Translational research in neuroendocrine tumors: pitfalls and opportunities

The uprise of RNA biology in neuroendocrine neoplasms: altered splicing and RNA species unveil translational opportunities

Neuroendocrine neoplasms (NENs) comprise a highly heterogeneous group of tumors arising from the diffuse neuroendocrine system. NENs mainly originate in gastrointestinal, pancreatic, and pulmonary tissues, and despite being rare, show rising incidence. The molecular mechanisms underlying NEN development are still poorly understood, although recent studies are unveiling their genomic, epigenomic and transcriptomic landscapes. RNA was originally considered as an intermediary between DNA and protein. Today, compelling evidence underscores the regulatory relevance of RNA processing, while new RNA molecules emerge with key functional roles in core cell processes. Indeed, correct functioning of the interrelated complementary processes comprising RNA biology, its processing, transport, and surveillance, is essential to ensure adequate cell homeostasis, and its misfunction is related to cancer at multiple levels. This review is focused on the dysregulation of RNA biology in NENs. In particular, we survey alterations in the splicing process and available information implicating the main RNA species and processes in NENs pathology, including their role as biomarkers, and their functionality and targetability. Understanding how NENs precisely (mis)behave requires a profound knowledge at every layer of their heterogeneity, to help improve NEN management. RNA biology provides a wide spectrum of previously unexplored processes and molecules that open new avenues for NEN detection, classification and treatment. The current molecular biology era is rapidly evolving to facilitate a detailed comprehension of cancer biology and is enabling the arrival of personalized, predictive and precision medicine to rare tumors like 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.

Cdk5 drives formation of heterogeneous pancreatic neuroendocrine tumors

Pancreatic neuroendocrine tumors (PanNETs) are a heterogeneous population of neoplasms that arise from hormone-secreting islet cells of the pancreas and have increased markedly in incidence over the past four decades. Non-functional PanNETs, which occur more frequently than hormone-secreting tumors, are often not diagnosed until later stages of tumor development and have poorer prognoses. Development of successful therapeutics for PanNETs has been slow, partially due to a lack of diverse animal models for pre-clinical testing. Here, we report development of an inducible, conditional mouse model of PanNETs by using a bi-transgenic system for regulated expression of the aberrant activator of Cdk5, p25, specifically in β-islet cells. This model produces a heterogeneous population of PanNETs that includes a subgroup of well-differentiated, non-functional tumors. Production of these tumors demonstrates the causative potential of aberrantly active Cdk5 for generation of PanNETs. Further, we show that human PanNETs express Cdk5 pathway components, are dependent on Cdk5 for growth, and share genetic and transcriptional overlap with the INS-p25OE model. The utility of this model is enhanced by the ability to form tumor-derived allografts. This new model of PanNETs will facilitate molecular delineation of Cdk5-dependent PanNETs and the development of new targeted therapeutics.

Exploring the Epigenome in Gastroenteropancreatic Neuroendocrine Neoplasias

Gastroenteropancreatic neuroendocrine neoplasias are a diverse group of neoplasms with different characteristics in terms of site, biological behaviour and metastatic potential. In comparison to other cancers, they are genetically quiet, harbouring relatively few somatic mutations. It is increasingly becoming evident that epigenetic changes are as relevant, if not more so, as somatic mutations in promoting oncogenesis. Despite significant tumour heterogeneity, it is obvious that DNA methylation, histone and chromatin modifications and microRNA expression profiles are distinctive for GEP-NEN subtypes and may correlate with clinical outcome. This review summarises existing knowledge on epigenetic changes, identifying potential contributions to pathogenesis and oncogenesis. In particular, we focus on epigenetic changes pertaining to well-differentiated neuroendocrine tumours, which make up the bulk of NENs. We also highlight both similarities and differences within the subtypes of GEP-NETs and how these relate and compare to other types of cancers. We relate epigenetic understanding to existing treatments and explore how this knowledge may be exploited in the development of novel treatment approaches, such as in theranostics and combining conventional treatment modalities. We consider potential barriers to epigenetic research in GEP-NENs and discuss strategies to optimise research and development of new therapies.

A multigenomic liquid biopsy biomarker for neuroendocrine tumor disease outperforms CgA and has surgical and clinical utility

BACKGROUND

Biomarkers are key tools in cancer management. In neuroendocrine tumors (NETs), Chromogranin A (CgA) was considered acceptable as a biomarker. We compared the clinical efficacy of a multigenomic blood biomarker (NETest) to CgA over a 5-year period.

PATIENTS AND METHODS

An observational, prospective, cross-sectional, multicenter, multinational, comparative cohort assessment. Cohort 1: NETest evaluation in NETs (n = 1684) and cancers, benign diseases, controls (n = 731). Cohort 2: (n = 1270): matched analysis of NETest/CgA in a sub-cohort of NETs (n = 922) versus other diseases and controls (n = 348). Disease status was assessed by response evaluation criteria in solid tumors (RECIST). NETest measurement: qPCR [upper limit of normal (ULN: 20)], CgA (EuroDiagnostica, ULN: 108 ng/ml).

STATISTICS

Mann-Whitney U-test, AUROC, chi-square and McNemar' test.

RESULTS

Cohort 1: NETest diagnostic accuracy was 91% (P < 0.0001) and identified pheochromocytomas (98%), small intestine (94%), pancreas (91%), lung (88%), gastric (80%) and appendix (79%). NETest reflected grading: G1: 40 ± 1, G2 (50 ± 1) and G3 (52 ± 1). Locoregional disease levels were lower (38 ± 1) than metastatic (52 ± 1, P < 0.0001). NETest accurately stratified RECIST-assessed disease extent: no disease (21 ± 1), stable (43 ± 2), progressive (62 ± 2) (P < 0.0001). NETest concordance with imaging (CT/MRI/⁶⁸Ga-SSA-PET) 91%. Presurgery, all NETs (n = 153) were positive (100%). After palliative R1/R2 surgery (n = 51) all (100%) remained elevated. After curative R0-surgery (n = 102), NETest levels were normal in 81 (70%) with no recurrence at 2 years. In the 31 (30%) with elevated levels, 25 (81%) recurred within 2 years. Cohort #2: NETest diagnostic accuracy was 87% and CgA 54% (P < 0.0001). NETest was more accurate than CgA for grading (chi-square = 7.7, OR = 18.5) and metastatic identification (chi-square = 180, OR = 8.4). NETest identified progressive disease (95%) versus CgA (57%, P < 0.0001). Imaging concordance for NETest was 91% versus CgA (46%) (P < 0.0001). Recurrence prediction after surgery was NETest-positive in >94% versus CgA 11%.

CONCLUSION

NETest accurately diagnoses NETs and is an effective surrogate marker for imaging, grade, metastases and disease status compared to CgA. A multigenomic liquid biopsy is an accurate biomarker of NET disease.

PI3K/mTOR Dual Inhibitor PF-04691502 Is a Schedule-Dependent Radiosensitizer for Gastroenteropancreatic Neuroendocrine Tumors

Patients with advanced-stage gastroenteropancreatic neuroendocrine tumors (GEP-NETs) have a poor overall prognosis despite chemotherapy and radiotherapy (e.g., peptide receptor radionuclide therapy (PRRT)). Better treatment options are needed to improve disease regression and patient survival. The purpose of this study was to examine a new treatment strategy by combining PI3K/mTOR dual inhibition and radiotherapy. First, we assessed the efficacy of two PI3K/mTOR dual inhibitors, PF-04691502 and PKI-402, to inhibit pAkt and increase apoptosis in NET cell lines (BON and QGP-1) and patient-derived tumor spheroids as single agents or combined with radiotherapy (XRT). Treatment with PF-04691502 decreased pAkt (Ser473) expression for up to 72 h compared with the control; in contrast, decreased pAkt expression was noted for less than 24 h with PKI-402. Simultaneous treatment with PF-04691502 and XRT did not induce apoptosis in NET cells; however, the addition of PF-04691502 48 h after XRT significantly increased apoptosis compared to PF-04691502 or XRT treatment alone. Our results demonstrate that schedule-dependent administration of a PI3K/mTOR inhibitor, combined with XRT, can enhance cytotoxicity by promoting the radiosensitivity of NET cells. Moreover, our findings suggest that radiotherapy, in combination with timed PI3K/mTOR inhibition, may be a promising therapeutic regimen for patients with GEP-NET.

Evaluation of circulating transcript analysis (NETest) in small intestinal neuroendocrine neoplasms after surgical resection

PURPOSE

Surgical resection is the only effective curative strategy for small intestinal neuroendocrine neoplasms (SINENs). Nevertheless, the evaluation of residual disease and prediction of disease recurrence/progression remains a problematic issue.

METHODS

We evaluated 13 SINENs that underwent surgical resection of the primary tumour and/or mesenteric mass. Patients were divided in three groups: (a) Group 1: SINENs that underwent resection with curative intent, (b) Group 2: SINENs treated with resection in the setting of metastatic disease, which remained stable and (c) Group 3: SINENs treated with resection in the setting of metastatic disease, with evidence of any progression at follow-up. NETest and chromogranin A were measured pre-operatively and post-operatively during a 22-month median follow-up period and compared with imaging studies. NETest score <20% was determined as normal, 20-40% low, 41-79% intermediate and ≥80% high score.

RESULTS

NETest score was raised in all (100%) SINENs pre-operatively. Surgery with curative intent resulted in NETest score reduction from 78.25 ± 15.32 to 25.25 ± 1.75 (p < 0.05). Low NETest scores post-operatively were evident in all cases without clinical evidence of residual disease (Group 1). However, the low disease activity score suggested the presence of microscopic residual disease. In three cases (75%) with stable disease (Group 2) the NETest score was low consistent with indolent disease. In the progressive disease group (Group 3), a high NETest score was present in three cases (60%) and an intermediate NETest score in the remainder (40%).

CONCLUSIONS

Blood NETest scores accurately identified SINENs and were significantly decreased by curative surgery. Monitoring NETest post-operatively may facilitate management by identifying the presence of residual/progressive disease.

An Update on Gastroenteropancreatic Neuroendocrine Neoplasms: From Mysteries to Paradigm Shifts

Although neuroendocrine neoplasms (NEN) were once thought to be rare and mostly "benign" diseases, they are now being redefined in light of recently discovered molecular information. NENs constitute a spectrum of variably differentiated neoplasms, ranging from well-differentiated tumors with a protracted course over many years to very aggressive neuroendocrine carcinomas. Although the majority of NEN are non-functional lesions, some of these tumors, do produce a hormonal hypersecretion syndrome. Their reappraisal has led scientist to unveil previously unknown oncogenic pathways and connections that resulted in a new category in the International Classification of Diseases (ICD-11) and a revised version of the World Health Organization Classification (WHO 2018). Complex diseases like NEN require a multidisciplinary approach that includes the perspectives of endocrinologists, medical and surgical oncologists, radiation oncologists, imaging specialists and pathologists. There are currently virtually thousands of ongoing trials evaluating the efficacy and safety of several molecular targeted therapies. The purpose of this review was to critically evaluate recent information regarding the pathogenesis, diagnosis and treatment of NEN.

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.

Circulating Neuroendocrine Gene Transcripts (NETest): A Postoperative Strategy for Early Identification of the Efficacy of Radical Surgery for Pancreatic Neuroendocrine Tumors

BACKGROUND

Surgery remains the only treatment for the cure of pancreatic neuroendocrine tumors (PanNETs). Biomarkers to identify the completeness of resection and predict recurrence are lacking.

OBJECTIVE

The aims of this study were to evaluate if the blood measurement of neuroendocrine gene transcripts (NETest) was diagnostic of PanNETs, and whether NETest blood levels could identify complete resection. We compared transcript analysis with the biomarker chromogranin A (CgA).

METHODS

This was a prospective, longitudinal, single-center study including 30 patients with a postoperative histological confirmation of PanNET. Blood for NETest and CgA was collected preoperatively and on postoperative day (POD) 1, POD5, and POD30. Transcripts were measured by real-time quantitative reverse transcription polymerase chain reaction and multianalyte algorithmic analysis (NETest; normal < 20), and CgA was measured by enzyme-linked immunosorbent assay (ELISA; normal < 109 ng/mL). Data are expressed as mean ± standard deviation (SD).

RESULTS

Pancreatic surgical resections (n = 30) were R0, 26; R1, 2; and R2, 2. Preoperatively, NETest score was elevated in all 30 patients (44.7 ± 27), but postoperatively, NETest scores significantly decreased (p = 0.006) to POD30 (24.7 ± 24). The proportion of patients (15/30) with an elevated score significantly decreased by POD30 (p < 0.0001). CgA levels were elevated preoperatively (184 ± 360 ng/mL) in only 9/30 patients, but did not decrease significantly postoperatively at POD30 (260 ± 589 ng/mL, p = 0.398). The number of patients with elevated CgA levels remained unchanged (9/30).

CONCLUSIONS

The NETest is an accurate diagnostic biomarker for PanNETs (100%). A decrease in NETest levels after radical resection suggests this blood test provides early assessment of surgical efficacy. CgA had no clinical utility.

EPB41L5 is Associated With the Metastatic Potential of Low-grade Pancreatic Neuroendocrine Tumors

BACKGROUND/AIM

Low-grade pancreatic neuroendocrine tumors (LG-PNETs) behave unpredictably. The aim of the study was to identify biomarkers that predict PNET metastasis to improve treatment selection.

PATIENTS AND METHODS

Five patients with primary non-metastatic LG-PNETs, six with primary LG-PNETs with synchronous or metachronous metastases (M-PNETs), and six metastatic to liver LG-PNETs (ML-PNETs) from the group of six M-PNET patients were selected. RNA data were normalized using iterative rank-order normalization. Student's t-test identified differentially-expressed genes in LG-PNETs versus M-PNETs. A 2-fold difference in expression was considered to be significant. Results were validated with an independent dataset of LG-PNETs and metastatic LG-PNETs.

RESULTS

Overall, 195 genes had a >2-fold change (in either direction). A total of 29 genes were differentially overexpressed in M-PNETs. Erythrocyte membrane protein band 4.1-like 5 (EPB41L5) had a 2.07-fold change increase in M-PNETs and the smallest p-value. EPB41L5 was not statistically different between M-PNETs and ML-PNETs. EPB41L5 differential expression between primary and metastatic LG-PNETs was confirmed by immunohistochemistry.

CONCLUSION

These results support further investigation into whether EPB41L5 is a biomarker of PNETs with high risk for metastases.

Anti-tumour activity of everolimus and sunitinib in neuroendocrine neoplasms

Comparisons between everolimus and sunitinib regarding their efficacy and safety in neuroendocrine neoplasms (NENs) are scarce. We retrospectively analysed the clinicopathological characteristics and outcomes in 92 patients with well-differentiated (WD) NEN of different origin (57 pancreatic NENs (PanNENs)), treated with molecular targeted therapy (MTT) with everolimus or sunitinib, first- (73:19) or second-line (sequential; 12:22) for progressive disease. Disease control rates (DCR: partial response or stable disease) at first-line were higher in all patients treated with everolimus than sunitinib (64/73 vs 12/19, P = 0.012). In PanNENs, DCR at first-line everolimus was 36/42 versus 9/15 with sunitinib (P = 0.062). Progression-free survival (PFS) at first-line everolimus was longer than sunitinib (31 months (95% CI: 23.1-38.9) vs 9 months (95% CI: 0-18.5); log-rank P < 0.0001) in the whole cohort and the subset of PanNENs (log-rank P < 0.0001). Median PFS at second-line MTT was 12 months with everolimus (95% CI: 4.1-19.9) vs 13 months with sunitinib (95% CI: 9.3-16.7; log-rank P = 0.951). Treatment with sunitinib (HR: 3.47; 95% CI: 1.5-8.3; P value: 0.005), KI67 >20% (HR: 6.38; 95% CI: 1.3-31.3; P = 0.022) and prior chemotherapy (HR: 2.71; 95% CI: 1.2-6.3; P = 0.021) were negative predictors for PFS at first line in multivariable and also confirmed at multi-state modelling analyses. Side effect (SE) analysis indicated events of serious toxicities (Grades 3 and 4: n = 13/85 for everolimus and n = 4/41 for sunitinib). Discontinuation rate due to SEs was 20/85 for everolimus versus 4/41 for sunitinib (P = 0.065). No additive toxicity of second-line MTT was confirmed. Based on these findings, and until reliable predictors of response become available, everolimus may be preferable to sunitinib when initiating MTT in progressive NENs.

The landscape of molecular alterations in pancreatic and small intestinal neuroendocrine tumours

Gastroenteropancreatic Neuroendocrine Neoplasms (GEP-NENs) arise throughout the gut and feature varying biological behaviour and malignant potential. GEP-NENs include two genetically different entities, well-differentiated neuroendocrine tumours (NETs) and poorly differentiated neuroendocrine carcinomas (NEC). NECs are characterized by a dismal prognosis and by distinctive TP53 and RB1 inactivation which sets them apart from NETs. The latter, conversely, have a wide spectrum of aggressiveness and molecular alterations. Knowledge on their biology has recently expanded thanks to high-throughput studies focused on two important groups of well-differentiated neuroendocrine neoplasms: pancreatic (PanNETs) and small intestinal (SiNETs) tumours. PanNETs have been among the most studied also due to genetic syndromes featuring their onset. Research stemming from this observation has uncovered the inactivation of MEN1, VHL, TSC1/2, and the hyperactivation of the PI3K/mTOR pathway as distinctive biological features of these neoplasms. Next-Generation Sequencing added information on the role of telomere lengthening via ATRX/DAXX inactivation in a fraction of PanNETs, while other display shortened telomeres and recurrent chromosomal alterations. The data so far disclosed a heterogeneous combination of driver events, yet converging into four pathways including DNA damage repair, cell cycle regulation, PI3K/mTOR signalling and telomere maintenance. SiNETs showed a lesser relationship with mutational driver events, even in the case of familial cases. High throughput studies identified putative driver mutations in CDKN1 and APC which, however, were reported in a minor fraction (∼10%) of cases. Tumorigenesis of SiNETs seems to depend more on chromosomal alterations (loss of chromosome 8, gains at 4, 5 and 20) and epigenetic events, which converge to hyperactivate the PI3K/mTOR, MAPK and Wnt pathways. While calling for further integrative studies, these data lay previous and recent findings in a more defined frame and provide clinical research with several candidate markers for patient stratification and companion diagnostics.

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.

Advances in the cytologic diagnosis of gastroenteropancreatic neuroendocrine neoplasms

Two-thirds of neuroendocrine neoplasms arising in the human body originate from the gastrointestinal system or pancreas. Gastroenteropancreatic neuroendocrine neoplasms are heterogeneous, comprising both well differentiated neuroendocrine tumors (NETs) and poorly differentiated neuroendocrine carcinomas (NECs). The clinical presentation, molecular characteristics, and behavior are distinct for NETs and NECs. Fine-needle aspiration is an important modality for the primary diagnosis and staging of these neoplasms and can provide information of prognostic and therapeutic significance. Our evolving understanding of neuroendocrine neoplasm biology has led to several iterations of classification. In this review, new concepts and issues most relevant to cytology diagnosis of gastroenteropancreatic neuroendocrine neoplasms are discussed, such as newer detection methods that aid in diagnosis and staging, recent changes in World Health Organization classification, practical issues related to grading these neoplasms on cytology, guidelines for diagnostic reporting, and panels of immunohistochemical stains for the diagnosis of metastasis. The current understanding of genetic and epigenetic events related to tumor development and potential applications for cytology also are presented as they relate to prognostication and recent therapeutic advances.

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.

Ghrelin-O-Acyltransferase (GOAT) Enzyme as a Novel Potential Biomarker in Gastroenteropancreatic Neuroendocrine Tumors

OBJECTIVES

The association between the presence and alterations of the components of the ghrelin system and the development and progression of neuroendocrine tumors (NETs) is still controversial and remains unclear.

METHODS

Here, we systematically evaluated the expression levels (by quantitative-PCR) of key ghrelin system components of in gastroenteropancreatic (GEP)-NETs, as compared to non-tumor adjacent (NTA; n = 42) and normal tissues (NT; n = 14). Then, we analyzed their putative associations with clinical-histological characteristics.

RESULTS

The results indicate that ghrelin and its receptor GHSR1a are present in a high proportion of normal tissues, while the enzyme ghrelin-O-acyltransferase (GOAT) and the splicing variants In1-ghrelin and GHSR1b were present in a lower proportion of normal tissues. In contrast, all ghrelin system components were present in a high proportion of tumor and NTA tissues. GOAT was significantly overexpressed (by quantitative-PCR (qPCR)) in tumor samples compared to NTA, while a trend was found for ghrelin, In1-ghrelin and GHSR1a. In addition, expression of these components displayed significant correlations with key clinical parameters. The marked overexpression of GOAT in tumor samples compared to NTA regions was confirmed by IHC, revealing that this enzyme is particularly overexpressed in gastrointestinal NETs, where it is directly correlated with tumor diameter.

CONCLUSIONS

These results provide novel information on the presence and potential pathophysiological implications of the ghrelin system components in GEP-NETs, wherein GOAT might represent a novel diagnostic biomarker.

Molecular Genetic Studies of Pancreatic Neuroendocrine Tumors: New Therapeutic Approaches

Pancreatic neuroendocrine tumors (PNETs) arise sporadically or as part of familial syndromes. Genetic studies of hereditary syndromes and whole exome sequencing analysis of sporadic NETs have revealed the roles of some genes involved in PNET tumorigenesis. The multiple endocrine neoplasia type 1 (MEN1) gene is most commonly mutated. Its encoded protein, menin, has roles in transcriptional regulation, genome stability, DNA repair, protein degradation, cell motility and adhesion, microRNA biogenesis, cell division, cell cycle control, and epigenetic regulation. Therapies targeting epigenetic regulation and MEN1 gene replacement have been reported to be effective in preclinical models.

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.

Genomic landscape of pancreatic neuroendocrine tumours: the International Cancer Genome Consortium

Neuroendocrine tumours (NETs) may arise throughout the body and are a highly heterogeneous, relatively rare class of neoplasms difficult to study also for the lack of disease models. Despite this, knowledge on their molecular alterations has expanded in the latest years, also building from genetic syndromes causing their onset. Pancreatic NETs (PanNETs) have been among the most studied, and research so far has outlined a series of recurring features, as inactivation of MEN1, VHL, TSC1/2 genes and hyperactivation of the PI3K/mTOR pathway. Next-generation sequencing has added new information by showing the key role of alternative lengthening of telomeres, driven in a fraction of PanNETs by inactivation of ATRX/DAXX. Despite this accumulation of knowledge, single studies often relied on few cases or were limited to the DNA, RNA, protein or epigenetic level with lack of integrative analysis. The International Cancer Genome Consortium aimed at removing these barriers through a strict process of data and samples collection, to produce whole-genome integrated analyses for many tumour types. The results of this effort on PanNETs have been recently published and, while confirming previous observations provide a first snapshot of how heterogeneous is the combination of genetic alterations that drive this tumour type, yet converging into four pathways whose alteration has been enriched by newly discovered mechanisms. While calling for further integration of genetic and epigenetic analyses, these data allow to reconcile previous findings in a defined frame and may provide clinical research with markers for patients stratification and to guide targeted therapy decisions.

Clinical and functional implication of the components of somatostatin system in gastroenteropancreatic neuroendocrine tumors

PURPOSE

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) comprise a heterogeneous group of malignancies often presenting with metastasis at diagnosis and whose clinical outcome is difficult to predict. Somatostatin (SST) analogs (SSAs) provide a valuable pharmacological tool to palliate hormonal symptoms, and control progression in some NETs. However, many patients do not respond to SSAs or develop resistance, and there are many uncertainties regarding pathophysiology of SST and its receptors (sst1-sst5) in GEP-NETs.

METHODS

The expression of SST system components in GEP-NETs was determined, compared with that of non-tumor adjacent and normal tissues and correlated with clinical and histological characteristics. Specifically, 58 patients with GEP-NETs and 14 normal samples were included. Cell viability in NET cell lines was determined in response to specific SSAs.

RESULTS

Normal samples and non-tumor adjacent tissues presented a similar expression profile, with appreciable expression of sst2 and sst3, and a lower expression of the other receptors. In contrast, cortistatin, sst1, sst4, and sst5 were overexpressed in tumors, while sst3 and sst4 seemed overexpressed in less differentiated tumors. Some SST system components were related to vascular/nerve invasion and metastasis. In vitro, sst1 and sst3 agonists reduced viability in BON-1 cells, while they, similar to octreotide and pasireotide, increased viability in QGP-1 cells.

CONCLUSIONS

These results provide novel information on SST system pathophysiology in GEP-NETs, including relevant associations with clinical-histological parameters, which might help to better understand the intrinsic heterogeneity of NETs and to identify novel biomarkers and/or targets with potential prognostic and/or therapeutic value for GEP-NETs patients.