Molecular imaging in neuroendocrine tumors: molecular uptake mechanisms and clinical results

Tumor metabolism in pheochromocytomas: clinical and therapeutic implications

Pheochromocytomas and paragangliomas (PPGLs) have emerged as one of the most common endocrine tumors. It epitomizes fascinating crossroads of genetic, metabolic, and endocrine oncology, providing a canvas to explore the molecular intricacies of tumor biology. Predominantly rooted in the aberration of metabolic pathways, particularly the Krebs cycle and related enzymatic functionalities, PPGLs manifest an intriguing metabolic profile, highlighting elevated levels of oncometabolites like succinate and fumarate, and furthering cellular malignancy and genomic instability. This comprehensive review aims to delineate the multifaceted aspects of tumor metabolism in PPGLs, encapsulating genetic factors, oncometabolites, and potential therapeutic avenues, thereby providing a cohesive understanding of metabolic disturbances and their ramifications in tumorigenesis and disease progression. Initial investigations into PPGLs metabolomics unveiled a stark correlation between specific genetic mutations, notably in the succinate dehydrogenase complex (SDHx) genes, and the accumulation of oncometabolites, establishing a pivotal role in epigenetic alterations and hypoxia-inducible pathways. By scrutinizing voluminous metabolic studies and exploiting technologies, novel insights into the metabolic and genetic aspects of PPGLs are perpetually being gathered elucidating complex interactions and molecular machinations. Additionally, the exploration of therapeutic strategies targeting metabolic abnormalities has burgeoned harboring potential for innovative and efficacious treatment modalities. This review encapsulates the profound metabolic complexities of PPGLs, aiming to foster an enriched understanding and pave the way for future investigations and therapeutic innovations in managing these metabolically unique tumors.

[18F]FDOPA PET/CT in Solid Pseudopapillary Tumor of the Pancreas: a Recurred Tumor Mimicking Splenosis

Solid pseudopapillary tumor (SPT) of the pancreas is a neoplasm with low malignant potential. It is often challenging to diagnose SPT due to its nonspecific clinical and radiological features, and [18F]FDOPA is effective in diagnosing SPT, particularly in differentiating SPT from benign conditions such as splenosis. A 55-year-old woman underwent distal pancreatectomy and splenectomy for histologically confirmed SPT. She was also initially diagnosed with splenosis. During follow-up, sizes of multiple nodular lesions were increased, raising the possibility of peritoneal seeding of SPT. For diagnosis, a spleen scan and SPECT/CT were performed using 99mTc-labeled damaged red blood cells, which showed no uptake in the peritoneal nodules. Subsequent [18F]FDOPA PET/CT revealed [18F]FDOPA-avidity of the nodules. The patient underwent tumor resection surgery, and the nodules were pathologically confirmed as SPT.

Somatostatin Receptor Imaging with [18F]FET-βAG-TOCA PET/CT and [68Ga]Ga-DOTA-Peptide PET/CT in Patients with Neuroendocrine Tumors: A Prospective, Phase 2 Comparative Study

There is a clinical need for 18F-labeled somatostatin analogs for the imaging of neuroendocrine tumors (NET), given the limitations of using [68Ga]Ga-DOTA-peptides, particularly with regard to widespread accessibility. We have shown that [18F]fluoroethyl-triazole-[Tyr3]-octreotate ([18F]FET-βAG-TOCA) has favorable dosimetry and biodistribution. As a step toward clinical implementation, we conducted a prospective, noninferiority study of [18F]FET-βAG-TOCA PET/CT compared with [68Ga]Ga-DOTA- peptide PET/CT in patients with NET. Methods: Forty-five patients with histologically confirmed NET, grades 1 and 2, underwent PET/CT imaging with both [18F]FET-βAG-TOCA and [68Ga]Ga-peptide performed within a 6-mo window (median, 77 d; range, 6-180 d). Whole-body PET/CT was conducted 50 min after injection of 165 MBq of [18F]FET-βAG-TOCA. Tracer uptake was evaluated by comparing SUVmax and tumor-to-background ratios at both lesion and regional levels by 2 unblinded, experienced readers. A randomized, blinded reading of both scans was also then undertaken by 3 experienced readers, and consensus was assessed at a regional level. The ability of both tracers to visualize liver metastases was also assessed. Results: A total of 285 lesions were detected on both imaging modalities. An additional 13 tumor deposits were seen in 8 patients on [18F]FET-βAG-TOCA PET/CT, and [68Ga]Ga-DOTA-peptide PET/CT detected an additional 7 lesions in 5 patients. Excellent correlation in SUVmax was observed between both tracers (r = 0.91; P < 0.001). No difference was observed between median SUVmax across regions, except in the liver, where the median tumor-to-background ratio of [18F]FET-βAG-TOCA was significantly lower than that of [68Ga]Ga-DOTA-peptide (2.5 ± 1.9 vs. 3.5 ± 2.3; P < 0.001). Conclusion: [18F]FET-βAG-TOCA was not inferior to [68Ga]Ga-DOTA-peptide in visualizing NET and may be considered in routine clinical practice given the longer half-life and availability of the cyclotron-produced fluorine radioisotope.

The Role of Receptor-Ligand Interaction in Somatostatin Signaling Pathways: Implications for Neuroendocrine Tumors

Neuroendocrine tumors (NETs) arise from neuroendocrine cells and manifest in diverse organs. Key players in their regulation are somatostatin and its receptors (SSTR1-SSTR5). Understanding receptor-ligand interactions and signaling pathways is vital for elucidating their role in tumor development and therapeutic potential. This review highlights SSTR characteristics, localization, and expression in tissues, impacting physiological functions. Mechanisms of somatostatin and synthetic analogue binding to SSTRs, their selectivity, and their affinity were analyzed. Upon activation, somatostatin initiates intricate intracellular signaling, involving cAMP, PLC, and MAP kinases and influencing growth, differentiation, survival, and hormone secretion in NETs. This review explores SSTR expression in different tumor types, examining receptor activation effects on cancer cells. SSTRs' significance as therapeutic targets is discussed. Additionally, somatostatin and analogues' role in hormone secretion regulation, tumor growth, and survival is emphasized, presenting relevant therapeutic examples. In conclusion, this review advances the knowledge of receptor-ligand interactions and signaling pathways in somatostatin receptors, with potential for improved neuroendocrine tumor treatments.

Unusual False Positive on 99mTc-Tektrotyd Scintigraphy Mimicking Bone Metastasis

Somatostatin receptor scintigraphy is a key diagnostic tool in the initial staging and therapeutic evaluation of neuroendocrine tumors. Its specificity can be compromised by the presence of false positives. We illustrate here the case of a vertebral hemangioma detected on 99mTc-Tektrotyd scintigraphy as an incidental finding in a 34-year-old man referred for the staging of a well-differentiated neuroendocrine tumor of the ampulla of Vater (Fig. 1).

Prognostic Implications of PET-Derived Tumor Volume and Uptake in Patients with Neuroendocrine Tumors

Historically, molecular imaging of somatostatin receptor (SSTR) expression in patients with neuroendocrine tumors (NET) was performed using SSTR scintigraphy (SRS). Sustained advances in medical imaging have led to its gradual replacement with SSTR positron-emission tomography (SSTR-PET). The higher sensitivity in comparison to SRS on the one hand and conventional cross-sectional imaging, on the other hand, enables more accurate staging and allows for image quantification. In addition, in recent years, a growing body of evidence has assessed the prognostic implications of SSTR-PET-derived prognostic biomarkers for NET patients, with the aim of risk stratification, outcome prognostication, and prediction of response to peptide receptor radionuclide therapy. In this narrative review, we give an overview of studies examining the prognostic value of advanced SSTR-PET-derived (semi-)quantitative metrics like tumor volume, uptake, and composite metrics. Complementing this analysis, a discussion of the current trends, clinical implications, and future directions is provided.

Primary grade 2 neuroendocrine tumor of the ileal mesentery: a case report

Background

The prevalence and incidence of neuroendocrine tumors (NETs) are increasing worldwide. Primary mesenteric NETs are extremely rare. Solid tumors that arise in the mesentery are typically metastatic. We present an extremely rare case of a primary grade 2 NET (NET G2) in the ileal mesentery.

Case presentation

A 54-year-old man was referred to our hospital for further examination of a previously diagnosed right mesenteric tumor. Mild tenderness was noted on the right side of the abdomen, but there were no palpable masses. Fluorodeoxyglucose-positron emission tomography (FDG-PET) revealed slight FDG uptake (maximum standardized uptake value, 2.0) in the right abdomen, and a benign or low-grade malignant tumor was suspected. We extracted the ileal mesenteric tumor with an ileal resection (90 cm). The cut surface of the 55 × 33 × 33 mm³ tumor was pale yellowish-white. Immunohistochemistry revealed diffuse staining for synaptophysin and chromogranin A, and focal staining for CD56. The Ki-67 index was 3%. The final pathological diagnosis was NET G2. The patient’s postoperative course was uneventful, and he developed no recurrence 1.5 years after surgery. Postoperative antitumor therapy was not performed for this patient because the histological diagnosis was NET G2, and it was determined that the tumor could be completely resected by surgery.

Conclusions

We report an extremely rare case of primary ileal mesenteric NET. Mesenteric tumors that show slight FDG uptake on FDG-PET examination should be considered well-differentiated NET.

Molecular imaging phenotyping for selecting and monitoring radioligand therapy of neuroendocrine neoplasms

Neuroendocrine neoplasia (NEN) is an umbrella term that includes a widely heterogeneous disease group including well-differentiated neuroendocrine tumours (NETs), and aggressive neuroendocrine carcinomas (NECs). The site of origin of the NENs is linked to the intrinsic tumour biology and is predictive of the disease course. It is understood that NENs demonstrate significant biologic heterogeneity which ultimately translates to widely varying clinical presentations, disease course and prognosis. Thus, significant emphasis is laid on the pre-therapy evaluation of markers that can help predict tumour behavior and dynamically monitors the response during and after treatment. Most well-differentiated NENs express somatostatin receptors (SSTRs) which make them appropriate for peptide receptor radionuclide therapy (PRRT). However, the treatment outcomes of PRRT depend heavily on the adequacy of patient selection by molecular imaging phenotyping not only utilizing pre-treatment SSTR PET but ¹⁸F-Fluorodeoxyglucose (¹⁸F-FDG) PET to provide insights into the intra- or inter-tumoural heterogeneity of the metastatic disease. Molecular imaging phenotyping may go beyond patient selection and provide useful information during and post-treatment for monitoring of temporal heterogeneity of the disease and dynamically risk-stratify patients. In addition, advances in the understanding of genomic-phenotypic classifications of pheochromocytomas and paragangliomas led to an archetypical example in precision medicine by utilizing molecular imaging phenotyping to guide radioligand therapy. Novel non-SSTR based peptide receptors have also been explored diagnostically and therapeutically to overcome the tumour heterogeneity. In this paper, we review the current molecular imaging modalities that are being utilized for the characterization of the NENs with special emphasis on their role in patient selection for radioligand therapy.

Targeting Amyloids with [18F]AV-45 for Medullary Thyroid Carcinoma Positron Emission Tomography/Computed Tomography Imaging: A Pilot Clinical Study

Medullary thyroid carcinoma (MTC) is a malignant neuroendocrine tumor with a high recurrence rate. Amyloid plaques formed from the misfolding of calcitonin are the key characteristics of MTC. Herein, we conducted a first-in-human pilot clinical study by applying a β-amyloid-specific radiotracer, [¹⁸F]AV-45, to positron emission tomography (PET)/computed tomography (CT) imaging of MTC. The presence of amyloid plaques in the tumor tissue sections from five MTC patients was confirmed by hematoxylin and eosin (H&E) and Congo Red staining. [¹⁸F]AV-45 selectively accumulated in the amyloid plaques in the continued tumor tissue sections with similar distribution patterns to the H&E and Congo Red staining. In addition, the [¹⁸F]AV-45 uptake can be largely blocked by its nonradioactive reference compound. The [¹⁸F]AV-45 accumulation in the thyroid, neck lymph nodes, and muscles in healthy human subjects is close to the background indicated by PET/CT imaging. In the comparison PET/CT imaging study of a recurrent MTC patient, 2-deoxy-2-[¹⁸F]fluoro-d-glucose ([¹⁸F]FDG) showed an elevated uptake by multiple neck lymph nodes. In contrast, only one of these neck lymph nodes had increased [¹⁸F]AV-45 uptake. Postoperative histopathological analysis confirmed the [¹⁸F]AV-45 PET-positive lymph node as MTC with amyloid deposition, while other [¹⁸F]FDG positive lymph nodes were free from MTC and amyloid plaques. Thus, [¹⁸F]AV-45 showed the promise for the clinical PET/CT imaging of MTC.

68Ga-DOTATATE PET/CT versus 111In-octreotide scintigraphy in patients with neuroendocrine tumors: a prospective study

Objective

To compare ⁶⁸Ga-DOTA-DPhe1,Tyr3-octreotate (⁶⁸Ga-DOTATATE) positron-emission tomography/computed tomography (PET/CT) findings with those of conventional ¹¹¹In-octreotide scintigraphy in patients with neuroendocrine tumors (NETs).

Materials and Methods

This was a single-center prospective study including 41 patients (25 males; mean age, 55.4 years) with biopsy-proven NETs who underwent whole-body ¹¹¹In-octreotide scintigraphy and whole-body ⁶⁸Ga-DOTATATE PET/CT. The patients had been referred for tumor staging (34.1%), tumor restaging (61.0%), or response evaluation (4.9%). Images were compared in a patient-by-patient analysis to identify additional lesions, and we attempted to determine the impact that discordant findings had on treatment planning.

Results

Compared with ¹¹¹In-octreotide scintigraphy, ⁶⁸Ga-DOTATATE PET/CT revealed more lesions, the additional lesions typically being in the liver or bowel. Changes in management owing to the additional information provided by ⁶⁸Ga-DOTATATE PET/CT occurred in five patients (12.2%), including intermodal changes in three (7.3%) and intramodal changes in two (4.9%). In addition, ⁶⁸Ga-DOTATATE PET/CT yielded incidental findings unrelated to the primary NET in three patients (7.3%): Hürthle cell carcinoma of the thyroid, bowel non-Hodgkin lymphoma, and a suspicious breast lesion.

Conclusion

We conclude that ⁶⁸Ga-DOTATATE PET/CT is superior to conventional ¹¹¹In-octreotide scintigraphy for the management of NETs because of its ability to determine the extent of the disease more accurately, which, in some cases, translates to changes in the treatment plan.

The effects of molar activity on [18F]FDOPA uptake in patients with neuroendocrine tumors

Background

6-[¹⁸F]fluoro-l-3,4-dihydroxyphenyl alanine ([¹⁸F]FDOPA) is a commonly used PET tracer for the detection and staging of neuroendocrine tumors. In neuroendocrine tumors, [¹⁸F]FDOPA is decarboxylated to [¹⁸F]dopamine via the enzyme amino acid decarboxylase (AADC), leading to increased uptake when there is increased AADC activity. Recently, in our hospital, a new GMP compliant multi-dose production of [¹⁸F]FDOPA has been developed, [¹⁸F]FDOPA-H, resulting in a higher activity yield, improved molar activity and a lower administered mass than the conventional method ([¹⁸F]FDOPA-L).

Aims

This study aimed to investigate whether the difference in molar activity affects the [¹⁸F]FDOPA uptake at physiological sites and in tumor lesions, in patients with NET. It was anticipated that the specific uptake of [¹⁸F]FDOPA-H would be equal to or higher than [¹⁸F]FDOPA-L.

Methods

We retrospectively analyzed 49 patients with pathologically confirmed NETs and stable disease who underwent PET scanning using both [¹⁸F]FDOPA-H and [¹⁸F]FDOPA-L within a time span of 5 years. A total of 98 [¹⁸F]FDOPA scans (49 [¹⁸F]FDOPA-L and 49 [¹⁸F]FDOPA-H with average molar activities of 8 and 107 GBq/mmol) were analyzed. The SUVmean was calculated for physiological organ uptake and SUVmax for tumor lesions in both groups for comparison, and separately in subjects with low tumor load (1–2 lesions) and higher tumor load (3–10 lesions).

Results

Comparable or slightly higher uptake was demonstrated in various physiological uptake sites in subjects scanned with [¹⁸F]FDOPA-H compared to [¹⁸F]FDOPA-L, with large overlap being present in the interquartile ranges. Tumor uptake was slightly higher in the [¹⁸F]FDOPA-H group with 3–10 lesion (SUVmax 6.83 vs. 5.19, p < 0.001). In the other groups, no significant differences were seen between H and L.

Conclusion

[18F]FDOPA-H provides a higher activity yield, offering the possibility to scan more patients with one single production. Minor differences were observed in SUV’s, with slight increases in uptake of [¹⁸F]FDOPA-H in comparison to [¹⁸F]FDOPA-L. This finding is not a concern for clinical practice, but could be of importance when quantifying follow-up scans while introducing new production methods with a higher molar activity of [¹⁸F]FDOPA.

Comparison of the detecting capability between 123I-mIBG and post-therapeutic 131I-mIBG scintigraphy for curie scoring in patients with neuroblastoma after chemotherapy

OBJECTIVE

To evaluate the detecting capability between planar imaging (PI) and PI combined with single-photon emission computed tomography/computed tomography (PICWS), including ¹²³I- and ¹³¹I-labeled metaiodobenzylguanidine (mIBG) and to compare the detecting capability between ¹²³I-mIBG and post-therapeutic ¹³¹I-mIBG scintigraphy including PI and PICWS for Curie scoring in patients with neuroblastoma.

METHODS

Sixty-two patients with 66 pairs of complete images with neuroblastoma were enrolled in this retrospective study.

RESULTS

Comparing the Curie scoring between ¹²³I-mIBG PI and PICWS and between post-therapeutic ¹³¹I-mIBG PI and PICWS, findings were concordantly negative in 28.79% and 18.18% of studies, concordantly positive in 66.67% and 74.24% of studies, and discordant in 4.54% and 7.58% of studies, respectively. PICWS was superior to PI including ¹²³I- and ¹³¹I-mIBG in the evaluation of Curie scoring for neuroblastoma patients (both P < 0.001). Comparing the Curie scores between ¹²³I- and post-therapeutic ¹³¹I-mIBG PI and between ¹²³I- and post-therapeutic ¹³¹I-mIBG PICWS, concordantly negative imaging was visualized in 22.73% and 19.70% of studies, concordantly positive imaging in 66.67% and 69.70% of studies, and discordant imaging in 10.60% and 10.60% of studies, respectively. Post-therapeutic ¹³¹I-mIBG was significantly better than that of ¹²³I-mIBG scintigraphy including PI and PICWS in detecting the Curie scoring for neuroblastoma patients (both P < 0.001).

CONCLUSION

The present study demonstrates that ¹³¹I- or ¹²³I-mIBG PICWS are more helpful in the evaluation of Curie scores than that of conventional PI and that post-therapeutic ¹³¹I-mIBG is superior to ¹²³I-mIBG scintigraphy for the detecting capability of Curie scoring in patients with neuroblastoma.

Nuclear Medicine Imaging in Neuroblastoma: Current Status and New Developments

Neuroblastoma is the most common extracranial solid malignancy in children. At diagnosis, approximately 50% of patients present with metastatic disease. These patients are at high risk for refractory or recurrent disease, which conveys a very poor prognosis. During the past decades, nuclear medicine has been essential for the staging and response assessment of neuroblastoma. Currently, the standard nuclear imaging technique is meta-[¹²³I]iodobenzylguanidine ([¹²³I]mIBG) whole-body scintigraphy, usually combined with single-photon emission computed tomography with computed tomography (SPECT-CT). Nevertheless, 10% of neuroblastomas are mIBG non-avid and [¹²³I]mIBG imaging has relatively low spatial resolution, resulting in limited sensitivity for smaller lesions. More accurate methods to assess full disease extent are needed in order to optimize treatment strategies. Advances in nuclear medicine have led to the introduction of radiotracers compatible for positron emission tomography (PET) imaging in neuroblastoma, such as [¹²⁴I]mIBG, [¹⁸F]mFBG, [¹⁸F]FDG, [⁶⁸Ga]Ga-DOTA peptides, [¹⁸F]F-DOPA, and [¹¹C]mHED. PET has multiple advantages over SPECT, including a superior resolution and whole-body tomographic range. This article reviews the use, characteristics, diagnostic accuracy, advantages, and limitations of current and new tracers for nuclear medicine imaging in neuroblastoma.

Which Is the Optimal Scan Time of 18F-DOPA PET/CT in Patients With Recurrent Medullary Thyroid Carcinoma?: Results From a Dynamic Acquisition Study

PURPOSE

The aim of this retrospective study was to determine, by dynamic acquisition, the optimal scan time of F-DOPA PET/CT in patients with recurrent medullary thyroid carcinoma (MTC).

METHODS

Twenty-one patients with suspected recurrent MTC underwent dynamic F-DOPA PET/CT (lasting 45 minutes) followed by whole-body scan. Three different time intervals of dynamic acquisition were evaluated: ultra-early phase (2-5 minutes), early phase (5-10 minutes), and late phase (40-45 minutes). The number and SUVmax of all detected lesions among the 3 dynamic acquisition phases were compared on qualitative and semiquantitative analyses. Time-activity curves, SUVmax washout rate between ultra-early or early phase and late phase, and signal-to-noise ratio (SNR) between lesion and background activity were also calculated.

RESULTS

At dynamic acquisition, 15 of 21 patients were classified as PET-positive and 6 of 21 as PET-negative, with overall 21 detected lesions. Ultra-early and early imaging provided a better lesion visualization than late phase in more than 70% of cases, as also reflected by SNR (mean SNR reduction between 2 and 45 minutes, -45% ± 19%). Time-activity curves showed a rapid tracer accumulation in MTC lesions, with an average maximum uptake at 2 minutes after injection. Mean lesion SUVmax was 2-fold higher in ultra-early frames compared with last frames (mean washout rate, -44% ± 33%). Finally, compared with whole-body imaging in the same field of view, dynamic acquisition identified 1 additional positive patient and 3 additional lesions in 2 patients.

CONCLUSIONS

Our study, showing a very fast F-DOPA uptake in MTC lesions, suggests the utility to obtain early PET/CT images, already at 2 to 5 minutes after tracer injection, when maximum lesion tracer uptake is reached.

Radionuclide imaging of neuroendocrine tumors

Neuroendocrine tumors (NETs) are relatively rare and heterogeneous with a variaty of clinical expression. They derive from the sensory and secretory neuroendocrine cells mainly within the pulmonary and gastrointestinal tract. They comprise less than 2% of all malignancies. On the basis of clinical behavior, histology, and proliferation rate, they are devided into well differentiated (low grade to intermediate grade) and poorly differentiated (high grade) neuroendocrine carcinoma. Tumor stage and grade have the impact on treatment and prognosis. The treatment of choice is surgery. More than 50% of the patients present metastatic disease at the time of diagnosis, thus the systemic treatment should be considered including somatostatin analogs, chemotherapy, targeted therapy, immunotherapy and peptide receptor radionuclide therapy (PRRT). For the diagnosis and follow-up of these tumors, various radiological methods are used (computed tomography, magnetic resonance imaging, ultrasound) as well as endoscopy. Nuclear medicine methods are used in order to exploit their unique properties mainly amine precursor uptake and decarboxylation system characteristics, as well as the expression of somatostatin receptors. These methods enable whole body examination, staging, selection of patient for PRRT and treatment monitoring as well. Imaging can be performed with gamma camera (SPECT, SPECT/CT) or positron emission tomography (PET/ CT). Radiopharmaceuticals used for imaging with gamma camera are usually 99mTc-(V)-DMSA, 99mTc-MIBI, 99mTc-HYNIC TOC, 111In-pentetreotide and 131I-MIBG/123I-MIBG. Positron emitting radiopharmaceuticals has superior spatial resolution and faster imaging, such as 68Ga-DOTA-somatostatin analogues, 18F-FDG (particularly for high-grade tumors), 18F-L-DOPA/11C-L-DOPA and 11C-5-hydroxytryptophan that have demonstrated excellent imaging results. The new targeted agents present a challenge in the evaluation procedure of treatment and, therefore, new imaging techniques and an improvement of currently available techniques are mandatory. In this mini-review, the most frequent methods and radiopharmaceuticals are presented, as well as potential development.

A side-by-side evaluation of [18F]FDOPA enantiomers for non-invasive detection of neuroendocrine tumors by positron emission tomography

Neuroendocrine tumors (NETs) are an extremely heterogenous group of malignancies with variable clinical behavior. Molecular imaging of patients with NETs allows for effective patient stratification and treatment guidance and is crucial in selection of targeted therapies. Positron emission tomography (PET) with the radiotracer L-[¹⁸F]FDOPA is progressively being utilized for non-invasive in vivo visualization of NETs and pancreatic β-cell hyperplasia. While L-[¹⁸F]FDOPA-PET is a valuable tool for disease detection and management, it also exhibits significant diagnostic limitations owing to its inherent physiological uptake in off-target tissues. We hypothesized that the D-amino acid structural isomer of that clinical tracer, D-[¹⁸F]FDOPA, may exhibit superior clearance capabilities owing to a reduced in vivo enzymatic recognition and enzyme-mediated metabolism. Here, we report a side-by-side evaluation of D-[¹⁸F]FDOPA with its counterpart clinical tracer, L-[¹⁸F]FDOPA, for the non-invasive in vivo detection of NETs. In vitro evaluation in five NET cell lines, including invasive small intestinal neuroendocrine carcinomas (STC-1), insulinomas (TGP52 and TGP61), colorectal adenocarcinomas (COLO-320) and pheochromocytomas (PC12), generally indicated higher overall uptake levels of L-[¹⁸F]FDOPA, compared to D-[¹⁸F]FDOPA. While in vivo PET imaging and ex vivo biodistribution studies in PC12, STC-1 and COLO-320 mouse xenografts further supported our in vitro data, they also illustrated lower off-target retention and enhanced clearance of D-[¹⁸F]FDOPA from healthy tissues. Cumulatively our results indicate the potential diagnostic applications of D-[¹⁸F]FDOPA for malignancies where the utility of L-[¹⁸F]FDOPA-PET is limited by the physiological uptake of L-[¹⁸F]FDOPA, and suggest D-[¹⁸F]FDOPA as a viable PET imaging tracer for NETs.

Intricacies of the Molecular Machinery of Catecholamine Biosynthesis and Secretion by Chromaffin Cells of the Normal Adrenal Medulla and in Pheochromocytoma and Paraganglioma

The adrenal medulla is composed predominantly of chromaffin cells producing and secreting the catecholamines dopamine, norepinephrine, and epinephrine. Catecholamine biosynthesis and secretion is a complex and tightly controlled physiologic process. The pathways involved have been extensively studied, and various elements of the underlying molecular machinery have been identified. In this review, we provide a detailed description of the route from stimulus to secretion of catecholamines by the normal adrenal chromaffin cell compared to chromaffin tumor cells in pheochromocytomas. Pheochromocytomas are adrenomedullary tumors that are characterized by uncontrolled synthesis and secretion of catecholamines. This uncontrolled secretion can be partly explained by perturbations of the molecular catecholamine secretory machinery in pheochromocytoma cells. Chromaffin cell tumors also include sympathetic paragangliomas originating in sympathetic ganglia. Pheochromocytomas and paragangliomas are usually locally confined tumors, but about 15% do metastasize to distant locations. Histopathological examination currently poorly predicts future biologic behavior, thus long term postoperative follow-up is required. Therefore, there is an unmet need for prognostic biomarkers. Clearer understanding of the cellular mechanisms involved in the secretory characteristics of pheochromocytomas and sympathetic paragangliomas may offer one approach for the discovery of novel prognostic biomarkers for improved therapeutic targeting and monitoring of treatment or disease progression.

Molecular imaging of bone metastases using tumor-targeted tracers

Bone metastasis is a disastrous manifestation of most malignancies, especially in breast, prostate and lung cancers. Since asymptomatic bone metastases are not uncommon, early detection, precise assessment, and localization of them are very important. Various imaging modalities have been employed in the setting of diagnosis of bone metastasis, from plain radiography and bone scintigraphy to SPECT, SPECT/CT, PET/CT, MRI. However, each modality showed its own limitation providing accurate diagnostic performance. In this regard, various tumor-targeted radiotracers have been introduced for molecular imaging of bone metastases using modern hybrid modalities. In this article we review the strength of different cancer-specific radiopharmaceuticals in the detection of bone metastases. As shown in the literature, among various tumor-targeted tracers, 68Ga DOTA-conjugated-peptides, 68Ga PSMA, 18F DOPA, 18F galacto-RGD integrin, 18F FDG, 11C/18F acetate, 11C/18F choline, 111In octreotide, 123/131I MIBG, 99mTc MIBI, and 201Tl have acceptable capabilities in detecting bone metastases depending on the cancer type. However, different study designs and gold standards among reviewed articles should be taken into consideration.

Metabolism of Stem and Progenitor Cells: Proper Methods to Answer Specific Questions

Stem cells can stay quiescent for a long period of time or proliferate and differentiate into multiple lineages. The activity of stage-specific metabolic programs allows stem cells to best adapt their functions in different microenvironments. Specific cellular phenotypes can be, therefore, defined by precise metabolic signatures. Notably, not only cellular metabolism describes a defined cellular phenotype, but experimental evidence now clearly indicate that also rewiring cells towards a particular cellular metabolism can drive their cellular phenotype and function accordingly. Cellular metabolism can be studied by both targeted and untargeted approaches. Targeted analyses focus on a subset of identified metabolites and on their metabolic fluxes. In addition, the overall assessment of the oxygen consumption rate (OCR) gives a measure of the overall cellular oxidative metabolism and mitochondrial function. Untargeted approach provides a large-scale identification and quantification of the whole metabolome with the aim to describe a metabolic fingerprinting. In this review article, we overview the methodologies currently available for the study of invitro stem cell metabolism, including metabolic fluxes, fingerprint analyses, and single-cell metabolomics. Moreover, we summarize available approaches for the study of in vivo stem cell metabolism. For all of the described methods, we highlight their specificities and limitations. In addition, we discuss practical concerns about the most threatening steps, including metabolic quenching, sample preparation and extraction. A better knowledge of the precise metabolic signature defining specific cell population is instrumental to the design of novel therapeutic strategies able to drive undifferentiated stem cells towards a selective and valuable cellular phenotype.

Adrenal tracer uptake by 18F-FDOPA PET/CT in patients with pheochromocytoma and controls

Context

¹⁸F-FDOPA PET/CT accurately localizes pheochromocytoma in patients with an established biochemical diagnosis. However, cut-off ¹⁸F-FDOPA levels of standardized uptake values (SUV_max) for both normal adrenal glands and pheochromocytoma are lacking.

Objective

Objectives of this study were to determine (1) reference maximum standardized uptake values (SUVmax) for normal adrenal ¹⁸F-DOPA tracer uptake and (2) the optimal diagnostic approach for pheochromocytoma localization by using ¹⁸F-DOPA SUVmax across a series of cut-off points: the affected adrenal gland (inter-individual analysis), the difference in SUVmax between the affected adrenal gland and the contralateral normal adrenal gland (intra-individual analysis), or a combination of these two.

Patients and methods

All patients with histologically confirmed pheochromocytoma diagnosed at our center between November 2009 and December 2017 were retrospectively analysed. Only those patients who underwent an ¹⁸F-FDOPA PET/CT-scan for localization purposes before adrenalectomy were included for further analysis. The control group consisted of patients who underwent ¹⁸F-FDOPA PET/CT for other indications and who had no genetic susceptibility for developing a pheochromocytoma. SUV_max of the volume of interest surrounding the adrenal glands was determined on EARL reconstructed images. Receiver operating characteristic (ROC) analysis was performed for adrenal gland SUV_max and intra-individual difference in SUV_max between affected and normal adrenal gland. In addition, binary logistic regression was performed for ROC analysis of the combined parameters.

Results

In total, 47 histologically confirmed pheochromocytomas were diagnosed in 45 patients, and 245 disease control patients were identified. In the control group, no statistical differences between the SUV_max of left and right adrenal glands were observed, and uptake values in both adrenal glands correlated significantly with each other (r = 0.865, p < 0.001). Median (range) adrenal gland SUV_max in pheochromocytomas and in the control group was 12 (2.6–50) and 2.9 (1.1–6.6), respectively (p < 0.001). ROC analysis revealed 93% sensitivity and 85% specificity at an SUV_max cut-off value of 4.1 (area under the curve (AUC) = 0.951), and 93% sensitivity and 96% specificity at an intra-individual SUV_max difference between the affected and normal adrenal gland of 1.0 (AUC = 0.992). The combination of both variables increased the AUC to 0.995.

Conclusions

¹⁸F-FDOPA PET/CT distinguishes pheochromocytoma from normal adrenal glands with the highest diagnostic accuracy when combining the SUVmax of the affected adrenal gland with the difference in SUV_max between affected and normal adrenal gland.

Gallium-68 DOTA-NOC PET/CT as an alternate predictor of disease activity in sarcoidosis

INTRODUCTION

We evaluated the role of gallium-68-labeled [1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid]-1-Nal3-octreotide (Ga-DOTA-NOC) PET/CT in assessing sarcoidosis disease activity.

PATIENTS AND METHODS

Patients diagnosed with sarcoidosis underwent Ga-DOTA-NOC-PET/CT. The maximum standardized uptake value (SUVmax) at the pathological site and in the descending thoracic aorta (reference standard, SUVmed) were assessed. A SUVmax/SUVmed ratio (disease activity score) of more than one was considered a marker of active disease and was compared with the clinical symptoms and serum angiotensin-converting enzyme and computed tomography (CT) scan. The primary outcome was to assess the efficacy of the scan in estimating disease activity.

RESULTS

Of the 39 patients enrolled in the study, 27 patients were symptomatic and the rest were asymptomatic at enrollment. Increased disease activity was present in 25 (92%) of the 27 symptomatic patients and two (16%) of the 12 asymptomatic patients. The sensitivity and specificity of the test were 92.5% (95% confidence interval=75.7-99.0) and 83.3% (95% confidence interval=51.5-97.9), respectively. Seven out of nine patients who became asymptomatic after treatment showed a significant decrease in the mean disease activity score in post-treatment scans (3.38±1.05 vs 1.20±0.82, P<0.001).

CONCLUSION

Ga-DOTA-NOC PET/CT emerged as a useful tool to assess the disease activity and treatment response in patients with sarcoidosis with thoracic involvement.

False-positive findings on 6-[18F]fluor-l-3,4-dihydroxyphenylalanine PET (18F-FDOPA-PET) performed for imaging of neuroendocrine tumors

BACKGROUND/AIM

PET with 6-[18F]fluor-l-3,4-dihydroxyphenylalanine (¹⁸F-FDOPA) has been shown to be a useful imaging tool with a high sensitivity for the visualization of neuroendocrine tumors (NETs). ¹⁸F-FDOPA uptake in tumors other than NETs has been suggested previously, but data on this phenomenon are limited. We therefore studied the non-physiological, false-positive uptake of ¹⁸F-FDOPA in a large population of patients with a NET or with a high clinical suspicion of harboring a NET.

PATIENTS AND METHODS

Retrospective single-center study among adult patients in whom ¹⁸F-FDOPA PET scintigraphy was performed between January 2004 and December 2014. The original scan report was compared with the original pathology report corresponding with the ¹⁸F-FDOPA PET-positive lesion. In case this was inconsistent with the diagnosis of a NET, both the scan and the pathology slides were reassessed. Specimens of these non-NET tissues were immunohistochemically stained for AADC.

RESULTS

1070 ¹⁸F-FDOPA PET scans from 705 patients were evaluated. Focal or multiple ¹⁸F-FDOPA-avid lesions were described in 709 ¹⁸F-FDOPA PET scans (66%). Histology of these ¹⁸F-FDOPA PET-positive lesions was present in 508 (72%) cases. In seven cases, the histopathology was not compatible with NET but showed squamous cell carcinoma of the cervix, multiple myeloma (two cases), hepatocellular carcinoma, Schwannoma, adrenocortical carcinoma and a skeletal myxoid chondrosarcoma, with positive immunohistochemical staining for AADC in 67%.

CONCLUSIONS

Pathological uptake of ¹⁸F-FDOPA does not always indicate the presence of a NET. The possibility of ¹⁸F-FDOPA uptake by tumor types other than NETs, although rare, should be considered.

Feasibility of a streamlined imaging protocol in technetium-99m-Tektrotyd somatostatin receptor SPECT/CT

AIM

To assess the feasibility and efficacy of a streamlined single time-point ^99mTc-HYNIC-Tyr3-octreotide (Tektrotyd) somatostatin receptor scintigraphy (SRS) protocol to differentiate pathological uptake by neuroendocrine tumours (NETs) from physiological activity.

METHODS AND MATERIALS

Tektrotyd imaging in 50 consecutive patients with NETs was reviewed retrospectively. Imaging was independently assessed by two experienced reporters with dual-certification in radiology and nuclear medicine and agreed in consensus. The presence of physiological bowel activity and/or further sites of equivocal uptake on 4-hour planar imaging and whether combined single-photon-emission computed tomography (SPECT)/computed tomography (CT) assessment allowed accurate diagnosis was tabulated. A judgement was also made in each case on whether 2-hour planar imaging was necessary for accurate diagnostic interpretation.

RESULTS

Thirty-six patients (72%) had positive findings on Tektrotyd SPECT/CT. Eight patients (16%) had bowel activity on 4-hour planar imaging, which could be considered to have hampered interpretation without access to SPECT/CT. Eleven studies in 10 patients (20%) demonstrated areas of indeterminate uptake on planar imaging; five in the uncinate process of the pancreas, three in the nasal cavity or paranasal sinuses, one in the adrenal glands, one in a focus of inflammation on the posterior abdominal wall, and one at the tip of a central venous line. In all cases, accurate interpretation of findings was possible with SPECT/CT, without the 2-hour planar image.

CONCLUSION

Two-hour planar imaging could be safely omitted from Tektrotyd SRS incorporating SPECT/CT imaging without reducing the accuracy of diagnostic interpretation. Streamlined imaging has the potential to reduce patient inconvenience and improve scanner and staff efficiency.

Clinical Significance of Pretreatment FDG PET/CT in MIBG-Avid Pediatric Neuroblastoma

PURPOSE

¹⁸F-fluorodeoxyglucose-positron emission tomography (FDG-PET) imaging is well known to have clinical significance in the initial staging and response evaluation of the many kinds of neoplasms. However, its role in the pediatric neuroblastoma is not clearly defined. In the present study, the clinical significance of FDG-PET/computed tomography (CT) in ¹²³I- or ¹³¹I-metaiodobenzylguanidine (MIBG)-avid pediatric neuroblastoma was investigated.

METHODS

Twenty patients with neuroblastoma who undertook pretreatment FDG PET/CT at our institute between 2008 and 2015 and showed MIBG avidity were retrospectively enrolled in the present study. Clinical information-including histopathology, and serum markers-and several PET parameters-including SUVmax of the primary lesion (Psuv), target-to-background ratio (TBR), metabolic tumor volume (MTV), and coefficient of variation (CV)-were analyzed. The prognostic effect of PET parameters was evaluated in terms of progression-free survival (PFS).

RESULTS

Total 20 patients (4.5 ± 3.5 years) were divided as two groups by disease progression. Six patients (30.0 %) experienced disease progression and one patient (5.0 %) died during follow-up period. There were not statistically significant in age, stage, MYCN status, primary tumor size, serum lactate dehydrogenase (LDH), neuron-specific enolase (NSE), and ferritin level between two groups with progression or no progression. However, Psuv (p = 0.017), TBR (p = 0.09), MTV (p = 0.02), and CV (p = 0.036) showed significant differences between two groups. In univariate analysis, PFS was significantly associated with Psuv (p = 0.021) and TBR (p = 0.023).

CONCLUSIONS

FDG-PET parameters were significantly related with progression of neuroblastoma. FDG-PET/CT may have the potential as a valuable modality for evaluating prognosis in the patients with MIBG-avid pediatric neuroblastoma.

Summary of emerging personalized medicine in neuroendocrine tumors: are we on track?

Neuroendocrine tumors (NETs) comprise a heterogeneous group of malignancies, with differences in prognosis and effective therapies. Traditionally, NETs have been characterized by tumor grade, site of primary tumor, functional status, and presence of underlying familial syndrome. However, increased feasibility and utilization of next-generation sequencing and other methodologies have revealed new genomic and epigenetic aberrations. In the last decade, treatment options available for metastatic well-differentiated gastroenteropancreatic (GEP) NETs have expanded, with approval of antiangiogenic and mTOR-directed targeted therapies, and our armamentarium of active therapies is likely to further increase. Cytotoxic therapies also are an important option for pancreatic NETs, and MGMT promoter methylation and protein expression may be an important biomarker for efficacy of alkylating agents. Peptide receptor radioligand therapy is an emerging treatment that uses functional imaging to personalize dosimetry to the tumor and avoid nephrotoxicity. Nevertheless, there is a critical need for further biomarkers, particularly multianalyte biomarkers, to aid in prognostication and predict efficacy of therapies.

Activatable iRGD-based peptide monolith: Targeting, internalization, and fluorescence activation for precise tumor imaging

A disulfide-bridged cyclic RGD peptide, named iRGD (internalizing RGD, c(CRGDK/RGPD/EC)), is known to facilitate tumor targeting as well as tissue penetration. After the RGD motif-induced targeting on αv integrins expressed near tumor tissue, iRGD encounters proteolytic cleavage to expose the CendR motif that promotes penetration into cancer cells via the interaction with neuropilin-1. Based on these proteolytic cleavage and internalization mechanism, we designed an iRGD-based monolithic imaging probe that integrates multiple functions (cancer-specific targeting, internalization and fluorescence activation) within a small peptide framework. To provide the capability of activatable fluorescence signaling, we conjugated a fluorescent dye to the N-terminal of iRGD, which was linked to the internalizing sequence (CendR motif), and a quencher to the opposite C-terminal. It turned out that fluorescence activation of the dye/quencher-conjugated monolithic peptide probe requires dual (reductive and proteolytic) cleavages on both disulfide and amide bond of iRGD peptide. Furthermore, the cleavage of the iRGD peptide leading to fluorescence recovery was indeed operative depending on the tumor-related angiogenic receptors (αvβ3 integrin and neuropilin-1) in vitro as well as in vivo. Compared to an 'always fluorescent' iRGD control probe without quencher conjugation, the dye/quencher-conjugated activatable monolithic peptide probe visualized tumor regions more precisely with lower background noise after intravenous injection, owing to the multifunctional responses specific to tumor microenvironment. All these results, along with minimal in vitro and in vivo toxicity profiles, suggest potential of the iRGD-based activatable monolithic peptide probe as a promising imaging agent for precise tumor diagnosis.

Effect of Carbidopa on 18F-FDOPA Uptake in Insulinoma: From Cell Culture to Small-Animal PET Imaging

Patient premedication with carbidopa seems to improve the accuracy of 6-¹⁸F-fluoro-3,4-dihydroxy-l-phenylalanine (¹⁸F-FDOPA) PET for insulinoma diagnosis. However, the risk of PET false-negative results in the presence of carbidopa is a concern. Consequently, we aimed to evaluate the effect of carbidopa on ¹⁸F-FDOPA uptake in insulinoma β-cells and an insulinoma xenograft model in mice.

METHODS

¹⁸F-FDOPA in vitro accumulation was assessed in the murine β-cell line RIN-m5F. In vivo small-animal PET experiments were performed on tumor-bearing nude mice after subcutaneous injection of RIN-m5F cells. Experiments were conducted with and without carbidopa pretreatment.

RESULTS

Incubation of RIN-m5F cells with 80 μM carbidopa did not significantly affect the cellular accumulation of ¹⁸F-FDOPA. Tumor xenografts were clearly detectable by small-animal PET in all cases. Insulinoma xenografts in carbidopa-treated mice showed significantly higher ¹⁸F-FDOPA uptake than those in nontreated mice. Regardless of carbidopa premedication, the xenografts were characterized by an early increase in ¹⁸F-FDOPA uptake and then a progressive reduction over time.

CONCLUSION

Carbidopa did not influence in vitro ¹⁸F-FDOPA accumulation in RIN-m5F cells but improved insulinoma imaging in vivo. Our findings increase current knowledge about the ¹⁸F-FDOPA uptake profile of RIN-m5F cells and a related xenograft model. To our knowledge, the present work represents the first preclinical research specifically focused on insulinomas, with potential translational implications.

PET-CT in the UK: current status and future directions

Combined positron-emission tomography and computed tomography (PET-CT) has taken the oncological world by storm since being introduced into the clinical domain in the early 21(st) century and is firmly established in the management pathway of many different tumour types. Non-oncological applications of PET-CT represent a smaller but steadily growing area of interest. PET-CT continues to be the focus of a large number of research studies and keeping up-to-date with the literature is important but represents a challenge. Consequently guidelines recommending PET-CT usage need to be revised regularly to encompass new developments. The purpose of this article is twofold: first, it provides a detailed review of the evidence-base underpinning the major uses of PET-CT in clinical practice, which may be of value to a wide-range of individuals, including those directly involved with PET-CT and to a much larger group with limited exposure, but for whom a précis of the current state-of-play may help inform other radiology and multidisciplinary team (MDT) work; the second purpose is as a companion to revised guidelines on evidence-based indications for PET-CT in the UK (being published concurrently) providing a detailed commentary on new indications with a summary of emerging data supporting these additional clinical uses of the technique.

Case 227: Endobronchial Carcinoid Tumor with Incidental Metastatic Breast Cancer Detected with Somatostatin Receptor Scintigraphy ((111)In Pentreotide)

HISTORY

A 30-year-old woman with polycystic ovarian syndrome who was undergoing hormone replacement therapy presented with a 6-month history of a nonproductive cough and a 1-day history of hemoptysis (approximately 20 mL). Intravenous contrast material-enhanced (100 mL of Omnipaque 350; GE Healthcare, Princeton, NJ) computed tomographic (CT) pulmonary angiography was performed to evaluate for pulmonary embolism. On the basis of the CT pulmonary angiographic findings, chromogranin A and 5-hydroxyindoleacetic acid levels were measured and were 7 nmol/L (343 µg/L) (high) and 2.9 mg per 24 hours (15.167 µmol/d) (normal), respectively. This patient underwent bronchoscopy and biopsy. After these tests, she was referred for whole-body scintigraphy, which revealed an unexpected finding that was further investigated with fluorine 18 ((18)F) flurodeoxyglucose (FDG) positron emission tomography (PET) and CT.

A novel statistical analysis method to improve the detection of hepatic foci of (111)In-octreotide in SPECT/CT imaging

Background

Low uptake ratios, high noise, poor resolution, and low contrast all combine to make the detection of neuroendocrine liver tumours by ¹¹¹In-octreotide single photon emission tomography (SPECT) imaging a challenge. The aim of this study was to develop a segmentation analysis method that could improve the accuracy of hepatic neuroendocrine tumour detection.

Methods

Our novel segmentation was benchmarked by a retrospective analysis of patients categorized as either ¹¹¹In-octreotide positive (¹¹¹In-octreotide(+)) or ¹¹¹In-octreotide negative (¹¹¹In-octreotide(−)) for liver tumours. Following a 3-year follow-up period, involving multiple imaging modalities, we further segregated ¹¹¹In-octreotide-negative patients into two groups: one with no confirmed liver tumours (¹¹¹In-octreotide(−)/radtech(−)) and the other, now diagnosed with liver tumours (¹¹¹In-octreotide(−)/radtech(+)). We retrospectively applied our segmentation analysis to see if it could have detected these previously missed tumours using ¹¹¹In-octreotide. Our methodology subdivided the liver and determined normalized numbers of uptake foci (nNUF), at various threshold values, using a connected-component labelling algorithm. Plots of nNUF against the threshold index (ThI) were generated. ThI was defined as follows: ThI = (c_max − c_thr)/c_max, where c_max is the maximal threshold value for obtaining at least one, two voxel sized, uptake focus; c_thr is the voxel threshold value. The maximal divergence between the nNUF values for ¹¹¹In-octreotide(−)/radtech(−), and ¹¹¹In-octreotide(+) livers, was used as the optimal nNUF value for tumour detection. We also corrected for any influence of the mean activity concentration on ThI. The nNUF versus ThI method (nNUFTI) was then used to reanalyze the ¹¹¹In-octreotide(−)/radtech(−) and ¹¹¹In-octreotide(−)/radtech(+) groups.

Results

Of a total of 53 ¹¹¹In-octreotide(−) patients, 40 were categorized as ¹¹¹In-octreotide(−)/radtech(−) and 13 as ¹¹¹In-octreotide(−)/radtech(+) group. Optimal separation of the nNUF values for ¹¹¹In-octreotide(−)/radtech(−) and ¹¹¹In-octreotide(+) groups was defined at the nNUF value of 0.25, to the right of the bell shaped nNUFTI curve. ThIs at this nNUF value were dependent on the mean activity concentration and therefore normalized to generate nThI; a significant difference in nThI values was found between the ¹¹¹In-octreotide(−)/radtech(−) and the ¹¹¹In-octreotide(−)/radtech(+) groups (P < 0.01). As a result, four of the 13 ¹¹¹In-octreotide(−)/radtech(+) livers were redesigned as ¹¹¹In-octreotide(+).

Conclusions

The nNUFTI method has the potential to improve the diagnosis of liver tumours using ¹¹¹In-octreotide.

Gastroenteropancreatic neuroendocrine tumours (GEP-NET) - Imaging and staging

Detection of gastroenteropancreatic neuroendocrine tumours (GEP-NETs) and monitoring of treatment response relies mainly on morphological imaging such as computed tomography (CT) and magnetic resonance imaging (MRI). Molecular imaging techniques also in combination with CT (hybrid imaging) greatly benefit patient management, including better localization of occult tumours and better staging. Somatostatin receptor scintigraphy (SRS) and somatostatin receptor (SSTR) positron emission tomography (PET) play a central role in the diagnostic work-up of patients with well-differentiated GEP-NETs. SSTR PET/CT is superior to SRS and should be used whenever available. (18)F-DOPA and (18)F-FDG PET/CT is inferior to SSTR PET/CT at least in patients with well-differentiated GEP-NETs. Both SSTR PET/CT and SRS have limitations, such as relatively low detection rate of benign insulinomas, poorly differentiated GEP-NETs and liver metastases. New innovations such as SSTR PET/MRI, radiolabelled SSTR antagonists and glucagon-like peptide-1 receptor (GLP-1R) agonists might further improve imaging of GEP-NETs.

Diagnostic tools for post-gastric bypass hypoglycaemia

In spite of its evident success, several late complications can occur after gastric bypass surgery. One of these is post-gastric bypass hypoglycaemia. No evidence-based guidelines exist in the literature on how to confirm the presence of this syndrome. This study aims to describe and compare the tests aimed at making a diagnosis of post-gastric bypass hypoglycaemia and to provide a diagnostic approach based upon the available evidence. A search was conducted in PubMed, Cochrane and Embase. A few questionnaires have been developed to measure the severity of symptoms in post-gastric bypass hypoglycaemia but none has been validated. The gold standard for provocation of a hypoglycaemic event is the oral glucose tolerance test or the liquid mixed meal tolerance test. Both show a high prevalence of hypoglycaemia in post-gastric bypass patients with and without hypoglycaemic complaints as well as in healthy volunteers. No uniformly established cut-off values for glucose concentrations are defined in the literature for the diagnosis of post-gastric bypass hypoglycaemia. For establishing an accurate diagnosis of post-gastric bypass hypoglycaemia, a validated questionnaire, in connection with the diagnostic performance of provocation tests, is the most important thing missing. Given these shortcomings, we provide recommendations based upon the current literature.

Gastrointestinal cancers in the era of theranostics: Updates and future perspectives

Theranostics are one of the practical aspects of personalized medicine. This concept was designed to describe a material combining diagnosis, treatment and follow up of a disease. It evolved and included molecular targeting and nanotechnologies that incorporate both diagnosis and therapeutics. In this editorial, we are presenting briefly the concept and evolution of theranostics, highlighting many applications of theranostics in daily practice and discussing future perspectives and aspects of this model in gastro-intestincal cancers.

Use of radioactive substances in diagnosis and treatment of neuroendocrine tumors

Radionuclides are needed both for nuclear medicine imaging as well as for peptide-receptor radionuclide therapy (PRRT) of neuroendocrine tumors (NET). Imaging is important in the initial diagnostic work-up and for staging NETs. In therapy planning, somatostatin receptor imaging (SRI) is used when treatment is targeted at the somatostatin receptors as with the use of somatostatin analogues or PRRT. SRI with gamma camera technique using the tracer (111)In-DTPA-octreotide has for many years been the backbone of nuclear imaging of NETs. However, increasingly PET tracers for SRI are now used. (68)Ga-DOTATATE, (68)Ga-DOTATOC and (68)Ga-DOTANOC are the three most often used PET tracers. They perform better than SPECT tracers and should be preferred. FDG-PET is well suited for visualization of most of the somatostatin receptor-negative tumors prognostic in NET patients. Also (11)C-5-HTP, (18)F-DOPA and (123)I-MIBG may be used in NET. However, with FDG-PET and somatostatin receptor PET at hand we see limited necessity of other tracers. PRRT is an important tool in the treatment of advanced NETs causing complete or partial response in 20% and minor response or tumor stabilization in 60% with response duration of up to 3 years. Grade 3-4 kidney or bone marrow toxicity is seen in 1.5% and 9.5%, respectively, but are completely or partly reversible in most patients. (177)Lu-DOTATATE seems to have less toxicity than (90)Y-DOTATOC. However, until now only retrospective, non-randomized studies have been performed and the role of PRRT in treatment of NETs remains to be established.

Endocrine scintigraphy with hybrid SPECT/CT

Nuclear medicine imaging of endocrine disorders takes advantage of unique cellular properties of endocrine organs and tissues that can be depicted by targeted radiopharmaceuticals. Detailed functional maps of biodistributions of radiopharmaceutical uptake can be displayed in three-dimensional tomographic formats, using single photon emission computed tomography (CT) that can now be directly combined with simultaneously acquired cross-sectional anatomic maps derived from CT. The integration of function depicted by scintigraphy and anatomy with CT has synergistically improved the efficacy of nuclear medicine imaging across a broad spectrum of clinical applications, which include some of the oldest imaging studies of endocrine dysfunction.

Dual tracer functional imaging of gastroenteropancreatic neuroendocrine tumors using 68Ga-DOTA-NOC PET-CT and 18F-FDG PET-CT: competitive or complimentary?

OBJECTIVE

This study aimed to compare the diagnostic performance of Ga-DOTANOC PET/CT with F-FDG PET/CT in the patients with gastroenteropancreatic neuroendocrine tumors (GEP-NETs).

PATIENTS AND METHODS

Data of 51 patients with definite histological diagnosis of GEP-NET who underwent both Ga-DOTA-NOC PET-CT and F-FDG PET-CT within a span of 15 days were selected for this retrospective analysis. Sensitivity, specificity, and predictive values were calculated for Ga-DOTA-NOC PET-CT and F-FDG PET-CT, and results were compared both on patientwise and regionwise analysis.

RESULTS

Ga-DOTA-NOC PET-CT is superior to F-FDG PET-CT on patientwise analysis (P < 0.0001). On regionwise analysis, Ga-DOTA-NOC PET-CT is superior to F-FDG PET-CT only for lymph node metastases (P < 0.003). Although Ga-DOTA-NOC PET-CT detected more liver and skeletal lesions compared with F-FDG PET-CT, the difference was not statistically significant. In addition, the results of combined imaging helped in selecting candidates who would undergo the appropriate mode of treatment, whether octreotide therapy or conventional chemotherapy

CONCLUSIONS

Ga-DOTA-NOC PET-CT seems to be superior to F-FDG PET-CT for imaging GEP-NETs. However, their role seems to be complementary because combination of Ga-DOTA-NOC PET-CT and F-FDG PET-CT in such patients helps demonstrate the total disease burden and segregate them to proper therapeutic groups.

Synthesis and biological evaluation of (18)F-labeled Fluoroethoxy tryptophan analogues as potential PET tumor imaging agents

As a continuation of our research efforts toward the development of tryptophan-based radiotracers for tumor imaging with positron emission tomography (PET), three new fluoroethoxy tryptophan analogues were synthesized and evaluated in vivo. These new tracers (namely, 4-(2-[(18)F]fluoroethoxy)-dl-tryptophan ([(18)F]4-FEHTP), 6-(2-[(18)F]fluoroethoxy)-dl-tryptophan ([(18)F]6-FEHTP), and 7-(2-[(18)F]fluoroethoxy)-dl-tryptophan ([(18)F]7-FEHTP) carry the fluoroethoxy side chain either at positions 4-, 6-, or 7- of the indole core. Reference compounds and precursors were synthesized by multistep approaches. Radiosynthesis was accomplished by no-carrier-added nucleophilic (18)F-fluorination following either an indirect approach (O-alkylation of the corresponding hydroxytryptophan with [(18)F]fluoroethyltosylate) or a direct approach (nucleophilic [(18)F] fluorination using a protected mesyl precursor). Radiochemical yields (decay corrected) for both methods were in the range of 10-18%. Small animal PET imaging with xenograft-bearing mice revealed the highest tumor/background ratio for [(18)F]6-FEHTP which, in a direct comparison, outperformed the other two tryptophan tracers and also the well-established tyrosine analogue O-(2-[(18)F]fluoroethyl)-l-tyrosine ([(18)F]l-FET). Investigation of the transport mechanism of [(18)F]6-FEHTP in small cell lung cancer cells (NCI-H69) revealed that it is most probably taken up exclusively via the large neutral amino acid transporter(s) (LAT).

Congenital hyperinsulinism: Role of fluorine-18L-3, 4 hydroxyphenylalanine positron emission tomography scanning

Congenital hyperinsulinism (CHI) is a rare but complex heterogeneous disorder caused by unregulated secretion of insulin from the β-cells of the pancreas leading to severe hypoglycaemia and neuroglycopaenia. Swift diagnosis and institution of appropriate management is crucial to prevent or minimise adverse neurodevelopmental outcome in children with CHI. Histologically there are two major subtypes of CHI, diffuse and focal disease and the management approach will significantly differ depending on the type of the lesion. Patients with medically unresponsive diffuse disease require a near total pancreatectomy, which then leads on to the development of iatrogenic diabetes mellitus and pancreatic exocrine insufficiency. However patients with focal disease only require a limited pancreatectomy to remove only the focal lesion thus providing complete cure to the patient. Hence the preoperative differentiation of the histological subtypes of CHI becomes paramount in the management of CHI. Fluorine-18L-3, 4-hydroxyphenylalanine positron emission tomography (¹⁸F-DOPA-PET) is now the gold standard for pre-operative differentiation of focal from diffuse disease and localisation of the focal lesion. The aim of this review article is to give a clinical overview of CHI, then review the role of dopamine in β-cell physiology and finally discuss the role of ¹⁸F-DOPA-PET imaging in the management of CHI.

The use of gallium-68 labeled somatostatin receptors in PET/CT imaging

68Ga-DOTA-SSTRTs PET/CT has become the most promising noninvasive procedure to study well-differentiated NET. Although the excellent diagnostic accuracy of the procedure is well known, its use is limited to specialized centers in Europe as parts of clinical trials. Literature reports confirm the superiority of 68Ga-DOTA-SSTRTs PET/CT for the assessment of well-differentiated NET over morphologic imaging procedures, SRS, and even PET/CT using metabolic radiotracers. 68Ga-DOTA-SSTRTs provide good visualization of NET lesions at both the primary and the metastatic sites (node, bone, liver, and unusual localizations). The advantages of their use over metabolic tracers (18F-DOPA, 18F-FDG) are not only limited to a better overall detection rate but also to the fact that they also provide data on SSTR expression on target lesions, resulting a fundamental procedure before starting therapy with either hot or cold somatostatin analogues. Moreover, they can be used also in centers without an on-site cyclotron. To interpret 68Ga-DOTA-SSTRTs images correctly, it is crucial to understand the tracer’s biodistribution as well as the conditions that may alter tracer uptake. Considering that SSTR are expressed on activated lymphocytes, all areas of inflammation show 68Ga-DOTA-SSTRTs uptake. Areas of increased uptake in frequent sites of inflammation (eg, thyroid, mediastinal nodes, inguinal nodes, and nodes adjacent to areas of recent surgery/trauma) should be interpreted with care. A detailed clinical history with particular attention to concomitant disorders (eg, sarcoidosis, chronic gastritis, chronic thryoiditis) and recent invasive procedures or trauma may often help image interpretation. The presence of uptake in the head of the pancreas should always be carefully evaluated because it may often be benign. Otherwise, because the pancreas is also a frequent site of NET onset, particular attention should be devoted to the evaluation of the uptake pattern (diffuse more likely to be benign) and to the comparison with other imaging techniques.

Neuroendocrine tumours: the role of imaging for diagnosis and therapy

In patients with neuroendocrine tumours (NETs), a combination of morphological imaging and nuclear medicine techniques is mandatory for primary tumour visualization, staging and evaluation of somatostatin receptor status. CT and MRI are well-suited for discerning small lesions that might escape detection by single photon emission tomography (SPECT) or PET, as well as for assessing the local invasiveness of the tumour or the response to therapy. Somatostatin receptor imaging, by (111)In-pentetreotide scintigraphy or PET with (68)Ga-labelled somatostatin analogues, frequently identifies additional lesions that are not visible on CT or MRI scans. Currently, somatostatin receptor scintigraphy with (111)In-pentetreotide is the more frequently available of the two techniques to determine somatostatin receptor expression and is needed to select patients for peptide receptor radionuclide therapy. In the future, because of its higher sensitivity, PET with (68)Ga-labelled somatostatin analogues is expected to replace somatostatin receptor scintigraphy. Whereas (18)F-FDG-PET is only used in high-grade neuroendocrine cancers, PET-CT with (18)F-dihydroxy-L-phenylalanine or (11)C-5-hydroxy-L-tryptophan is a useful problem-solving tool and could be considered for the evaluation of therapy response in the future. This article reviews the role of imaging for the diagnosis and management of intestinal and pancreatic NETs. Response evaluation and controversies in NET imaging will also be discussed.