Current knowledge on the sensitivity of the (68)Ga-somatostatin receptor positron emission tomography and the SUVmax reference range for management of pancreatic neuroendocrine tumours

Ga-68-Edotreotide Positron Emission Tomography/Computed Tomography Somatostatin Receptors Tumor Volume Predicts Outcome in Patients With Primary Gastroenteropancreatic Neuroendocrine Tumors

BACKGROUND

We retrospectively aimed to assess the prognostic significance of somatostatin receptor (SSTR) standardized uptake value (SUVmax_sstr), SSTR representative tumor volume (RTV_sstr) and total lesion SSTR expression (TL_sstr) obtained by [⁶⁸Ga]Ga-edotreotide PET/CT ([⁶⁸Ga]Ga-SSTR PET/CT) in patients with primary gastroenteropancreatic neuroendocrine tumors (GEP-NET) before surgery.

MATERIAL AND METHODS

We analyzed patients who underwent [⁶⁸Ga]Ga-SSTR PET/CT 3-6 weeks before surgery from February 2020 to April 2022. The mean SUVmax_sstr value, the RTV_sstr (cm3; 42% threshold) and the TL_sstr (g) were registered. Thereafter the patients were followed up 10.3 months (range 3-27). The PET/CT results were compared to the event free survival (EFS).

RESULTS

Forty-two patients (61 ± 13 years) have been enrolled. At multivariate analysis only RTV_sstr values were predictive. The Kaplan-Meier survival analysis for RTV_sstr showed a significant better EFS in patients presenting lower values as compared to those having greater (P = .003, log-rank test). SUVmax_sstr was not suitable for predicting EFS, TL_sstr mildly.

CONCLUSION

RTV_sstr represents a valuable volumetric parameter able to predict the outcome in GEP-NET patients who underwent surgery. The magnitude of the SSTR representative tumor burden holds a predominant value for determining the response to therapy in GEP-NET patients before surgery, rather than the maximal SSTR representation at single voxel.

Prevalence and significance of incidental findings on 68 Ga-DOTA-conjugated somatostatin receptor-targeting peptide PET/CT: a systematic review of the literature

Aim

We aimed to evaluate the prevalence of incidental ⁶⁸ Ga-DOTA-conjugated somatostatin receptor-targeting peptide PET/CT (SSTR PET/CT) findings, their clinical significance in the need for follow-up, and their risk of malignancy.

Materials and methods

Studies reporting incidental SSTR PET/CT findings were systematically searched in PubMed, Cochrane, Embase and Web of Science literature published prior to 1^st of May 2020. Studies were filtered by two independent readers for eligibility based on title and abstract, and subsequently on full text. The main exclusion criteria were: 1) pathological findings that matched scan indication, 2) known organ specific disease and/or incidental findings confirmed on other scan modality prior to SSTR PET/CT, 3) lack of diagnosis and/or follow up, and 4) results published in proceedings or conference abstracts.

Results

Twenty-one studies, comprising a total of 2906 subjects, were eligible for the analysis. Studies included were retrospective cohort studies on incidental SSTR PET/CT findings in a specific organ (n = 2888, 7/21) or case reports (n = 18, 14/21). A total of 133 subjects had incidental SSTR PET/CT findings. Incidental findings were predominantly seen in the thyroid gland (n = 65), spine (n = 30), brain (n = 26) and breast (n = 6). Seventeen of 133 (13%) incidental findings were malignant on final diagnosis. Incidental breast findings were associated with the highest risk of malignancy (67%). In the thyroid, incidental SSTR uptake was caused by malignancy in 8%, all presenting as focal uptake. The lowest risk was seen in the spine with a malignancy rate of 3% in patients with incidental SSTR uptake and benign cases were interpreted as vertebral hemangiomas on CT. Incidental SSTR PET/CT findings in other locations were of malignant etiology in two out of six cases (33%) and should be evaluated individually.

Conclusion

The most incidental SSTR PET/CT findings were found in the thyroid gland, spine, and brain. The risk of malignancy was greatest in incidental SSTR PET/CT findings in the breast, cranially, and thyroid gland. The results of the present study can prove useful in the interpretation of atypical findings on SSTR PET/CT and in the counseling of clinicians.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40644-022-00484-0.

Recent advances in diagnosis and treatment of gastroenteropancreatic neuroendocrine neoplasms

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) are a rare group of tumors originating from neuroendocrine cells of the digestive system. Their incidence has increased over the last decades. The specific pathogenetic mechanisms underlying GEP-NEN development have not been completely revealed. Unfunctional GEP-NENs are usually asymptomatic; some grow slowly and thus impede early diagnosis, which ultimately results in a high rate of misdiagnosis. Therefore, many GEP-NEN patients present with later staged tumors. Motivated hereby, research attention for diagnosis and treatment for GEP-NENs increased in recent years. The result of which is great progress in clinical diagnosis and treatment. According to the most recent clinical guidelines, improved grading standards can accurately define poorly differentiated grade 3 neuroendocrine tumors and neuroendocrine carcinomas (NECs), which are subclassified into large and small cell NECs. Combining different functional imaging methods facilitates precise diagnosis. The expression of somatostatin receptors helps to predict prognosis. Genetic analyses of mutations affecting death domain associated protein (DAXX), multiple endocrine neoplasia type 1 (MEN 1), alpha thalassemia/intellectual disability syndrome X-linked (ATRX), retinoblastoma transcriptional corepressor 1 (RB 1), and mothers against decapentaplegic homolog 4 (SMAD 4) help distinguishing grade 3 NENs from poorly differentiated NECs. The aim of this review is to summarize the latest research progress on diagnosis and treatment of GEP-NENs.

68 Ga-DOTATATE PET/CT imaging in endogenous hyperinsulinemic hypoglycemia: A tertiary endocrine centre experience

OBJECTIVE

Literature regarding utility of ⁶⁸ Ga-DOTATATE PET/CT in insulinoma localization across various subgroups [benign/malignant/multiple endocrine neoplasia-1 (MEN-1) syndrome associated] remains scarce. In this study, the performance of ⁶⁸ Ga-DOTATATE PET/CT was compared with contrast-enhanced computed tomography (CECT) and ⁶⁸ Ga-NODAGA-Exendin-4 PET/CT (whenever available) in an endogenous hyperinsulinemic hypoglycemia (EHH) cohort.

DESIGN

Retrospective audit.

PATIENTS

EHH patients [N = 36, lesions (n) = 49, final diagnosis: benign sporadic insulinoma (BSI) (N = 20), malignant insulinoma (N = 4, n = 14), MEN-1 syndrome associated insulinoma (N = 9, n = 15), Munchausen syndrome (N = 2) and drug-induced hypoglycemia (N = 1)] having both preoperative imaging modalities (CECT and ⁶⁸ Ga-DOTATATE PET/CT).

MEASUREMENTS

Per-lesion sensitivity (Sn) and positive predictive value (PPV) for histopathological diagnosis of insulinoma.

RESULTS

Sn and PPV of ⁶⁸ Ga-DOTATATE PET/CT were 67.3% and 89.2%; 55% and 100%; 85.7% and 100%; and 66.7% and 77% for overall EHH, BSI, malignant, and MEN-1 syndrome associated insulinoma cohorts respectively. Despite having comparatively lower sensitivity in BSI cohort, ⁶⁸ Ga-DOTATATE PET/CT localized a pancreatic tail lesion missed by other modalities. ⁶⁸ Ga-DOTATATE PET/CT had comparatively higher sensitivity in malignant insulinoma than BSI cohort. ⁶⁸ Ga-DOTATATE PET/CT also paved the way for successful response to ¹⁷⁷ Lu-based peptide receptor radionuclide therapy (PRRT). In MEN-1 cases, lower PPV as compared with BSI was due to uptake in non-insulinoma pancreatic neuroendocrine tumours (Pan-NET).

CONCLUSIONS

⁶⁸ Ga-DOTATATE PET/CT has supplemental role in selected cases of BSI with negative and/or discordant results with CECT and ⁶⁸ Ga-NODAGA-Exendin-4 PET/CT. In malignant insulinoma, ⁶⁸ Ga-DOTATATE-PET/CT has an additional theranostic potential. Interference due to uptake in non-insulinoma Pan-NET in MEN-1 syndrome may hinder insulinoma localization with ⁶⁸ Ga-DOTATATE-PET/CT.

A Retrospective Analysis of the Correlation between Functional Imaging and Clinical Outcomes in Grade 3 Neuroendocrine Tumors (NETs G3)

Grade 3 (G3) neuroendocrine tumors (NETs) are a novel category among digestive neuroendocrine neoplasms, characterized by Ki-67 >20% and a well-differentiated morphology, presenting high intra-tumor heterogeneity. We aimed to explore the role of dual-tracer PET imaging (68Gallium (Ga)-DOTATOC and 18Fluorodeoxyglucose (FDG)) as overall survival (OS) predictor in NET G3 patients. We performed a retrospective analysis in NET G3 patients treated at our institution between 2003 and 2021. Accordingly, 30 NET G3 patients were analyzed. 68Ga-DOTA-TOC and 18F-FDG uptake were assessed by tumor/non-tumor (T-nonT) ratio. We reported a slightly better OS for patients with ≥75% concordance between 68Ga-DOTA-TOC and 18F-FDG PET/CT (p = 0.42). Among patients with discordant functional imaging, we reported a better 5-y OS rate for patients with a prevalent 68Ga-DOTATOC vs. 18F-FDG PET/CT (p = 0.016). In positive 18F-FDG PET/CT cases, we reported a better OS for <4 vs. ≥4 T/non-T ratio (p = 0.021). Among upfront-NET G3 patients with concordant exams, 5-y OS rate was 83.3% (95% CI: 27.3-97.5). Among patients with discordant exams, 5-y OS rate was 81.3% (52.5-93.5), 100% for those with prevalent receptor expression, and 50% (11.1-80.4) for those with prevalent 18F-FDG uptake. Our findings suggest that dual-tracer PET/CT can be considered as a predictor of patient outcome, able to stratify NET G3 patients with poorer prognosis.

PET/Computed Tomography in Thyroid Cancer

Primary thyroid cancers demonstrate distinct biological behaviors depending on their histologic characteristics. The ability to accumulate radioiodine by differentiated thyroid cancer cells is lost in primary aggressive, poorly differentiated and dedifferentiated tumor cells. PET imaging comes into play in these challenging situations where it can provide additive information to radioiodine scintigraphy and conventional imaging. This review focuses on the current guidelines and future prospects of PET imaging in thyroid cancers.

Biodistribution of 18F-AlF-NOTA-octreotide in Different Organs and Characterization of Uptake in Neuroendocrine Neoplasms

PURPOSE

The aims of this study were threefold: [1] to describe the biodistribution of ¹⁸F-AlF-NOTA-octreotide (¹⁸F-OC) in normal organs; [2] to evaluate the range of uptake of NEN and benign lesions using the maximum standardized uptake value (SUV_max); and [3] to compare the difference in ¹⁸F-OC uptake among tumors of different grades.

METHODS

This study included 162 patients (67 females and 95 males) who received ¹⁸F-OC positron emission tomography (PET)/computed tomography (CT), 128 of whom were diagnosed with neuroendocrine neoplasms (NENs). The SUV_max and SUV_mean of ¹⁸F-OC were measured in 21 normal anatomical structures. We compared the differences among G1, G2, and G3 NENs, as well as between NENs and benign lesions.

RESULTS

High physiological uptake of ¹⁸F-OC (SUV_max > 6.77) was detected in the spleen, adrenal gland, renal parenchyma, pituitary gland, and liver. Moderate uptake (SUV_max 3.00-6.77) was found in the uncinate process of the pancreas (PU), prostate, thyroid, and uterus. Mild uptake (SUV_max 1.34-3.00) was observed in the small intestine, pancreas (pancreas uptake except for the head of the pancreas), gallbladder, and transverse colon. The SUV_max of NENs was higher than that of benign lesions, including fractures, inflamed tissue, reactive hyperplasia, and degenerative disease. However, overlap was noted between the two groups. The SUV_max of ¹⁸F-OC uptake by tumors was significantly correlated with tumor grade in primary lesions and those of the lymph node, bone, and other sites (all P < 0.01).

CONCLUSIONS

The results obtained from the majority of the samples in this study show the biodistribution of ¹⁸F-OC in normal organs and have significance as a reference. Although some benign lesions show variable uptake, the uptake by these lesions is still different from that of NENs. NENs of different grades have differences in ¹⁸F-OC uptake levels.

Theragnostics in Neuroendocrine Tumors

Several studies have demonstrated the effectiveness of somatostatin receptor (SSTR)-targeted imaging for diagnosis, staging, evaluating the possibility of treatment with cold somatostatin analogs, as well peptide receptor radionuclide therapy (PRRT), and evaluation of treatment response. PET with ⁶⁸Ga-labeled somatostatin analogs provides excellent sensitivity and specificity for diagnosing and staging neuroendocrine tumors (NETs). Metabolic imaging with PET with fludeoxyglucose ¹⁸F/computed tomography (CT) complements the molecular imaging with ⁶⁸Ga-SSTR PET/CT toward a personalized therapy in NET patients. The documented response rate of PRRT in NET summing up complete response, partial response, minor response, and stable disease is 70% to 80%.

PET/CT Variants and Pitfalls in Liver, Biliary Tract, Gallbladder and Pancreas

A wide variety of pathological anomalies may occur in the liver, biliary system, and pancreas. It is a necessity to use many different imaging techniques in order to distinguish such varied pathologies, especially those from malignant processes. Positron Emission Tomography/Computed Tomography (PET/CT) is an imaging method that has proven its diagnostic value in oncology and can be used for different clinical purposes. Fluoro-18 fluoro-2-deoxy-D-glucose has a wide range of uses as a dominant radiopharmaceutical in routine molecular imaging, however, molecular imaging has started to play a more important role in personalized cancer treatment in recent years with new Fluoro-18 and Gallium-68 labeled tracers. Although molecular imaging has a strong diagnostic effect, the surprises and pitfalls of molecular imaging can lead us to unexpected and misleading results. Prior to PET/CT analysis and reporting, information about possible technical and physiological pitfalls, normal histological features of tissues, inflammatory pathologies, specific clinical features of the case, treatment-related complications and past treatments should be evaluated in advance to avoid misinterpretation. In this review, the physiological and pathophysiological variants as well as pitfalls encountered in PET/CT imaging of the liver, biliary tract, gallbladder, and pancreas will be examined. Other benign and malignant pathologies that have been reported to date and that have led to incorrect evaluation will be listed. It is expected that the devices, software, and artificial intelligence applications that will be developed in the near future will enable much more effective and faster imaging that will reduce the potential causes of error. However, as a result of the dynamic and evolving structure of the information obtained by molecular imaging, the inclusion of the newly developed radiopharmaceuticals in routine practice will continue to carry new potentials as well as new troubles. Although molecular imaging will be the flagship of diagnostic oncology in the 21st century, the correct analysis and interpretation by the physician will continue to form the basis of achieving optimal performance.

Added value of [68Ga]Ga-DOTA-TOC PET/CT for characterizing pancreatic neuroendocrine neoplasms: a comparison with contrast-enhanced CT and/or MRI in a large study cohort

OBJECTIVES

To investigate an additional value of [⁶⁸Ga]Ga-DOTA-TOC PET/CT for characterizing suspected pancreatic neuroendocrine neoplasms (NENs) in a large study cohort.

METHODS

This retrospective study included 167 patients who underwent [⁶⁸Ga]Ga-DOTA-TOC PET/CT for suspected pancreatic NENs detected by contrast-enhanced CT (n = 153) and/or MRI (n = 85). Two board-certified radiologists independently reviewed CT and/or MRI as well as [⁶⁸Ga]Ga-DOTA-TOC PET/CT and scored the probability of NEN on a 5-point scale. Radiologists' diagnostic performances with and without [⁶⁸Ga]Ga-DOTA-TOC PET/CT were compared using pathologic findings as the standard of reference.

RESULTS

All 167 patients were pathologically diagnosed with NENs (n = 131) or non-NENs (n = 36) by surgery (n = 93) or biopsy (n = 74). The non-NEN group included focal pancreatitis (n = 7), gastrointestinal stromal tumor (n = 6), serous cystadenoma (n = 5), metastatic renal cell carcinoma (n = 4), intrapancreatic accessory spleen (n = 4), ductal adenocarcinoma (n = 3), solid pseudopapillary neoplasm (n = 2), intraductal papillary mucinous carcinoma (n = 1), adenosquamous carcinoma (n = 1), schwannoma (n = 1), paraganglioma (n = 1), and solitary fibrous tumor (n = 1). Radiologists' diagnostic performance significantly improved after the addition of [⁶⁸Ga]Ga-DOTA-TOC PET/CT (AUC of CT: 0.737 vs. 0.886 for reviewer 1 [p = 0.0004]; 0.709 vs. 0.859 for reviewer 2 [p = 0.0002], AUC of MRI: 0.748 vs. 0.872 for reviewer 1 [p = 0.023]; 0.670 vs. 0.854 for reviewer 2 [p = 0.001]). [⁶⁸Ga]Ga-DOTA-TOC PET/CT significantly improved sensitivity (CT: 87.4% vs. 96.6% for reviewer 1 [p = 0.001]; 74.8% vs. 92.5% for reviewer 2 [p = 0.0001], MRI: 86.9% vs. 98.4% for reviewer 1 [p = 0.016]; 70.5% vs. 91.8% for reviewer 2 [p = 0.002]).

CONCLUSIONS

[⁶⁸Ga]Ga-DOTA-TOC PET/CT provided an additional value over conventional CT or MRI for the characterization of suspected pancreatic NENs.

KEY POINTS

• [⁶⁸Ga]Ga-DOTA-TOC PET/CT could provide additional value over conventional CT and/or MRI for the exact characterization of suspected pancreatic NENs by increasing AUC values and sensitivity. • Diagnostic improvement was significant, especially in NENs showing an atypical enhancement pattern. • The inter-observer agreement was improved when [⁶⁸Ga]Ga-DOTA-TOC PET/CT was added to CT and/or MRI.

Exendin-4-based imaging in endogenous hyperinsulinemic hypoglycaemia cohort: A tertiary Endocrine centre experience

CONTEXT

Insulinoma needs accurate preoperative localization for minimally invasive surgery. Exendin-4-based imaging has shown promising results.

OBJECTIVE

To evaluate performance parameters of exendin-4-based imaging in insulinoma localization and compare with other imaging modalities.

DESIGN

Retrospective cross-sectional study.

PATIENTS

We report 14 patients with endogenous hyperinsulinemic hypoglycaemia (EHH) managed at our centre; in whom, the final diagnosis was insulinoma (n = 11), Munchausen syndrome (MS) (n = 2) and inconclusive (n = 1). Retrospective reporting of CECT, ⁶⁸ Ga-DOTATATE PET/CT and ⁶⁸ Ga-NODAGA-exendin-4-PET/CT was done. With per-lesion analysis, performance parameters were calculated for the histopathological diagnosis of insulinoma.

MAIN OUTCOME MEASURES

True positive (TP), false positive (FP), false negative (FN), true negative (TN), sensitivity (Sn), specificity (Sp), positive predictive value (PPV), negative predictive value (NPV) for insulinoma localization.

RESULTS

In our cohort, 12 histopathologically proven insulinoma lesions [(TP): 11 primary lesions, 1 metastasis] were detected in 11 patients, whereas two patients had MS (TN). Sn and PPV were 75% and 100%, 33.3% and 80% and 83.3% and 71.4% for CECT, ⁶⁸ Ga-DOTATATE PET/CT and ⁶⁸ Ga-NODAGA-exendin-4-PET/CT, respectively. With exendin-4-based imaging, FP uptake in normal pancreatic tissue and FN results in the pancreatic tail lesion was seen. In one patient, TN result suggested the correct diagnosis of MS.

CONCLUSION

⁶⁸ Ga-NODAGA-exendin-4-PET/CT has higher sensitivity than ⁶⁸ Ga-DOTATATE PET/CT and CECT for insulinoma localization. FP uptake in normal pancreas and FN result in tail lesions are limitations of currently utilized exendin-4-based imaging.

Functional imaging in ectopic Cushing syndrome

PURPOSE OF REVIEW

Ectopic adrenocorticotropic hormone (ACTH)-secreting tumors are commonly small, yet they often lead to fulminant forms of Cushing syndrome. High-resolution functional imaging modalities, such as [Ga]-DOTATATE, have been recently introduced in clinical practice for the identification of neuroendocrine tumors. In this review, we focus on the performance of [Ga]-DOTATATE as a tool for localizing primary and metastatic sources of ectopic Cushing syndrome (ECS).

RECENT FINDINGS

Prompt surgical removal of ectopic ACTH-secreting tumors is the mainstay of therapy in patients with ECS. Detecting such tumors with conventional cross-sectional imaging is often unsuccessful, owing to their small size. [Ga]-DOTATATE has been approved in 2016 by the Federal Drug Administration for imaging well differentiated neuroendocrine tumors. Data regarding the performance of [Ga]-DOTATATE for detecting ectopic ACTH-secreting tumors remain limited, in part owing to the recent introduction of this imaging modality in clinical practice, and in part because of the low prevalence of ECS. Nevertheless, [Ga]-DOTATATE has been reported to be useful in identifying primary and metastatic ectopic ACTH-secreting lesions that were not apparent on other imaging studies, impacting the clinical care of many patients with ECS.

SUMMARY

[Ga]-DOTATATE-based imaging, which targets the somatostatin receptors abundantly expressed in neuroendocrine tumors, has generally high, although variable resolution in detecting the source(s) of ECS.

Comparative evaluation of 68Ga-labelled TATEs: the impact of chelators on imaging

Background

⁶⁸Ga-labelled peptides targeting somatostatin receptor 2 (SSTR2) have demonstrated encouraging results in managing patients with neuroendocrine tumours (NETs). In addition to metal chelation, bifunctional chelators have also been found to impact imaging outcomes due to their differences in stability, charge, hydrophilicity, etc. In the present work, a comparative pharmacokinetic evaluation and imaging characteristics were performed between ⁶⁸Ga-labelled somatostatin analogues (TATE) using NOTA (1,4,7-triazacyclononane-1,4,7-triacetic acid) and DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) as bifunctional chelating agents (BFCAs).

Results

Both ⁶⁸Ga-NOTA-TATE and ⁶⁸Ga-DOTA-TATE were obtained with high radiochemical purity. ⁶⁸Ga-NOTA-TATE demonstrated higher in vitro stability (≥ 99%) than ⁶⁸Ga-DOTA-TATE (≥ 95%) after 3 h of incubation. The water solubilities (partition coefficients, − 1.76 ± 0.06 vs. − 2.72 ± 0.16) and plasma protein binding rates (12.12% vs. 30.6%) were lower for ⁶⁸Ga-NOTA-TATE than for ⁶⁸Ga-DOTA-TATE. Differential pharmacokinetics and comparable tumour affinities (within 1 h) were observed in AR42J tumour-bearing mice. Healthy volunteer imaging studies showed comparable distribution patterns of these two imaging agents. However, the maximum standardized uptake values (SUVmax) of the two tracers varied in each organ. The two PET agents demonstrated almost identical SUVmax values in the kidneys. ⁶⁸Ga-NOTA-TATE did have a lower SUVmax in most other organs compared with ⁶⁸Ga-DOTA-TATE, including the liver (4.2 vs. 10.1), potentially due to the lower protein binding rate.

Conclusion

⁶⁸Ga-NOTA-TATE and ⁶⁸Ga-DOTA-TATE demonstrated comparable tumour uptake in an AR42J mouse model. An initial clinical study revealed that ⁶⁸Ga-NOTA-TATE may have reduced background uptake in the major organs such as the liver. Although the subject numbers were limited, further investigation of ⁶⁸Ga-NOTA-TATE is warranted for detecting SSTR2-positive neuroendocrine tumours.

The North American Neuroendocrine Tumor Society Consensus Paper on the Surgical Management of Pancreatic Neuroendocrine Tumors

This manuscript is the result of the North American Neuroendocrine Tumor Society consensus conference on the surgical management of pancreatic neuroendocrine tumors from July 19 to 20, 2018. The group reviewed a series of questions of specific interest to surgeons taking care of patients with pancreatic neuroendocrine tumors, and for each, the available literature was reviewed. What follows are these reviews for each question followed by recommendations of the panel.

Receptor radionuclide targeting for neuroendocrine tumors (NET) diagnostic and therapy

Neuroendocrine tumors (NET) represent a heterogeneous group of tumors originating from cells of neuroendocrine origin, which express somatostatin receptors (SSTR). This property allowed the successful development of radionuclides for diagnostic and peptide radionuclide radiation therapy (PRRT). This is the paradigm for the theragnostic concept in NET personalized medicine. The only phase III study to date (NETTER-1) clearly demonstrated the ability of ¹⁷⁷Lutetium-based PRRT to improve progression-free survival in advanced intestinal NETs. In clinical practice, the indications are limited to G1-G2 well-differentiated NETs with high expression of SSTR. NETs with a low tumor burden and slow progression are probably the optimal indication. This treatment is now available in France. However, its precise position in the treatment algorithm remains to be explored. We provide an overview of receptor radionuclide utilization and mechanism in diagnostic and pretherapeutic imaging and we focus on PRRT for endocrine tumors.

Molecular imaging and therapy of somatostatin receptor positive tumors

Somatostatin receptors (SSTR) are upregulated in the cells of origin that define numerous neuroendocrine neoplasms. PET imaging with ⁶⁸Ga-DOTATATE allows specific targeting of SSTR2A, a single species of SSTR receptor, which is commonly overexpressed in a variety of gastroenteropancreatic neuroendocrine tumors, as well as pulmonary carcinoid and head and neck tumors. Due to more specific targeting of SSTR2 as well as lower radiation dose, shorter study length, ability to quantify uptake, and lower cost, ⁶⁸Ga-DOTATATE has demonstrated superior imaging attributes when compared to ¹¹¹In-pentetreotide. As with any novel imaging modality, dedicated training, increasing experience and staying up-to-date with scientific publications are required to provide optimal patient care. The purpose of this review is to summarize the current state of the art in SSTR-targeted molecular imaging and discuss ongoing and future potential diagnostic and therapeutic applications.

68Ga-somatostatin receptor analogs and 18F-FDG PET/CT in the localization of metastatic pheochromocytomas and paragangliomas with germline mutations: a meta-analysis

BACKGROUND

Metastatic pheochromocytoma and paraganglioma (PCs/PGLs) show high germline mutation, and ¹⁸F-FDG and ⁶⁸Ga-DOTA peptide positron emission tomography/computed tomography (PET/CT) imaging are recommended for the diagnosis of metastatic of PCs. However, there has been lack of direct comparison of the two modalities in the diagnosis of metastatic of PCs up to now.

PURPOSE

To evaluate and compare the value of localization of ⁶⁸Ga-somatostatin receptor analogs and ¹⁸F-FDG in the diagnosis of metastatic PCs/PGLs.

MATERIAL AND METHODS

A comprehensive literature search of PubMed/MEDLINE, ScienceDirect, and Web of Science was performed in accordance with the Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) guidelines published in August 2016. We critically reviewed all studies based on the PICOS criteria. QUADAS-2 was used to evaluate the quality of the methodology of the included studies.

RESULTS

This meta-analysis included 17 studies (629 patients, average age [mean ± SD] = 42.7 ± 6.3 years). The pooled sensitivity and specificity of ¹⁸F-FDG and ⁶⁸Ga peptides were 0.85 (95% confidence interval [CI] = 0.78-0.91) and 0.55 (95% CI = 0.37-0.73), and 0.95 (95% CI = 0.92-0.97) and 0.87 (95% CI = 0.63-0.96), respectively. The area under the sROC curves of the ¹⁸F-FDG and ⁶⁸Ga peptides were 0.88 (95% CI = 0.85-0.91) and 0.78 (95% CI = 0.74-0.81), respectively. A subgroup analysis demonstrated that the difference at the per-lesion level and gene mutation level was significant.

CONCLUSION

Compared to ¹⁸F-FDG PET/CT, the ⁶⁸Ga-somatostatin receptor demonstrated good performance in the localization of metastatic PCs/PGLs, especially those with germline mutations. The use of the ⁶⁸Ga-somatostatin receptor can be a new tool in the diagnosis of metastatic PCs/PGLs.

The theranostic promise for Neuroendocrine Tumors in the late 2010s - Where do we stand, where do we go?

More than 25 years after the first peptide receptor radionuclide therapy (PRRT), the concept of somatostatin receptor (SSTR)-directed imaging and therapy for neuroendocrine tumors (NET) is seeing rapidly increasing use. To maximize the full potential of its theranostic promise, efforts in recent years have expanded recommendations in current guidelines and included the evaluation of novel theranostic radiotracers for imaging and treatment of NET. Moreover, the introduction of standardized reporting framework systems may harmonize PET reading, address pitfalls in interpreting SSTR-PET/CT scans and guide the treating physician in selecting PRRT candidates. Notably, the concept of PRRT has also been applied beyond oncology, e.g. for treatment of inflammatory conditions like sarcoidosis. Future perspectives may include the efficacy evaluation of PRRT compared to other common treatment options for NET, novel strategies for closer monitoring of potential side effects, the introduction of novel radiotracers with beneficial pharmacodynamic and kinetic properties or the use of supervised machine learning approaches for outcome prediction. This article reviews how the SSTR-directed theranostic concept is currently applied and also reflects on recent developments that hold promise for the future of theranostics in this context.

Increased Expression of GLP-1R in Proliferating Islets of Men1 Mice is Detectable by [68Ga]Ga-DO3A-VS-Cys40-Exendin-4 /PET

Multiple endocrine neoplasia type 1 (MEN1) is an endocrine tumor syndrome caused by heterozygous mutations in the MEN1 tumor suppressor gene. The MEN1 pancreas of the adolescent gene carrier frequently contain diffusely spread pre-neoplasias and microadenomas, progressing to macroscopic and potentially malignant pancreatic neuroendocrine tumors (P-NET), which represents the major death cause in MEN1. The unveiling of the molecular mechanism of P-NET which is not currently understood fully to allow the optimization of diagnostics and treatment. Glucagon-like peptide 1 (GLP-1) pathway is essential in islet regeneration, i.e. inhibition of β-cell apoptosis and enhancement of β-cell proliferation, yet involvement of GLP-1 in MEN1 related P-NET has not yet been demonstrated. The objective of this work was to investigate if normal sized islets of Men1 heterozygous mice have increased Glucagon-like peptide-1 receptor (GLP-1R) expression compared to wild type islets, and if this increase is detectable in vivo with positron emission tomography (PET) using [68Ga]Ga-DO3A-VS-Cys40-Exendin-4 (68Ga-Exendin-4). 68Ga-Exendin-4 showed potential for early lesion detection in MEN1 pancreas due to increased GLP1R expression.

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.