Peptide receptor radionuclide therapy of neuroendocrine tumours

Resistant gastroenteropancreatic neuroendocrine tumors: a definition and guideline to medical and surgical management

Gastroenteropancreatic neuroendocrine tumors (NETs), also historically known as carcinoids, are tumors derived of hormone-secreting enteroendocrine cells. Carcinoids may be found in the esophagus, stomach, small intestine, appendix, colon, rectum, or pancreas. The biologic behavior of carcinoids differs based on their location, with gastric and appendiceal NETs among the least aggressive and small intestinal and pancreatic NETs among the most aggressive. Ultimately, however, biologic behavior is most heavily influenced by tumor grade. The incidence of NETs has increased by 6.4 times over the past 40 years. Surgery remains the mainstay for management of most carcinoids. Medical management, however, is a useful adjunct and/or definitive therapy in patients with symptomatic functional carcinoids, in patients with unresectable or incompletely resected carcinoids, in some cases of recurrent carcinoid, and in postoperative patients to prevent recurrence. Functional tumors with persistent symptoms or progressive metastatic carcinoids despite therapy are called "resistant" tumors. In patients with unresectable disease and/or carcinoid syndrome, an array of medical therapies is available, mainly including somatostatin analogues, molecular-targeted therapy, and peptide receptor radionuclide therapy. Active research is ongoing to identify additional targeted therapies for patients with resistant carcinoids.

Recombinant α1-Microglobulin (rA1M) Protects against Hematopoietic and Renal Toxicity, Alone and in Combination with Amino Acids, in a 177Lu-DOTATATE Mouse Radiation Model

¹⁷⁷Lu-DOTATATE peptide receptor radionuclide therapy (PRRT) is used clinically to treat metastasized or unresectable neuroendocrine tumors (NETs). Although ¹⁷⁷Lu-DOTATATE is mostly well tolerated in patients, bone marrow suppression and long-term renal toxicity are still side effects that should be considered. Amino acids are often used to minimize renal radiotoxicity, however, they are associated with nausea and vomiting in patients. α₁-microglobulin (A1M) is an antioxidant with heme- and radical-scavenging abilities. A recombinant form (rA1M) has previously been shown to be renoprotective in preclinical models, including in PRRT-induced kidney damage. Here, we further investigated rA1M's renal protective effect in a mouse ¹⁷⁷Lu-DOTATATE model in terms of administration route and dosing regimen and as a combined therapy with amino acids (Vamin). Moreover, we investigated the protective effect of rA1M on peripheral blood and bone marrow cells, as well as circulatory biomarkers. Intravenous (i.v.) administration of rA1M reduced albuminuria levels and circulatory levels of the oxidative stress-related protein fibroblast growth factor-21 (FGF-21). Dual injections of rA1M (i.e., at 0 and 24 h post-¹⁷⁷Lu-DOTATATE administration) preserved bone marrow cellularity and peripheral blood reticulocytes. Administration of Vamin, alone or in combination with rA1M, did not show any protection of bone marrow cellularity or peripheral reticulocytes. In conclusion, this study suggests that rA1M, administered i.v. for two consecutive days in conjunction with ¹⁷⁷Lu-DOTATATE, may reduce hematopoietic and kidney toxicity during PRRT with ¹⁷⁷Lu-DOTATATE.

Efficacy and Safety of [177Lu]Lu-DOTA-TATE in Adults with Inoperable or Metastatic Somatostatin Receptor-Positive Pheochromocytomas/Paragangliomas, Bronchial and Unknown Origin Neuroendocrine Tumors, and Medullary Thyroid Carcinoma: A Systematic Literature Review

Background: We have performed a systematic review to evaluate the efficacy and safety of [177Lu]Lu-DOTA-TATE, a radioligand therapy, in advanced somatostatin receptor-positive pheochromocytoma/paraganglioma (PPGL), thymic neuroendocrine tumor (NET), bronchial NET, unknown primary NET, or medullary thyroid carcinoma (MTC). Methods: Studies identified in PubMed from inception to 13 May 2021 must have assessed [177Lu]Lu-DOTA-TATE as a single agent and reported outcome data for the specific NET types of interest. Results: Two independent reviewers performed the screening and data extraction, resulting in 16 publications: PPGL (n = 7), bronchial NETs (n = 6; one also included NETs of unknown origin), and MTC (n = 3). Overall, [177Lu]Lu-DOTA-TATE offers encouraging antitumor activity (overall tumor response rates and disease control rates) across NET types. Safety was favorable with most adverse events mild to moderate in severity, transient, and consistent with those seen in patients with gastroenteropancreatic (GEP)-NETs. Conclusions: [177Lu]Lu-DOTA-TATE has been used effectively in clinical practice to treat NETs of non-GEP origin.

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.

Dual-Tracer (68Ga-DOTATOC and 18F-FDG-)-PET/CT Scan and G1-G2 Nonfunctioning Pancreatic Neuroendocrine Tumors: A Single-Center Retrospective Evaluation of 124 Nonmetastatic Resected Cases

INTRODUCTION

The combined use of 68gallium (68Ga)-DOTA-peptides and 18fluorine-fluoro-2-deoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) scans in the workup of pancreatic neuroendocrine tumors (PanNETs) is controversial. This study aimed at assessing both tracers' capability to identify tumors and to assess its association with pathological predictors of recurrence.

METHODS

Prospectively collected, preoperative, dual-tracer PET/CT scan data of G1-G2, nonmetastatic, PanNETs that underwent surgery between January 2013 and October 2019 were retrospectively analyzed.

RESULTS

The final cohort consisted of 124 cases. There was an approximately equal distribution of males and females (50.8%/49.2%) and G1 and G2 tumors (49.2%/50.8%). The disease was detected in 122 (98.4%) and 64 (51.6%) cases by 68Ga-DOTATOC and by 18F-FDG PET/CT scans, respectively, with a combined sensitivity of 99.2%. 18F-FDG-positive examinations found G2 tumors more often than G1 (59.4 vs. 40.6%; p = 0.036), and 18F-FDG-positive PanNETs were larger than negative ones (median tumor size 32 mm, interquartile range [IQR] 21 vs. 26 mm, IQR 20; p = 0.019). The median Ki67 for 18F-FDG-positive and -negative examinations was 3 (IQR 4) and 2 (IQR 4), respectively (p = 0.029). At least 1 pathological predictor of recurrence was present in 74.6% of 18F-FDG-positive cases (vs. 56.7%; p = 0.039), whereas this was not found when dichotomizing the PanNETs by their dimensions (≤/>20 mm). None of the 2 tracers predicted nodal metastasis. The receiver operating characteristic curve analysis showed that 18F-FDG uptake higher than 4.2 had a sensitivity of 49.2% and specificity of 73.3% for differentiating G1 from G2 (AUC = 0.624, p = 0.009).

CONCLUSION

The complementary adoption of 68Ga-DOTATOC and 18F-FDG tracers may be valuable in the diagnostic workup of PanNETs despite not being a game-changer for the management of PanNETs ≤20 mm.

Necrosis binding of Ac-Lys0(IRDye800CW)-Tyr3-octreotate: a consequence from cyanine-labeling of small molecules

Background

There is a growing body of nuclear contrast agents that are repurposed for fluorescence-guided surgery. New contrast agents are obtained by substituting the radioactive tag with, or adding a fluorescent cyanine to the molecular structure of antibodies or peptides. This enables intra-operative fluorescent detection of cancerous tissue, leading to more complete tumor resection. However, these fluorescent cyanines can have a remarkable influence on pharmacokinetics and tumor uptake, especially when labeled to smaller targeting vectors such as peptides. Here we demonstrate the effect of cyanine-mediated dead cell-binding of Ac-Lys⁰(IRDye800CW)-Tyr³-octreotate (800CW-TATE) and how this can be used as an advantage for fluorescence-guided surgery.

Results

Binding of 800CW-TATE could be blocked with DOTA⁰-Tyr³-octreotate (DOTA-TATE) on cultured SSTR₂-positive U2OS cells and was absent in SSTR₂ negative U2OS cells. However, strong binding was observed to dead cells, which could not be blocked with DOTA-TATE and was also present in dead SSTR₂ negative cells. No SSTR₂-mediated binding was observed in frozen tumor sections, possibly due to disruption of the cells in the process of sectioning the tissue before exposure to the contrast agent. DOTA-TATE blocking resulted in an incomplete reduction of 61.5 ± 5.8% fluorescence uptake by NCI-H69-tumors in mice. Near-infrared imaging and dead cell staining on paraffin sections from resected tumors revealed that fluorescence uptake persisted in necrotic regions upon blocking with DOTA-TATE.

Conclusion

This study shows that labeling peptides with cyanines can result in dead cell binding. This does not hamper the ultimate purpose of fluorescence-guided surgery, as necrotic tissue appears in most solid tumors. Hence, the necrosis binding can increase the overall tumor uptake. Moreover, necrotic tissue should be removed as much as possible: it cannot be salvaged, causes inflammation, and is tumorigenic. However, when performing binding experiments to cells with disrupted membrane integrity, which is routinely done with nuclear probes, this dead cell-binding can resemble non-specific binding. This study will benefit the development of fluorescent contrast agents.

Supplementary information

The online version contains supplementary material available at 10.1186/s13550-021-00789-4.

Systemic Treatment of Advanced Gastroenteropancreatic Neuroendocrine Tumors in Korea: Literature Review and Expert Opinion

Neuroendocrine tumors (NETs) are a group of malignancies arising from neuroendocrine cells and frequently originate in the gastrointestinal tract and pancreas. Although curative resection is the main treatment for localized disease, systemic therapy is needed for relapsed or metastatic/unresectable gastroenteropancreatic NETs (GEP-NETs). Although there are several NET treatment guidelines from various countries, the geographical discrepancies between patient clinical characteristics, the regulatory approval status for therapeutic agents, and medical practices necessitate specific guidelines for Korean patients. We here provide a consensus review of the diagnosis, staging and systemic treatment of Korean GEP-NET patients. Systemic therapy options and the current Korean expert consensus on these treatments, including somatostatin analogs, targeted therapies such as everolimus and sunitinib, peptide receptor radionuclide treatments, and cytotoxic chemotherapies are addressed.

Gastroenteropancreatic neuroendocrine neoplasms: A clinical snapshot

Our understanding about the epidemiological aspects, pathogenesis, molecular diagnosis, and targeted therapies of neuroendocrine neoplasms (NENs) have drastically advanced in the past decade. Gastroenteropancreatic (GEP) NENs originate from the enteroendocrine cells of the embryonic gut which share common endocrine and neural differentiation factors. Most NENs are well-differentiated, and slow growing. Specific neuroendocrine biomarkers that are used in the diagnosis of functional NENs include insulin, glucagon, vasoactive intestinal polypeptide, gastrin, somatostatin, adrenocorticotropin, growth hormone releasing hormone, parathyroid hormone-related peptide, serotonin, histamine, and 5-hydroxy indole acetic acid (5-HIAA). Biomarkers such as pancreatic polypeptide, human chorionic gonadotrophin subunits, neurotensin, ghrelin, and calcitonin are used in the diagnosis of non-functional NENs. 5-HIAA levels correlate with tumour burden, prognosis and development of carcinoid heart disease and mesenteric fibrosis, however several diseases, medications and edible products can falsely elevate the 5-HIAA levels. Organ-specific transcription factors are useful in the differential diagnosis of metastasis from an unknown primary of well-differentiated NENs. Emerging novel biomarkers include circulating tumour cells, circulating tumour DNA, circulating micro-RNAs, and neuroendocrine neoplasms test (NETest) (simultaneous measurement of 51 neuroendocrine-specific marker genes in the peripheral blood). NETest has high sensitivity (85%-98%) and specificity (93%-97%) for the detection of gastrointestinal NENs, and is useful for monitoring treatment response, recurrence, and prognosis. In terms of management, surgery, radiofrequency ablation, symptom control with medications, chemotherapy and molecular targeted therapies are all considered as options. Surgery is the mainstay of treatment, but depends on factors including age of the individual, location, stage, grade, functional status, and the heredity of the tumour (sporadic vs inherited). Medical management is helpful to alleviate the symptoms, manage inoperable lesions, suppress postoperative tumour growth, and manage recurrences. Several molecular-targeted therapies are considered second line to somatostatin analogues. This review is a clinical update on the pathophysiological aspects, diagnostic algorithm, and management of GEP NENs.

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.

Targeted systemic and peptide radio-ligand therapy for aggressive pituitary tumors and carcinomas

Aggressive pituitary tumors comprise a rare but challenging subset of pituitary tumors. A major issue currently is the absence of a holistic definition that reliably identifies these tumors in a prospective manner. Although comprehensive evaluation of patient gender, age, local invasiveness, treatment responses, radiological and histopathological features may be informative to assess the potential for aggressiveness, a definitive diagnosis of this entity cannot be confidently made until disease progression is actually observed despite standard medical and surgical therapy. Failure to diagnose these aggressive pituitary tumors early may impede initiation of suitable intensive stepwise multimodal treatments, and lessen their ultimate therapeutic success. Even though current therapeutic options for aggressive pituitary tumors are suboptimal in many cases, large-scale randomized prospective clinic trials are impractical and will likely never be conducted due to the rarity of this disease entity. Therefore, the majority of novel therapies in this subset of tumors derive from case reports or small case series, which greatly reduces their validity to make strong recommendations. This chapter, as part of this series on aggressive pituitary tumors, focuses on the role of systemic targeted medical and peptide radio-receptor therapy in treatment of aggressive pituitary tumors and carcinomas, and discusses future directions in these fields.

Evaluation of Somatostatin and CXCR4 Receptor Expression in a Large Set of Prostate Cancer Samples Using Tissue Microarrays and Well-Characterized Monoclonal Antibodies

BACKGROUND: Prostate cancer (PCa) is the most common type of cancer among men in Western countries. Despite numerous therapeutic options, few treatments are available for patients with end-stage disease. In the present study, different somatostatin receptors (SSTs) and the chemokine receptor CXCR4 were evaluated for their suitability as novel therapeutic targets in PCa. MATERIALS AND METHODS: The expression of SST subtypes 1, 2A, 3, and 5 and of CXCR4 was evaluated in 276 PCa tumor samples on a tissue microarray (TMA) in 23 whole-block tumor samples and in 3 PCa cell lines by immunohistochemistry using well-characterized monoclonal antibodies. RESULTS: Overall, the frequency and intensity of expression of SSTs and CXCR4 were very low among the PCa samples investigated. Specifically, SST5, SST2A, and SST3 were expressed, albeit at low intensity, in 10.5%, 9.1%, and 0.7% of the TMA samples, respectively. None of the TMA samples showed SST1 or CXCR4 expression. Only a single small-cell-type neuroendocrine carcinoma that was coincidentally included among the whole-block samples exhibited strong SST2A, SST5, and CXCR4 and moderate SST3 expression. Independent of the tumor cells, the tumor capillaries in many of the PCa samples were strongly positive for SST2A, SST3, SST5, or CXCR4 expression. SST expression in the tumor cells was associated with advanced tumor grade and stage. CONCLUSION: Overall, SST and CXCR4 expression levels are clearly of no therapeutic relevance in PCa. SST- or CXCR4-based therapy might be feasible, however, in rare cases of small-cell-type neuroendocrine carcinoma of the prostate.

Development of Novel 111-In-Labelled DOTA Urotensin II Analogues for Targeting the UT Receptor Overexpressed in Solid Tumours

Overexpression of G protein-coupled receptors (GPCRs) in tumours is widely used to develop GPCR-targeting radioligands for solid tumour imaging in the context of diagnosis and even treatment. The human vasoactive neuropeptide urotensin II (hUII), which shares structural analogies with somatostatin, interacts with a single high affinity GPCR named UT. High expression of UT has been reported in several types of human solid tumours from lung, gut, prostate, or breast, suggesting that UT is a valuable novel target to design radiolabelled hUII analogues for cancer diagnosis. In this study, two original urotensinergic analogues were first conjugated to a DOTA chelator via an aminohexanoic acid (Ahx) hydrocarbon linker and then -hUII and DOTA-urantide, complexed to the radioactive metal indium isotope to successfully lead to radiolabelled DOTA-Ahx-hUII and DOTA-Ahx-urantide. The ¹¹¹In-DOTA-hUII in human plasma revealed that only 30% of the radioligand was degraded after a 3-h period. DOTA-hUII and DOTA-urantide exhibited similar binding affinities as native peptides and relayed calcium mobilization in HEK293 cells expressing recombinant human UT. DOTA-hUII, not DOTA-urantide, was able to promote UT internalization in UT-expressing HEK293 cells, thus indicating that radiolabelled ¹¹¹In-DOTA-hUII would allow sufficient retention of radioactivity within tumour cells or radiolabelled DOTA-urantide may lead to a persistent binding on UT at the plasma membrane. The potential of these radioligands as candidates to target UT was investigated in adenocarcinoma. We showed that hUII stimulated the migration and proliferation of both human lung A549 and colorectal DLD-1 adenocarcinoma cell lines endogenously expressing UT. In vivo intravenous injection of ¹¹¹In-DOTA-hUII in C57BL/6 mice revealed modest organ signals, with important retention in kidney. ¹¹¹In-DOTA-hUII or ¹¹¹In-DOTA-urantide were also injected in nude mice bearing heterotopic xenografts of lung A549 cells or colorectal DLD-1 cells both expressing UT. The observed significant renal uptake and low tumour/muscle ratio (around 2.5) suggest fast tracer clearance from the organism. Together, DOTA-hUII and DOTA-urantide were successfully radiolabelled with ¹¹¹Indium, the first one functioning as a UT agonist and the second one as a UT-biased ligand/antagonist. To allow tumour-specific targeting and prolong body distribution in preclinical models bearing some solid tumours, these radiolabelled urotensinergic analogues should be optimized for being used as potential molecular tools for diagnosis imaging or even treatment tools.

Synthesis and Evaluation of 177Lu-DOTA-DN(PTX)-BN for Selective and Concomitant Radio and Drug-Therapeutic Effect on Breast Cancer Cells

The peptide-receptor radionuclide therapy (PRRT) is a successful approach for selectively delivering radiation within tumor sites through specific recognition of radiolabeled peptides by overexpressed receptors on cancer cell surfaces. The efficacy of PRRT could be improved by using polymeric radio- and drug- therapy nanoparticles for a concomitant therapeutic effect on malignant cells. This research aimed to prepare and evaluate, a novel drug and radiation delivery nanosystem based on the ¹⁷⁷Lu-labeled polyamidoamine (PAMAM) dendrimer (DN) loaded with paclitaxel (PTX) and functionalized on the surface with the Lys¹Lys³(DOTA)-bombesin (BN) peptide for specific targeting to gastrin-releasing peptide receptors (GRPr) overexpressed on breast cancer cells. DN was first conjugated covalently to BN and DOTA (chemical moiety for lutetium-177 complexing) and subsequently loaded with PTX. The characterization by microscopic and spectroscopic techniques, in-vitro drug delivery tests as well as in in-vitro and in-vivo cellular uptake of ¹⁷⁷Lu-DOTA-DN(PTX)-BN by T47D breast cancer cells (GRPr-positive), indicated the formation of an improved delivery nanosystem with target-specific recognition by GRPr. Results of the ¹⁷⁷Lu-DOTA-DN(PTX)-BN effect on T47D cell viability (1.3%, compared with 10.9% of ¹⁷⁷Lu-DOTA-DN-BN and 14.0% of DOTA-DN-(PTX)-BN) demonstrated the concomitant radiotherapeutic and chemotherapeutic properties of the polymeric nanosystem as a potential agent for the treatment of GRPr-positive tumors.

Somatostatin analogs in association with peptide receptor radionucleotide therapy in advanced well-differentiated NETs

Aim: Data from 69 well-differentiated gastroenteropancreatic neuroendocrine tumors treated with peptide receptor radionucleotide therapy + somatostatin analogs (SSAs) after SSA treatment failure were evaluated. Methods: We identified two groups: S1 - patients who kept the same SSA treatment beyond progression; S2 - patients who switched the SSA with another SSA after progression. Results: Median progression-free survival was 53 and 127 months in S1 and S2, respectively (p = 0.001; hazard ratio: 0.31; 95% CI: 0.15-0.63). Median overall survival was 69 versus 150 months in S1 and S2, respectively (p = 0.004; hazard ratio: 0.32; 95% CI: 0.14-0.71). Conclusion: In patients with advanced well-differentiated gastroenteropancreatic neuroendocrine tumors treated with peptide receptor radionucleotide therapy plus SSA after SSA failure, the 'switch' strategy of SSA after progression improve progression-free survival and overall survival.

Peptide Receptor Radionuclide Therapy for Pancreatic Neuroendocrine Tumours

Background:

The incidence of pancreatic Neuroendocrine Tumours (pNETs) has increased considerably in the last few decades. The characteristic features of this tumour and the development of new investigative and therapeutic methods had a great impact on its management.

Objective:

The aim of this review is to investigate the outcome of Peptide Receptor Radionuclide Therapy (PRRT) in the treatment of pancreatic neuroendocrine tumours.

Methods:

A comprehensive literature search strategy was used based on two databases (SCOPUS, and PubMed). We considered all studies published in English, evaluating the use of PRRT (177Luteciuim- DOTA-conjugated peptides and 90Yetrium- DOTA- conjugated peptides) in the treatment of pancreatic neuroendocrine tumours as a standalone entity or as a subgroup within the wider category of Gastroenteropancreatic Neuroendocrine Tumours (GEP NETs).

Results:

PRRT was found to be an effective treatment modality as a monotherapy or in combination with other therapies in the treatment of non-operable and metastatic pNETs where other options are limited. Complete response was reported to be between 2-6% while partial response was achieved in up to 60% of cases. Survival analysis was also impressive. Progression Free Survival (PFS) reached a mean of 34 months and Overall Survival (OS) of 53 months. PRRT also proved to improve patients’ Quality of Life (QoL). Acute and sub-acute side effects like nephrotoxicity and haematotoxicity are usually mild and reversible.

Conclusion:

PRRT is well tolerated and effective treatment option for non-operable and/or metastatic pNETs. Side effects are usually mild and reversible. Larger randomized controlled trails need to be done to compare PRRT with other treatment modalities and to provide more detailed guidelines regarding patient selections, the choice of PRRT, follow up and response assessment to maximum potential benefit.

Carcinoid Syndrome: Updates and Review of Current Therapy

OPINION STATEMENT

Carcinoid syndrome (CS) is a complex disorder caused by functional neuroendocrine tumors (NETs). This debilitating disease is characterized by hyper-secretion of biologically active substances eliciting major hormonal symptoms burden and fibrotic changes that are often challenging for management. There have been a number of insights that have substantially advanced treatments since the introduction of somatostatin analogs (SSAs). Second-line treatments are needed in a substantial proportion of patients with advanced disease that have uncontrolled hormone secretion on the highest labeled doses of SSAs. International guidelines suggest several available options including dose escalation of SSAs, interferon alpha, everolimus, radionuclide therapy, liver-directed therapies, and the novel tryptophan hydroxylase 1 inhibitor, telotristat ethyl. The clear preference of one second-line therapy over the other is not stated since their relative and long-term efficacy are largely unknown, and standardized approach of hormonal response assessment is lacking in the literature. In the clinical setting, the treatment of CS is guided in conjunction with patients' performance status, tumor origin, grade, stage, and growth rate, with regard to both anti-hormonal, as well as anti-proliferative effect. There is an unmet need for further well-designed randomized placebo-controlled and head-to-head studies that systematically assess CS symptom control and biochemical response following a specific intervention.

111In-Pentetreotide Scintigraphy Versus 68Ga-DOTATATE PET: Impact on Krenning Scores and Effect of Tumor Burden

Eligibility for somatostatin receptor (SSTR) radionuclide therapy uses the qualitative Krenning score based on ¹¹¹In-pentetreotide planar scintigraphy as was performed in the NETTER-1 trial. The purpose of this study was to determine the effect of using SSTR PET-based Krenning score in comparison to ¹¹¹In-pentetreotide. Methods: This was a post hoc head-to-head comparison of ⁶⁸Ga-DOTATATE-based and ¹¹¹In-pentetreotide-based Krenning scores in 150 patients included in a prospective phase 2 study (NCT01967537). Patients were imaged using ⁶⁸Ga-DOTATATE PET/CT, ¹¹¹In-pentetreotide planar scintigraphy, and SPECT/CT within 1 wk. SSTR ligand uptake was graded using the Krenning score independently by 3 readers. Results: The detection rate of SSTR-expressing disease (Krenning scores 2-4) was 23%, 38%, and 72% with planar imaging, SPECT, and SSTR PET, respectively. The Krenning score was higher with SSTR PET (2.71 ± 1.74) than with planar imaging (0.75 ± 1.37; P < 0.001) or SPECT (1.23 ± 1.57; P < 0.001). In patients with a Krenning score of at least 3 on SSTR PET, the detection rate of planar imaging and SPECT was lower for lesions smaller than 2 cm than lesions 2 cm or larger: 15% and 24% versus 78% and 89%, respectively (P < 0.001). For lesions larger than 5 cm, Krenning scores between SSTR PET and ¹¹¹In-pentetreotide were nearly equivalent. Lesion size did not have an impact on SSTR PET Krenning scores. Interreader agreement was higher for SSTR PET than for planar imaging or SPECT (0.79 vs. 0.67 and 0.50, respectively). Conclusion: SSTR PET results in higher Krenning scores than ¹¹¹In-pentetreotide, particularly when lesions measured 2 cm or less. Small lesion size resulted in low Krenning scores using ¹¹¹In-pentetreotide, but lesion size did not affect SSTR PET-based Krenning scores. The results of the NETTER-1 trial cannot be directly applied to patients with small lesions. Further study of peptide receptor radionuclide therapy in patients with small lesions negative on ¹¹¹In-pentetreotide imaging and positive on SSTR PET is warranted.

Peptide receptor radionuclide therapy with 177Lu-DOTA-TATE as a promising treatment of malignant insulinoma: a series of case reports and literature review

INTRODUCTION

Insulinomas are a rare type of pancreatic neuroendocrine tumours characterized by insulin hypersecretion. They are considered malignant when metastases are present. Traditional therapies often promote only temporarily symptomatic relief and may be associated with severe adverse effects. There is scarce experience in treating malignant insulinomas with peptide receptors radionuclide therapy (PRRNT).

PATIENTS AND METHODS

We describe PRRNT results in four patients with inoperable malignant insulinomas with poorly controllable hypoglycaemia. All patients received therapy with ¹⁷⁷Lu-DOTA-TATE after conventional therapies failed in controlling disease progression and symptoms. The activity administered per cycle was 4.8-7.4 GBq. The interval between cycles was 10-16 weeks. Haematology, liver and kidney function tests were performed before treatment initiation and 5 and 10 weeks after each cycle.

RESULTS

Patient 1 presented significant clinical benefit for 13 months after PRRNT, with imaging improvement. Patient 2 obtained reduction of the number and severity of hypoglycaemic episodes during 15 months after therapy. Patient 3 is asymptomatic since PRRNT first cycle performed 23 months ago and revealed significant imaging improvement. Patient 4 had resolution of hypoglycaemia only 3 days after PRRNT first cycle and today, 16 months after therapy, the disease seems to be in remission and the patient maintains euglycaemic state. PRRNT was well tolerated, with only hematologic grade 2 toxicity in patient 1 and mild kidney toxicity in patient 3.

CONCLUSIONS

After the start of ¹⁷⁷Lu-DOTA-TATE all patients achieved hypoglycaemia symptomatic control and had evident improvement of their quality of life. Three patients showed imagiological improvement suggesting reduced tumour load.

Resection of Liver Metastases: A Treatment Provides a Long-Term Survival Benefit for Patients with Advanced Pancreatic Neuroendocrine Tumors: A Systematic Review and Meta-Analysis

Purpose

Nonsurgical therapies, including biotherapy, chemotherapy, and liver-directed therapy, provided a limit survival benefit for PNET patients with hepatic metastases. With the development of liver resection technique, there was a controversy on whether to perform a liver resection for these patients.

Methods

A computerized search was made of the Medline/PubMed, EMbase, Cochrane Library, and SinoMed (CBM) before March 2018. A meta-analysis was performed to investigate the differences in the efficacy of liver resection and nonliver resection treatments based on the evaluation of morbidity, 30-day mortality, symptom relief rate, and 1-, 3-, and 5-year survival. Two investigators reviewed all included articles and extracted the data of them. The meta-analysis was performed via Review Manager 5.3 software.

Results

A total of 13 cohort studies with 1524 patients were included in this meta-analysis. Compared with the nonliver resection group, liver resection group had a longer 1-, 3-, and 5-year survival time and a higher symptom relief with an acceptable mortality and morbidity.

Conclusions

Liver resection is a safe treatment and could significantly prolong the long-term prognosis for highly selected patients with resectable liver metastases from PNET. Further randomized, controlled trials are needed.

New Treatments for the Carcinoid Syndrome

Neuroendocrine tumors, including carcinoids, are rare and insidiously growing tumors. Related to their site of origin, tumors can be functional, causing various forms of the carcinoid syndrome, owing to the overproduction of serotonin, histamine, or other bioactive substances. They often invade adjacent structures or metastasize to the liver and elsewhere. Treatment includes multimodal approaches, including cytoreductive surgery, locoregional embolization, cytotoxic therapy, peptide receptor radionuclide therapy, and various targeted therapies with goals of symptom relief and control of tumor growth. This article summarizes current and emerging approaches to management and reviews several promising future therapies.

When and How to Use Somatostatin Analogues

Long-acting depot formulations of the currently available somatostatin analogues are considered the first-line treatment for control of hormonal excess by hormone-producing neuroendocrine tumors of the gastrointestinal tract and pancreas. These drugs are currently also considered the first-line treatment for tumor control of both hormone-producing and non-hormone-producing neuroendocrine tumors of the gastrointestinal tract and pancreas. These drugs need coupling and interaction with specific somatostatin receptor subtypes, which are expressed on the cells of neuroendocrine tumors of the gastrointestinal tract and pancreas.

Current treatment strategies for patients with advanced gastroenteropancreatic neuroendocrine tumors (GEP-NETs)

Background

Neuroendocrine tumors (NETs) are rare neoplasms, with an estimated annual incidence of ~ 6.9/100,000. NETs arise throughout the body from cells of the diffuse endocrine system. More than half originate from endocrine cells of the gastrointestinal tract and the pancreas, thus being referred to as gastroenteropancreatic NETs (GEP NETs). The only treatment that offers a cure is surgery, however most patients are diagnosed with metastatic disease, and curative surgery is usually not an option.Since the majority of patients are not candidate for curative surgery, they can be offered long-term systemic treatment, for both symptomatic relief and tumor growth suppression. Evidence based treatment options include somatostatin analogues, everolimus (an mTOR inhibitor), sunitinib (a tyrosine kinase inhibitor), peptide receptor radionuclide therapy (PRRT), chemotherapy, etc., alone or combined with cytoreductive procedures (surgery or liver directed procedures). However, there is an increasing need for novel therapies. Other treatment options being investigated are immunotherapy and epigenetic assessment that may lead to more personalized interventions. Following first line therapy with somatostatin analogues, there is no clear information to date indicating a preferred treatment sequence, and therefore the treatment approach should be individualized based on each NET patient characteristics.

Conclusions

NET patients are increasingly diagnosed throughout the world, usually with metastatic disease and requiring systemic therapy. We believe that each patient should be therefore thoroughly evaluated and individually discussed by a multidisciplinary and dedicated NET-expert team, updated with all treatment options including ongoing clinical trials, and before selecting the proper treatment sequence.

Neuropeptide G Protein-Coupled Receptors as Oncotargets

Neuropeptide G protein-coupled receptors (GPCRs) are overexpressed on numerous cancer cells. In a number of tumors, such as small cell lung cancer (SCLC), bombesin (BB) like peptides and neurotensin (NTS) function as autocrine growth factors whereby they are secreted from tumor cells, bind to cell surface receptors and stimulate growth. BB-drug conjugates and BB receptor antagonists inhibit the growth of a number of cancers. Vasoactive intestinal peptide (VIP) increases the secretion rate of BB-like peptide and NTS from SCLC leading to increased proliferation. In contrast, somatostatin (SST) inhibits the secretion of autocrine growth factors from neuroendocrine tumors (NETs) and decreases proliferation. SST analogs such as radiolabeled octreotide can be used to localize tumors, is therapeutic for certain cancer patients and has been approved for four different indications in the diagnosis/treatment of NETs. The review will focus on how BB, NTS, VIP, and SST receptors can facilitate the early detection and treatment of cancer.

An evaluation in vitro of the efficacy of nutlin-3 and topotecan in combination with 177Lu-DOTATATE for the treatment of neuroblastoma

Targeted radiotherapy of metastatic neuroblastoma using the somatostatin receptor (SSTR)-targeted octreotide analogue DOTATATE radiolabelled with lutetium-177 (¹⁷⁷Lu-DOTATATE) is a promising strategy. This study evaluates whether its effectiveness may be enhanced by combination with radiosensitising drugs. The growth rate of multicellular tumour spheroids, derived from the neuroblastoma cell lines SK-N-BE(2c), CHLA-15 and CHLA-20, was evaluated following treatment with ¹⁷⁷Lu-DOTATATE, nutlin-3 and topotecan alone or in combination. Immunoblotting, immunostaining and flow cytometric analyses were used to determine activation of p53 signalling and cell death. Exposure to ¹⁷⁷Lu-DOTATATE resulted in a significant growth delay in CHLA-15 and CHLA-20 spheroids, but not in SK-N-BE(2c) spheroids. Nutlin-3 enhanced the spheroid growth delay induced by topotecan in CHLA-15 and CHLA-20 spheroids, but not in SK-N-BE(2c) spheroids. Importantly, the combination of nutlin-3 with topotecan enhanced the spheroid growth delay induced by X-irradiation or by exposure to ¹⁷⁷Lu-DOTATATE. The efficacy of the combination treatments was p53-dependent. These results indicate that targeted radiotherapy of high risk neuroblastoma with ¹⁷⁷Lu-DOTATATE may be improved by combination with the radiosensitising drugs nutlin-3 and topotecan.

Practical management of toxicities associated with targeted therapies for advanced gastroenteropancreatic neuroendocrine tumors

Neuroendocrine tumors are heterogeneous, rare malignancies that arise most frequently in the gastroenteropancreatic tract (GEPNET). The therapeutic armamentarium for the treatment of GEPNETs has expanded significantly over the last two decades, however the ideal sequencing strategy remains controversial. As this disease may be relatively slow-growing, patients are expected to be treated for longer periods, so that even mild toxicities can influence quality of life, compliance and outcome in the long run. Prospective data on optimal adverse event management are lacking and recommendations are largely based on expert opinion and drug prescribing information. This review summarizes practical recommendations for toxicity management associated with the most commonly used GEPNET treatment options and stresses important focus points for future clinical trials.

Results and adverse events of personalized peptide receptor radionuclide therapy with 90Yttrium and 177Lutetium in 1048 patients with neuroendocrine neoplasms

Introduction

Peptide receptor radionuclide therapy (PRRT) of patients with somatostatin receptor expressing neuroendocrine neoplasms has shown promising results in clinical trials and a recently published phase III study.

Methods

In our center, 2294 patients were screened between 2004 and 2014 by ⁶⁸Ga somatostatin receptor (SSTR) PET/CT. Intention to treat analysis included 1048 patients, who received at least one cycle of ⁹⁰Yttrium or ¹⁷⁷Lutetium-based PRRT. Progression free survival was determined by ⁶⁸Ga SSTR-PET/CT and EORTC response criteria. Adverse events were determined by CTCAE criteria.

Results

Overall survival (95% confidence interval) of all patients was 51 months (47.0-54.9) and differed significantly according to radionuclide, grading, previous therapies, primary site and functionality. Progression free survival (based on PET/CT) of all patients was 19 months (16.9-21), which was significantly influenced by radionuclide, grading, and origin of neuroendocrine neoplasm. Progression free survival after initial progression and first and second resumption of PRRT after therapy-free intervals of more than 6 months were 11 months (9.4-12.5) and 8 months (6.4-9.5), respectively. Myelodysplastic syndrome or leukemia developed in 22 patients (2.1%) and 5 patients required hemodialysis after treatment, other adverse events were rare.

Conclusion

PRRT is effective and overall survival is favorable in patients with neuroendocrine neoplasms depending on the radionuclide used for therapy, grading and origin of the neuroendocrine neoplasm which is not exactly mirrored in progression free survival as determined by highly sensitive ⁶⁸Ga somatostatin receptor PET/CT using EORTC criteria for determining response to therapy.

Translational Diagnostics and Therapeutics in Pancreatic Neuroendocrine Tumors

Pancreatic neuroendocrine tumors (PNET) are rare tumors, but have been increasing in incidence. Although typically thought of as indolent, more than half of patients present with metastatic disease. For many years, the only mutations commonly known in these tumors were those in the MEN1 gene. Recently, the genetics underlying PNETs have been further defined through exome sequencing. The most frequent alterations found in sporadic PNETs are in MEN1, DAXX/ATRX, and a variety of genes in the mTOR pathway. Confirmation of these mutations has prompted trials with a number of drugs active in these pathways, and two drugs were eventually approved in 2011-sunitinib and everolimus. New data additionally identify the MET and CD47 receptors as potential novel drug targets. Yet despite improvements in progression-free survival with sunitinib and everolimus, further studies defining when to use these agents and factors associated with limitations in their utility are needed. As more discoveries are made in the laboratory that elucidate additional molecular mechanisms important in the initiation and metastasis of PNETs, continued efforts to translate these discoveries into distinct new therapies will be needed to improve patient survival. Clin Cancer Res; 22(20); 5022-9. ©2016 AACR SEE ALL ARTICLES IN THIS CCR FOCUS SECTION, "ENDOCRINE CANCERS REVISING PARADIGMS".

Update in the Therapy of Advanced Neuroendocrine Tumors

OPINION STATEMENT

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

Somatostatin analogs in the treatment of neuroendocrine tumors: current and emerging aspects

INTRODUCTION

Neuroendocrine tumors (NETs) harbor somatostatin receptors and there is a strong rationale for using somatostatin analogs (SSAs) for treatment of NETs. Areas covered: This article discusses i) pharmacology of somatostatin and its analogs; ii) antisecretory and anti-proliferative effects of SSAs in NETs; iii) efficacy and safety of emerging therapeutic regimens with first generation SSAs administered at either high doses or in combination with antineoplastic drugs; iv) efficacy and safety of pasireotide and chimeric molecules; v) efficacy of radionuclide therapy of NETs using SSAs. Expert opinion: SSAs are the first-line medical therapy for functioning and non-functioning well-differentiated NETs. In patients not responder to first generation SSAs, the increase of drug dose over the conventional regimens, the combination of SSAs with other biotherapies or molecular targeted therapies, the switch to pasireotide or the use of SSAs in radionuclide therapy may improve the therapeutic success.

Imaging of Neuroendocrine Tumors: Indications, Interpretations, Limits, and Pitfalls

Imaging is critical in the diagnosis, prognosis, and management of neuroendocrine tumors (NETs). NETs share common imaging features, but each type exhibits unique features. Computed tomography scans or MRI of the abdomen is used to assess tumor burden routinely. Functional imaging with octreotide scan or gallium-68 somatostatin analog PET is used selectively to confirm diagnosis and guide therapy. Clinicians and radiologists should be familiar with the indications and interpretations of imaging modalities. Novel functional imaging modalities likely will be developed to detect small NETs, predict prognosis, guide therapeutic choices, and design novel therapies.

Management of the hormonal syndrome of neuroendocrine tumors

Gastroenteropancreatic neuroendocrine tumors (GEP/NET) are unusual and rare neoplasms that present many clinical challenges. They characteristically synthesize store and secrete a variety of peptides and neuroamines which can lead to the development of distinct clinical syndrome, however many are clinically silent until late presentation with mass effects. Management strategies include surgery cure and cytoreduction with the use of somatostatin analogues. Somatostatin have a broad range of biological actions that include inhibition of exocrine and endocrine secretions, gut motility, cell proliferation, cell survival and angiogenesis. Five somatostatin receptors (SSTR1-SSTR5) have been cloned and characterized. Somatostatin analogues include octreotide and lanreotide are effective medical tools in the treatment and present selectivity for SSTR2 and SSTR5. During treatment is seen disapperance of flushing, normalization of bowel movements and reduction of serotonin and 5-hydroxyindole acetic acid (5-HIAA) secretion. Telotristat represents a novel approach by specifically inhibiting serotonin synthesis and as such, is a promising potential new treatment for patients with carcinoid syndrome. To pancreatic functionig neuroendocrine tumors belongs insulinoma, gastrinoma, glucagonoma and VIP-oma. Medical management in patients with insulinoma include diazoxide which suppresses insulin release. Also mTOR inhibitors may inhibit insulin secretion. Treatment of gastrinoma include both proton pump inhibitors (PPIs) and histamine H2 - receptor antagonists. In patients with glucagonomas hyperglycaemia can be controlled using insulin and oral blood glucose lowering drugs. In malignant glucagonomas smatostatin analogues are effective in controlling necrolytic migratory erythemia. Severe cases of the VIP-oma syndrome require supplementation of fluid losses. Octreotide reduce tumoral VIP secretion and control secretory diarrhoea.

Gastro-entero-pancreatic neuroendocrine tumors in multiple endocrine neoplasia type 1: a therapy update

Gastro-entero-pancreatic neuroendocrine tumors (GEP-NETs) are the second most common tumors in multiple endocrine neoplasia type 1 (MEN1), mainly occurring in pancreatic islets and duodenum, usually as multiple tumors. They can manifest as both nonfunctioning and functioning tumors. Currently, surgical removal of GEP-NETs in MEN1 represents the gold standard curative approach. Conventional medical therapies for sporadic GEP-NETs showed to be effective also in a percentage of MEN1 patients. Innovative medical therapies, that have demonstrated to be effective on sporadic GEP-NETs, still need to be evaluated on MEN1 patients in prospective clinical trials and long-term follow-up. This review resumes current knowledge of MEN1 GEP-NETs, discussing surgical and medical approaches, genetic and molecular bases of tumorigenesis, and presenting novel possible drug therapies.

Imaging of Prostate Cancer Using Urokinase-Type Plasminogen Activator Receptor PET

Urokinase-type plasminogen activator receptor (uPAR) overexpression is an important biomarker for aggressiveness in cancer including prostate cancer (PC) and provides independent clinical information in addition to prostate-specific antigen and Gleason score. This article focuses on uPAR PET as a new diagnostic and prognostic imaging biomarker in PC. Many preclinical uPAR-targeted PET imaging studies using AE105 in cancer models have been undertaken with promising results. A major breakthrough was obtained with the recent human translation of uPAR PET in using ⁶⁴Cu- and ⁶⁸Ga-labelled versions of AE105, respectively. Clinical results from patients with PC included in these studies are encouraging and support continuation with large-scale clinical trials.

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.

Neuroendocrine tumor liver metastases treated with yttrium-90 radioembolization

OBJECTIVE

Yttrium-90 (Y-90) radioembolization is an emerging treatment option for unresectable neuroendocrine liver metastases (NELM). However, the data regarding this treatment are currently limited. This study evaluates the efficacy and tolerability of Y-90 radioembolization and identifies prognostic factors for radiographic response and survival.

METHODS AND MATERIALS

Thirty-eight patients underwent Y-90 radioembolization for NELM at our institution between April 2004 and February 2012. Patients were assessed radiographically (RECIST criteria, enhancement), serologically, and clinically at 1month, and then at every 3months after treatment for tumor response, toxicity, and survival outcomes.

RESULTS

Median length of follow-up was 17.0months (IQR, 9.0-37.0). Median survival was 29.2months. Three patients (9%) had a radiographic complete response to treatment, 6 (17%) had a partial response, 21 (60%) had stable disease, and 5 (14%) developed progressive disease. Two factors were significantly associated with a good radiographic response (complete/partial response): islet cell histological subtype (p=0.043) and hepatic tumor burden ≥33% (p=0.031). Multivariate analysis revealed that patients requiring multiple Y-90 treatments (HR 2.9, p=0.035) and patients who had previously failed systemic therapy with octreotide/chemotherapy (HR 4.4, p=0.012) had worse survival. Grade 3 serologic toxicity was observed in 2 patients (5%; hyperbilirubinemia, elevated alkaline phosphatase) after treatment. Grade 3 non-serologic toxicities included abdominal pain (11%), fatigue (11%), nausea/vomiting (5%), ascites (5%), dyspnea (3%), diarrhea (3%), and peripheral edema (3%). No grade 4 or 5 toxicity was reported.

CONCLUSIONS

Y-90 radioembolization is a promising treatment option for inoperable NELM and is associated with low rates of grade≥3 toxicity.

Subtype classification and management of gastric neuroendocrine neoplasms

Gastric neuroendocrine neoplasms (g-NENs) are a group of heterogeneous tumors arising from endocrine cells in the stomach. Because of the low incidence, clinical misdiagnosis and mismanagement of g-NENs may occasionally occur. In this review, I summarize the epidemiology, pathology, tumor staging, clinical classification, diagnostic algorithm, treatment and prognosis of g-NENs, to explain the standard diagnosis and management, as well as the latest advances in g-NEN research. The author advocates the four-type classification of g-NENs, and emphasizes that type 1 g-NENs are a recurrent disease which needs long-term follow-up. Molecular mechanism of recurrence of and medical therapy for type 1 g-NENs are the future research direction for neuroendocrine neoplasms.

PET imaging of urokinase-type plasminogen activator receptor (uPAR) in prostate cancer: current status and future perspectives

Overexpression of urokinase-type plasminogen activator receptors (uPAR) represents an important biomarker for aggressiveness in most common malignant diseases, including prostate cancer (PC). Accordingly, uPAR expression either assessed directly in malignant PC tissue or assessed directly in plasma (intact/cleaved forms)—provides independent additional clinical information to that contributed by PSA, Gleason score, and other relevant pathological and clinical parameters. In this respect, non-invasive molecular imaging by positron emission tomography (PET) offers a very attractive technology platform, which can provide the required quantitative information on the uPAR expression profile, without the need for invasive procedures and the risk of missing the target due to tumor heterogeneity. These observations support non-invasive PET imaging of uPAR in PC as a clinically relevant diagnostic and prognostic imaging method. In this review, we will focus on the recent development of uPAR PET and the relevance within prostate cancer imaging. Novel antibody and small-molecule radiotracers-targeting uPAR, including a series of uPAR-targeting PET ligands, based on the high affinity peptide ligand AE105, have been synthesized and tested in vitro and in vivo in preclinical murine xenograft models and, recently, in a first-ever clinical uPAR PET study in cancer patients, including patients with PC. In this phase I study, a high and specific uptake of the tracer ⁶⁴Cu-DOTA-AE105 was found in both primary tumors and lymph node metastases. The results are encouraging and support large-scale clinical trials to determine the utility of uPAR PET in the management of patients with PC with the goal of improving outcome.