The evolution in the use of MIBG scintigraphy in pheochromocytomas and paragangliomas

Diffuse Large B-cell Lymphoma: Unexpected Uptake Observed on Cardiac 123I-MIBG Scintigraphy

ABSTRACT

A 77-year-old man with parkinsonism was referred to the department of neurology for further examination. Cardiac 123I-MIBG scintigraphy unexpectedly showed strong uptake in the left shoulder, suggestive of MIBG-avid tumors including paraganglioma. MRI revealed multiple nodules suggestive of lymphoma. A biopsy was performed, which led to the pathological diagnosis of diffuse large B-cell lymphoma. Cardiac MIBG scintigraphy sometimes shows unexpected findings outside the mediastinum. In addition, lymphoma should also be added to the list of differential diagnoses for MIBG-positive tumors.

The emerging role of cell surface receptor and protein binding radiopharmaceuticals in cancer diagnostics and therapy

Targeting specific cell membrane markers for both diagnostic imaging and radionuclide therapy is a rapidly evolving field in cancer research. Some of these applications have now found a role in routine clinical practice and have been shown to have a significant impact on patient management. Several molecular targets are being investigated in ongoing clinical trials and show promise for future implementation. Advancements in molecular biology have facilitated the identification of new cancer-specific targets for radiopharmaceutical development.

Molecular imaging of norepinephrine transporter-expressing tumors: current status and future prospects

The human norepinephrine transporter (hNET) is a transmembrane protein responsible for reuptake of norepinephrine in presynaptic sympathetic nerve terminals and adrenal chromaffin cells. Neural crest tumors, such as neuroblastoma, paraganglioma and pheochromocytoma often show high hNET expression. Molecular imaging of these tumors can be done using radiolabeled norepinephrine analogs that target hNET. Currently, the most commonly used radiopharmaceutical for hNET imaging is meta-[123I]iodobenzylguanidine ([123I]MIBG) and this has been the case since its development several decades ago. The γ-emitter, iodine-123 only allows for planar scintigraphy and single photon emission computed tomography imaging. These modalities typically have a poorer spatial resolution and lower sensitivity than positron emission tomography (PET). Additional practical disadvantages include the fact that a two-day imaging protocol is required and the need for thyroid blockade. Therefore, several PET alternatives for hNET imaging are actively being explored. This review gives an in-depth overview of the current status and recent developments in clinical trials leading to the next generation of clinical PET ligands for imaging of hNET-expressing tumors.

Pheochromocytoma: An approach to diagnosis

Pheochromocytomas are rare neuroendocrine chromaffin-derived tumors that arise within the adrenal medulla. They are usually benign, but if not diagnosed or if left untreated, they can have devastating consequences. Clinical consideration of the diagnosis is paramount, as they may have protean manifestations, and a high index of suspicion is essential if serious consequences are to be avoided. An accurate biochemical diagnosis is crucial for the management of these patients: either plasma or urinary metanephrines are both highly sensitive and specific if correctly employed, but knowledge of pre- and post-analytic interference is essential. Diagnostic imaging with cross-sectional CT and/or MRI offers high sensitivity in their detection, but lack specificity. The introduction of PET/CT/MR has led to a dramatic improvement in the localization of both pheochromocytomas and paragangliomas, together with the increasing availability of new functional imaging radionuclides. Optimal investigation and accurate diagnosis is best achieved at 'centers of excellence' with expert multidisciplinary teams.

A phase I clinical trial for [131I]meta-iodobenzylguanidine therapy in patients with refractory pheochromocytoma and paraganglioma

Refractory pheochromocytoma and paraganglioma (PPGL) have a poor prognosis and the treatment strategy remains to be established. This multi-institutional phase I study was performed to determine the safety, dose-limiting toxicity (DLT), and efficacy of [¹³¹I]-meta-iodobenzylguanidine (¹³¹I-mIBG) therapy for refractory PPGLs. Twenty patients with refractory PPGL were enrolled in this study. We administered fixed doses of ¹³¹I-mIBG to all patients, delivering a second and third course of ¹³¹I-mIBG to eight and three patients, respectively. During the 20 weeks after ¹³¹I-mIBG injection, the authors surveyed the adverse events in accordance with the Common Terminology Criteria for Adverse Events. All patients experienced adverse events and adverse reactions, but none experienced a grade 4 adverse event. Twelve weeks after ¹³¹I-mIBG injection, examinations for the evaluation of therapeutic effects was performed in accordance with the Response Evaluation Criteria in Solid Tumours (RECIST). The best overall response rates (based on RECIST categories) were 10% (complete response), 65% (stable disease), 15% (progressive disease), and 10% (not all evaluated). The efficacy and safety of ¹³¹I-mIBG therapy was shown in patients with refractory PPGL, and DLT was observed in neither single nor repeated ¹³¹I-mIBG therapy, indicating a tolerability for ¹³¹I-mIBG therapy.

Current status of functional imaging in neuroblastoma, pheochromocytoma, and paraganglioma disease

Diagnostic imaging plays an important role in the detection of paraganglioma (PGL), pheochromocytoma (PCC), and neuroblastoma (NB). Anatomic imaging, for example CT or MRI, offers high sensitivity in these neuroendocrine tumors (NET) but only moderate specificity, often associated with difficulties in clearly distinguishing between NET and non-NET. Functional imaging, as in the use of different radioisotopes, is indispensable in oncological imaging. The introduction of PET and PET/CT, respectively, led to a dramatic improvement in both malignant and non-malignant PGL, PCC, and NB, assessing the exact tumor extent. This review gives an overview of functional and anatomical imaging in PGL, PCC, and NB.

FDG-PET and CT findings of activated brown adipose tissue in a patient with paraganglioma

A 17-year-old female had been complaining of a headache for 6 years. She presented severe hypertension (200/138 mmHg) on admission. CT showed a hypervascular tumor behind the urinary bladder and a swelling of the right internal obturator node. Intense FDG uptakes were identified in the both lesions. High FDG accumulation was also observed in the brown adipose tissue (BAT) throughout the patient's body, and intense contrast enhancement was found in the BAT on CT. The diagnosis was a malignant paraganglioma with obturator node metastasis. The post-surgery FDG-PET/ CT examination revealed that the FDG accumulations in the BAT had completely disappeared.

A practical, automated synthesis of meta-[(18)F]fluorobenzylguanidine for clinical use

Many neuroendocrine tumors, such as neuroblastoma (NB), arise from neural crest cells of the sympathetic nervous system. This nerve-like phenotype has been exploited for functional imaging using radioactive probes originally designed for neuronal and adrenal medullary applications. NB imaging with meta-[(123)I]iodobenzylguanidine ([(123)I]MIBG) is limited by the emissions of (123)I, which lead to poor image resolution and challenges in quantification of its accumulation in tumors. meta-[(18)F]Fluorobenzylguanidine ([(18)F]MFBG) is a promising alternative to [(123)I]MIBG that could change the standard of practice for imaging neuroendocrine tumors, but interest in this PET radiotracer has suffered due to its complex and inefficient radiosynthesis. Here we report a two-step, automated method for the routine production of [(18)F]MFBG by thermolysis of a diaryliodonium fluoride and subsequent acid deprotection. The synthesis was adapted for use on a commercially available synthesizer for routine production. Full characterization of [(18)F]MFBG produced by this route demonstrated the tracer's suitability for human use. [(18)F]MFBG was prepared in almost 3-fold higher yield than previously reported (31% corrected to end of bombardment, n = 9) in a synthesis time of 56 min with >99.9% radiochemical purity. Other than pH adjustment and dilution of the final product, no reformulation was necessary after purification. This method permits the automated production of multidose batches of clinical grade [(18)F]MFBG. Moreover, if ongoing clinical imaging trials of [(18)F]MFBG are successful, this methodology is suitable for rapid commercialization and can be easily adapted for use on most commercial automated radiosynthesis equipment.