocrine Neoplasms

Neuroendocrine neoplasms (NENs) comprise a heterogeneous group of rare malignancies, mainly originating from hormone-secreting cells, which are widespread in human tissues. The identification of mutations in ATRX/DAXX genes in sporadic NENs, as well as the high burden of mutations scattered throughout the multiple endocrine neoplasia type 1 (MEN-1) gene in both sporadic and inherited syndromes, provided new insights into the molecular biology of tumour development. Other molecular mechanisms, such as the NOTCH signalling pathway, have shown to play an important role in the pathogenesis of NENs. NOTCH receptors are expressed on neuroendocrine cells and generally act as tumour suppressor proteins, but in some contexts can function as oncogenes. The biological heterogeneity of NENs suggests that to fully understand the role and the potential therapeutic implications of gene mutations and NOTCH signalling in NENs, a comprehensive analysis of genetic alterations, NOTCH expression patterns and their potential role across all NEN subtypes is required.

Resistance to targeted treatment of gastroenteropancreatic neuroendocrine tumors

The mammalian target of rapamycin (mTOR) is part of the phosphoinositide-3-kinase (PI3K)/protein kinase B (Akt)/mTOR signaling. The PI3K/Akt/mTOR pathway has a pivotal role in the oncogenesis of neuroendocrine tumors (NETs). In addition, vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) drive angiogenesis in NETs and therefore contributes to neuroendocrine tumor development. Hence, mTOR and angiogenesis inhibitors have been developed. Everolimus, a first-generation mTOR inhibitor, has shown significant survival benefit in advanced gastroenteropancreatic NETs. Sunitinib, a pan-tyrosine kinase inhibitor that targets the VEGF receptor, has proven to increase progression-free survival in advanced pancreatic NETs. Nevertheless, primary and acquired resistance to rapalogs and sunitinib has limited the clinical benefit for NET patients. Despite the identification of multiple molecular mechanisms of resistance, no predictive biomarker has made it to the clinic. This review is focused on the mTOR signaling and angiogenesis in NET, the molecular mechanisms of primary and acquired resistance to everolimus and sunitinib and how to overcome this resistance by alternative drug compounds.

Hotspot DAXX, PTCH2 and CYFIP2 mutations in pancreatic neuroendocrine neoplasms

Mutations in DAXX/ATRX, MEN1 and genes involved in the phosphoinositide-3-kinase/Akt/mammalian target of rapamycin (PI3K/Akt/mTOR) pathway have been implicated in pancreatic neuroendocrine neoplasms (pNENs). However, mainly mutations present in the majority of tumor cells have been identified, while proliferation-driving mutations could be present only in small fractions of the tumor. This study aims to identify high- and low-abundance mutations in pNENs using ultra-deep targeted resequencing. Formalin-fixed paraffin-embedded matched tumor-normal tissue of 38 well-differentiated pNENs was sequenced using a HaloPlex targeted resequencing panel. Novel amplicon-based algorithms were used to identify both single nucleotide variants (SNVs) and insertion-deletions (indels) present in >10% of reads (high abundance) and in <10% of reads (low abundance). Found variants were validated by Sanger sequencing. Sequencing resulted in 416,711,794 reads with an average target base coverage of 2663 ± 1476. Across all samples, 32 high-abundance somatic, 3 germline and 30 low-abundance mutations were withheld after filtering and validation. Overall, 92% of high-abundance and 84% of low-abundance mutations were predicted to be protein damaging. Frequently, mutated genes were MEN1, DAXX, ATRX, TSC2, PI3K/Akt/mTOR and MAPK-ERK pathway-related genes. Additionally, recurrent alterations on the same genomic position, so-called hotspot mutations, were found in DAXX, PTCH2 and CYFIP2. This first ultra-deep sequencing study highlighted genetic intra-tumor heterogeneity in pNEN, by the presence of low-abundance mutations. The importance of the ATRX/DAXX pathway was confirmed by the first-ever pNEN-specific protein-damaging hotspot mutation in DAXX. In this study, both novel genes, including the pro-apoptotic CYFIP2 gene and hedgehog signaling PTCH2, and novel pathways, such as the MAPK-ERK pathway, were implicated in pNEN.

Neoplasms of the Neuroendocrine Pancreas: An Update in the Classification, Definition, and Molecular Genetic Advances

This review focuses on discussing the main modifications of the recently published 2017 WHO Classification of Neoplasms of the Neuroendocrine Pancreas (panNEN). Recent updates separate pancreatic neuroendocrine tumors into 2 broad categories: well-differentiated pancreatic neuroendocrine tumors (panNET) and poorly differentiated pancreatic neuroendocrine carcinoma (panNEC), and incorporates a new subcategory of "well-differentiated high-grade NET (G3)" to the well-differentiated NET category. This new classification algorithm aims to improve the prediction of clinical outcomes and survival and help clinicians select better therapeutic strategies for patient care and management. In addition, these neuroendocrine neoplasms are capable of producing large quantity of hormones leading to clinical hormone hypersecretion syndromes. These functioning tumors include, insulinomas, glucagonomas, somatostatinomas, gastrinomas, VIPomas, serotonin-producing tumors, and ACTH-producing tumors. Although most panNENs arise as sporadic diseases, a subset of these heterogeneous tumors present as parts on inherited genetic syndromes, such as multiple endocrine neoplasia type 1, von Hippel-Lindau, neurofibromatosis type 1, tuberous sclerosis, and glucagon cell hyperplasia and neoplasia syndromes. Characteristic clinical and morphologic findings for certain functioning and syndromic panNENs should alert both pathologists and clinicians as appropriate patient management and possible genetic counseling may be necessary.

Mouse models in endocrine tumors

Endocrine and neuroendocrine tumors comprise a highly heterogeneous group of neoplasms that can arise from (neuro)endocrine cells, either from endocrine glands or from the widespread diffuse neuroendocrine system, and, consequently, are widely distributed throughout the body. Due to their diversity, heterogeneity and limited incidence, studying in detail the molecular and genetic alterations that underlie their development and progression is still a highly elusive task. This, in turn, hinders the discovery of novel therapeutic options for these tumors. To circumvent these limitations, numerous mouse models of endocrine and neuroendocrine tumors have been developed, characterized and used in pre-clinical, co-clinical (implemented in mouse models and patients simultaneously) and post-clinical studies, for they represent powerful and necessary tools in basic and translational tumor biology research. Indeed, different in vivo mouse models, including cell line-based xenografts (CDXs), patient-derived xenografts (PDXs) and genetically engineered mouse models (GEMs), have been used to delineate the development, progression and behavior of human tumors. Results gained with these in vivo models have facilitated the clinical application in patients of diverse breakthrough discoveries made in this field. Herein, we review the generation, characterization and translatability of the most prominent mouse models of endocrine and neuroendocrine tumors reported to date, as well as the most relevant clinical implications obtained for each endocrine and neuroendocrine tumor type.

Multilayered heterogeneity as an intrinsic hallmark of neuroendocrine tumors

Neuroendocrine tumors (NETs) comprise a complex and highly heterogeneous group of neoplasms that can arise all over the body, originating from neuroendocrine cells. NETs are characterized by a general lack of symptoms until they are in advanced phase, and early biomarkers are not as available and useful as required. Heterogeneity is an intrinsic, pivotal feature of NETs that derives from diverse causes and ultimately shapes tumor fate. The different layers that conform NET heterogeneity include a wide range of distinct characteristics, from the mere location of the tumor to its clinical and functional features, and from its cellular properties, to the core signaling and (epi)genetic components defining the molecular signature of the tumor. The importance of this heterogeneity resides in that it translates into a high variability among tumors and, hence, patients, which hinders a more precise diagnosis and prognosis and more efficacious treatment of these diseases. In this review, we highlight the significance of this heterogeneity as an intrinsic hallmark of NETs, its repercussion on clinical approaches and tumor management, and some of the possible factors associated to such heterogeneity, including epigenetic and genetic elements, post-transcriptional regulation, or splicing alterations. Notwithstanding, heterogeneity can also represent a valuable and actionable feature, towards improving medical approaches based on personalized medicine. We conclude that NETs can no longer be viewed as a single disease entity and that their diagnosis, prognosis and treatment must reflect and incorporate this heterogeneity.

Advanced neuroendocrine tumours of the small intestine and pancreas: clinical developments, controversies, and future strategies

In this Review, we discuss clinical developments and controversies in the treatment of neuroendocrine tumours (NETs) that are relevant for clinicians and clinical researchers. We describe advances in genetics, blood-based biomarkers, functional imaging, and systemic therapy of advanced NETs and discuss results of recent phase 3 studies, systemic treatment of advanced disease with peptide receptor radionuclide therapy, biotherapy, chemotherapy, and molecularly targeted therapy, and the potential role of immunotherapy in the treatment of NETs. Suggested treatment algorithms for NETs of ileal or jejunal origin and of pancreatic origin are presented.

Neuroendocrine neoplasms of rectum: A management update

The estimated annual incidence of R-NENs is 1.04 per 100,000 persons although the real incidence may be underestimated, as not all R-NEN are systematically reported in registers. Also the prevalence has increased substantially, reflecting the rising incidence and indolent nature of R-NENs, showing the highest prevalence increase among all site of origin of NENs. The size of the tumor reveals the behavior of R-NENs where the risk for metastatic spread increases for lesions > 10 mm. Applying the WHO 2010 grading system to whole NENs originating in the gastroenteropancreatic system, R-NENs are classified as Well-Differentiated Neuroendocrine Tumors (WD-NET), which contain NET G1 and NET G2, and Poorly-Differentiated Carcinomas (PD-NEC) enclosing only G3 neoplasms for which the term carcinoma is applied. The treatment is endoscopic resection in most cases: conventional polypectomy or endoscopic mucosal resection (EMR) for smaller lesions or endoscopic submucosal resection with a ligation device (ESMR-L), cap-assisted EMR (EMR-C) and endoscopic submucosal dissection (ESD). However it is important to know when the endoscopic treatment is not enough, and surgical treatment is indicated, or when the latter could be unnecessary. For PD-NECs, it has recently been demonstrated that chemoradiotherapy is associated with a similar long-term survival to that obtained with surgery. As well, new targeted-agents chemotherapy may be indicated for metastatic WD-NETs.

Gastroenteropancreatic neuroendocrine neoplasms: genes, therapies and models

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) refer to a group of heterogeneous cancers of neuroendocrine cell phenotype that mainly fall into one of two subtypes: gastroenteropancreatic neuroendocrine tumors (GEP-NETs; well differentiated) or gastroenteropancreatic neuroendocrine carcinomas (GEP-NECs; poorly differentiated). Although originally defined as orphan cancers, their steadily increasing incidence highlights the need to better understand their etiology. Accumulating epidemiological and clinical data have shed light on the pathological characteristics of these diseases. However, the relatively low number of patients has hampered conducting large-scale clinical trials and hence the development of novel treatment strategies. To overcome this limitation, tractable disease models that faithfully reflect clinical features of these diseases are needed. In this Review, we summarize the current understanding of the genetics and biology of these diseases based on conventional disease models, such as genetically engineered mouse models (GEMMs) and cell lines, and discuss the phenotypic differences between the models and affected humans. We also highlight the emerging disease models derived from human clinical samples, including patient-derived xenograft models and organoids, which may provide biological and therapeutic insights into GEP-NENs.

The Role of Genetics in Sporadic GEP-NETs: A Comprehensive Review of the Literature

Neuroendocrine tumors (NETs) are composed of a heterogeneous group of malignancies from neuroendocrine cell compartments, with roles in both the endocrine and the nervous system. The majority of NETs are gastroenteropancreatic (GEP) in origin, arising in the foregut, midgut, or hindgut. The genomic landscape of GEP-NETs has been scarcely studied in terms of genomic profiling.The following algorithm was followed using the keywords neuroendocrine, genomics, targeted therapy, personalized medicine, gastroenteropancreatic and NET. The search was performed in PubMed and ScienceDirect database. Our current knowledge of sporadic GEP-NETs genetics must be further advanced to elucidate the molecular basis and pathogenesis of the disease, improve the accuracy of diagnosis, and guide tailor-made therapies.

Hereditary pancreatic cancer: related syndromes and clinical perspective

Pancreatic cancer is a very aggressive disease with a poor prognosis. The majority of them are attributed to sporadic causes, especially to many modifiable risk factors such as tobacco or alcohol abuse. The principal histologic subtype of pancreatic cancer is ductal adenocarcinoma. Pancreatic neuroendocrine tumors, which constitute a more indolent entity, represent second type of pancreatic cancer in terms of incidence. Individuals with a family history of pancreatic cancer carry an increased risk of developing the disease, which may be related to an underlying hereditary component. Unfortunately, in the majority of these families the suspected germline genetic cause responsible of the disease will not be identified, but approximately in a 20% of the cases a hereditary cancer predisposition syndrome with increased risk of pancreatic cancer development can be recognized. This review will be focused on the leading hereditary cancer syndromes related to pancreatic ductal adenocarcinoma and pancreatic neuroendocrine tumors. Additionally, we will try to explain clinical aspects related to the identification of germline mutations in pancreatic cancer patients and their potential implications in oncologic treatment decisions.

Novel targets in the treatment of neuroendocrine tumors: RBP2

Retinoblastoma binding protein 2, also known as RBP2, JARID1A or KDM5A, is an H3K4 demethylase implicated in a variety of non-neuroendocrine, and more recently, neuroendocrine tumors (NETs). NETs are tumors that form from neuroendocrine cells in tissues of the GI tract, endocrine pancreas, lung, skin and other tissues. RBP2 is expressed at abnormally high levels in NETs and recent work demonstrates that modulation of RBP2 in vitro and in vivo impacts end points of tumorigenesis. Interestingly, the demethylase activity of RBP2 is not exclusively responsible for these changes, as RBP2's binding partners may mediate its activity in a tissue- or context-dependent manner. Here, we discuss the features of RBP2 and its role in cell cycle regulation, angiogenesis and drug resistance in cancer.

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.

Identification of immunotherapeutic targets by genomic profiling of rectal NET metastases

Neuroendocrine tumors (NETs) of the gastrointestinal tract are a rare and heterogeneous group of neoplasms with unique tumor biology and clinical management issues. While surgery is the only curative treatment option in patients with early stage NETs, the optimal management strategy for patients with advanced metastatic NETs is unknown. Based on the tremendous success of immunotherapeutic approaches, we sought to investigate such approaches in a case of metastatic rectal NET. Here, we apply an integrative approach using various computational and experimental methods to explore several aspects of the tumor-host immune interactions for immunotherapeutic options. Sequencing of six different liver metastases revealed a quite homogenous set of mutations, and further analysis of these mutations for immunogenicity revealed few neo-epitopes with pre-existing T cell reactivity, which can be used in therapeutic vaccines. Staining for immunomodulatory proteins and cytokine profiling showed that the immune setting is surprisingly different, when compared to liver metastases of colorectal cancer for instance. Taken together, our results highlight the broad range and complexity of tumor-host immune interaction and underline the value of an integrative approach.