PET tracers for somatostatin receptor imaging of neuroendocrine tumors: current status and review of the literature

Somatostatin Receptors and Analogs in Pheochromocytoma and Paraganglioma: Old Players in a New Precision Medicine World

Neuroendocrine tumors overexpress somatostatin receptors, which serve as important and unique therapeutic targets for well-differentiated advanced disease. This overexpression is a well-established finding in gastroenteropancreatic neuroendocrine tumors which has guided new medical therapies in the administration of somatostatin analogs, both "cold", particularly octreotide and lanreotide, and "hot" analogs, chelated to radiolabeled isotopes. The binding of these analogs to somatostatin receptors effectively suppresses excess hormone secretion and tumor cell proliferation, leading to stabilization, and in some cases, tumor shrinkage. Radioisotope-labeled somatostatin analogs are utilized for both tumor localization and peptide radionuclide therapy, with ⁶⁸Ga-DOTATATE and ¹⁷⁷Lu-DOTATATE respectively. Benign and malignant pheochromocytomas and paragangliomas also overexpress somatostatin receptors, irrespective of embryological origin. The pattern of somatostatin receptor overexpression is more prominent in succinate dehydrogenase subunit B gene mutation, which is more aggressive than other subgroups of this disease. While the Food and Drug Administration has approved the use of ⁶⁸Ga-DOTATATE as a radiopharmaceutical for somatostatin receptor imaging, the use of its radiotherapeutic counterpart still needs approval beyond gastroenteropancreatic neuroendocrine tumors. Thus, patients with pheochromocytoma and paraganglioma, especially those with inoperable or metastatic diseases, depend on the clinical trials of somatostatin analogs. The review summarizes the advances in the utilization of somatostatin receptor for diagnostic and therapeutic approaches in the neuroendocrine tumor subset of pheochromocytoma and paraganglioma; we hope to provide a positive perspective in using these receptors as targets for treatment in this rare condition.

Role of Somatostatin Receptor in Pancreatic Neuroendocrine Tumor Development, Diagnosis, and Therapy

Pancreatic neuroendocrine tumors (pNETs) are rare and part of the diverse family of neuroendocrine neoplasms (NENs). Somatostatin receptors (SSTRs), which are widely expressed in NENs, are G-protein coupled receptors that can be activated by somatostatins or its synthetic analogs. Therefore, SSTRs have been widely researched as a diagnostic marker and therapeutic target in pNETs. A large number of studies have demonstrated the clinical significance of SSTRs in pNETs. In this review, relevant literature has been appraised to summarize the most recent empirical evidence addressing the clinical significance of SSTRs in pNETs. Overall, these studies have shown that SSTRs have great value in the diagnosis, treatment, and prognostic prediction of pNETs; however, further research is still necessary.

Comparison of 5 Different PET Radiopharmaceuticals for the Detection of Recurrent Medullary Thyroid Carcinoma: A Network Meta-analysis

PURPOSE

The aim of this study is to investigate and compare the performance of different PET radiopharmaceuticals for the detection of recurrent medullary thyroid carcinoma (MTC) by performing a network meta-analysis (NMA) using direct comparison studies with 2 or more PET radiopharmaceuticals.

METHODS

PubMed and EMBASE were searched for the studies evaluating the performance of PET or PET/CT for the detection of recurrent MTC. The NMA was performed for different PET radiopharmaceuticals in both patient- and lesion-based analyses and with a threshold of serum calcitonin or carcinoembryonic antigen (CEA) levels and calcitonin doubling time. The consistency was evaluated by examining the agreement between direct and indirect treatment effects, and publication bias was assessed by funnel plot asymmetry tests. The surface under the cumulative ranking curve values were obtained to calculate the probability of each PET modality being the most effective diagnostic method.

RESULTS

A total of 306 patients from 14 direct comparison studies using 5 different PET radiopharmaceuticals (F-FDG, F-DOPA, Ga-somatostatin analogs, 3-O-methyl-6-[F]fluoro-DOPA, and C-methionine) for the detection of recurrent MTC was included. The detection rate of F-DOPA PET was significantly higher than that of FDG PET in both patient- and lesion-based analyses (patient-based analysis: odds ratio, 2.44; 95% confidence interval, 1.4-4.31; lesion-based analysis: odds ratio, 5.74; 95% confidence interval, 1.65-23.4). Among all PET radiopharmaceuticals, F-DOPA showed the highest surface under the cumulative ranking curve value in both patient- and lesion-based analyses regardless of serum calcitonin or CEA levels and calcitonin doubling time.

CONCLUSIONS

The results from this NMA indicate that F-DOPA PET clearly showed a best performance for the detection of recurrent MTC in both patient- and lesion-based analyses regardless of serum calcitonin or CEA levels and calcitonin doubling time.

Incidental primary breast cancer detected on surveillance 68Ga-DOTATATE PET/CT in a patient with metastatic neuroendocrine carcinoma

We present a case of a 53-year-old woman with metastatic neuroendocrine tumor, presumed primary in the small intestine with metastases to the liver and mesenteric lymph nodes. The patient was being treated with lanreotide and followed with somatostatin receptor (SSTR)-targeted 68Ga-labeled 1,4,7,10-tetraazacyclododecane-N,N', N'',N'''-tetraacetic acid-d-Phe(1)-Tyr(3)-octreotate (⁶⁸Ga-DOTATATE) positron emission tomography – computed tomography (PET/CT). On a follow-up exam, the patient's primary and metastatic disease had improved but she had new ⁶⁸Ga-DOTATATE-avid lesions in the right breast and right axilla. Subsequent breast imaging workup and biopsy demonstrated a primary breast cancer and axillary lymph node metastasis.

High somatostatin receptor expression and efficacy of somatostatin analogues in patients with metastatic Merkel cell carcinoma

BACKGROUND

Merkel cell carcinoma (MCC) is an aggressive, high-grade, cutaneous neuroendocrine tumour (NET). Agents blocking programmed death 1/programmed death ligand 1 have efficacy in metastatic MCC (mMCC), but half of patients do not derive durable benefit. Somatostatin analogues (SSAs) are commonly used to treat low- and moderate-grade NETs that express somatostatin receptors (SSTRs).

OBJECTIVES

To assess SSTR expression and the efficacy of SSAs in mMCC, a high-grade NET. Methods In this retrospective study of 40 patients with mMCC, SSTR expression was assessed radiologically by somatostatin receptor scintigraphy (SRS; n = 39) and/or immunohistochemically when feasible (n = 9). Nineteen patients (18 had SRS uptake in MCC tumours) were treated with SSA. Disease control was defined as progression-free survival (PFS) of ≥ 120 days after initiation of SSA.

RESULTS

Thirty-three of 39 patients (85%) had some degree (low 52%, moderate 23%, high 10%) of SRS uptake. Of 19 patients treated with SSA, seven had a response-evaluable target lesion; three of these seven patients (43%) experienced disease control, with a median PFS of 237 days (range 152-358). Twelve of 19 patients did not have a response-evaluable lesion due to antecedent radiation; five of these 12 (42%) experienced disease control (median PFS of 429 days, range 143-1757). The degree of SSTR expression (determined by SRS and/or immunohistochemistry) did not correlate significantly with the efficacy endpoints.

CONCLUSIONS

In contrast to other high-grade NETs, mMCC tumours appear frequently to express SSTRs. SSAs can lead to clinically meaningful disease control with minimal side-effects. Targeting of SSTRs using SSA or other novel approaches should be explored further for mMCC.

Tumour-to-liver ratio determined by [68Ga]Ga-DOTA-TOC PET/CT as a prognostic factor of lanreotide efficacy for patients with well-differentiated gastroenteropancreatic-neuroendocrine tumours

Abstract

Background

Lanreotide is a long-acting somatostatin analogue with proven antitumour effects against well-differentiated (WD) gastroenteropancreatic-neuroendocrine tumours (GEP-NETs). However, there are no globally established prognostic factors associated with the efficacy of lanreotide as a treatment for GEP-NETs. We investigated the prognostic value of [⁶⁸Ga]Ga-DOTA-TOC positron emission tomography (PET)/computed tomography (CT) somatostatin receptor imaging for patients with WD GEP-NETs treated with lanreotide.

Methods

In this retrospective study, we included 31 patients with unresectable or metastatic WD GEP-NETs who received lanreotide and underwent [⁶⁸Ga]Ga-DOTA-TOC PET/CT before receiving lanreotide. We captured the following clinicopathological variables: Eastern Cooperative Oncology Group (ECOG) performance status, primary tumour site, NET World Health Organization grade, existence of carcinoid symptoms, previous surgery, previous chemotherapy, and hepatic tumour volume assessed by CT or magnetic resonance imaging (MRI). We also assessed the following [⁶⁸Ga]Ga-DOTA-TOC PET/CT variables: Krenning score, tumour-to-liver ratio (TLR), maximum standardized uptake value (SUVmax), whole tumour volume (WTV), and total receptor expression (TRE, WTV multiplied by SUVmean). The associations between these markers and progression-free survival (PFS) with lanreotide were analysed.

Results

The mean age was 55.1 ± 15.5 years (range 16.0–81.0). The most common primary tumour site was the pancreas, followed by the stomach, and rectum. The median PFS interval with lanreotide was 14.4 months (range 1.3–34.9), with identified disease progression in 20 patients (64.5%). Among the [⁶⁸Ga]Ga-DOTA-TOC PET/CT variables, TLR (< 8.1 vs. ≥ 8.1; p = 0.013), SUVmax (< 42.9 vs. ≥ 42.9; p = 0.037), and WTV (≥ 58.9 cm³ vs. < 58.9 cm³; p = 0.030) were significantly associated with PFS in the univariate analyses, but only TLR (hazard ratio 3.182 [95% CI 1.189–8.514], p = 0.021) remained an independent factor for PFS in the multivariate analysis.

Conclusions

Low TLR, determined via [⁶⁸Ga]Ga-DOTA-TOC PET/CT, can be a factor of worse prognosis in patients with advanced WD GEP-NETs treated with lanreotide.

Medical Treatment of Advanced Pancreatic Neuroendocrine Neoplasms

Pancreatic neuroendocrine neoplasms (panNENs) are relatively rare but their incidence has increased almost sevenfold over the last four decades. Neuroendocrine neoplasms are classified according to their histologic differentiation and their grade. Their grade is based on their Ki-67 proliferation index and mitotic index. Their prognosis is highly variable according to these elements and treatments also vary according to their classification. Surgery is the only curative treatment for localized and advanced panNENs and offers a better prognosis than non-surgical treatments. In the case of an advanced panNEN without the possibility of resection and/or ablation, medical treatment remains the cornerstone for improving survival and preserving quality-of-life. PanNENs are considered as chemosensitive tumors, unlike midgut neuroendocrine tumors. Thus, panNENs can be treated with chemotherapy, but targeted therapies and somatostatin analogs are also treatment options. The scarcity and heterogeneity of NENs make their management difficult. The present review aims to clarify the medical treatments currently available for advanced panNENs, based on their characteristics, and to propose a treatment algorithm.

Evaluation of 177Lu-Dotatate treatment in patients with metastatic neuroendocrine tumors and prognostic factors

BACKGROUND

¹⁷⁷Lu peptide receptor radionuclide therapy (PRRT) is a recently approved therapy in Spain that has been demonstrated to be a well-tolerated therapy for positive somatostatin receptor advanced gastroenteropancreatic neuroendocrine tumors.

AIM

To determine the impact of PRRT on quality of life, radiologic and metabolic response, overall survival, prognostic factors and toxicity.

METHODS

Thirty-six patients treated with ¹⁷⁷Lu-PRRT from 2016 to 2019 were included. The most frequent location of the primary tumor was the gastrointestinal tract (52.8%), pancreas (27.8%), and nongastropancreatic neuroendocrine tumor (11.1%). The liver was the most common site of metastasis (91.7%), followed by distant nodes (50.0%), bone (27.8%), peritoneum (25.0%) and lung (11.1%). Toxicity was evaluated after the administration of each dose. Treatment efficacy was evaluated by two parameters: stable disease and disease progression in response evaluation criteria in solid tumors 1.1 criterion and prognostic factors were tested.

RESULTS

From 36 patients, 55.6% were men, with a median age of 61.1 ± 11.8 years. Regarding previous treatments, 55.6% of patients underwent surgery of the primary tumor, 100% of patients were treated with long-acting somatostatin analogues, 66.7% of patients were treated with everolimus, 27.8% of patients were treated with tyrosine kinase inhibitor, and 27.8% of patients were treated with interferon. One patient received radioembolization, three patients received chemoembolization, six patients received chemotherapy. Hematological toxicity was registered in 14 patients (G1-G2: 55.5% and G3: 3.1%). Other events presented were intestinal suboclusion in 4 cases, cholestasis in 2 cases and carcinoid crisis in 1 case. The median follow-up time was 3 years. Currently, 24 patients completed treatment. Nineteen are alive with stable disease, two have disease progression, eight have died, and nine are still receiving treatment. The median overall survival was 12.5 mo (95% confidence interval range: 9.8–15.2), being inversely proportional to toxicity in previous treatments (P < 0.02), tumor grade (P < 0.01) and the presence of bone lesions (P = 0.009) and directly proportional with matching lesion findings between Octreoscan and computed tomography pre-PRRT (P < 0.01), , primary tumor surgery (P = 0.03) and metastasis surgery (P = 0.045). In a multivariate Cox regression analysis, a high Ki67 index (P = 0.003), a mismatch in the lesion findings between Octreoscan and computed tomography pre-PRRT (P < 0.01) and a preceding toxicity in previous treatments (P < 0.05) were risk factors to overall survival.

CONCLUSION

Overall survival was inversely proportional to previous toxicity, tumor grade and the presence of bone metastasis and directly proportional to matching lesion findings between Octreoscan and computed tomography pre-PRRT and primary tumor and metastasis surgery.

Advances in the Diagnosis and Management of Well-Differentiated Neuroendocrine Neoplasms

Neuroendocrine neoplasms constitute a diverse group of tumors that derive from the sensory and secretory neuroendocrine cells and predominantly arise within the pulmonary and gastrointestinal tracts. The majority of these neoplasms have a well-differentiated grade and are termed neuroendocrine tumors (NETs). This subgroup is characterized by limited proliferation and patients affected by these tumors carry a good to moderate prognosis. A substantial subset of patients presenting with a NET suffer from the consequences of endocrine syndromes as a result of the excessive secretion of amines or peptide hormones, which can impair their quality of life and prognosis. Over the past 15 years, critical developments in tumor grading, diagnostic biomarkers, radionuclide imaging, randomized controlled drug trials, evidence-based guidelines, and superior prognostic outcomes have substantially altered the field of NET care. Here, we review the relevant advances to clinical practice that have significantly upgraded our approach to NET patients, both in diagnostic and in therapeutic options.

[68Ga]Ga-DOTA-TOC: The First FDA-Approved 68Ga-Radiopharmaceutical for PET Imaging

In the United States, [⁶⁸Ga]Ga-DOTA-TOC has been approved by the Food and Drug Administration (FDA) in 2019 as the first ⁶⁸Ga-radiopharmaceutical for imaging of somatostatin receptor (SSTR) positive gastroenteropancreatic neuroendocrine tumors while employing positron emission tomography (PET). In Europe (Austria, Germany, France), [⁶⁸Ga]Ga-DOTA-TOC was already approved back in 2016. This radiopharmaceutical combines the radionuclide ⁶⁸Ga with the somatostatin analogue DOTA-TOC for specific imaging of tumor cells expressing SSTRs. Such a targeting approach can also be used for therapy planning in the case of both localized as well as disseminated disease and potentially for the evaluation of treatment response.

CT texture analysis of liver metastases in PNETs versus NPNETs: Correlation with histopathological findings

PURPOSE

To compare CT and Texture features of liver metastases in Pancreatic Neuroendocrine Tumors (PNETs) and in Non-Pancreatic Neuroendocrine Tumors (NPNETs) according to tumor grading, overall survival (OS), time to progression (TTP) and Ki67 index.

METHODS

23 patients with PNETs and 25 patients with NPNETs affected by liver metastases were compared. The lesions were G1 and G2 according to WHO classification of tumors. Texture parameters (Mean, Standard Deviation, Entropy, Kurtosis, Skewness, Mean of Positive Pixel) at different spatial scale image filtration (SSF) were evaluated in both arterial and portal phase using a dedicated software for volumetric analysis. All CT images were acquired before the beginning of any medical treatment.

RESULTS

The following significant results (P < 0.05) were found: in the arterial phase for value of Skewness between PNETs G2 and NPNETs G2; in the portal phase between PNETs versus NPNETs, PNETs G1 versus NPNETs G1, PNETs G2 versus NPNETs G2; value of Mean in portal phase in PNETs vs NPNETs. Regarding PNETs, a P < 0.05 was found in: inverse correlation between Entropy and TTP; direct correlation between Mean and OS; correlating Kurtosis and high risk of death; correlating Skewness and low risk of death. Regarding NPNETs, P < 0.05 was found in: inverse correlation between Entropy and OS; correlating Entropy and high risk of dying.

CONCLUSIONS

This study shows that CT texture features are significantly different in PNETs from NPNETs. Additionally, textural features such as Entropy, Kurtosis and Skewness, were found to have significant correlation with higher mortality risk.

64Cu-DOTATATE PET/CT and Prediction of Overall and Progression-Free Survival in Patients with Neuroendocrine Neoplasms

Overexpression of somatostatin receptors (SSTRs) in patients with neuroendocrine neoplasms (NENs) is used for both diagnosis and treatment. Receptor density may reflect tumor differentiation and thus be associated with prognosis. Noninvasive visualization and quantification of SSTR density is possible by SSTR imaging (SRI) using PET. Recently, we introduced ⁶⁴Cu-DOTATATE for SRI, and we hypothesized that uptake of this tracer could be associated with overall survival (OS) and progression-free survival (PFS). Methods: We evaluated patients with NENs who underwent ⁶⁴Cu-DOTATATE PET/CT SRI in 2 prospective studies. Tracer uptake was determined as the maximal SUV (SUV_max) for each patient. Kaplan-Meier analysis with log-rank was used to determine the predictive value of ⁶⁴Cu-DOTATATE SUV_max for OS and PFS. Specificity, sensitivity, and accuracy were calculated for prediction of outcome at 24 mo after ⁶⁴Cu-DOTATATE PET/CT. Results: In total, 128 patients with NENs were included and followed for a median of 73 mo (range, 1-112 mo). During follow-up, 112 experienced disease progression, and 69 died. The optimal cutoff for ⁶⁴Cu-DOTATATE SUV_max was 43.3 for prediction of PFS, with a hazard ratio of 0.56 (95% confidence interval, 0.38-0.84) for patients with an SUV_max of more than 43.3. However, no significant cutoff was found for prediction of OS. In multiple Cox regression adjusted for age, sex, primary tumor site, and tumor grade, the SUV_max cutoff hazard ratio was 0.50 (range, 0.32-0.77) for PFS. The accuracy was moderate for predicting PFS (57%) at 24 mo after ⁶⁴Cu-DOTATATE PET/CT. Conclusion: In this first study to report the association of ⁶⁴Cu-DOTATATE PET/CT and outcome in patients with NENs, tumor SSTR density as visualized with ⁶⁴Cu-DOTATATE PET/CT was prognostic for PFS but not OS. However, the accuracy of prediction of PFS at 24 mo after ⁶⁴Cu-DOTATATE PET/CT SRI was moderate, limiting the value on an individual-patient basis.

Prognostic value of a three-scale grading system based on combining molecular imaging with 68Ga-DOTATATE and 18F-FDG PET/CT in patients with metastatic gastroenteropancreatic neuroendocrine neoplasias

We investigated on the added prognostic value of a three-scale combined molecular imaging with ⁶⁸Ga-DOTATATE and ¹⁸F-FDG PET/CT, (compared to Ki-67 based histological grading), in gastroenteropancreatic neuroendocrine neoplasia patients. 85 patients with histologically proven metastatic gastroenteropancreatic neuroendocrine neoplasias, who underwent combined PET/CT imaging were retrospectively evaluated. Highest Ki-67 value available at time of ¹⁸F-FDG PET/CT was recorded. Patients were classified according to World Health Organization/European Neuroendocrine Tumor Society histological grades (G1, G2, G3) and into three distinct imaging categories (C1: all lesions are ¹⁸F-FDG negative/⁶⁸Ga-DOTATATE positive, C2: patients with one or more ¹⁸F-FDG positive lesions, all of them ⁶⁸Ga-DOTATATE positive, C3: patients with one or more ¹⁸F-FDG positive lesions, at least one of them ⁶⁸Ga-DOTATATE negative). The primary endpoint of the study was Progression-Free Survival, assessed from the date of ¹⁸F-FDG PET/CT to the date of radiological progression according to Response Evaluation Criteria In Solid Tumors version 1.1. Classification according to histological grade did not show significant statistical difference in median Progression-Free Survival between G1 and G2 but was significant between G2 and G3 patients. In contrast, median Progression-Free Survival was significantly higher in C1 compared to C2 and in C2 compared to C3 patients, revealing three distinctive imaging categories, each with highly distinctive prognosis. Our three-scale combined ⁶⁸Ga-DOTATATE/¹⁸F-FDG PET imaging classification holds high prognostic value in patients with metastatic gastroenteropancreatic neuroendocrine neoplasias.

Radiolabelled Peptides for Positron Emission Tomography and Endoradiotherapy in Oncology

This review deals with the development of peptide-based radiopharmaceuticals for the use with positron emission tomography and peptide receptor radiotherapy. It discusses the pros and cons of this class of radiopharmaceuticals as well as the different labelling strategies, and summarises approaches to optimise metabolic stability. Additionally, it presents different target structures and addresses corresponding tracers, which are already used in clinical routine or are being investigated in clinical trials.

64Cu-DOTATATE PET/CT for Imaging Patients with Known or Suspected Somatostatin Receptor-Positive Neuroendocrine Tumors: Results of the First U.S. Prospective, Reader-Masked Clinical Trial

Studies demonstrate that the investigational ⁶⁴Cu-DOTATATE radiopharmaceutical may provide diagnostic and logistical benefits over available imaging agents for patients with somatostatin receptor (SSTR)-positive neuroendocrine tumors (NETs). Accordingly, we aimed to prospectively determine the lowest dose of ⁶⁴Cu-DOTATATE that facilitates diagnostic-quality scans and evaluated the diagnostic performance and safety in a phase III study of patients with SSTR-expressing NETs. Methods: A dose-ranging study was conducted on 12 patients divided into 3 dose groups (111 MBq [3.0 mCi], 148 MBq [4.0 mCi], and 185 MBq [5.0 mCi] ± 10%) to determine the lowest dose of ⁶⁴Cu-DOTATATE that produced diagnostic-quality PET/CT images. Using the ⁶⁴Cu-DOTATATE dose identified in the dose-ranging study, 3 independent nuclear medicine physicians who were masked to all clinical information read PET/CT scans from 21 healthy volunteers and 42 NET-positive patients to determine those with disease or no disease, as well as those with localized versus metastatic status. Masked-reader evaluations were compared with a patient-specific standard of truth, which was established by an independent oncologist who used all previously available pathology, clinical, and conventional imaging data. Diagnostic performance calculated for ⁶⁴Cu-DOTATATE included sensitivity, specificity, negative predictive value, positive predictive value, and accuracy. Inter- and intrareader reliability, as well as ability to differentiate between localized and metastatic disease, was also determined. Adverse events were recorded from ⁶⁴Cu-DOTATATE injection through 48 h after injection. Results: The dose-ranging study identified 148 MBq (4.0 mCi) as the optimal dose to obtain diagnostic-quality PET/CT images. After database lock, diagnostic performance from an initial majority read of the 3 independent readers showed a significant 90.9% sensitivity (P = 0.0042) and 96.6% specificity (P < 0.0001) for detecting NETs, which translated to a 100.0% sensitivity and 96.8% specificity after correcting for an initial standard-of-truth misread. Excellent inter- and intrareader reliability, as well as ability to distinguish between localized and metastatic disease, was also noted. No adverse events were related to ⁶⁴Cu-DOTATATE, and no serious adverse events were observed. Conclusion: ⁶⁴Cu-DOTATATE PET/CT is a safe imaging technique that provides high-quality and accurate images at a dose of 148 MBq (4.0 mCi) for the detection of somatostatin-expressing NETs.

[Gastric neuroendocrine tumors]

Gastrointestinal neuroendocrine tumors are rare neoplasms. Currently, incidence of gastric neuroendocrine tumors (gNETs) is being significantly increased. There are 3 groups of gNETs: types I, II and III. Each type has important features regarding clinical picture, prognosis and treatment strategy. Type I is the most common (70-80%) and associated with chronic atrophic gastritis including autoimmune gastritis and Helicobacter associated atrophic gastritis. Type II (5-6%) is associated with multiple endocrine neoplasia type I and Zollinger-Ellison syndrome (MEN I - ZES). Both types are characterized by hypergastrinemia and small tumor dimension. These neoplasms are multiple and mostly benign. On the contrary, NETs type III (10-15%) is not associated with hypergastrinemia and represented by single large neoplasms. Tumors are malignant as a rule. Therefore, surgical resection and chemotherapy are preferred for these tumors. Endoscopic surgery followed by observation is acceptable for almost all NETS type I and II. At the same time, this approach is advisable only for small and highly differentiated neoplasms type III.

64Cu-DOTATOC PET-CT in Patients with Neuroendocrine Tumors

Introduction

Several radiolabeled somatostatin analogues have been developed for molecular imaging of neuroendocrine tumors (NETs) with single-photon emission computed tomography (SPECT) and positron-emission tomography (PET). The aim of the present study was to report our first results using ⁶⁴Cu-DOTATOC in patients with NETs.

Methods

Thirty-three patients with NETs (15 female, 18 male; mean age 64 ± 13 years) were included in this retrospective study. ⁶⁴Cu-DOTATOC PET–CT scans were performed on all patients.

Results

Five out of 33 patients with a history of NET after surgical removal of the primary lesion showed no pathological lesions on PET–CT imaging and 8/33 patients had enhanced uptake in the area of recurrent meningioma at the skull base. The remaining 20/33 patients had a history of neuroendocrine tumor in the gastrointestinal tract (GEP-NET) and were presented with at least one pathological lesion.

Conclusion

The high detection rate of suspected lesions in patients with NETs and the high target-to-background contrast found in this study hold promise for the safe application of ⁶⁴Cu-DOTATOC in patients with NET.

Evaluation of [68Ga]Ga-DATA-TOC for imaging of neuroendocrine tumours: comparison with [68Ga]Ga-DOTA-NOC PET/CT

PURPOSE

Recently, the new hybrid chelator DATA (6-amino-1,4-diazepine-triacetate) has been introduced, which has the advantage of high yield and radiolabelling of DATA-based octreotide derivative (TOC) at room temperature in contrast to tetraazacyclododecane-1,4,7,10-tetraacetate (DOTA) that needs 95 °C for effective labelling. However, the diagnostic potential of DATA-TOC has not been studied with other chelators in humans. The aim of this study was to compare the diagnostic efficacy of [⁶⁸Ga]Ga-DATA-TOC with [⁶⁸Ga]Ga-DOTA-NOC (which is the current standard for imaging neuroendocrine tumours (NET)) in patients of gastroenteropancreatic neuroendocrine tumours (GEP-NETs).

METHODS

Fifty patients (thirty-one males and nineteen females) with biopsy-proven GEP-NETs were included in the study. Patients age ranged from 14 to 75 years (mean 46.11 years). All patients underwent two PET studies with [⁶⁸Ga]Ga-DATA-TOC and [⁶⁸Ga]Ga-DOTA-NOC. Images were evaluated visually and semi-quantitatively using maximum standardized uptake values (SUVmax) of tumour, mediastinum and liver. Tumour-to-liver (T/L) and tumour-to-mediastinum (T/M) SUVmax ratios were computed. For the purpose of comparison, patient-wise as well as lesion-wise analysis was carried out. The nonparametric-related samples Wilcoxon signed-rank test was used for comparison of the SUVmax values and ratios.

RESULTS

On visual evaluation, the biodistribution and image quality of [⁶⁸Ga]Ga-DATA-TOC was similar to [⁶⁸Ga]Ga-DOTA-NOC. Physiological liver uptake was lower in [⁶⁸Ga]Ga-DATA-TOC as compared with [⁶⁸Ga]Ga-DOTA-NOC, 7.65 ± 5.37 vs 8.94 ± 5.95 (p = 0.009), respectively. On a patient-wise analysis, both [⁶⁸Ga]Ga-DATA-TOC and [⁶⁸Ga]Ga-DOTA-NOC were lesion-positive in the 44 patients (88%) and were negative in the 6 patients (12%). On a lesion-based analysis, [⁶⁸Ga]Ga-DATA-TOC had 98.6% concordance with [⁶⁸Ga]Ga-DOTA-NOC (232 out of 235 lesions detected). The target tumour SUVmax on [⁶⁸Ga]Ga-DATA-TOC and [⁶⁸Ga]Ga-DOTA-NOC were 36.63 ± 32.24 and 40.82 ± 36.89, respectively (p = 0.097). The T/L SUVmax ratios were not significantly different (5.99 ± 5.52 vs 5.67 ± 4.96, p = 0.77).

CONCLUSION

[⁶⁸Ga]Ga-DATA-TOC PET/CT imaging produced results that were comparable with [⁶⁸Ga]Ga-DOTA-NOC. It, thus, has potential utility as an effective and safe alternative to ⁶⁸Ga-DOTA-NOC with the added benefit of ease, cost-effective and improved yield of instant kit-type synthesis.

Current status of PET imaging in neuro-oncology

Over the past decades, a variety of PET tracers have been used for the evaluation of patients with brain tumors. For clinical routine, the most important clinical indications for PET imaging in patients with brain tumors are the identification of neoplastic tissue including the delineation of tumor extent for the further diagnostic and therapeutic management (ie, biopsy, resection, or radiotherapy planning), the assessment of response to a certain anticancer therapy including its (predictive) effect on the patients’ outcome and the differentiation of treatment-related changes (eg, pseudoprogression and radiation necrosis) from tumor progression at follow-up. To serve medical professionals of all disciplines involved in the diagnosis and care of patients with brain tumors, this review summarizes the value of PET imaging for the latter-mentioned 3 clinically relevant indications in patients with glioma, meningioma, and brain metastases.

Fully automated peptide radiolabeling from [18F]fluoride

The biological properties of receptor-targeted peptides have made them popular diagnostic imaging and therapeutic agents. Typically, the synthesis of fluorine-18 radiolabeled receptor-targeted peptides for positron emission tomography (PET) imaging is a time consuming, complex, multi-step synthetic process that is highly variable based on the peptide. The complexity associated with the radiolabeling route and lack of robust automated protocols can hinder translation into the clinic. A fully automated batch production to radiolabel three peptides (YGGFL, cRGDyK, and Pyr-QKLGNQWAVGHLM) from fluorine-18 using the ELIXYS FLEX/CHEM® radiosynthesizer in a two-step process is described. First, the prosthetic group, 6-[18F]fluoronicotinyl-2,3,5,6-tetrafluorophenyl ester ([18F]FPy-TFP) was synthesized and subsequently attached to the peptide. The [18F]FPy-peptides were synthesized in 13-26% decay corrected yields from fluorine-18 with high molar activity 1-5 Ci μmol-1 and radiochemical purity of >99% in an overall synthesis time of 97 ± 3 minutes.

Bench to Bedside: Albumin Binders for Improved Cancer Radioligand Therapies

Radioligand therapy (RLT) relies on the use of pharmacophores to selectively deliver ionization energy to cancers to exert its tumoricidal effects. Cancer cells that are not directly targeted by a radioconjugate remain susceptible to RLT because of the crossfire effect. This is significant given the inter- and intra-heterogeneity of tumors. In recent years, reversible albumin binders have been used as simple "add-ons" for radiopharmaceuticals to modify pharmacokinetics and to enhance therapeutic efficacy. In this Review, we discuss recent advances in albumin binder platforms used in RLT, with an emphasis on 4-( p-iodophenyl)butyric acid and Evans blue derivatives. We focus on four biological systems pertinent to oncology that utilize this class of compounds: folate receptor, integrin αvβ3, somatostatin receptor, and prostate-specific membrane antigen. Finally, we offer our perspectives on albumin binders for RLT, highlighting future areas of research that will help propel the technology further for clinical use.

Fundamental study of radiogallium-labeled aspartic acid peptides introducing octreotate derivatives

OBJECTIVE

Somatostatin receptors are highly expressed in neuroendocrine tumors, and many radiolabeled somatostatin analogs for diagnosis and treatment have been developed. To simultaneously detect not only primary cancer but also bone metastases, this study aimed to develop a positron emission tomography probe using generator-produced nuclide Gallium-68 (T_1/2 = 68 min), in which a carrier for primary cancer, a carrier for bone metastases lesions, and a stable gallium complex are introduced into the one molecule. Based on this strategy, the somatostatin receptor-targeted peptide, [Tyr³]-octreotate (TATE), aspartic acid peptide (D_n) with high binding affinity for hydroxyapatite, and Ga-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) as a stable gallium complex were selected. The novel complexes, Ga-DOTA-D_n-TATE (n = 0, 2, 5, 8, or 11), were designed, synthesized, and evaluated. The radiogallium complexes were prepared using the easy-to-handle radioisotope ⁶⁷Ga due to relatively long half-life.

METHODS

The radiogallium complex precursor DOTA-D_n-TATE was synthesized by the Fmoc-based solid-phase method and by the air oxidation method to form the disulfide bond. [⁶⁷Ga]Ga-DOTA-D_n-TATE was synthesized by reacting DOTA-D_n-TATE and ⁶⁷Ga. Hydroxyapatite binding assays, in vitro cellular uptake experiments in AR42J tumor cells, in biodistribution experiments in AR42J tumor-bearing mice, were performed using [⁶⁷Ga]Ga-DOTA-D_n-TATE.

RESULTS

The radiochemical purities of [⁶⁷Ga]Ga-DOTA-D_n-TATE were > 96.0%. In in vitro and in vivo experiments, [⁶⁷Ga]Ga-DOTA-D₁₁-TATE had a high affinity for hydroxyapatite and highly accumulated in bone. However, the uptake of [⁶⁷Ga]Ga-DOTA-D₁₁-TATE into somatostatin receptor-positive AR42J cells was lower than that of [⁶⁷Ga]Ga-DOTA-TATE, and the accumulation of [⁶⁷Ga]Ga-DOTA-D₁₁-TATE in tumor was significantly low.

CONCLUSION

Ga-DOTA-D₁₁-TATE may not be recognized by somatostatin receptor by the introduction of D₁₁, and the charge adjustment may be important for somatostatin receptor-positive cell uptake.

Copper-64: a real theranostic agent

Ongoing studies of physiological and pathological processes have led to a corresponding need for new radiopharmaceuticals, especially when studies are limited by the absence of a particular radiolabeled target. Thus, the development of new radioactive tracers is highly relevant and can represent a significant contribution to efforts to elucidate important phenomena in biology. Currently, theranostics represents a new frontier in the fields of medicine and nuclear medicine, with the same compound being used for both diagnosis and treatment. In the human body, copper (Cu) is the third most abundant metal and it plays a crucial role in many biological functions. Correspondingly, in various acquired and inherited pathological conditions, such as cancer and Alzheimer’s disease, alterations in Cu levels have been found. Moreover, a wide spectrum of neurodegenerative disorders are associated with higher or lower levels of Cu, as well as inappropriately bound or distributed levels of Cu in the brain. In human cells, the membrane protein, hCtr1, binds Cu in its Cu(I) oxidation state in an energy-dependent manner. Copper-64 (⁶⁴Cu) is a cyclotron-produced radionuclide that has exhibited physical properties that are complementary for diagnosis and/or therapeutic purposes. To date, very few reports have described the clinical development of ⁶⁴Cu as a radiotracer for cancer imaging. In this review, we highlight recent insights in our understanding and use of ⁶⁴CuCl₂ as a theranostic agent for various types of tumors. To the best of our knowledge, no adverse effects or clinically observable pharmacological effects have been described for ⁶⁴CuCl₂ in the literature. Thus, ⁶⁴Cu represents a revolutionary radiopharmaceutical for positron emission tomography imaging and opens a new era in the theranostic field.

Successful Localization Using 68Ga-DOTATOC PET/CT of a Phosphaturic Mesenchymal Tumor Causing Osteomalacia in a Patient with Concurrent Follicular Lymphoma

Diagnosing tumor-induced osteomalacia is often challenging because conventional imaging modalities may fail to locate the responsible tumor. This report describes the ability of ⁶⁸Ga-DOTATOC PET/CT to successfully distinguish between the responsible phosphaturic mesenchymal tumor and concurrent lymphoma lesions. A 52-year-old man with bone pain for several years was diagnosed with a vitamin D-resistant hypophosphatemic osteomalacia. Whole body ¹⁸F-FDG PET/CT revealed multiple enlarged hypermetabolic lymph nodes in his bilateral cervical, axillary, mediastinal, abdominal, pelvic, and inguinal regions. Core needle biopsy of the right cervical lymph node confirmed the diagnosis of follicular lymphoma. However, lymphoma was not considered the cause of osteomalacia. ⁶⁸Ga-DOTATOC PET/CT before chemotherapy showed a small nodule with intensely increased uptake in the right inguinal region, which was distinguished from the other enlarged lymph nodes. The nodule was surgically removed and histopathologically consistent with phosphaturic mesenchymal tumor. After surgery, the patient's serum phosphorus and alkaline phosphatase levels normalized without nutritional supplement.

Novel Functional Imaging of Neuroendocrine Tumors

Somatostatin receptor imaging constitutes an integral part in neuroendocrine tumor visualization and should, because of its vastly superior performance, use ⁶⁸Ga-DOTA-somatostatin analogue-PET/computed tomography rather than scintigraphy; it is particularly valuable for detecting metastases to lymph nodes, bone, peritoneum, and liver, which may be missed by morphologic imaging. ¹⁸FDG-PET/computed tomography is better suited for G3 and high-G2 neuroendocrine tumors. ¹⁸FDG-PET/computed tomography provides prognostic information. Alternative available PET tracers are ¹⁸F-DOPA and ¹¹C-5-hydroxytryptophan. To take full advantage of the technique PET/computed tomography should include diagnostic intravenous contrast-enhanced computed tomography. PET/MRI is currently mainly investigational.

Incidental finding of a breast carcinoma on Ga-68-DOTA-1-Nal3-octreotide positron emission tomography/computed tomography performed for the evaluation of a pancreatic neuroendocrine tumor: A case report

RATIONALE

Functional imaging using radiolabeled somatostatin analogues plays an important role in the management of patients with neuroendocrine tumors, and it is a promising tool in the new era of theragnosis and personalized medicine.

PATIENTS CONCERNS

The authors present the case of a 63-year-old woman referred for evaluation of a suspected pancreatic neuroendocrine tumor by Ga-68-DOTA-1-Nal3-octreotide positron emission tomography/computed tomography (Ga-68-DOTA-NOC PET/CT).

DIAGNOSES

PET/CT confirmed increased uptake of Ga-68-DOTA-NOC in a pancreatic lesion compatible with hyperexpression of somatostatin receptors in a neuroendocrine tumor. Furthermore, PET/CT revealed increased uptake in a breast lesion and in lymphadenomegalies (less intense than in the pancreatic tumor), which conducted to the incidental diagnosis of a breast carcinoma with lymph node metastases.

INTERVENTIONS

For the breast cancer, the patient underwentneoadjuvant chemotherapy and anti-HER2 monoclonal antibody, after which she was submitted to surgery. Regarding thepancreatic neuroendocrine tumor, it was decided to maintain itunder surveillance.

OUTCOMES

Breast carcinomas are known to express somatostatin receptors and this is the first report of Ga-68-DOTA-NOC uptake in a breast tumor.

LESSONS

Ga-68-DOTA-NOC PET/CT could be useful for the management of breast cancer patients in the new era of theragnosis and personalized medicine.

Imaging of pancreatic neuroendocrine tumors: recent advances, current status, and controversies

INTRODUCTION

Recently, there have been a number of advances in imaging pancreatic neuroendocrine tumors (panNETs), as well as other neuroendocrine tumors (NETs), which have had a profound effect on the management and treatment of these patients, but in some cases are also associated with controversies. Areas covered: These advances are the result of numerous studies attempting to better define the roles of both cross-sectional imaging, endoscopic ultrasound, with or without fine-needle aspiration, and molecular imaging in both sporadic and inherited panNET syndromes; the increased attempt to develop imaging parameters that correlate with tumor classification or have prognostic value; the rapidly increasing use of molecular imaging in these tumors and the attempt to develop imaging parameters that correlate with treatment/outcome results. Each of these areas and the associated controversies are reviewed. Expert commentary: There have been numerous advances in all aspects of the imaging of panNETs, as well as other NETs, in the last few years. The advances are leading to expanded roles of imaging in the management of these patients and the results being seen in panNETs/GI-NETs with these newer techniques are already being used in more common tumors.

Primary hepatic neuroendocrine tumor case with a preoperative course of 26 years: A case report and literature review

Primary hepatic neuroendocrine tumor (PHNET) is an extremely rare liver tumor. Patients often have no clinical symptoms or have only non-specific symptoms, such as abdominal pain and abdominal mass. The clinical manifestations, disease development, treatment methods, and treatment outcomes of PHNET vary greatly among cases. Here we report a case of PHNET with a confirmed 26-year survival before surgery. The patient was a 56-year-old female. A large right hepatic mass was detected when the patient was 30 years old. The tumor could not be removed during exploratory laparotomy, and constriction of the right hepatic artery and biopsy were conducted. Pathological results indicated a diagnosis of benign tumor, but a confirmed diagnosis was not reached. Twenty-six years after the patient had been living with the tumor, she sought treatment again because of tumor progression. After systematic evaluation of the resectability, the tumor was resected. Based on the examination results of the gastrointestinal tract and lungs, intraoperative examination results, pathological findings, and long-term follow-up results, the diagnosis of PHNET was confirmed. This case represents the longest reported survival time for a PHNET patient before removal of the tumor.

Diagnostic performance and impact on patient management of 68Ga-DOTA-TOC PET/CT for detecting osteomalacia-associated tumours

PURPOSE

Oncogenic osteomalacia is an endocrine disorder induced by small benign tumours (TIO) producing excessive fibroblast growth factor-23 (FGF23). The only way of curing oncogenic osteomalacia is surgical resection of the culprit TIO, which is extremely difficult to detect using conventional imaging modalities due to its small size and variable location in the body. Since TIO frequently overexpress somatostatin receptors, a clinical utility of SPECT or PET with radiolabelled somatostatin analogues has been reported. Among them, ⁶⁸Ga-DOTA-TOC has recently been granted a marketing authorization, facilitating its routine application. We report here the results of the first series evaluating the diagnostic performance of ⁶⁸Ga-DOTA-TOC PET/CT in detecting TIO and its impact on patient management.

METHODS

⁶⁸Ga-DOTA-TOC PET/CT and clinical and imaging data from 15 patients with clinical and biochemical signs of oncogenic osteomalacia were retrospectively reviewed. The ⁶⁸Ga-DOTA-TOC PET/CT findings were compared with the results of post-surgical pathology and clinical and biochemical follow-up.

RESULTS

⁶⁸Ga-DOTA-TOC PET/CT resulted in the detection of one focus suspicious for TIO in nine of 15 patients (60%), and a tumour was surgically removed in eight. Post-operative pathology confirmed a TIO in those eight patients whose symptoms diminished promptly and biochemical anomalies resolved. ⁶⁸Ga-DOTA-TOC PET/CT sensitivity, specificity and accuracy were 73%, 67% and 71%, respectively. ⁶⁸Ga-DOTA-TOC PET/CT findings affected patient management in 67% of cases. In particular, ⁶⁸Ga-DOTA-TOC PET/CT was able to detect the TIO with a negative or a false-positive result of a previous ¹¹¹In-pentetreotide SPECT/CT in 5/8 patients (63%) or a previous FDG PET/CT in 7/11 patients (64%). No close relationship was found between the positivity of ⁶⁸Ga-DOTA-TOC PET/CT and the serum level of a biochemical marker. However, a true-positive result of ⁶⁸Ga-DOTA-TOC PET/CT was obtained in only one patient with a non-elevated serum level of FGF23.

CONCLUSION

⁶⁸Ga-DOTA-TOC PET/CT is an accurate imaging modality in the detection of TIO; in particular, it is worthwhile after failure of somatostatin receptor SPECT(/CT) or FDG PET/CT.

The Evolution of Neuroendocrine Tumor Treatment Reflected by ENETS Guidelines

In 2016, the third version of guidelines for the diagnosis and treatment of neuroendocrine tumors (NETs) has been published by the European Neuroendocrine Tumor Society (ENETS). These guidelines reflect the progress in treatment of NETs, and by comparing the newest guidelines with the first guidelines of 2001, this progress can be clearly recognized. Diagnostic accuracy has been increased by the introduction of PET-CT with Ga-labelled somatostatin analogs, and multiple new treatments and treatment schedules have been developed, like peptide receptor radiotherapy with radiolabeled somatostatin analogs, or targeted therapies. Evidence and indications for these therapies are discussed in the ENETS guidelines. In this review, we aim to show the progress in NET diagnosis and treatment on the basis of the advances in the guidelines, but also to discuss the unsolved questions and unmet needs which still remain.

The utility of 68Ga-DOTATATE positron-emission tomography/computed tomography in the diagnosis, management, follow-up and prognosis of neuroendocrine tumors

Neuroendocrine tumors (NETs) are rare neoplasms that emerge mainly from the GI tract, pancreas and respiratory tract. The incidence of NETs has increased more than sixfold in the last decades. NETs typically express somatostatin receptors on their cell surface, which can be targeted by 'cold' somatostatin analogs for therapy or by 'hot' radiolabeled somatostatin analogs for tumor localization and treatment. 68-Gallium-DOTA peptides (DOTATATE, DOTATOC, DOTANOC) positron emission tomography/computed tomography is a highly accurate imaging modality for NETs that has been found to be more sensitive for NET detection than other imaging modalities. In the current review, we will discuss the clinical utility of 68-Gallium-DOTATATE positron emission tomography/computed tomography for the diagnosis and management of patients with NETs.

PET imaging in patients with meningioma-report of the RANO/PET Group

Meningiomas are the most frequent nonglial primary brain tumors and represent about 30% of brain tumors. Usually, diagnosis and treatment planning are based on neuroimaging using mainly MRI or, rarely, CT. Most common treatment options are neurosurgical resection and radiotherapy (eg, radiosurgery, external fractionated radiotherapy). For follow-up after treatment, a structural imaging technique such as MRI or CT is used. However, these structural imaging modalities have limitations, particularly in terms of tumor delineation as well as diagnosis of posttherapeutic reactive changes. Molecular imaging techniques such as PET can characterize specific metabolic and cellular features which may provide clinically relevant information beyond that obtained from structural MR or CT imaging alone. Currently, the use of PET in meningioma patients is steadily increasing. In the present article, we provide recommendations for the use of PET imaging in the clinical management of meningiomas based on evidence generated from studies being validated by histology or clinical course.

Catching the Zebra: Clinical Pearls and Pitfalls for the Successful Diagnosis of Zollinger-Ellison Syndrome

Zollinger-Ellison syndrome (ZES) results from an ectopic gastrin-secreting tumor leading to peptic ulcer disease, reflux, and chronic diarrhea. While early recognition portends an excellent prognosis with >80% survival at 15 years, symptoms are often nonspecific making the diagnosis difficult to establish. Diagnosis involves a series of tests, including fasting gastrin, gastric pH, chromogranin A, and secretin stimulation. Performing these tests in the correct sequence and at the proper time is essential to avoid inaccurate results. Tumor localization is equally nuanced. Although providers have classically used ¹¹¹indium-radiolabeled octreotide with somatostatin receptor scintigraphy to evaluate tumor size and metastases, recent studies have shown superior results with newer imaging modalities. In particular, ⁶⁸gallium (⁶⁸Ga)-labeled somatostatin radiotracers (i.e., ⁶⁸Ga-DOTATOC, ⁶⁸Ga-DOTANOC and ⁶⁸Ga-DOTATATE) used with positron emission tomography/computed tomography can provide excellent results. Endoscopic ultrasound is another useful modality, particularly in patients with ZES in the setting of multiple endocrine neoplasia type 1. This review aims to provide clinicians with an overview of ZES with a focus on both clinical presentation and the proper utilization of the various biochemical and imaging tests available.

Long-Acting Somatostatin Analog Therapy Differentially Alters 68Ga-DOTATATE Uptake in Normal Tissues Compared with Primary Tumors and Metastatic Lesions

Synthetic somatostatin analogs have been posed as a potential source of error in somatostatin receptor imaging through interference with tumor detection; however, experimental models and clinical studies have shown a complex mechanism of the effect of octreotide on tumors. The aim of this study was to assess whether ⁶⁸Ga-DOTATATE uptake before treatment with long-acting somatostatin analogs differs from that after treatment. Methods: Thirty patients (15 men; age [mean ± SD], 64.6 ± 13.4 y) who had intermediately differentiated to well-differentiated neuroendocrine tumors and who underwent ⁶⁸Ga-DOTATATE PET/CT scanning before and after receiving long-acting repeatable octreotide (Sandostatin LAR) were included in the study. The SUV_max and SUV_mean of healthy target organs, residual primary tumor, and up to 5 lesions with the highest SUV_max in each organ were compared before and after octreotide treatment. Results: The mean time interval between the 2 ⁶⁸Ga-DOTATATE studies was 9.6 ± 7.2 mo, and the mean time gap between the last Sandostatin LAR injection and the second ⁶⁸Ga-DOTATATE study was 25.1 ± 14.8 d. The pretreatment mean SUV_max and SUV_mean were both significantly higher in the thyroid, liver, and spleen (P < 0.05) than the values measured after the administration of Sandostatin LAR. No significant differences were found among the uptake indices for residual primary tumor or any metastatic lesions in the liver, bone, lung, or lymph nodes before and after Sandostatin LAR administration (P > 0.05). Conclusion: Long-acting octreotide treatment diminished ⁶⁸Ga-DOTATATE uptake in the liver, spleen, and thyroid but did not compromise tracer uptake in residual primary tumor and metastatic lesions. These findings have a direct impact on the interpretation of ⁶⁸Ga-DOTATATE PET/CT scans.

Synthesis of a Fluorescently Labeled 68Ga-DOTA-TOC Analog for Somatostatin Receptor Targeting

Fluorescently labeled imaging agents can identify surgical margins in real-time to help achieve complete resections and minimize the likelihood of local recurrence. However, photon attenuation limits fluorescence-based imaging to superficial lesions or lesions that are a few millimeters beneath the tissue surface. Contrast agents that are dual-labeled with a radionuclide and fluorescent dye can overcome this limitation and combine quantitative, whole-body nuclear imaging with intraoperative fluorescence imaging. Using a multimodality chelation (MMC) scaffold, IRDye 800CW was conjugated to the clinically used somatostatin analog, ⁶⁸Ga-DOTA-TOC, to produce the dual-labeled analog, ⁶⁸Ga-MMC(IRDye 800CW)-TOC, with high yield and specific activity. In vitro pharmacological assays demonstrated retention of receptor-targeting properties for the dual-labeled compound with robust internalization that was somatostatin receptor (SSTR) 2-mediated. Biodistribution studies in mice identified the kidneys as the primary excretion route for ⁶⁸Ga-MMC(IRDye 800CW)-TOC, along with clearance via the reticuloendothelial system. Higher uptake was observed in most tissues compared to ⁶⁸Ga-DOTA-TOC but decreased as a function of time. The combination of excellent specificity for SSTR2-expressing cells and suitable biodistribution indicate potential application of ⁶⁸Ga-MMC(IRDye 800CW)-TOC for intraoperative detection of SSTR2-expressing tumors.

The North American Neuroendocrine Tumor Society Consensus Guidelines for Surveillance and Medical Management of Midgut Neuroendocrine Tumors

There have been significant developments in diagnostic and therapeutic options for patients with neuroendocrine tumors (NETs). Key phase 3 studies include the CLARINET trial, which evaluated lanreotide in patients with nonfunctioning enteropancreatic NETs; the RADIANT-2 and RADIANT-4 studies, which evaluated everolimus in functioning and nonfunctioning NETs of the gastrointestinal tract and lungs; the TELESTAR study, which evaluated telotristat ethyl in patients with refractory carcinoid syndrome; and the NETTER-1 trial, which evaluated Lu-DOTATATE in NETs of the small intestine and proximal colon (midgut). Based on these and other advances, the North American Neuroendocrine Tumor Society convened a multidisciplinary panel of experts with the goal of updating consensus-based guidelines for evaluation and treatment of midgut NETs. The medical aspects of these guidelines (focusing on systemic treatment, nonsurgical liver-directed therapy, and postoperative surveillance) are summarized in this article. Surgical guidelines are described in a companion article.

Molecular imaging in neuroendocrine tumors: recent advances, controversies, unresolved issues, and roles in management

PURPOSE OF REVIEW

The purpose is to review recent advances in molecular imaging of neuroendocrine tumors (NETs), discuss unresolved issues, and review how these advances are affecting clinical management.

RECENT FINDINGS

Molecular imaging of NETs underwent a number of important changes in the last few years, leading to some controversies, unresolved issues, and significant changes in clinical management. The most recent changes are reviewed in this article. Particularly important is the rapid replacement in somatostatin receptor scintigraphy of In-diethylenetriamine penta-acetic acid-single-photon emission computed tomography/computed tomography (CT) by Ga-fluorodopa(F-D)PA), 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-peptide-PET/CT imaging, which is now approved in many countries including the USA. Numerous studies in many different types of NETs demonstrate the greater sensitivity of Ga-DOTA-peptide PET/CT, its high specificity, and its impact on management. Other important developments in somatostatin receptor scintigraphy/molecular imaging include demonstrating the prognostic value of both Ga-DOTA-peptide PET/CT and F-fluoro-deoxyglucose PET/CT; how their use can be complementary; comparing the sensitivities and usefulness of Ga-DOTA-peptide PET/CT and F-FDOPA PET/CT; introducing new linkers and radiolabeled ligands such as Cu-DOTA-peptides with a long half-life, enhancing utility; and the introduction of somatostatin receptor antagonists which show enhanced uptake by NETs. In addition, novel ligands which interact with other receptors (GLP-1, bombesin, cholecystokinin, gastric inhibitory polpeptide, integrin, chemokines) are described, which show promise in the imaging of both NETs and other tumors.

SUMMARY

Molecular imaging is now required for all aspects of the management of patients with NETs. Its results are essential not only for the proper diagnostic management of the patient, but also for assessing whether the patient is a candidate for peptide receptor radionuclide therapy with Lu and also for providing prognostic value.

Peptide-based imaging agents for cancer detection

Selective receptor-targeting peptide based agents have attracted considerable attention in molecular imaging of tumor cells that overexpress corresponding peptide receptors due to their unique properties such as rapid clearance from circulation as well as high affinities and specificities for their targets. The rapid growth of chemistry modification techniques has enabled the design and development of various peptide-based imaging agents with enhanced metabolic stability, favorable pharmacokinetics, improved binding affinity and selectivity, better imaging ability as well as biosafety. Among them, many radiolabeled peptides have already been translated into the clinic with impressive diagnostic accuracy and sensitivity. This review summarizes the current status in the development of peptide-based imaging agents with an emphasis on the consideration of probe design including the identification of suitable peptides, the chemical modification of probes and the criteria for clinical translation. Specific examples in clinical trials have been provided as well with respect to their diagnostic capability compared with other FDA approved imaging agents.

The Accessory Spleen Is an Important Pitfall of 68Ga-DOTANOC PET/CT in the Workup for Pancreatic Neuroendocrine Neoplasm

OBJECTIVE

The aim of the study was to assess the value and potential pitfalls of Ga-DOTANOC positron emission tomography/computed tomography (PET/CT) in patients with suspected pancreatic neuroendocrine neoplasms (pNEN).

METHODS

Consecutive patients referred for Ga-DOTANOC PET/CT for suspected pNEN between May 1, 2011, and October 31, 2014, were retrospectively assessed. Scan data were compared with cytological/histological final diagnosis. Pancreatic neuroendocrine neoplasm detection rate was determined on per-patient and per-lesion basis. Maximum standardized uptake values of lesions were determined.

RESULTS

Fifty-eight patients with 65 lesions were enrolled. Twelve patients had nonconfirmed diagnosis; of these, 7 were positive and 5 negative at PET/CT. Of 46 patients with confirmed diagnosis, 36 had pNEN; of these, 33 were positive, 1 negative, and 2 nonevaluable at PET/CT. Ten patients had non-NE lesions, of which 8 were positive, 1 negative, and 1 nonevaluable at PET/CT. Of 48 patients with positive PET/CT, 8 proved to have non-NE lesions, of which 6 were intrapancreatic accessory spleen. No significant maximum standardized uptake values difference was found between pNEN and non-NE lesions.

CONCLUSIONS

Intrapancreatic accessory spleen is an important pitfall in Ga-DOTANOC PET/CT for suspected pNEN. Cytological/histological confirmation is mandatory before any surgical procedure is undertaken.