Expression of somatostatin receptors 2 and 5 in circulating tumour cells from patients with neuroendocrine tumours

PET imaging of [52 Mn]Mn-DOTATATE and [52 Mn]Mn-DOTA-JR11

Manganese-52 is gaining interest as an isotope for PET imaging due to its desirable decay and chemical properties for radiopharmaceutical development. Somatostatin receptor 2 (SSTR2) is significantly overexpressed by neuroendocrine tumors (NETs) and is an important target for nuclear imaging and therapy. As an agonist, [68Ga]Ga-DOTATATE has demonstrated significant internalization upon interaction with receptor ligands, whereas [68Ga]Ga-DOTA-JR11(as an antagonist) exhibits limited internalization but better pharmacokinetics and increased tumor uptake. The goal of this study was to label both DOTATATE and DOTA-JR11 peptides with 52Mn in high radiochemical yields (RCY) and sufficient specific activity. A comparison of these two compounds was performed in in vitro and in vivo studies in animals with somatostatin receptor-positive xenografts to characterize differences in cell, tumor, and tissue uptake. Radiolabeling of DOTATATE and DOTA-JR11 was carried out by combining varying concentrations of the peptides with [52Mn]MnCl2. In vitro stability of the radiotracers was determined in mouse serum. In vitro cell uptake and internalization assays were performed in SSTR2 + AR42J cells and negative controls. In vivo biodistribution and longitudinal PET imaging was evaluated in mice bearing AR42J tumors. Both [52Mn]Mn-DOTATATE and [52Mn]Mn-DOTA-JR11showed affinity for SSTR2 in AR42J cells. However, the uptake of [52Mn]Mn-DOTATATE was higher (11.95 ± 0.71%/ mg) compared to [52Mn]Mn-DOTA-JR11 (7.31 ± 0.38%/ mg) after 2 h incubation. After 4 h incubation, 53.13 ± 1.83% of the total activity of [52Mn]Mn-DOTATATE was internalized, whereas only 20.85 ± 0.59% of the total activity of [52Mn]Mn-DOTA-JR11 was internalized. The PET images revealed similar biodistribution results, with [52Mn]Mn-DOTATATE showing a significant tumor uptake of 11.16 ± 2.97% ID/g, while [52Mn]Mn-DOTA-JR11 exhibited a lower tumor uptake of 2.11 ± 0.30% ID/g 4 h post-injection. The synthesis of both radiotracers was accomplished with high RCY and purity. The cell uptake and internalization of [52Mn]Mn-DOTATATE showed higher levels compared to [52Mn]Mn-DOTA-JR11. PET images of the radiotracers in AR42J tumor bearing mice demonstrated similar biodistribution in all organs except the tumor, with [52Mn]Mn-DOTATATE showing higher tumor uptake compared to [52Mn]Mn-DOTA-JR11. The variations in properties of these tracers could be used to guide further imaging and treatment studies.

Dosimetry and pharmacokinetics of [177Lu]Lu-satoreotide tetraxetan in patients with progressive neuroendocrine tumours

PURPOSE

To evaluate the dosimetry and pharmacokinetics of the novel radiolabelled somatostatin receptor antagonist [177Lu]Lu-satoreotide tetraxetan in patients with advanced neuroendocrine tumours (NETs).

METHODS

This study was part of a phase I/II trial of [177Lu]Lu-satoreotide tetraxetan, administered at a median cumulative activity of 13.0 GBq over three planned cycles (median activity/cycle: 4.5 GBq), in 40 patients with progressive NETs. Organ absorbed doses were monitored at each cycle using patient-specific dosimetry; the cumulative absorbed-dose limits were set at 23.0 Gy for the kidneys and 1.5 Gy for bone marrow. Absorbed dose coefficients (ADCs) were calculated using both patient-specific and model-based dosimetry for some patients.

RESULTS

In all evaluated organs, maximum [177Lu]Lu-satoreotide tetraxetan uptake was observed at the first imaging timepoint (4 h after injection), followed by an exponential decrease. Kidneys were the main route of elimination, with a cumulative excretion of 57-66% within 48 h following the first treatment cycle. At the first treatment cycle, [177Lu]Lu-satoreotide tetraxetan showed a median terminal blood half-life of 127 h and median ADCs of [177Lu]Lu-satoreotide tetraxetan were 5.0 Gy/GBq in tumours, 0.1 Gy/GBq in the bone marrow, 0.9 Gy/GBq in kidneys, 0.2 Gy/GBq in the liver and 0.8 Gy/GBq in the spleen. Using image-based dosimetry, the bone marrow and kidneys received median cumulative absorbed doses of 1.1 and 10.8 Gy, respectively, after three cycles.

CONCLUSION

[177Lu]Lu-satoreotide tetraxetan showed a favourable dosimetry profile, with high and prolonged tumour uptake, supporting its acceptable safety profile and promising efficacy.

TRIAL REGISTRATION

NCT02592707. Registered October 30, 2015.

A Neuroendocrine Tumor of Unknown Primary Origin: A Case Report and Review of the Literature

Neuroendocrine tumors (NETs) are uncommon malignancies that develop from neuroendocrine cells which most commonly occur in the GI tract, lung, and pancreas. Treatment courses for these tumors are largely dictated by the primary origin site, which can present diagnostic and therapeutic challenges in NETs of unknown primary origin. Herein, we present a case of an NET of unknown primary origin with significant liver metastases. Our aim is to highlight the key components of the workup of NETs of unknown primary origin and detail the biochemical, histopathological, and imaging modalities as recommended by current literature. We highlight the importance of a multidisciplinary approach to both diagnosis and treatment of these patients as well as touch upon therapeutic options.

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

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

The Molecular Biology of Midgut Neuroendocrine Neoplasms

Midgut neuroendocrine neoplasms (NENs) are one of the most common subtypes of NEN, and their incidence is rising globally. Despite being the most frequently diagnosed malignancy of the small intestine, little is known about their underlying molecular biology. Their unusually low mutational burden compared to other solid tumors and the unexplained occurrence of multifocal tumors makes the molecular biology of midgut NENs a particularly fascinating field of research. This review provides an overview of recent advances in the understanding of the interplay of the genetic, epigenetic, and transcriptomic landscape in the development of midgut NENs, a topic that is critical to understanding their biology and improving treatment options and outcomes for patients.

Circulating Tumor Cells: How Far Have We Come with Mining These Seeds of Metastasis?

Circulating tumor cells (CTCs) are cancer cells that slough off from the tumor and circulate in the peripheral blood and lymphatic system as micro metastases that eventually results in macro metastases. Through a simple blood draw, sensitive CTC detection from clinical samples has proven to be a useful tool for determining the prognosis of cancer. Recent technological developments now make it possible to detect CTCs reliably and repeatedly from a simple and straightforward blood test. Multicenter trials to assess the clinical value of CTCs have demonstrated the prognostic value of these cancer cells. Studies on CTCs have filled huge knowledge gap in understanding the process of metastasis since their identification in the late 19th century. However, these rare cancer cells have not been regularly used to tailor precision medicine and or identify novel druggable targets. In this review, we have attempted to summarize the milestones of CTC-based research from the time of identification to molecular characterization. Additionally, the need for a paradigm shift in dissecting these seeds of metastasis and the possible future avenues to improve CTC-based discoveries are also discussed.

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

OPINION STATEMENT

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

Precision medicine in gastroenteropancreatic neuroendocrine neoplasms: Where are we in 2023?

Precision medicine describes a target-related approach to tailoring diagnosis and treatment of the individual patient. While this personalized approach is revoluzionizing many areas of oncology, it is quite late in the field of gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs), in which there are few molecular alterations to be therapeutically targeted. We critically reviewed the current evidence about precision medicine in GEP NENs, focusing on potential clinically relevant actionable targets for GEP NENs, such as the mTOR pathway, MGMT, hypoxia markers, RET, DLL-3, and some general agnostic targets. We analysed the main investigational approaches with solid and liquid biopsies. Furthermore, we reviewed a model of precision medicine more specific for NENs that is the theragnostic use of radionuclides. Overall, currently no true predictive factors for therapy have been validated so far in GEP NENs, and the personalized approach is based more on clinical thinking within a NEN-dedicated multidisciplinary team. However, there is a robust background to suppose that precision medicine, with the theragnostic model will yield new insights in this context soon.

Octreotide and Octreotide-derived delivery systems

Pharmaceutical peptide Octreotide is a somatostatin analog with targeting and therapeutic abilities. Over the last decades, Octreotide has been developed and approved to treat acromegaly and neuroendocrine tumours, and Octreotide-based radioactive conjugates have been leveraged clinically to detect small neuroendocrine tumour sites. Meanwhile, variety of Octreotide-derived delivery strategies have been proposed and explored for tumour targeted therapeutics or diagnostics in preclinical or clinical settings. In this review, we especially focus on the preclinical development and applications of Octreotide-derived drug delivery systems, diagnostic nanosystems, therapeutic nanosystems and multifunctional nanosystems, we also briefly discuss challenges and prospects of these Octreotide-derived delivery systems.

Risk Stratification of Pancreatic Neuroendocrine Neoplasms Based on Clinical, Pathological, and Molecular Characteristics

Pancreatic neuroendocrine neoplasms consist of heterogeneous diseases. Depending on the novel features detected by various modern technologies, their classification and related prognosis predictions continue to change and develop. The role of traditional clinicopathological prognostic factors, including classification systems, is also being refined, and several attempts have been made to predict a more accurate prognosis through novel serum biomarkers, genetic factors, and epigenetic factors that have been identified through various state-of-the-art molecular techniques with multiomics sequencing. In this review article, the latest research results including the traditional approach to prognostic factors and recent advanced strategies for risk stratification of pancreatic neuroendocrine neoplasms based on clinical, pathological, and molecular characteristics are summarized. Predicting prognosis through multi-factorial assessments seems to be more efficacious, and prognostic factors through noninvasive methods are expected to develop further advances in liquid biopsy in the future.

Spatiotemporal heterogeneity and clinical challenge of pancreatic neuroendocrine tumors

During the course of pancreatic neuroendocrine tumors (NETs), they generally become more heterogeneous with individual cells exhibiting distinct molecular fingerprints. This heterogeneity manifests itself through an unequal distribution of genetically-variant, tumor cell subpopulations within disease locations (i.e., spatial heterogeneity) or changes in the genomic landscape over time (i.e., temporal heterogeneity); these characteristics complicate clinical diagnosis and treatment. Effective, feasible tumor heterogeneity detection and eradication methods are essential to overcome the clinical challenges of pancreatic NETs. This review explores the molecular fingerprints of pancreatic NETs and the spectrum of tumoral heterogeneity. We then describe the challenges of assessing heterogeneity by liquid biopsies and imaging modalities and the therapeutic challenges for pancreatic NETs. In general, navigating these challenges, refining approaches for translational research, and ultimately improving patient care are available once we have a better understanding of intratumoral spatiotemporal heterogeneity.

Well-Differentiated Grade 3 Neuroendocrine Tumors: Characteristics, Treatments, and Outcomes From a Population-Based Study

OBJECTIVES

We evaluated a population-based cohort of metastatic well-differentiated grade 3 gastroenteropancreatic neuroendocrine tumors (G3 NETs) to describe their characteristics, prognosis, and treatment outcomes.

METHODS

The British Columbia provincial database was queried for G3 NETs diagnosed 2004 to 2021, and charts were reviewed to describe clinical features and outcomes.

RESULTS

Forty-one patients were identified, most were diagnosed with pancreatic (58.5%) or midgut (26.8%) primary tumor and Ki-67 was less than 55% in 68.3%. The primary was resected in 19 (46.3%) with median disease-free survival of 25.2 months. Once metastatic, patients received a median of one line of systemic therapy. Median overall survival with metastatic disease was 33.8 months. Median progression-free survival was longest in patients treated with capecitabine-temozolomide (20.6 months) or somatostatin analogs (7.9 months), while etoposide-platinum provided little benefit (2.4 months). Limited data of efficacy for targeted therapies and radionuclide therapy was available. Seven patients (17.1%) were also treated with local therapies, which were associated with improved overall survival (median not reached, hazard ratio, 0.23; P = 0.012).

CONCLUSIONS

Capecitabine-temozolomide and somatostatin analogs were associated with clinically meaningful benefit, and use of local therapies provided benefits in selected patients. Multidisciplinary discussion is essential to optimize individual outcomes in this heterogeneous population.

Mixed neuroendocrine-non-neuroendocrine neoplasm associated with autoimmune gastritis

A 60-year-old woman presented with a protruding tumor at the anterior wall of the middle gastric body, and she was positive for anti-parietal cells antibodies with elevated serum gastrin level. Final diagnosis was a mixed neuroendocrine-non-neuroendocrine neoplasm consisting of adenocarcinoma (tub1) and neuroendocrine tumor G2 with autoimmune gastritis.

Perspectives on the diagnostic, predictive and prognostic markers of neuroendocrine neoplasms (Review)

Neuroendocrine neoplasms (NENs) are a heterogeneous group of rare tumors with different types of physiology and prognosis. Therefore, prognostic information, including morphological differentiation, grade, tumor stage and primary location, are invaluable and contribute to the formulation of treatment decisions. Biomarkers that are currently used, including chromogranin A (CgA), serotonin and neuron-specific enolase, are singular parameters that cannot be used to accurately predict variables associated with tumor growth, including proliferation, metabolic rate and metastatic potential. In addition, site-specific biomarkers, such as insulin and gastrin, cannot be applied to all types of NENs. The clinical application of broad-spectrum markers, as it is the case for CgA, remains controversial despite being widely used. Due to limitations of the currently available mono-analyte biomarkers, recent studies were conducted to explore novel parameters for NEN diagnosis, prognosis, therapy stratification and evaluation of treatment response. Identification of prognostic factors for predicting NEN outcome is a critical requirement for the planning of adequate clinical management. Advances in ‘liquid’ biopsies and genomic analysis techniques, including microRNA, circulating tumor DNA or circulating tumor cells and sophisticated biomathematical analysis techniques, such as NETest or molecular image-based biomarkers, are currently under investigation as potentially novel tools for the management of NENs in the future. Despite these recent findings yielding promising observations, further research is necessary. The present review therefore summarizes the existing knowledge and recent advancements in the exploration of biochemical markers for NENs, with focus on gastroenteropancreatic-neuroendocrine tumors.

Somatostatin receptor 2 is highly sensitive and specific for Epstein-Barr virus-associated nasopharyngeal carcinoma

Viruses are known drivers of head and neck squamous cell carcinomas (HNSCC), particularly Epstein-Barr virus (EBV) and human papillomavirus (HPV). Both EBV-positive nasopharyngeal carcinoma (EBVNPC) and HPV-positive oropharyngeal SCC (OPSCC) can have overlapping histomorphology and molecular signatures, including nuclear factor kappa-light-chain-enhancer of activated B cells (NFKB) pathway mutations. A recent study showed that NFKB activation in EBVNPC drives somatostatin receptor 2 (SSTR2) expression that is detectable by immunohistochemistry and by imaging with 68-Gadolinium-DOTA-peptide radioconjugate. However, whether a similar NFKB-SSTR2 signaling mechanism exists for other virus-positive HNSCC, namely HPV-positive sinonasal carcinomas and OPSCC, remains unclear. Here we examined SSTR2 expression in a cohort of EBV-positive, HPV-positive, and virus-negative HNSCC with immunohistochemistry. SSTR2 immunohistochemistry was performed on our cohort of primary and/or metastatic EBVNPC, HPV-positive sinonasal SCC, OPSCC, HPV-negative sinonasal and oral cavity SCC, and benign tonsil and adenoid tissue. For SSTR2 staining, the extent was categorized as focal, multifocal, or diffuse, and the intensity was categorized as weak, moderate, or strong. Multifocal/diffuse SSTR2 staining of any intensity was considered positive. Among primary, recurrent, and/or undifferentiated NPC, 90% showed multifocal to diffuse strong SSTR2 expression. One HPV-positive sinonasal carcinoma showed patchy SSTR2 staining. None of the remaining HPV-positive sinonasal carcinomas, OPSCC, or oral cavity HNSCC showed significant SSTR2 staining. Overall, SSTR2 is highly sensitive and specific for EBVNPC and could represent a surrogate biomarker. Among HNSCC assessed here, we recommend testing primary NPC for SSTR2 because of its relevance for diagnosis, associated imaging modalities, and its therapeutic implications for patient care.

Recent Advances in Herbal Nanomedicines for Cancer Treatment

Cancer continues to be one of the deadliest diseases that adversely impacts the large population of the world. A stack of scientific documents reflects a huge number of potent plant-based anticancer drugs such as curcumin (CUR), podophyllotoxin, camptothecin (CPT), vincristine, vinblastine, paclitaxel (PTX), etc. that have been integrated into the modern practice of cancer treatment. The demand for natural products raises exponentially as they are generally considered to be safe, and devoid of critical toxic effects at the therapeutic dose when compared to their synthetic counterparts. Despite rising interest towards the potent phytoconstituents, formulation developer faces various challenges in drug development processes such as poor water solubility, low bioavailability, marginal permeability, and nonspecific drug delivery at the target site, etc. Further, adverse drug reaction and multidrug resistance are other critical issues that need to be addressed. Nanomedicines owing to their unique structural and functional attributes help to fix the above challenges for improved translational outcomes. This review summarises the prospects and challenges of a nanotechnology-based drug delivery approach for the delivery of plant-based anticancer drugs.

Prognostic Threshold for Circulating Tumor Cells in Patients With Pancreatic and Midgut Neuroendocrine Tumors

BACKGROUND

Circulating tumor cells (CTCs) are detectable in patients with neuroendocrine tumors (NETs) and are accurate prognostic markers although the optimum threshold has not been defined.

OBJECTIVE

This work aims to define optimal prognostic CTC thresholds in PanNET and midgut NETs.

PATIENTS AND METHODS

CellSearch was used to enumerate CTCs in 199 patients with metastatic pancreatic (PanNET) (90) or midgut NETs (109). Patients were followed for progression-free survival (PFS) and overall survival (OS) for a minimum of 3 years or until death.

RESULTS

The area under the receiver operating characteristic curve (AUROC) for progression at 12 months in PanNETs and midgut NETs identified the optimal CTC threshold as 1 or greater and 2 or greater, respectively. In multivariate logistic regression analysis, these thresholds were predictive for 12-month progression with an odds ratio (OR) of 6.69 (P < .01) for PanNETs and 5.88 (P < .003) for midgut NETs. The same thresholds were found to be optimal for predicting death at 36 months, with an OR of 2.87 (P < .03) and 5.09 (P < .005) for PanNETs and midgut NETs, respectively. In multivariate Cox hazard regression analysis for PFS in PanNETs, 1 or greater CTC had a hazard ratio (HR) of 2.6 (P < .01), whereas 2 or greater CTCs had an HR of 2.25 (P < .01) in midgut NETs. In multivariate analysis OS in PanNETs, 1 or greater CTCs had an HR of 3.16 (P < .01) and in midgut NETs, 2 or greater CTCs had an HR of 1.73 (P < .06).

CONCLUSIONS

The optimal CTC threshold to predict PFS and OS in metastatic PanNETs and midgut NETs is 1 and 2, respectively. These thresholds can be used to stratify patients in clinical practice and clinical trials.

The Potential Role of Liquid Biopsies in Advancing the Understanding of Neuroendocrine Neoplasms

Tumour tissue as a source for molecular profiling and for in vivo models has limitations (e.g., difficult access, limited availability, single time point, potential heterogeneity between primary and metastatic sites). Conversely, liquid biopsies provide an easily accessible approach, enabling timely and longitudinal interrogation of the tumour molecular makeup, with increased ability to capture spatial and temporal intra-tumour heterogeneity compared to tumour tissue. Blood-borne biomarker assays (e.g., circulating tumour cells (CTCs), circulating free/tumour DNA (cf/ctDNA)) pose unique opportunities for aiding in the molecular characterisation and phenotypic subtyping of neuroendocrine neoplasms and will be discussed in this article.

Cost-effectiveness of lutetium (177Lu) oxodotreotide vs everolimus in gastroenteropancreatic neuroendocrine tumors in Norway and Sweden

BACKGROUND

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) represent a relatively rare and heterogenous group of tumors. Currently available treatment options for patients with progressive GEP-NETs include lutetium (¹⁷⁷Lu) oxodotreotide (¹⁷⁷Lu-Dotatate) and everolimus [as well as sunitinib for patients with pancreatic NETs (P-NETs)].

AIM

To perform a health economic analysis to determine the cost-effectiveness of ¹⁷⁷Lu-Dotatate compared with everolimus in patients with unresectable or metastatic midgut-NETs or P-NETs in both Sweden and Norway.

METHODS

Simulations were performed using a three-state partitioned survival model and analyses were performed separately for patients with midgut-NETs and P-NETs. Clinical input data were sourced from an indirect comparison that utilized survival data from clinical trials of ¹⁷⁷Lu-Dotatate and everolimus. The analyses were performed from the healthcare payer perspective over a time horizon of 20 years. For Sweden, future costs and clinical outcomes were discounted at 3% per annum. For Norway, a discount rate of 4% per annum was applied.

RESULTS

For Sweden, improved survival outcomes and higher lifetime costs with ¹⁷⁷Lu-Dotatate resulted in an incremental cost-effectiveness ratio (ICER) of SEK 391194 per quality-adjusted life year (QALY) gained for midgut NETs and SEK 16764 per QALY gained for P-NETs for ¹⁷⁷Lu-Dotatate compared with everolimus. For Norway, the corresponding ICERs were NOK 244444 per QALY gained and NOK 106451 per QALY gained, respectively. One-way sensitivity analyses revealed that the results were most sensitive to changes in drug acquisition costs and health state utility values.

CONCLUSION

In both Sweden and Norway, from a healthcare provider perspective, ¹⁷⁷Lu-Dotatate is likely to be considered cost-effective relative to everolimus for the treatment of patients with unresectable or metastatic, progressive midgut-NETs or P-NETs. 

Clinical and Translational Research Challenges in Neuroendocrine Tumours

Neuroendocrine tumours (NETs) represent a range of neoplasms that may arise from any (neuro)endocrine cell situated in any part of the human body. As any other rare diseases, NETs face several difficulties in relation to research. This review will describe some of the main challenges and proposed solutions faced by researchers with expertise in rare malignancies. Some of the most common challenges in clinical and translational research are enumerated in this review, covering aspects from clinical, translational and basic research. NETs being a heterogeneous group of diseases and a limited sample size of clinical and translational research projects are the main challenges. Challenges with NETs lay over the disparities between healthcare models to tackle rare diseases. NETs add an extra layer of complexity due to a numerous group of different entities. Prospective real-world data trials are an opportunity for rare cancers with the revolution of electronic health technologies. This review explores potential solutions to these challenges that could be useful not only to the NET community but also to other rare tumours researchers.

Prognostic impact of somatostatin receptor expression in advanced bladder cancer

INTRODUCTION AND OBJECTIVES

Somatostatin receptors (SSTR) recently have been identified as potential targets for treatment of solid tumors. Furthermore, they have been shown to be of high relevance for tumor biology and prognosis in various types of cancer. However, there is a lack of clinical data for SSTR in bladder cancer (BC). Aim of this study was to determine the expression of all relevant somatostatin receptor subtypes in benign urothelium and tumor tissue of patients with muscle invasive BC. Furthermore, their potential role as prognostic factor for cancer-specific survival (CSS) and overall survival (OS) was evaluated.

METHODS

The collective included BC and benign urothelium tissue of 103 patients (Median age 69; range 32-84, 79 male, 24 female) who underwent a radical cystectomy. A tissue microarray with subsequent immunohistochemical staining was used to assess membranous expression of SSTR1-5. Results were correlated to clinical and histopathological data as well as CSS and OS.

RESULTS

Expressions of SSTR1-4 were significantly decreased in BC compared to benign urothelium (P < 0.002 each), whereas SSTR5 expression was increased (P = 0.0017). Expression of SSTR1 was associated with organ-confined disease (≤pT2) (P = 0.0477). No correlation between SSTR1-5 expression and N- and M-stage was observed. Univariate analyses showed a significantly longer CSS and OS in patients with high expression of SSTR3 (P = 0.0316 and 0.0044). Multivariate analyses confirmed SSTR3 expression as independent marker of improved CSS and OS (P = 0.0324 and 0.0076).

CONCLUSIONS

The majority of somatostatin receptor subtypes exhibit decreased expression in BC compared to benign bladder tissue. Expression of SSTR3 is an indicator for favorable prognosis in patients with muscle-invasive BC. These results support preclinical investigations using somatostatin receptor analogues such as octreotide to influence BC growth.

Radiopharmaceuticals for Breast Cancer and Neuroendocrine Tumors: Two Examples of How Tissue Characterization May Influence the Choice of Therapy

Molecular medicine has gained clinical relevance for the detection and staging of oncological diseases, to guide therapy decision making and for therapy follow-up due to the availability of new highly sensitive hybrid imaging camera systems and the development of new tailored radiopharmaceuticals that target specific molecules. The knowledge of the expression of different receptors on the primary tumor and on metastases is important for both therapeutic and prognostic purposes and several approaches are available aiming to achieve personalized medicine in different oncological diseases. In this review, we describe the use of specific radiopharmaceuticals to image and predict therapy response in breast cancer and neuroendocrine tumors since they represent a paradigmatic example of the importance of tumoral characterization of hormonal receptors in order to plan a tailored treatment. The most attractive radiopharmaceuticals for breast cancer are 16α-[¹⁸F]-fluoro-17β-estradiol for PET assessment of the estrogen expression, radiolabeled monoclonal antibody trastuzumab to image the human epidermal growth factor receptor 2, but also the imaging of androgen receptors with [¹⁸F]-fluorodihydrotestosterone.

Blood Chromogranin A Is Not Effective as a Biomarker for Diagnosis or Management of Bronchopulmonary Neuroendocrine Tumors/Neoplasms

BACKGROUND

Identification of circulating tumor markers for clinical management in bronchopulmonary (BP) neuroendocrine tumors/neoplasms (NET/NEN) is of considerable clinical interest. Chromogranin A (CgA), a "universal" NET biomarker, is considered controversial as a circulating biomarker of BPNEN.

AIM

Assess utility of CgA in the diagnosis and management of BPNEN in a multicentric study.

MATERIAL AND METHODS

CgA diagnostic metrics were assessed in lung NET/NENs (n = 200) and controls (n = 140), randomly assigned to a Training and Test set (100 BPC and 70 controls in each). Assay specificity was evaluated in neoplastic lung disease (n = 137) and nonneoplastic lung disease (n = 77). CgA efficacy in predicting clinical status was evaluated in the combined set of 200 NET/NENs. CgA levels in bronchopulmonary neuroendocrine tumor (BPNET) subtypes (atypical [AC] vs. typical [TC]) and grade was examined. The clinical utility of an alteration of CgA levels (±25%) was evaluated in a subset of 49 BPNET over 12 months. CgA measurement was by NEOLISATM kit (EuroDiagnostica).

RESULTS

Sensitivity and specificity in the training set were 41/98%, respectively. Test set data were 42/87%. Training set area under receiver operator characteristic analysis differentiated BPC from control area under the curve (AUC) 0.61 ± 0.05 p = 0.015. Test set the data were AUC 0.58 ± 0.05, p = 0.076. In the combined set (n = 200), 67% BPNET/NEN (n = 134) had normal CgA levels. CgA levels did not distinguish histological subtypes (TC vs. AC, AUC 0.56 ± 0.04, p = 0.21), grade (p = 0.45-0.72), or progressive from stable disease (AUC 0.53 ± 0.05 p = 0.47). There was no correlation of CgA with Ki-67 index (Pearson r = 0.143, p = 0.14). For nonneoplastic diseases (chronic obstructive pulmonary disorder and idiopathic pulmonary fibrosis), CgA was elevated in 26-37%. For neoplastic disease (NSCLC, squamous cell carcinoma), CgA was elevated in 11-16%. The neuroendocrine SCLC also exhibited elevated CgA (50%). Elevated CgA was not useful for differentiating BPNET/NEN from these other pathologies. Monitoring BPNET/NEN over a 12-month period identified neither CgA levels per se nor changes in CgA were reflective of somatostatin analog treatment outcome/efficacy or the natural history of the disease (progression).

CONCLUSIONS

Blood CgA levels are not clinically useful as a biomarker for lung BPNET/NEN. The low specificity and elevations in both nonneoplastic as well as other common neoplastic lung diseases identified limited clinical utility for this biomarker.

Clinical Epigenetics of Neuroendocrine Tumors: The Road Ahead

Neuroendocrine tumors, or NETs, are cancer originating in neuroendocrine cells. They are mostly found in the gastrointestinal tract or lungs. Functional NETs are characterized by signs and symptoms caused by the oversecretion of hormones and other substances, but most NETs are non-functioning and diagnosis in advanced stages is common. Thus, novel diagnostic and therapeutic strategies are warranted. Epigenetics may contribute to refining the diagnosis, as well as to identify targeted therapy interfering with epigenetic-sensitive pathways. The goal of this review was to discuss the recent advancement in the epigenetic characterization of NETs highlighting their role in clinical findings.

Clinical applications of (epi)genetics in gastroenteropancreatic neuroendocrine neoplasms: Moving towards liquid biopsies

High-throughput analysis, including next-generation sequencing and microarrays, have strongly improved our understanding of cancer biology. However, genomic data on rare cancer types, such as neuroendocrine neoplasms, has been lagging behind. Neuroendocrine neoplasms (NENs) develop from endocrine cells spread throughout the body and are highly heterogeneous in biological behavior. In this challenging disease, there is an urgent need for new therapies and new diagnostic, prognostic, follow-up and predictive biomarkers to aid patient management. The last decade, molecular data on neuroendocrine neoplasms of the gastrointestinal tract and pancreas, termed gastroenteropancreatic NENs (GEP-NENs), has strongly expanded. The aim of this review is to give an overview of the recent advances on (epi)genetic level and highlight their clinical applications to address the current needs in GEP-NENs. We illustrate how molecular alterations can be and are being used as therapeutic targets, how mutations in DAXX/ATRX and copy number variations could be used as prognostic biomarkers, how far we are in identifying predictive biomarkers and how genetics can contribute to GEP-NEN classification. Finally, we discuss recent studies on liquid biopsies in the field of GEP-NENs and illustrate how liquid biopsies can play a role in patient management. In conclusion, molecular studies have suggested multiple potential biomarkers, but further validation is ongoing.

Circulating tumour cells and their association with bone metastases in patients with neuroendocrine tumours

Background

Bone metastases are associated with a worse outcome in patients with neuroendocrine tumours (NETs). Tumour overexpression of C-X-C chemokine receptor 4 (CXCR4) appears predictive of skeletal involvement. We investigated the role of circulating tumour cells (CTCs) and CXCR4 expression on CTCs as potential predictors of skeleton invasion.

Methods

Blood from patients with metastatic bronchial, midgut or pancreatic NET (pNET) was analysed by CellSearch. CXCR4 immunohistochemistry was performed on matched formalin-fixed paraffin-embedded (FFPE) samples.

Results

Two hundred and fifty-four patients were recruited with 121 midgut and 119 pNETs, of which 51 and 36% had detectable CTCs, respectively. Bone metastases were reported in 30% of midgut and 23% of pNET patients and were significantly associated with CTC presence (p = 0.003 and p < 0.0001). In a subgroup of 40 patients, 85% patients with CTCs had CTCs positive for CXCR4 expression. The proportion of CXCR4-positive CTCs in patients with bone metastases was 56% compared to 35% in those without (p = 0.18) it. Staining for CXCR4 on matched FFPE tissue showed a trend towards a correlation with CXCR4 expression on CTCs (p = 0.08).

Conclusions

CTC presence is associated with bone metastases in NETs. CXCR4 may be involved in CTC osteotropism and present a therapeutic target to reduce skeletal morbidity.

The long noncoding RNA landscape of neuroendocrine prostate cancer and its clinical implications

Background

Treatment-induced neuroendocrine prostate cancer (tNEPC) is an aggressive variant of late-stage metastatic castrate-resistant prostate cancer that commonly arises through neuroendocrine transdifferentiation (NEtD). Treatment options are limited, ineffective, and, for most patients, result in death in less than a year. We previously developed a first-in-field patient-derived xenograft (PDX) model of NEtD. Longitudinal deep transcriptome profiling of this model enabled monitoring of dynamic transcriptional changes during NEtD and in the context of androgen deprivation. Long non-coding RNA (lncRNA) are implicated in cancer where they can control gene regulation. Until now, the expression of lncRNAs during NEtD and their clinical associations were unexplored.

Results

We implemented a next-generation sequence analysis pipeline that can detect transcripts at low expression levels and built a genome-wide catalogue (n = 37,749) of lncRNAs. We applied this pipeline to 927 clinical samples and our high-fidelity NEtD model LTL331 and identified 821 lncRNAs in NEPC. Among these are 122 lncRNAs that robustly distinguish NEPC from prostate adenocarcinoma (AD) patient tumours. The highest expressed lncRNAs within this signature are H19, LINC00617, and SSTR5-AS1. Another 742 are associated with the NEtD process and fall into four distinct patterns of expression (NEtD lncRNA Class I, II, III, and IV) in our PDX model and clinical samples. Each class has significant (z-scores >2) and unique enrichment for transcription factor binding site (TFBS) motifs in their sequences. Enriched TFBS include (1) TP53 and BRN1 in Class I, (2) ELF5, SPIC, and HOXD1 in Class II, (3) SPDEF in Class III, (4) HSF1 and FOXA1 in Class IV, and (5) TWIST1 when merging Class III with IV. Common TFBS in all NEtD lncRNA were also identified and include E2F, REST, PAX5, PAX9, and STAF. Interrogation of the top deregulated candidates (n = 100) in radical prostatectomy adenocarcinoma samples with long-term follow-up (median 18 years) revealed significant clinicopathological associations. Specifically, we identified 25 that are associated with rapid metastasis following androgen deprivation therapy (ADT). Two of these lncRNAs (SSTR5-AS1 and LINC00514) stratified patients undergoing ADT based on patient outcome.

Discussion

To date, a comprehensive characterization of the dynamic landscape of lncRNAs during the NEtD process has not been performed. A temporal analysis of the PDX-based NEtD model has for the first time provided this dynamic landscape. TFBS analysis identified NEPC-related TF motifs present within the NEtD lncRNA sequences, suggesting functional roles for these lncRNAs in NEPC pathogenesis. Furthermore, select NEtD lncRNAs appear to be associated with metastasis and patients receiving ADT. Treatment-related metastasis is a clinical consequence of NEPC tumours. Top candidate lncRNAs FENDRR, H19, LINC00514, LINC00617, and SSTR5-AS1 identified in this study are implicated in the development of NEPC. We present here for the first time a genome-wide catalogue of NEtD lncRNAs that characterize the transdifferentiation process and a robust NEPC lncRNA patient expression signature. To accomplish this, we carried out the largest integrative study that applied a PDX NEtD model to clinical samples. These NEtD and NEPC lncRNAs are strong candidates for clinical biomarkers and therapeutic targets and warrant further investigation.

Role of biomarker tests for diagnosis of neuroendocrine tumours

Neuroendocrine tumours (NETs) are neoplasms that arise from neuroendocrine cells. Neuroendocrine cells and their tumours can secrete a wide range of amines and polypeptide hormones into the systemic circulation. This feature has triggered widespread investigation into circulating biomarkers for the diagnosis of NETs as well as for the prediction of the biological behaviour of tumour cells. Classic examples of circulating biomarkers for gastroenteropancreatic NETs include chromogranin A, neuron-specific enolase and pancreatic polypeptide as well as hormones that elicit clinical syndromes, such as serotonin and its metabolites, insulin, glucagon and gastrin. Biomarker metrics of general markers for diagnosing all gastroenteropancreatic NET subtypes are limited, but specific hormonal measurements can be of diagnostic value in select cases. In the past decade, methods for detecting circulating transcripts and tumour cells have been developed to improve the diagnosis of patients with NETs. Concurrently, modern scanning techniques and superior radiotracers for functional imaging have markedly expanded the options for clinicians dealing with NETs. Here, we review the latest research on biomarkers in the NET field to provide clinicians with a comprehensive overview of relevant diagnostic biomarkers that can be implemented in dedicated situations.

Liquid Biopsies for Neuroendocrine Tumors: Circulating Tumor Cells, DNA, and MicroRNAs

Effective management of neuroendocrine tumors depends on early diagnosis, personalized risk stratification, and monitoring response to therapy. During cancer progression, tumors shed circulating tumor cells, circulating tumor DNA, and microRNAs into the bloodstream. Analysis of these biomarkers offers the prospect of a liquid biopsy to predict/monitor therapeutic responses, assess drug resistance, and quantify residual disease. Compared with single-site biopsies, these entities have the potential to inform intratumor heterogeneity and tumor evolution in a reproducible and less invasive way. This article summarizes the state-of-the-art on the potential role of these markers as prognostic and predictive factors in neuroendocrine tumors.

Clinical applications of the CellSearch platform in cancer patients

The CellSearch® system (CS) enables standardized enrichment and enumeration of circulating tumor cells (CTCs) that are repeatedly assessable via non-invasive "liquid biopsy". While the association of CTCs with poor clinical outcome for cancer patients has clearly been demonstrated in numerous clinical studies, utilizing CTCs for the identification of therapeutic targets, stratification of patients for targeted therapies and uncovering mechanisms of resistance is still under investigation. Here, we comprehensively review the current benefits and drawbacks of clinical CTC analyses for patients with metastatic and non-metastatic tumors. Furthermore, the review focuses on approaches beyond CTC enumeration that aim to uncover therapeutically relevant antigens, genomic aberrations, transcriptional profiles and epigenetic alterations of CTCs at a single cell level. This characterization of CTCs may shed light on the heterogeneity and genomic landscapes of malignant tumors, an understanding of which is highly important for the development of new therapeutic strategies.

Merkel cell carcinoma: An update and review: Current and future therapy

Merkel cell carcinoma (MCC) is a rare neuroendocrine tumor of the skin associated with a high risk of local recurrence and distant metastases. It most commonly occurs on sun-exposed areas of white patients >65 years of age. The Merkel cell polyomavirus (MCV) is thought to be responsible for malignant transformation in approximately 80% of cases in the northern hemisphere, while ultraviolet radiation-induced DNA damage is implicated in MCV-negative tumors. The overall incidence of MCC is low, with approximately 1600 cases diagnosed annually in the United States. The rate is much higher in patients with lymphoproliferative malignancies, solid organ transplants, and HIV infection. The low overall incidence of this tumor makes it challenging to conduct prospective clinical trials with sufficient power. As a result, most management recommendations are based on case series, retrospective reviews, and expert opinion. The pathogenesis, diagnosis, and staging of MCC was discussed in the first article in this continuing medical education series. This article focuses on current management guidelines and promising new therapies in development. Because of the complexity, aggressive nature, and individuality of each case, MCC is best treated by a multidisciplinary team.