Recent advances in the management of malignant pheochromocytoma and paraganglioma: focus on tyrosine kinase and hypoxia-inducible factor inhibitors

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.

Molecular classification and tumor microenvironment characteristics in pheochromocytomas

Pheochromocytomas (PCCs) are rare neuroendocrine tumors that originate from chromaffin cells in the adrenal gland. However, the cellular molecular characteristics and immune microenvironment of PCCs are incompletely understood. Here, we performed single-cell RNA sequencing (scRNA-seq) on 16 tissues from 4 sporadic unclassified PCC patients and 1 hereditary PCC patient with Von Hippel-Lindau (VHL) syndrome. We found that intra-tumoral heterogeneity was less extensive than the inter-individual heterogeneity of PCCs. Further, the unclassified PCC patients were divided into two types, metabolism-type (marked by NDUFA4L2 and COX4I2) and kinase-type (marked by RET and PNMT), validated by immunohistochemical staining. Trajectory analysis of tumor evolution revealed that metabolism-type PCC cells display phenotype of consistently active metabolism and increased metastasis potential, while kinase-type PCC cells showed decreased epinephrine synthesis and neuron-like phenotypes. Cell-cell communication analysis showed activation of the annexin pathway and a strong inflammation reaction in metabolism-type PCCs and activation of FGF signaling in the kinase-type PCC. Although multispectral immunofluorescence staining showed a lack of CD8+ T cell infiltration in both metabolism-type and kinase-type PCCs, only the kinase-type PCC exhibited downregulation of HLA-I molecules that possibly regulated by RET, suggesting the potential of combined therapy with kinase inhibitors and immunotherapy for kinase-type PCCs; in contrast, the application of immunotherapy to metabolism-type PCCs (with antigen presentation ability) is likely unsuitable. Our study presents a single-cell transcriptomics-based molecular classification and microenvironment characterization of PCCs, providing clues for potential therapeutic strategies to treat PCCs.

Whole transcriptome analysis of canine pheochromocytoma and paraganglioma

Pheochromocytomas and paragangliomas (PPGLs) are neuroendocrine tumors arising from the chromaffin cells in the adrenal medulla and extra-adrenal paraganglia, respectively. Local invasion, concurrent disorders, and metastases prevent surgical removal, which is the most effective treatment to date. Given the current lack of effective medical treatment, there is a need for novel therapeutic strategies. To identify druggable pathways driving PPGL development, we performed RNA sequencing on PPGLs (n = 19) and normal adrenal medullas (NAMs; n = 10) of dogs. Principal component analysis (PCA) revealed that PPGLs clearly clustered apart from NAMs. In total, 4,218 genes were differentially expressed between PPGLs and NAMs. Of these, 232 had a log2 fold change of >3 or < -3, of which 149 were upregulated in PPGLs, and 83 were downregulated. Compared with NAMs, PPGLs had increased expression of genes related to the cell cycle, tumor development, progression and metastasis, hypoxia and angiogenesis, and the Wnt signaling pathway, and decreased expression of genes related to adrenal steroidogenesis. Our data revealed several overexpressed genes that could provide targets for novel therapeutics, such as Ret Proto-Oncogene (RET), Dopamine Receptor D2 (DRD2), and Secreted Frizzled Related Protein 2 (SFRP2). Based on the PCA, PPGLs were classified into 2 groups, of which group 1 had significantly higher Ki67 scores (p = 0.035) and shorter survival times (p = 0.04) than group 2. Increased expression of 1 of the differentially expressed genes between group 1 and 2, pleiotrophin (PTN), appeared to correlate with a more aggressive tumor phenotype. This study has shed light on the transcriptomic profile of canine PPGL, yielding new insights into the pathogenesis of these tumors in dogs, and revealed potential novel targets for therapy. In addition, we identified 2 transcriptionally distinct groups of PPGLs that had significantly different survival times.

Management of pheochromocytomas and paragangliomas: Review of current diagnosis and treatment options

Pheochromocytomas (PCCs) are rare neuroendocrine tumors derived from the chromaffin cells of the adrenal medulla. When these tumors have an extra-adrenal location, they are called paragangliomas (PGLs) and arise from sympathetic and parasympathetic ganglia, particularly of the para-aortic location. Up to 25% of PCCs/PGLs are associated with inherited genetic disorders. The majority of PCCs/PGLs exhibit indolent behavior. However, according to their affiliation to molecular clusters based on underlying genetic aberrations, their tumorigenesis, location, clinical symptomatology, and potential to metastasize are heterogenous. Thus, PCCs/PGLs are often associated with diagnostic difficulties. In recent years, extensive research revealed a broad genetic background and multiple signaling pathways leading to tumor development. Along with this, the diagnostic and therapeutic options were also expanded. In this review, we focus on the current knowledge and recent advancements in the diagnosis and treatment of PCCs/PGLs with respect to the underlying gene alterations while also discussing future perspectives in this field.

Metformin Treatment Induces Different Response in Pheochromocytoma/Paraganglioma Tumour Cells and in Primary Fibroblasts

Simple Summary

Pheochromocytoma/paragangliomas (PPGLs) are neuroendocrine tumours and are often non-metastatic. However, no effective treatment is available for their metastatic form. Recent studies have shown that metformin exhibits antiproliferative activity in many human cancers, including PPGLs. Nevertheless, no data are available concerning whether metformin is also able to inhibit PPGL metastatic spread. A tumour is a very complex system, comprising not only cancer cells, but also other cells that all together form the so-called tumour microenvironment. Cancer-associated fibroblasts are residential or recruited fibroblasts, transformed by cancer cells, to promote tumour growth and spread. Therefore, the interplay between tumour cells and cancer-associated fibroblasts has become an interesting target for cancer therapy. Here, we demonstrate that metformin has different effects on cancer cells and fibroblasts, providing evidence that metformin may hold promise for altering tumour microenvironment homeostasis. Improving our knowledge on malignant tumour microenvironment properties could lead to develop complementary strategies to target tumour spread and progression.

Abstract

Pheochromocytoma/paragangliomas (PPGLs) are neuroendocrine tumours, often non-metastatic, but without available effective treatment for their metastatic form. Recent studies have shown that metformin exhibits antiproliferative activity in many human cancers, including PPGLs. Nevertheless, no data are available on the role of metformin on PPGL cells (two-dimension, 2D) and spheroids (three-dimension, 3D) migration/invasion. In this study, we observed that metformin exerts an antiproliferative effect on 2D and 3D cultures of pheochromocytoma mouse tumour tissue (MTT), either silenced or not for the SDHB subunit. However, metformin did not affect MTT migration. On the other hand, metformin did not have a short-term effect on the proliferation of mouse primary fibroblasts, but significantly decreased their ability to migrate. Although the metabolic changes induced by metformin were similar between MTT and fibroblasts (i.e., an overall decrease of ATP production and an increase in intracellular lactate concentration) the activated signalling pathways were different. Indeed, after metformin administration, MTT showed a reduced phosphorylation of Akt and Erk1/2, while fibroblasts exhibited a downregulation of N-Cadherin and an upregulation of E-Cadherin. Herein, we demonstrated that metformin has different effects on cell growth and spread depending on the cell type nature, underlining the importance of the tumour microenvironment in dictating the drug response.

Metastatic pheochromocytomas and paragangliomas: where are we?

Pheochromocytomas and paragangliomas (PPGLs) can metastasize in approximately 15-20% of cases. This review discusses the available evidence on the biology and treatment of metastatic PPGLs. Chemotherapy is the first-line treatment option for this evolving and symptomatic disease. In patients with high MIBG uptake and positive PETGa-68, radiometabolic treatment may be considered. The efficacy of sunitinib has been shown in observational studies, and pembrolizumab has been evaluated in phase II clinical studies, while other agents investigated in this setting are anti-angiogenic drugs cabozantinib, dovitinib, axitinib and lenvatinib. As these agents' efficacy and safety data, alone or in combination, are scant and based on few treated patients, enrollment in clinical trials is mandatory. Future therapeutic options may be represented by DNA repair system inhibitors (such as olaparib), HIF2 inhibitors and immunotherapy.

A First Case Report of Orbital Extra-Adrenal Paraganglioma in Cat

Paraganglioma is a rare neuroendocrine neoplasm originating from paraganglia and consisting of neuroendocrine cells of the sympathetic and parasympathetic nervous system. Extra-adrenal paraganglioma occurs with a low incidence in both humans and animals. This report presents the first case of paraganglioma in a cat with orbital primary location. An 18-year-old spayed female European domestic shorthair cat of 3.60 kg body weight was evaluated in a private veterinary clinic in Perugia, Italy, for a pronounced exophthalmos of the right eye. The cat underwent surgery for the enucleation of the right eye and of the mass. The biopsy samples of the removed tissue were fixed in 10% buffered neutral formalin for histological and immunohistochemical evaluations. Therefore, specific markers were used for immunohistochemical investigations, such as anti-neuron specific enolase (NSE), anti-synaptophysin, anti-glial fibrillary acid protein, anti-cytokeratin and anti-chromogranin. The results of these investigations allowed establishing the final diagnosis of ocular extra-adrenal paraganglioma of the cat.

The use of immunotherapy treatment in malignant pheochromocytomas/paragangliomas: a case report

Background

Pheochromocytomas are a subset of paragangliomas, which are a rare group of neural crest cell-derived tumors. Malignant cases of both pheochromocytomas and paragangliomas are even rarer, and currently there is no standard of care. This case report details the use of off-label immunotherapy and its efficacy in the management of the aforementioned tumor.

Case presentation

Herein is presented a case of a 60-year-old Caucasian female with a rare malignant pheochromocytoma. The tumor was determined to be unresectable because of involvement of surrounding organs. Radiation therapy was also not a viable option because of concerns over appreciable toxicity in relation to mass size. As there is no standard of care for malignant cases, the patient was started on chemotherapeutic agents but was soon shown to be intolerant to this treatment. As she was ineligible for several clinical trials, the patient was started on the off-label immunotherapeutic agents nivolumab and ipilimumab. Immunotherapy use resulted in decreased tumor size, improved quality of life, and reconsideration for radiation therapy.

Conclusions

The use of immunotherapy in pheochromocytoma in this patient clearly demonstrated substantial benefit, as she was able to be reconsidered for radiation therapy. Not only has the patient been tolerant of this treatment, but she has exhibited progression-free survival of over 20 months. As there is no current standard treatment for malignant pheochromocytomas, the success of its use in this patient lends support to the ongoing clinical trials regarding the use of immunotherapy in rare tumors, including pheochromocytomas.

HIF-Prolyl Hydroxylase Domain Proteins (PHDs) in Cancer-Potential Targets for Anti-Tumor Therapy?

Solid tumors are typically associated with unbridled proliferation of malignant cells, accompanied by an immature and dysfunctional tumor-associated vascular network. Consequent impairment in transport of nutrients and oxygen eventually leads to a hypoxic environment wherein cells must adapt to survive and overcome these stresses. Hypoxia inducible factors (HIFs) are central transcription factors in the hypoxia response and drive the expression of a vast number of survival genes in cancer cells and in cells in the tumor microenvironment. HIFs are tightly controlled by a class of oxygen sensors, the HIF-prolyl hydroxylase domain proteins (PHDs), which hydroxylate HIFs, thereby marking them for proteasomal degradation. Remarkable and intense research during the past decade has revealed that, contrary to expectations, PHDs are often overexpressed in many tumor types, and that inhibition of PHDs can lead to decreased tumor growth, impaired metastasis, and diminished tumor-associated immune-tolerance. Therefore, PHDs represent an attractive therapeutic target in cancer research. Multiple PHD inhibitors have been developed that were either recently accepted in China as erythropoiesis stimulating agents (ESA) or are currently in phase III trials. We review here the function of HIFs and PHDs in cancer and related therapeutic opportunities.

Management and outcome of metastatic pheochromocytomas/paragangliomas: an overview

BACKGROUND

Metastatic pheochromocytomas and paragangliomas (PPGLs) occur in about 5-26% of cases and are characterized by a heterogeneous prognosis. Metastases can be synchronous at the initial diagnosis, but they can occur also many years after surgery for the primary tumor. To date, the treatment of patients affected by metastatic PPGLs represents a clinical challenge because of the lack of guidelines.

AIM

The aim of this article is to review the available management options and their impact on the outcomes of patients with metastatic PPGLs.

RESULTS

Generally, treatments are not curative. Surgery, when possible, can be used to reduce hormonal symptoms and cardiovascular morbidity. Chemotherapy plays a role in patients with high burden tumor and rapid disease progression. Tyrosine kinases inhibitors (TKIs) might be considered for their ability to block the angiogenesis and cell growth. Radiation therapy and interventional radiology techniques can help in the management of local metastases to control symptoms and avoid tumor progression. On the other hand, peptide receptor radionuclide therapy (PRRT), using ⁹⁰Y or ¹⁷⁷Lu-DOTATATE, could be a promising therapy. In addition, high specific ¹³¹I-MIBG was approved by the Food and Drug Administration (FDA) in the US for the treatment of patients affected by metastatic and unresectable ¹³¹I-MIBG positive PPGLs. Considering the different pathways involved in the pathogenesis of PPGLs, several target therapies have been proposed and are under evaluation in clinical trials.

CONCLUSIONS

The choice of the appropriate treatment should be based on multidisciplinary and personalized approach taking into account the rarity and the variability of these tumors.

Succinate Dehydrogenase and Ribonucleic Acid Networks in Cancer and Other Diseases

Simple Summary

Although the dysfunction of the succinate dehydrogenase complex in mitochondria leads to cancer and other diseases due to aberrant metabolic reactions and signaling pathways, it is not well known how the succinate dehydrogenase complex is regulated. Our review highlights that non-coding ribonucleic acids (RNAs), RNA editing enzymes, and RNA modifying enzymes regulate expressions and functions of the succinate dehydrogenase complex. This research will provide new strategies for treating succinate dehydrogenase-relevant diseases in a clinic.

Abstract

Succinate dehydrogenase (SDH) complex connects both the tricarboxylic acid (TCA) cycle and the electron transport chain (ETC) in the mitochondria. However, SDH mutation or dysfunction-induced succinate accumulation results in multiple cancers and non-cancer diseases. The mechanistic studies show that succinate activates hypoxia response and other signal pathways via binding to 2-oxoglutarate-dependent oxygenases and succinate receptors. Recently, the increasing knowledge of ribonucleic acid (RNA) networks, including non-coding RNAs, RNA editors, and RNA modifiers has expanded our understanding of the interplay between SDH and RNA networks in cancer and other diseases. Here, we summarize recent discoveries in the RNA networks and their connections to SDH. Additionally, we discuss current therapeutics targeting SDH in both pre-clinical and clinical trials. Thus, we propose a new model of SDH–RNA network interaction and bring promising RNA therapeutics against SDH-relevant cancer and other diseases.

A review of the tumour spectrum of germline succinate dehydrogenase gene mutations: Beyond phaeochromocytoma and paraganglioma

The citric acid cycle, also known as the Krebs cycle, plays an integral role in cellular metabolism and aerobic respiration. Mutations in genes encoding the citric acid cycle enzymes succinate dehydrogenase, fumarate hydratase and malate dehydrogenase all predispose to hereditary tumour syndromes. The succinate dehydrogenase enzyme complex (SDH) couples the oxidation of succinate to fumarate in the citric acid cycle and the reduction of ubiquinone to ubiquinol in the electron transport chain. A loss of function in the succinate dehydrogenase (SDH) enzyme complex is most commonly caused by an inherited mutation in one of the four SDHx genes (SDHA, SDHB, SDHC and SDHD). This mechanism was first implicated in familial phaeochromocytoma and paraganglioma. However, over the past two decades the spectrum of tumours associated with SDH deficiency has been extended to include gastrointestinal stromal tumours (GIST), renal cell carcinoma (RCC) and pituitary adenomas. The aim of this review is to describe the extended tumour spectrum associated with SDHx gene mutations and to consider how functional tests may help to establish the role of SDHx mutations in new or unexpected tumour phenotypes.

Emerging Treatments for Advanced/Metastatic Pheochromocytoma and Paraganglioma

OPINION STATEMENT

The incidence of metastatic pheochromocytoma (PHEO) and paraganglioma (PGL) may occur in as many as 35% of patients particularly with PGL and even more frequently in those with specific mutations. Biochemical, morphological, and molecular markers have been investigated for use in the distinction of benign from malignant PHEO/PGL. PHEO/PGL metastasizes via hematogenous or lymphatic routes and shows differences based on mutational status. The most common sites of involvement in patients that have an SDHB mutation are the bone (78%), lungs (45%), lymph nodes (36%), and liver (35%). In patients with sporadic PHEO/PGL, the most common sites of metastasis are the bones (64%), lungs (47%), lymph nodes (36%), and liver (32%). Metastases may be present at presentation or may occur later. Metastases to the liver and lungs are associated with a shorter survival. Overall, the estimated 5-year survival rates are between 34 and 74%. Currently, treatments for metastatic PHEO/PGL are essentially palliative. Surgery is potentially curative; however, tumor dissemination limits the chance for a curative resection. When surgical intervention is not amenable, the therapeutic options include radiolabeled MIBG (Azedra®-iobenguane 131 was recently FDA-approved for patients > 12 years and older with iobenguane scan positive) or systemic chemotherapy with cyclophosphamide, vincristine, and dacarbazine (CVD) with an overall objective response rate (ORR) of less than 40%; however, it is not clear if the administration of CVD impacts overall survival, as nearly all patients develop progressive and ultimately fatal disease. Other treatment modalities under investigation include cytoreductive techniques, novel radiopharmaceuticals, chemotherapy, radiotherapy, immunotherapy, and experimental therapies. Here we are discussing emerging treatment for advanced/metastatic PHEO/PGL.

Recent advances in the management of pheochromocytoma and paraganglioma

Pheochromocytomas and paragangliomas (PPGLs) are rare tumors that cause refractory hypertension and hypertensive crisis. Although metastatic disease accounts for 30% of PPGLs, the diagnosis of malignancy is difficult without the presence of metastatic lesions. Here, we review several advancements in the diagnosis and treatment of PPGL. A nationwide epidemiological survey in Japan revealed that the annual number of patients with PPGL was 3000, which was higher than that reported previously. While plasma and urine fractionated metanephrines are recommended for use in specific biochemical testing for diagnosis, creatinine-corrected fractionated metanephrines in spot urine samples that had been widely used in Japan as a convenient screening test were shown to be as useful as 24-h urine fractionated metanephrines. Regarding imaging studies, a more specific functional imaging for PPGLs, ⁶⁸Ga DOTATATE, was newly developed. ⁶⁸Ga DOTATATE provides a clear image with high sensitivity and specificity. Currently, PASS or GAPP histological scores and SDHB immunostaining are clinically used to attempt to discriminate benign from malignant tumors. However, since this distinguishing process remains difficult, all cases were classified as malignant with the possibility of metastasis in the WHO classification of endocrine tumors updated in 2017. Approximately 60% of PPGLs have germline mutations in PPGL-related genes. Currently, the genes are classified into two clusters based on their mechanism for the etiology of tumorigenesis. Based on the possible mechanisms of tumor development associated with gene mutations, several molecular target drugs are under evaluation to explore more promising treatments for malignant PPGL.

Metastatic pheochromocytoma and paraganglioma: Management of endocrine manifestations, surgery and ablative procedures, and systemic therapies

Metastatic pheochromocytomas and paragangliomas (MPPGs) are rare neuroendocrine tumors. Most patients present with advanced disease that is associated with manifestations of catecholamine release. Surgical resection of the primary tumor and ablative therapies of metastases-whenever possible-may improve clinical outcomes and, perhaps, lengthen the patient's overall survival. Significant steps in understanding the genetic alterations linked to MPPGs and scientific progress made on cancers that share a similar pathogenesis are leading to the recognition of potential systemic therapeutic options. Data derived from clinical trials evaluating targeted therapies such as tyrosine kinase inhibitors, radiopharmaceuticals, immunotherapy, and combinations of these will likely improve the outcomes of patients with advanced and progressive MPPGs. Exemplary of this success is the recent approval in the United States of the high-specific-activity iodine¹³¹ meta-iodine-benzylguanidine (MIBG) for patients with unresectable and progressive MPPGs that express the noradrenaline transporter. This review will discuss the therapeutic approaches for patients with MPPGs.

Pheochromocytoma

Pheochromocytomas are rare tumors originating in the adrenal medulla. They may be sporadic or in the context of a hereditary syndrome. A considerable number of pheochromocytomas carry germline or somatic gene mutations, which are inherited in the autosomal dominant way. All patients should undergo genetic testing. Symptoms are due to catecholamines over production or to a mass effect. Diagnosis is confirmed by raised plasma or urine metanephrines or normetanephrines. Radiology assists in the tumor location and any local invasion or metastasis. All the patients should have preoperative preparation with α-blockers and/or other medications to control hypertension, arrhythmia, and volume expansion. Surgery is the definitive treatment. Follow up should be life-long.

Diagnostic des phéochromocytomes et paragangliomes

Les phéochromocytomes et les paragangliomes sont des tumeurs rares responsables d’une surmorbidité et d’une surmortalité. Au cours de ces 20 dernières années, de nombreuses avancées ont permis de mieux les caractériser sur le plan phénotypique (via l’imagerie métabolique) et génotypique (avec la mise en évidence de nombreux gènes de prédisposition). La prise en charge d’un phéochromocytome ou d’un paragangliome nécessite désormais le recours à un centre expert dès la phase diagnostique. L’objectif de cette revue est de souligner les principales caractéristiques de ces tumeurs, et ce, afin de sensibiliser le clinicien aux différentes étapes permettant d’aboutir à une prise en charge optimale.

'Peptide receptor radionuclide therapy in the management of advanced pheochromocytoma and paraganglioma: A systematic review and meta-analysis'

OBJECTIVE

Inoperable and metastatic pheochromocytomas and paragangliomas (PPGLs) present a therapeutic challenge with current treatment options being limited to radiolabelled meta-iodo-benzyl-guanidine (MIBG) and systemic chemotherapy. Peptide receptor radionuclide therapy (PRRT) seems to be a promising option for these patients with few studies reporting favourable response. This systematic review was conducted to evaluate the efficacy and safety of PRRT in patients with advanced PPGLs.

METHODS

This review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. Searches in PubMed, Scopus and Embase were made using relevant keywords and articles up to May 2019 were included. Data on efficacy and toxicity were extracted from the individual articles, and pooled estimates were generated using meta-analysis.

RESULTS

Twelve articles consisting of 201 patients with advanced PPGLs were included. Overall, treatment with PRRT achieved an objective response rate of 25% (95% CI: 19%-32%) and a disease control rate of 84% (95% CI: 77%-89%). Clinical and biochemical responses were seen in 61% and 64% of the patients, respectively. Among the PRRTs, similar tumour response rates were noted for ⁹⁰ Y-yttrium- and ¹⁷⁷ Lu-lutetium-based agents. Treatment-related adverse effects were minimal with grade 3/4 neutropenia, thrombocytopenia, lymphopenia and nephrotoxicity observed in 3%, 9%, 11% and 4% of the patients, respectively. Treatment discontinuation was noted in five out of 102 patients.

CONCLUSIONS

Peptide receptor radionuclide therapy is a safe and efficacious treatment option for advanced PPGLs and may be considered a viable alternative to chemotherapy and I-¹³¹ MIBG.

Mutational profile and genotype/phenotype correlation of non-familial pheochromocytoma and paraganglioma

About 30%-40% of patients with pheochromocytoma (PCC) and paraganglioma (PGL) have underlying germline mutations in certain susceptibility genes despite absent family history of these tumors. Here, we present mutational profile of 101 such patients with PCC/PGL (PPGL) from the highly consanguineous population of Saudi Arabia. Results: Of 101 cases with PPGL, 37/101 (36.6%) had germline mutations. Mutations were detected in 30 cases by PCR and direct Sanger sequencing and in 7 additional cases by NGS. The most commonly mutated gene was SDHB (21/101 cases, 20.8%) and the most common SDHB mutation was c.268C>T, p.R90X occurring in 12/21 (57%) cases. Mutations also occurred in SDHC (4/101, 3.96%), SDHD (3/101, 3%), VHL (2/101, 2%) and MAX (2/101, 2%) genes. The following genes were mutated in 1 patient each (1%), RET, SDHA, SDHAF2, TMEM127 and NF1. Metastatic PPGL occurred in 6/21 cases (28.6%) with SDHB mutations and in 1 case with SDHAF2 mutation. Patients and Methods: DNA was isolated from peripheral blood (53 patients) or from non-tumorous formalin fixed paraffin embedded (FFPE) tissue (48 patients). PCR and direct Sanger sequencing of RET, SDHx, VHL, MAX and TMEM127 genes were performed. Cases without mutations were subjected to whole exome sequencing using next generation sequencing (NGS). Conclusion: About 37% of PPGL without family history of such tumors harbor germline mutations. The most commonly mutated gene is SDHB followed by SDHC, SDHD, VHL, MAX and rarely RET, SDHA, SDHAF2, TMEM127 and NF1. SDHB mutations were associated with metastatic PPGL in more than a quarter of cases.

Diagnostic efficacy of 18F-FDG PET/CT in patients with adrenal incidentaloma

BACKGROUND

The management of adrenal incidentaloma is still a challenge with respect to determining its functionality (hormone secretion) and malignancy. In this light, we performed 18F-FDG PET/CT scan to assess the SUVmax values in different adrenal masses including Cushing syndrome, pheochromocytoma, primary hyperaldosteronism and non-functional adrenal adenomas.

METHODS

Total 109 (73 F, 36 M) patients with adrenal mass (incidentaloma), mean age of 53.3 ± 10.2 years (range, 24-70) were screened by 18F-FDG PET/CT. Data of 18F-FDG PET/CT imaging of the patients were assessed by the same specialist. Adrenal masses were identified according to the calculated standardized uptake values (SUVs). Clinical examination, 24-h urine cortisol, catecholamine metabolites, 1-mg dexamethasone suppression test, aldosterone/renin ratio and serum electrolytes were analyzed.

RESULTS

Based on the clinical and hormonal evaluations, there were 100 patients with non-functional adrenal mass, four with cortisol-secreting, four with pheochromocytomas and one with aldosterone-secreting adenoma. Mean adrenal mass diameter of 109 patients was 2.1 ± 4.3 (range, 1-6.5 cm). The 18F-FDG PET/CT imaging of the patients revealed that lower SUVmax values were found in non-functional adrenal masses (SUVmax 3.2) when compared to the functional adrenal masses including four with cortisol-secreting adenoma (SUVmax 10.1); four with pheochromcytoma (SUVmax 8.7) and one with aldosterone-secreting adenomas (SUVmax 3.30). Cortisol-secreting (Cushing syndrome) adrenal masses showed the highest SUVmax value (10.1), and a cut-off SUVmax of 4.135 was found with an 84.6% sensitivity and 75.6% specificity cortisol-secreting adrenal adenoma.

CONCLUSIONS

Consistent with the similar studies, non-functional adrenal adenomas typically do not show increased FDG uptake and a certain form of functional adenoma could present various FDG uptake in FDG PET/CT. Especially functional adrenal adenomas (cortisol secreting was the highest) showed increased FDG uptake in comparison to the non-functional adrenal masses. Therefore, setting a specific SUVmax value in the differentiation of malignant adrenal lesion from the benign one is risky and further studies, including a high number of functional adrenal mass are needed.

Malignant Pheochromocytomas/Paragangliomas and Ectopic Hormonal Secretion: A Case Series and Review of the Literature

Malignant pheochromocytomas (PCs) and paragangliomas (PGLs) are rare neuroendocrine neoplasms defined by the presence of distant metastases. There is currently a relatively paucity of data regarding the natural history of PCs/PGLs and the optimal approach to their treatment. We retrospectively analyzed the clinical, biochemical, imaging, genetic and histopathological characteristics of fourteen patients with metastatic PCs/PGLs diagnosed over 15 years, along with their response to treatment. Patients were followed-up for a median of six years (range: 1-14 years). Six patients had synchronous metastases and the remaining developed metastases after a median of four years (range 2-10 years). Genetic analysis of seven patients revealed that three harbored succinate dehydrogenase subunit B/D gene (SDHB/D) mutations. Hormonal hypersecretion occurred in 70% of patients; normetanephrine, either alone or with other concomitant hormones, was the most frequent secretory component. Patients were administered multiple first and subsequent treatments including surgery (n = 12), chemotherapy (n = 7), radionuclide therapy (n = 2) and radiopeptides (n = 5). Seven patients had stable disease, four had progressive disease and three died. Ectopic hormonal secretion is rare and commonly encountered in benign PCs. Ectopic secretion of interleukin-6 in one of our patients, prompted a literature review of ectopic hormonal secretion, particularly from metastatic PCs/PGLs. Only four cases of metastatic PC/PGLs with confirmed ectopic secretion of hormones or peptides have been described so far.

Pheochromocytomas and Paragangliomas: Bypassing Cellular Respiration

Abstract: Pheochromocytomas and paragangliomas (PPGL) are rare neuroendocrine tumors that show the highest heritability of all human neoplasms and represent a paradoxical example of genetic heterogeneity. Amongst the elevated number of genes involved in the hereditary predisposition to the disease (at least nineteen) there are eleven tricarboxylic acid (TCA) cycle-related genes, some of which are also involved in the development of congenital recessive neurological disorders and other cancers such as cutaneous and uterine leiomyomas, gastrointestinal tumors and renal cancer. Somatic or germline mutation of genes encoding enzymes catalyzing pivotal steps of the TCA cycle not only disrupts cellular respiration, but also causes severe alterations in mitochondrial metabolite pools. These latter alterations lead to aberrant accumulation of "oncometabolites" that, in the end, may lead to deregulation of the metabolic adaptation of cells to hypoxia, inhibition of the DNA repair processes and overall pathological changes in gene expression. In this review, we will address the TCA cycle mutations leading to the development of PPGL, and we will discuss the relevance of these mutations for the transformation of neural crest-derived cells and potential therapeutic approaches based on the emerging knowledge of underlying molecular alterations.

Clinical implications of the oncometabolite succinate in SDHx-mutation carriers

Succinate dehydrogenase (SDH) mutations lead to the accumulation of succinate, which acts as an oncometabolite. Germline SDHx mutations predispose to paraganglioma (PGL) and pheochromocytoma (PCC), as well as to renal cell carcinoma and gastro‐intestinal stromal tumors. The SDHx genes were the first tumor suppressor genes discovered which encode for a mitochondrial enzyme, thereby supporting Otto Warburg's hypothesis in 1926 that a direct link existed between mitochondrial dysfunction and cancer. Accumulation of succinate is the hallmark of tumorigenesis in PGL and PCC. Succinate accumulation inhibits several α‐ketoglutarate dioxygenases, thereby inducing the pseudohypoxia pathway and causing epigenetic changes. Moreover, SDH loss as a consequence of SDHx mutations can lead to reprogramming of cell metabolism. Metabolomics can be used as a diagnostic tool, as succinate and other metabolites can be measured in tumor tissue, plasma and urine with different techniques. Furthermore, these pathophysiological characteristics provide insight into therapeutic targets for metastatic disease. This review provides an overview of the pathophysiology and clinical implications of oncometabolite succinate in SDHx mutations.