I-131 Metaiodobenzylguanidine Therapy of Pheochromocytoma and Paraganglioma

Approach to the Patient: Concept and Application of Targeted Radiotherapy in the Paraganglioma Patient

Paragangliomas can metastasize, posing potential challenges both in symptomatic management and disease control. Systemic targeted radiotherapies using 131I-MIBG and 177Lu-DOTATATE are a mainstay in the treatment of metastatic paragangliomas. This clinical scenario and discussion aim to enhance physicians' knowledge of the stepwise approach to treat these patients with paraganglioma-targeted radiotherapies. It comprehensively discusses current approaches to selecting paraganglioma patients for targeted radiotherapies and how to choose between the two radiotherapies based on specific patient and tumor characteristics, when either therapy is feasible, or one is superior to another. The safety, efficacy, toxicity profiles, and optimization of these radiotherapies are also discussed, along with other therapeutic options including radiotherapies, available for patients besides these two therapies. Perspectives in radiotherapies of paraganglioma patients are outlined since they hold promising approaches in the near future that can improve patient outcomes.

Management of metastatic pheochromocytomas and paragangliomas: when and what

Recently, the treatment landscape for metastatic pheochromocytomas and paragangliomas (MPPGL) has seen both progress and setbacks. We provide an up-to-date review of the multimodality management of MPPGL and discuss novel opportunities and current challenges in the treatment landscape. Given the unique clinical presentation of MPPGL, we discuss the management of hormone-related clinical sequelae and traditional modalities of therapy. Advances in the understanding of the molecular biology of these diverse tumors have enabled novel strategies such as augmenting DNA damage by targeted delivery of radionuclides such as 131I and 177Lu, abrogating tumor angiogenesis, hypoxia resistance, and DNA damage repair. Despite progress, we address the significant challenges still faced by patients and researchers engaged in efforts to improve outcomes in these rare cancers.

Imaging of Pheochromocytomas and Paragangliomas

Pheochromocytomas/paragangliomas are unique in their highly variable molecular landscape driven by genetic alterations, either germline or somatic. These mutations translate into different clusters with distinct tumor locations, biochemical/metabolomic features, tumor cell characteristics (eg, receptors, transporters), and disease course. Such tumor heterogeneity calls for different imaging strategies in order to provide proper diagnosis and follow-up. This also warrants selection of the most appropriate and locally available imaging modalities tailored to an individual patient based on consideration of many relevant factors including age, (anticipated) tumor location(s), size, and multifocality, underlying genotype, biochemical phenotype, chance of metastases, as well as the patient's personal preference and treatment goals. Anatomical imaging using computed tomography and magnetic resonance imaging and functional imaging using positron emission tomography and single photon emission computed tomography are currently a cornerstone in the evaluation of patients with pheochromocytomas/paragangliomas. In modern nuclear medicine practice, a multitude of radionuclides with relevance to diagnostic work-up and treatment planning (theranostics) is available, including radiolabeled metaiodobenzylguanidine, fluorodeoxyglucose, fluorodihydroxyphenylalanine, and somatostatin analogues. This review amalgamates up-to-date imaging guidelines, expert opinions, and recent discoveries. Based on the rich toolbox for anatomical and functional imaging that is currently available, we aim to define a customized approach in patients with (suspected) pheochromocytomas/paragangliomas from a practical clinical perspective. We provide imaging algorithms for different starting points for initial diagnostic work-up and course of the disease, including adrenal incidentaloma, established biochemical diagnosis, postsurgical follow-up, tumor screening in pathogenic variant carriers, staging and restaging of metastatic disease, theranostics, and response monitoring.

Management of phaeochromocytoma and paraganglioma in patients with germline SDHB pathogenic variants: an international expert Consensus statement

Adult and paediatric patients with pathogenic variants in the gene encoding succinate dehydrogenase (SDH) subunit B (SDHB) often have locally aggressive, recurrent or metastatic phaeochromocytomas and paragangliomas (PPGLs). Furthermore, SDHB PPGLs have the highest rates of disease-specific morbidity and mortality compared with other hereditary PPGLs. PPGLs with SDHB pathogenic variants are often less differentiated and do not produce substantial amounts of catecholamines (in some patients, they produce only dopamine) compared with other hereditary subtypes, which enables these tumours to grow subclinically for a long time. In addition, SDHB pathogenic variants support tumour growth through high levels of the oncometabolite succinate and other mechanisms related to cancer initiation and progression. As a result, pseudohypoxia and upregulation of genes related to the hypoxia signalling pathway occur, promoting the growth, migration, invasiveness and metastasis of cancer cells. These factors, along with a high rate of metastasis, support early surgical intervention and total resection of PPGLs, regardless of the tumour size. The treatment of metastases is challenging and relies on either local or systemic therapies, or sometimes both. This Consensus statement should help guide clinicians in the diagnosis and management of patients with SDHB PPGLs.

Pheochromocytoma: a changing perspective and current concepts

This article aims to review current concepts in diagnosing and managing pheochromocytoma and paraganglioma (PPGL). Personalized genetic testing is vital, as 40-60% of tumors are linked to a known mutation. Tumor DNA should be sampled first. Next-generation sequencing is the best and most cost-effective choice and also helps with the expansion of current knowledge. Recent advancements have also led to the increased incorporation of regulatory RNA, metabolome markers, and the NETest in PPGL workup. PPGL presentation is highly volatile and nonspecific due to its multifactorial etiology. Symptoms mainly derive from catecholamine (CMN) excess or mass effect, primarily affecting the cardiovascular system. However, paroxysmal nature, hypertension, and the classic triad are no longer perceived as telltale signs. Identifying high-risk subjects and diagnosing patients at the correct time by using appropriate personalized methods are essential. Free plasma/urine catecholamine metabolites must be first-line examinations using liquid chromatography with tandem mass spectrometry as the gold standard analytical method. Reference intervals should be personalized according to demographics and comorbidity. The same applies to result interpretation. Threefold increase from the upper limit is highly suggestive of PPGL. Computed tomography (CT) is preferred for pheochromocytoma due to better cost-effectiveness and spatial resolution. Unenhanced attenuation of >10HU in non-contrast CT is indicative. The choice of extra-adrenal tumor imaging is based on location. Functional imaging with positron emission tomography/computed tomography and radionuclide administration improves diagnostic accuracy, especially in extra-adrenal/malignant or familial cases. Surgery is the mainstay treatment when feasible. Preoperative α-adrenergic blockade reduces surgical morbidity. Aggressive metastatic PPGL benefits from systemic chemotherapy, while milder cases can be managed with radionuclides. Short-term postoperative follow-up evaluates the adequacy of resection. Long-term follow-up assesses the risk of recurrence or metastasis. Asymptomatic carriers and their families can benefit from surveillance, with intervals depending on the specific gene mutation. Trials primarily focusing on targeted therapy and radionuclides are currently active. A multidisciplinary approach, correct timing, and personalization are key for successful PPGL management.

Efficacy and Safety of Tyrosine Kinase Inhibitors in Patients with Metastatic Pheochromocytomas/Paragangliomas

CONTEXT

Tyrosine kinase inhibitors (TKIs) can be used to treat locally unresectable or distantly metastatic pheochromocytomas/paragangliomas (PPGLs), such as sunitinib, according to the National Comprehensive Cancer Network guidelines in 2022. However, the precise effect of different TKIs in metastatic PPGLs is still unclear.

OBJECTIVE

The aim of this meta-analysis is to assess the efficacy and safety of TKIs in metastatic PPGLs.

METHODS

The PubMed, Cochrane Library, Scopus, Clinical Trial, and Embase databases were searched by synonyms of 48 TKIs and metastatic PPGLs from inception up to August 2022. Outcomes were tumor response or survival data and the incidence of adverse events (AEs) after treatment. The MIONRS scale and the JBI's tools for case series were used for interventional and observational studies to assess risk of bias, respectively. The combined effects with fixed- or random-effect models, the combined median with the weighted median of medians method and their 95% CIs were reported.

RESULTS

A total of 7 studies with 160 patients were included. Tumor responses in metastatic PPGLs in 5 studies with available data showed the pooled proportion of partial response (PR), stable disease, and disease control rate (DCR) of, respectively, 0.320 (95% CI 0.155-0.486), 0.520 (95% CI 0.409-0.630), and 0.856 (95% CI 0.734-0.979). The combined median progressive-free survival in 6 studies was 8.9 months (95% CI 4.1-13.5) and the proportion of those who discontinued due to AEs in 5 studies was 0.143 (95% CI 0.077-0.209).

CONCLUSION

This meta-analysis suggests that patients with metastatic PPGLs can benefit from TKI therapy with PR and DCR up to more than 30% and 80%. However, because of restricted studies, larger clinical trials should be performed in the future.

I-131 metaiodobenzylguanidine therapy is a significant treatment option for pheochromocytoma and paraganglioma

AIM

Pheochromocytomas and paragangliomas (PPGLs) are rare neuroendocrine tumours of chromaffin cells. Several modalities are currently available to treat patients with PPGL. These treatment modalities include surgery, chemotherapy, molecular targeted therapy and radiopharmaceuticals.

METHODS

I-131 metaiodobenzylguanidine (mIBG), a classic radiopharmaceutical, can be taken up through specific receptors and sited into many, but not all, PPGL cells.

RESULTS

Many studies have investigated the efficacy and toxicity of I-131 mIBG therapy. These studies reported significant results in terms of objective, hormonal and symptomatic responses as well as tolerable toxicities in patients.

CONCLUSION

This article reviews the reported experiences of patients who underwent I-131 mIBG therapy for PPGL with a focus on functions and deficiencies of the therapy.

Functional imaging for evaluation of cancers and biologically conformal radiotherapy: Past-history and present-day perspectives

Over the past twenty years, nuclear medicine has enhanced the role of functional imaging in cancerology. A major milestone was achieved in the early 2000s with widespread availability of the positron emitter tracer 18F- deoxyglucose (FDG) and the introduction of hybrid imagers, i.e. positron imagers coupled with an X CT, providing anatomical landmarks and potently contributing to attenuation and scatter correction of the images. Other technical advances have progressively increased the quality of positron images. To date, the most widely used tracer remains FDG, which is highly beneficial in terms of sensitivity and specificity in detection of tumor sites, also providing biological information on tumors and early evaluation of treatment response for most cancers. Other highly specific tracers have been developed and are now routinely used for pheochromocytoma and paraganglioma, neuroendocrine tumors, and prostate cancer. Biological Radiotherapy has two aspects: Internal radiotherapy consisting in administration of a tumor-specific molecule radiolabeled with an isotope delivering an adequate radiation dose to the targeted tumor sites (on the model of thyroid cancer treated with radioiodine) and external radiotherapy designed to determine tumor volume, assess response and to dose radiation according to the tumor characteristics shown by functional imaging.

Management of Pheochromocytomas and Paragangliomas: A Case-Based Review of Clinical Aspects and Perspectives

Paraganglioma and pheochromocytoma are rare medical conditions. Thus, there are still a small number of studies, clinical trials, and evidence-based data in this field. This makes clinical decisions more difficult. In this study, we present a case report enriched with a short review of available essential clinical data, indicating the need for constant metoxycatecholamine level observation and a proper diagnostic imaging approach, especially in terms of ongoing pandemics. Our research also provides a summary of the molecular background of these diseases, indicating their future role in clinical management. We analyzed the ClinicalTrials.gov dataset in order to show future perspectives. In this paper, the use of the PET-CT before MRI or CT is proposed in specific cases during diagnosis processes contrary to the guidelines. PET-CT may be as effective as standard procedures and may provide a faster diagnosis, which is important in periods with more difficult access to health care, such as during the COVID-19 pandemic.

Similar Findings on 18F-MFBG PET/CT and 68Ga-DOTATATE PET/CT in a Patient With Widespread Metastatic Pheochromocytoma

ABSTRACT

A 27-year-old woman with known malignant pheochromocytoma was enrolled in a clinical trial to compare efficacy of 68Ga-DOTATATE PET/CT and 18F-MFBG PET/CT. Images from both studies detected similar number of the metastatic lesions. In addition, both studies detected more lesions than 131I-MIBG imaging.

Dosimetry in Clinical Radiopharmaceutical Therapy of Cancer: Practicality Versus Perfection in Current Practice

The use of radiopharmaceutical therapies (RPTs) in the treatment of cancers is growing rapidly, with more agents becoming available for clinical use in last few years and many new RPTs being in development. Dosimetry assessment is critical for personalized RPT, insofar as administered activity should be assessed and optimized in order to maximize tumor-absorbed dose while keeping normal organs within defined safe dosages. However, many current clinical RPTs do not require patient-specific dosimetry based on current Food and Drug Administration-labeled approvals, and overall, dosimetry for RPT in clinical practice and trials is highly varied and underutilized. Several factors impede rigorous use of dosimetry, as compared with the more convenient and less resource-intensive practice of empiric dosing. We review various approaches to applying dosimetry for the assessment of activity in RPT and key clinical trials, the extent of dosimetry use, the relative pros and cons of dosimetry-based versus fixed activity, and practical limiting factors pertaining to current clinical practice.

Systemic Radiopharmaceutical Therapy of Pheochromocytoma and Paraganglioma

Whereas benign pheochromocytomas and paragangliomas are often successfully cured by surgical resection, treatment of metastatic disease can be challenging in terms of both disease control and symptom control. Fortunately, several options are available, including chemotherapy, radiation therapy, and surgical debulking. Radiolabeled metaiodobenzylguanidine (MIBG) and somatostatin receptor imaging have laid the groundwork for use of these radiopharmaceuticals as theranostic agents. 131I-MIBG therapy of neuroendocrine tumors has a long history, and the recent approval of high-specific-activity 131I-MIBG for metastatic or inoperable pheochromocytoma or paraganglioma by the U.S. Food and Drug Administration has resulted in general availability of, and renewed interest in, this treatment. Although reports of peptide receptor radionuclide therapy of pheochromocytoma and paraganglioma with 90Y- or 177Lu-DOTA conjugated somatostatin analogs have appeared in the literature, the approval of 177Lu-DOTATATE in the United States and Europe, together with National Comprehensive Cancer Network guidelines suggesting its use in patients with metastatic or inoperable pheochromocytoma and paraganglioma, has resulted in renewed interest. These agents have shown evidence of efficacy as palliative treatments in patients with metastatic or inoperable pheochromocytoma or paraganglioma. In this continuing medical education article, we discuss the therapy of pheochromocytoma and paraganglioma with 131I-MIBG and 90Y- or 177Lu-DOTA-somatostatin analogs.

Theranostics in Nuclear Medicine: Emerging and Re-emerging Integrated Imaging and Therapies in the Era of Precision Oncology

Theranostics refers to the pairing of diagnostic biomarkers with therapeutic agents that share a specific target in diseased cells or tissues. Nuclear medicine, particularly with regard to applications in oncology, is currently one of the greatest components of the theranostic concept in clinical and research scenarios. Theranostics in nuclear medicine, or nuclear theranostics, refers to the use of radioactive compounds to image biologic phenomena by means of expression of specific disease targets such as cell surface receptors or membrane transporters, and then to use specifically designed agents to deliver ionizing radiation to the tissues that express these targets. The nuclear theranostic approach has sparked increasing interest and gained importance in parallel to the growth in molecular imaging and personalized medicine, helping to provide customized management for various diseases; improving patient selection, prediction of response and toxicity, and determination of prognosis; and avoiding futile and costly diagnostic examinations and treatment of many diseases. The authors provide an overview of theranostic approaches in nuclear medicine, starting with a review of the main concepts and unique features of nuclear theranostics and aided by a retrospective discussion of the progress of theranostic agents since early applications, with illustrative cases emphasizing the imaging features. Advanced concepts regarding the role of fluorine 18-fluorodeoxyglucose PET in theranostics, as well as developments in and future directions of theranostics, are discussed. ^©RSNA, 2020 See discussion on this article by Greenspan and Jadvar.

Neuroendocrine Tumor Theranostics: An Update and Emerging Applications in Clinical Practice

OBJECTIVE. Theranostics have shown great promise for delivering precision medicine, particularly in neuroendocrine tumors (NETs). The clinical applications of radiolabeled somatostatin analogues in imaging and radionuclide therapy have been rapidly increasing over the past 2 decades and are currently integrated into the management guidelines of NETs. This article summarizes the available literature on different somatostatin receptor-targeting radiopharmaceuticals with theranostic potential in NETs, pheochromocytomas, and paragangliomas. We discuss the clinical application, administration, and toxicity of recent FDA-approved radionuclide therapies, including ¹⁷⁷Lu-DOTATATE in advanced gastroenteropancreatic NETs and ¹³¹I-MIBG in advanced paragangliomas and pheochromocytomas. CONCLUSION. Several studies support the safety and clinical efficacy of peptide receptor radionuclide therapies in disease control and quality-of-life improvement in patients with NETs and report potential benefits of combined radionuclide treatment approaches. The utility and pitfalls of functional imaging in therapy response assessment and surveillance of NETs remain to be established.

General Concepts in Theranostics

Theranostics describes the pairing of diagnostic biomarkers and therapeutic agents with common specific targets. Nuclear medicine is the greatest theranostics protagonist, relying on radioactive tracers for imaging biologic phenomena and delivering ionizing radiation to the tissues that take up those tracers. The concept has gained importance with the growth of personalized medicine, allowing customized management for diseases, refining patient selection, better predicting responses, reducing toxicity, and estimating prognosis. This work provides an overview of the general concepts of the theranostics approach in nuclear medicine discussing its background, features, and future directions in imaging and therapy.

Multidisciplinary practice guidelines for the diagnosis, genetic counseling and treatment of pheochromocytomas and paragangliomas

Pheochromocytomas and paragangliomas (PPGLs) are rare neuroendocrine tumors that arise from chromaffin cells of the adrenal medulla and the sympathetic/parasympathetic neural ganglia, respectively. The heterogeneity in its etiology makes PPGL diagnosis and treatment very complex. The aim of this article was to provide practical clinical guidelines for the diagnosis and treatment of PPGLs from a multidisciplinary perspective, with the involvement of the Spanish Societies of Endocrinology and Nutrition (SEEN), Medical Oncology (SEOM), Medical Radiology (SERAM), Nuclear Medicine and Molecular Imaging (SEMNIM), Otorhinolaryngology (SEORL), Pathology (SEAP), Radiation Oncology (SEOR), Surgery (AEC) and the Spanish National Cancer Research Center (CNIO). We will review the following topics: epidemiology; anatomy, pathology and molecular pathways; clinical presentation; hereditary predisposition syndromes and genetic counseling and testing; diagnostic procedures, including biochemical testing and imaging studies; treatment including catecholamine blockade, surgery, radiotherapy and radiometabolic therapy, systemic therapy, local ablative therapy and supportive care. Finally, we will provide follow-up recommendations.

High-Specific-Activity-131I-MIBG versus 177Lu-DOTATATE Targeted Radionuclide Therapy for Metastatic Pheochromocytoma and Paraganglioma

Targeted radionuclide therapies (TRT) using ¹³¹I-metaiodobenzylguanidine (¹³¹I-MIBG) and peptide receptor radionuclide therapy (¹⁷⁷Lu or ⁹⁰Y) represent several of the therapeutic options in the management of metastatic/inoperable pheochromocytoma/paraganglioma. Recently, high-specific-activity-¹³¹I-MIBG therapy was approved by the FDA and both ¹⁷⁷Lu-DOTATATE and ¹³¹I-MIBG therapy were recommended by the National Comprehensive Cancer Network guidelines for the treatment of metastatic pheochromocytoma/paraganglioma. However, a clinical dilemma often arises in the selection of TRT, especially when a patient can be treated with either type of therapy based on eligibility by MIBG and somatostatin receptor imaging. To address this problem, we assembled a group of international experts, including oncologists, endocrinologists, and nuclear medicine physicians, with substantial experience in treating neuroendocrine tumors with TRTs to develop consensus and provide expert recommendations and perspectives on how to select between these two therapeutic options for metastatic/inoperable pheochromocytoma/paraganglioma. This article aims to summarize the survival outcomes of the available TRTs; discuss personalized treatment strategies based on functional imaging scans; address practical issues, including regulatory approvals; and compare toxicities and risk factors across treatments. Furthermore, it discusses the emerging TRTs.

Use of radioiodine in nuclear medicine-A brief overview

Radioiodines have a long history in nuclear medicine. Herein, we discuss the production, properties and applications of these versatile iodine-based imaging and theragnostic agents. There are 38 isotopes of iodine (I) including one stable form (127 I). The most common radionuclides used in medical imaging and treatment, including Iodine-123 (123 I), Iodine-124 (124 I), Iodine-125 (125 I) and Iodine-131 (131 I), are discussed in this review.

Adrenal pheochromocytoma treated by combination of adrenal arterial embolization and radiofrequency ablation

Combined therapy with adrenal arterial embolization and RF ablation may represent a useful therapeutic option with curative properties in select patients with pheochromocytoma.

Absorbed dose simulation of meta-211At-astato-benzylguanidine using pharmacokinetics of 131I-MIBG and a novel dose conversion method, RAP

OBJECTIVE

We aimed to estimate in vivo 211At-labeled meta-benzylguanidine (211At-MABG) absorbed doses by the two dose conversion methods, using 131I-MIBG biodistribution data from a previously reported neuroblastoma xenograft model. In addition, we examined the effects of different cell lines and time limitations using data from two other works.

METHODS

We used the framework of the Monte Carlo method to create 3200 virtual experimental data sets of activity concentrations (kBq/g) to get the statistical information. Time activity concentration curves were produced using the fitting method of a genetic algorithm. The basic method was that absorbed doses of 211At-MABG were calculated based on the medical internal radiation dose formalism with the conversion of the physical half-life time of 131I to that of 211At. We have further improved the basic method; that is, a novel dose conversion method, RAP (Ratio of Pharmacokinetics), using percent injected dose/g.

RESULTS

Virtual experiments showed that 211At-MABG and 131I-MIBG had similar properties of initial activity concentrations and biological components, but the basic method did not simulate the 211At-MABG dose. Simulated 211At-MABG doses from 131I-MIBG using the RAP method were in agreement with those from 211At-MABG, so that their boxes overlapped in the box plots. The RAP method showed applicability to the different cell lines, but it was difficult to predict long-term doses from short-term experimental data.

CONCLUSIONS

The present RAP dose conversion method could estimate 211At-MABG absorbed doses from the pharmacokinetics of 131I-MIBG with some limitations. The RAP method would be applicable to a large number of subjects for targeted nuclide therapy.

Asymptomatic Presacral Paraganglioma: Management of an Unpredictable Intraoperative Finding

Paragangliomas are rare neuroendocrine tumors originating from the embryological neural crest. We report a rare case of a patient with an asymptomatic presacral mass (incidentaloma) who experienced an unpredictable intraoperative hypertensive crisis after manipulation of the tumor. Presacral neoplasms pose a diagnostic and therapeutic challenge due to their obscure anatomical location and the difficulty in performing an R0 excision. Furthermore, the management of asymptomatic paragangliomas requires a high level of clinical suspicion and expertise due to potential life-threatening intraoperative complications.

Long-Term Outcomes of 125 Patients With Metastatic Pheochromocytoma or Paraganglioma Treated With 131-I MIBG

CONTEXT

Prognosis of metastatic pheochromocytoma/paraganglioma following 131-Iodine metaiodobenzylguanidine (MIBG) is incompletely characterized due to small samples and shorter follow-up in these rare, often indolent tumors.

OBJECTIVE

To describe long-term survival, frequency, and prognostic impact of imaging, biochemical, and symptomatic response to 131-I MIBG.

DESIGN

Retrospective chart and imaging review at a tertiary referral center.

PATIENTS

Six hundred sixty-eight person-years of follow-up in 125 patients with metastatic pheochromocytoma/paraganglioma with progression through prior multimodal treatment.

INTERVENTION

Median 18 800 MBq 131-I MIBG.

MAIN OUTCOME MEASURES

Overall survival, Response Evaluation Criteria in Solid Tumors, version 1.1 (RECIST) imaging response, symptomatic response per chart review, and biochemical response (20% change over 2 consecutive assays of catecholamines, vanillylmandelic acid, metanephrines, or chromogranin A).

RESULTS

Median survival standard deviation [SD] from diagnosis was 11.5 years [2.4]; following metastasis, 6.5 years [0.8]; post treatment, 4.3 years [0.7]. Among 88 participants with follow-up imaging, 1% experienced complete response, 33% partial response, 53% stability, and 13% progression. Fifty-one percent showed subsequent progression, median progression-free survival [SD] of 2.0 years [0.6]. Stability/response vs progression at first imaging follow-up (3-6 months) predicted improved survival, 6.3 vs 2.4 years (P = 0.021). Fifty-nine percent of 54 patients demonstrated biochemical response. Fifty percent of these relapsed, with median time to laboratory progression [SD] of 2.8 years [0.7]. Biochemical response did not predict extended survival. Seventy-five percent of 83 patients reported improvement in pretreatment symptoms, consisting primarily of pain (42%), fatigue (27%), and hypertension (14%). Sixty-one percent of these patients experienced subsequent symptomatic progression at median [SD] 1.8 years [0.4]. Symptomatic response did not predict extended survival.

CONCLUSIONS

Imaging, symptomatic, and laboratory response to multimodal treatment including high-dose 131-I MIBG were achieved on long-term follow-up in metastatic pheochromocytoma or paraganglioma. Imaging response at 3 to 6 months was prognostic.

Pheochromocytoma/paraganglioma: recent updates in genetics, biochemistry, immunohistochemistry, metabolomics, imaging and therapeutic options

Pheochromocytomas and paragangliomas (PPGLs), rare chromaffin/neural crest cell tumors, are commonly benign in their clinical presentation. However, there are a number of cases presenting as metastatic and their diagnosis and management becomes a dilemma because of their rarity. PPGLs are constantly evolving entities in the field of endocrinology brought about by endless research and discoveries, especially in genetics. Throughout the years, our knowledge and perception of these tumors and their genetic background has greatly expanded and changed, and each new discovery leads to advancement in the diagnosis, treatment and follow-up of PPGLs. In this review, we discuss the recent updates in the genetics, biochemistry, immunohistochemistry, metabolomics, imaging and treatment options of PPGLs.

Single Photon Emission Computed Tomography Tracer

Single photon emission computed tomography (SPECT) is the state-of-the-art imaging modality in nuclear medicine despite the fact that only a few new SPECT tracers have become available in the past 20 years. Critical for the future success of SPECT is the design of new and specific tracers for the detection, localization, and staging of a disease and for monitoring therapy. The utility of SPECT imaging to address oncologic questions is dependent on radiotracers that ideally exhibit excellent tissue penetration, high affinity to the tumor-associated target structure, specific uptake and retention in the malignant lesions, and rapid clearance from non-targeted tissues and organs. In general, a target-specific SPECT radiopharmaceutical can be divided into two main parts: a targeting biomolecule (e.g., peptide, antibody fragment) and a γ-radiation-emitting radionuclide (e.g., ^99mTc, ¹²³I). If radiometals are used as the radiation source, a bifunctional chelator is needed to link the radioisotope to the targeting entity. In a rational SPECT tracer design, these single components have to be critically evaluated in order to achieve a balance among the demands for adequate target binding, and a rapid clearance of the radiotracer. The focus of this chapter is to depict recent developments of tumor-targeted SPECT radiotracers for imaging of cancer diseases. Possibilities for optimization of tracer design and potential causes for design failure are discussed and highlighted with selected examples.

Changes over the years in radiopharmaceutical design

Of the many uses of radiopharmaceuticals, developing radiotracers that contribute significantly to diagnosis and therapy of patients has been a major focus. This requires a broad spectrum of expertise including that of the attending physician who lends insight to an unmet clinical need neither addressed by other imaging techniques nor by analysis of tissue, blood, and urine for diagnostics and addressed by pharmaceuticals for therapeutic applications. The design criteria have depended on radiochemistry, on matching the radiopharmaceutical with the imaging devices, and basing the design on current pharmaceuticals. The chelates of technetium-99m were based on radiochemistry rather than clinical need yet are still used today in >70% of the clinical studies. Targeted radiotracers in neurologic and psychiatric disorders, inflammation, cardiovascular disease, and oncology have all been studied with the goal of determining the change in the density of a target protein as a function of disease or treatment or, especially in oncology, detection of the total extent of disease. In latter approach PET in university settings leads the way; however, the use of SPECT/CT has increased the specificity of SPECT imaging to complement the cost- effective generator and instant kits already available. Remarkable advances has been achieved in radionuclide therapy using theragnostic agents, with the exclusive domain of oncology For this application the design of radionuclide therapy follows that used for diagnostics. The increased impact of the discipline depends on the opportunity to continue the search for the most appropriate radiopharmaceutical for each individual patient.

Molecular imaging and radionuclide therapy of pheochromocytoma and paraganglioma in the era of genomic characterization of disease subgroups

In recent years, advancement in genetics has profoundly helped to gain a more comprehensive molecular, pathogenic, and prognostic picture of pheochromocytomas and paragangliomas (PPGLs). Newly discovered molecular targets, particularly those that target cell membranes or signaling pathways have helped move nuclear medicine in the forefront of PPGL precision medicine. This is mainly based on the introduction and increasing experience of various PET radiopharmaceuticals across PPGL genotypes quickly followed by implementation of novel radiotherapies and revised imaging algorithms. Particularly, 68Ga-labeled-SSAs have shown excellent results in the diagnosis and staging of PPGLs and in selecting patients for PRRT as a potential alternative to 123/131I-MIBG theranostics. PRRT using 90Y/177Lu-DOTA-SSAs has shown promise for treatment of PPGLs with improvement of clinical symptoms and/or disease control. However, more well-designed prospective studies are required to confirm these findings, in order to fully exploit PRRT's antitumoral properties to obtain the final FDA approval. Such an approval has recently been obtained for high-specific-activity 131I-MIBG for inoperable/metastatic PPGL. The increasing experience and encouraging preliminary results of these radiotherapeutic approaches in PPGLs now raises an important question of how to further integrate them into PPGL management (e.g. monotherapy or in combination with other systemic therapies), carefully taking into account the PPGLs locations, genotypes, and growth rate. Thus, targeted radionuclide therapy (TRT) should preferably be performed at specialized centers with an experienced interdisciplinary team. Future perspectives include the introduction of dosimetry and biomarkers for therapeutic responses for more individualized treatment plans, α-emitting isotopes, and the combination of TRT with other systemic therapies.

Metastatic pheochromocytoma to the pancreas diagnosed by endoscopic ultrasound-guided fine needle aspiration: A case report and review of literature

Pancreatic pheochromocytomas are rare and typically diagnosed by local resection. We present the first reported case of metastatic pheochromocytoma to the pancreas diagnosed by endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) and cytology. A 67-year-old female presented with 2 to 3 months of abdominal pain. A CT scan showed a large mass in the head of the pancreas engulfing the superior mesentery artery and vein, along with a large mass in the left adrenal gland. An EUS-FNA was performed on the pancreatic mass with a 22-gauge needle, yielding an adequate sample. Papanicolaou stain, Diff-Quik, and cell block showed loosely cohesive clustered tumor cells and singly dispersed pleomorphic naked tumor nuclei with anisonucleosis and cytoplasmic vacuolization. Tumor cells stained positive for synaptophysin, chromogranin A, and CD56 and negative for CK AE1/3 and CK AE1/3-CAM5.2 cytokeratin cocktail. Because of cytokeratin negativity, diffusely positive neuroendocrine markers, and the presence of an adrenal mass, a metastatic malignant pheochromocytoma was suspected. Additional testing showed elevations in plasma metanephrines and normetanephrines, urine metanephrine-to-creatinine and normetanephrine-to-creatinine ratios, and serum chromogranin A. An iodine¹²³ -metaiodobenzylguanidine (MIBG) scan was obtained, which showed significantly increased MIBG uptake in the left adrenal lesion. A diagnosis of metastatic malignant pheochromocytoma was made. Surgical oncology was consulted, who recommended against resection of the adrenal mass in favor of outpatient management. Metastatic pheochromocytoma to the pancreas are rare tumors that may yield diagnostic material by EUS-FNA with a 22-gauge needle.

Targeted Radionuclide Therapy for Patients with Metastatic Pheochromocytoma and Paraganglioma: From Low-Specific-Activity to High-Specific-Activity Iodine-131 Metaiodobenzylguanidine

Low-specific-activity iodine-131–radiolabeled metaiodobenzylguanidine (I-131-MIBG) was introduced last century as a potential systemic therapy for patients with malignant pheochromocytomas and paragangliomas. Collective information derived from mainly retrospective studies has suggested that 30–40% of patients with these tumors benefit from this treatment. A low index of radioactivity, lack of therapeutic standardization, and toxicity associated with intermediate to high activities (absorbed radiation doses) has prevented the implementation of I-131-MIBG’s in clinical practice. High-specific-activity, carrier-free I-131-MIBG has been developed over the past two decades as a novel therapy for patients with metastatic pheochromocytomas and paragangliomas that express the norepinephrine transporter. This drug allows for a high level of radioactivity, and as yet is not associated with cardiovascular toxicity. In a pivotal phase two clinical trial, more than 90% of patients achieved partial responses and disease stabilization with the improvement of hypertension. Furthermore, many patients exhibited long-term persistent antineoplastic effects. Currently, the high-specific-activity I-131-MIBG is the only approved therapy in the US for patients with metastatic pheochromocytomas and paragangliomas. This review will discuss the historical development of high-specific-activity I-131-MIBG, its benefits and adverse events, and future directions for clinical practice applicability and trial development.

Anti-tumor effects and potential therapeutic response biomarkers in α-emitting meta-211At-astato-benzylguanidine therapy for malignant pheochromocytoma explored by RNA-sequencing

Targeted α-particle therapy is a promising option for patients with malignant pheochromocytoma. Recent observations regarding meta-²¹¹At-astato-benzylguanidine (²¹¹At-MABG) in a pheochromocytoma mouse model showed a strong anti-tumor effect, though the molecular mechanism remains elusive. Here, we present the first comprehensive RNA-sequencing (RNA-seq) data for pheochromocytoma cells based on in vitro²¹¹At-MABG administration experiments. Key genes and pathways in the tumor α-particle radiation response are also examined to obtain potential response biomarkers.

Methods: We evaluated genome-wide transcriptional alterations in the rat pheochromocytoma cell line PC12 at 3, 6, and 12 h after ²¹¹At-MABG treatment; a control experiment using ⁶⁰Co γ-ray irradiation was carried out to highlight ²¹¹At-MABG-specific gene expression. For comparisons, 10% and 80% iso-survival doses (0.8 and 0.1 kBq/mL for ²¹¹At-MABG and 10 and 1 Gy for ⁶⁰Co γ-rays) were used.

Results: Enrichment analysis of differentially expressed genes (DEGs) and analysis of the gene expression profiles of cell cycle checkpoints revealed similar modes of cell death via the p53-p21 signaling pathway after ²¹¹At-MABG treatment and γ-ray irradiation. The top list of ranked DEGs demonstrated the expression of key genes on the decrease in the survival following ²¹¹At-MABG exposure, and four potential genes (Mien1, Otub1, Vdac1 and Vegfa genes) of ²¹¹At-MABG therapy. Western blot analysis indicated increased expression of TSPO in ²¹¹At-MABG-treated cells, suggesting its potential as a PET imaging probe.

Conclusion: Comprehensive RNA-seq revealed contrasting cellular responses to γ-ray and α-particle therapy, leading to the identification of four potential candidate genes that may serve as molecular imaging and ²¹¹At-MABG therapy targets.

Concomitant 177Lu-DOTATATE and capecitabine therapy in malignant paragangliomas

BACKGROUND

The role of concomitant peptide receptor radionuclide therapy (PRRT) and capecitabine therapy has shown benefit in gastroenteropancreatic neuroendocrine tumors. However, data reporting its role in paraganglioma (PGL) patients is lacking. The aim of this study was to evaluate the role of combined capecitabine and ¹⁷⁷Lu-DOTATATE in malignant PGL patients.

METHODS

In this retrospective, single-institutional, single-arm, observational study, data of consecutive advanced stage PGL patients treated with concomitant ¹⁷⁷Lu-DOTATATE-capecitabine therapy, between July 2009 and March 2017, were collected and analyzed.

RESULTS

Twenty-five PGL patients received an average dose of 22.86 ± 9.54 (14.43-50) GBq ¹⁷⁷Lu-DOTATATE and 1250 mg/m² capecitabine from days 0 to 14, commencing on the morning of PRRT. The median overall survival (OS) was not attained in this patient cohort; however, the median PFS was 32 months. Morphological response according to RECIST 1.1 criteria was achieved in 28% (7/25) patients. Biochemical response with > 50% reduction in chromogranin A levels was observed in 28% of the patients.

CONCLUSIONS

Our data confirm that ¹⁷⁷Lu-DOTATATE-capecitabine therapy is effective in achieving an objective response in 28% and symptomatic response in 43% patients. In comparison to published PRRT monotherapy outcomes in PGL, we did not observe any great advantage of concomitant therapy; however, it could be due to under-powered study. We recommend a large randomized trial to prove or disprove the utility of capecitabine as a radiosensitizer for PRRT in PGL patients.

65 YEARS OF THE DOUBLE HELIX: Genetics informs precision practice in the diagnosis and management of pheochromocytoma

Although the authors of the present review have contributed to genetic discoveries in the field of pheochromocytoma research, we can legitimately ask whether these advances have led to improvements in the diagnosis and management of patients with pheochromocytoma. The answer to this question is an emphatic Yes! In the field of molecular genetics, the well-established axiom that familial (genetic) pheochromocytoma represents 10% of all cases has been overturned, with >35% of cases now attributable to germline disease-causing mutations. Furthermore, genetic pheochromocytoma can now be grouped into five different clinical presentation types in the context of the ten known susceptibility genes for pheochromocytoma-associated syndromes. We now have the tools to diagnose patients with genetic pheochromocytoma, identify germline mutation carriers and to offer gene-informed medical management including enhanced surveillance and prevention. Clinically, we now treat an entire family of tumors of the paraganglia, with the exact phenotype varying by specific gene. In terms of detection and classification, simultaneous advances in biochemical detection and imaging localization have taken place, and the histopathology of the paraganglioma tumor family has been revised by immunohistochemical-genetic classification by gene-specific antibody immunohistochemistry. Treatment options have also been substantially enriched by the application of minimally invasive and adrenal-sparing surgery. Finally and most importantly, it is now widely recognized that patients with genetic pheochromocytoma/paraganglioma syndromes should be treated in specialized centers dedicated to the diagnosis, treatment and surveillance of this rare neoplasm.

Pheochromocytomas and Hypertension

PURPOSE OF REVIEW

Pheochromocytomas and paragangliomas (PPGLs) are uncommon catecholamine-producing neuroendocrine neoplasms that usually present with secondary hypertension. This review is to update the current knowledge about these neoplasms, the pathophysiology, genetic aspects and diagnostic and therapeutic algorithms based on scientific literature mostly within the past 3 years.

RECENT FINDINGS

Eighty to eighty-five percent of PPGLs arise from the adrenal medulla (pheochromocytomas; PCCs) and the remainder from the autonomic neural ganglia (paragangliomas; PGLs). Catecholamine excess causes chronic or paroxysmal hypertension associated with sweating, headaches and palpitations, the presenting features of PPGLs, and increases the cardiovascular morbidity and mortality. Genetic testing should be considered in all cases as mutations are reported in 35-40% of cases; 10-15% of PCCs and 20-50% of PGLs can be malignant. Measurements of plasma-free metanephrines or 24-h urine-fractionated metanephrines help biochemical diagnosis with high sensitivity and specificity. Initial anatomical localization after biochemical confirmation is usually with computed tomography (CT) or magnetic resonance imaging (MRI). ¹²³Iodine metaiodobenzylguanidine (¹²³I-MIBG) scintigraphy, positron emission tomography (PET) or single-photon emission computed tomography (SPECT) is often performed for functional imaging and prognostication prior to curative or palliative surgery. Clinical and biochemical follow-up is recommended at least annually after complete tumour excision. Children, pregnant women and older people have higher morbidity and mortality risk. De-bulking surgery, chemotherapy, radiotherapy, radionuclide agents and ablation procedures are useful in the palliation of incurable disease. PPGLs are unique neuroendocrine tumours that form an important cause for endocrine hypertension. The diagnostic and therapeutic algorithms are updated in this comprehensive article.

Norepinephrine Transporter as a Target for Imaging and Therapy

The norepinephrine transporter (NET) is essential for norepinephrine uptake at the synaptic terminals and adrenal chromaffin cells. In neuroendocrine tumors, NET can be targeted for imaging as well as therapy. One of the most widely used theranostic agents targeting NET is metaiodobenzylguanidine (MIBG), a guanethidine analog of norepinephrine. ¹²³I/¹³¹I-MIBG theranostics have been applied in the clinical evaluation and management of neuroendocrine tumors, especially in neuroblastoma, paraganglioma, and pheochromocytoma. ¹²³I-MIBG imaging is a mainstay in the evaluation of neuroblastoma, and ¹³¹I-MIBG has been used for the treatment of relapsed high-risk neuroblastoma for several years, however, the outcome remains suboptimal. ¹³¹I-MIBG has essentially been only palliative in paraganglioma/pheochromocytoma patients. Various techniques of improving therapeutic outcomes, such as dosimetric estimations, high-dose therapies, multiple fractionated administration and combination therapy with radiation sensitizers, chemotherapy, and other radionuclide therapies, are being evaluated. PET tracers targeting NET appear promising and may be more convenient options for the imaging and assessment after treatment. Here, we present an overview of NET as a target for theranostics; review its current role in some neuroendocrine tumors, such as neuroblastoma, paraganglioma/pheochromocytoma, and carcinoids; and discuss approaches to improving targeting and theranostic outcomes.

Malignant pheochromocytoma-paraganglioma: pathogenesis, TNM staging, and current clinical trials

PURPOSE OF REVIEW

Pheochromocytomas and paragangliomas (PPGs) are rare neuroendocrine tumors. Over the last 15 years, substantial progress has been made toward understanding the clinical aspects and molecular origins of this disease. Nevertheless, predicting and managing malignancy remains the biggest challenge in clinical practice. The natural history of patients with malignant PPGs has not yet been described, and their prognosis varies. Currently, the diagnosis of malignant PPGs relies on the presence of metastases, by which time the disease is usually advanced. Better understanding of the clinical and molecular characteristics of patients with malignant PPGs has spurred several prospective clinical trials.

RECENT FINDINGS

Several molecular targeted therapies, a novel radiopharmaceutical medication that targets the catecholamine transporter, and immunotherapy are under evaluation for the treatment of patients with malignant PPGs. Furthermore, the identification of clinical predictors of malignancy and survival has led to the first TNM staging classification for PPGs.

SUMMARY

Prospective clinical trials are providing patients with therapeutic options beyond systemic chemotherapy. The knowledge derived from these trials and from the evaluation of the TNM staging in clinical practice will help to clarify how to most effectively treat malignant PPGs.

NVP-AUY922, a novel HSP90 inhibitor, inhibits the progression of malignant pheochromocytoma in vitro and in vivo

Purpose

Malignant pheochromocytoma (PCC) is a rare tumor with a very poor prognosis and no effective treatments. The aim of this study was to assess the efficacy of a novel second-generation synthetic heat-shock protein 90 (HSP90) inhibitor, NVP-AUY922, to treat malignant PCC in vitro and in vivo.

Materials and methods

Cell Counting Kit-8 (CCK-8) and Transwell assays were used to assess the effects of NVP-AUY922 on the proliferation and migration of the PCC cell line PC12. Flow cytometry was used to determine the effects of NVP-AUY922 on apoptosis and cell-cycle progression. Activation of phosphatidylinositol-3-kinase (PI3K)/protein kinase B (PKB/AKT) and mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) signaling was measured using a Western blot analysis. In vivo, a mouse xenograft model was used to test the effects of intraperitoneal injection of NVP-AUY922 on tumor growth.

Results

NVP-AUY922 was found to be cytotoxic in PC12 cells at lower concentrations compared with 17-allylamino-17-demethoxygeldanamcyin (17-AAG). NVP-AUY922 inhibited the proliferation of PC12 cells in a time- and concentration-dependent manner and decreased the rate of migration of PC12 cells. Furthermore, we found that HSP90 inhibition induced cell-cycle arrest and apoptosis. In vivo, administration of NVP-AUY922 reduced PCC tumor growth without significant weight loss. Finally, we observed the modulation of MEK/ERK and PI3K/AKT signaling in response to NVP-AUY922 exposure.

Conclusion

NVP-AUY922 exhibits potent anti-PCC activities in vitro and in vivo and represents a promising therapeutic small molecule for treating malignant PCC.

Urology pertinent neuroendocrine tumors: focusing on renal pelvis, bladder, prostate located sympathetic functional paragangliomas

Urology pertinent neuroendocrine neoplasias are more and more driving to research attractive contributions mainly as regards the urinary tract paragangliomas, besides the prostate cancer neuroendocrine differentiation. About such visceral sympathetic paragangliomas, a considerable attention is aroused by those concerning the renal pelvis, urinary bladder and, particularly, the prostate gland. Essential catecholamine/adrenergic signal-mediated pathophysiological implications and outlined diagnostic approaches are here taken into consideration. Particularly, to reach an accurate functional diagnostic assessment, both plasma and urine catecholamine level tests are required together with ¹²³I or ¹³¹I-meta-iodobenzylguanidine (MIBG) scan while ¹³¹I-, instead of ¹²³I-, labeled MIBG, proving to be also useful to targeted radionuclide therapy of sympathetic paragangliomas. Nevertheless, a thorough diagnostic confirmation should be obtained by a proper histologic/ immunohistochemical study, so that it respectively highlighting the typical "zellballen" cell setting and neuroendocrine tumor cell specific biomarkers such as chromogranin-A, synaptophysin, neuron-specific enolase. Open/laparoscopic/robot-assisted surgical procedures are performed under α1 (doxazosin, prazosin) - and β(propranolol)-adrenergic blockade to avoid the risk of an intraoperative adrenergic signal-triggered hypertensive crisis, what moreover may occur also during cystoscopy and biopsy in case of bladder or prostate paraganglioma. Given a conceivable likeness, about some adrenergic-mediated pathophysiological implications, between prostate paraganglioma and prostate cancer neuroendocrine transdifferentiation - although as regards two obviously different diseases - a reliable pathogenetic matter concerning prostate paraganglioma is requiring novel research approaches.