Radiological Surveillance Screening in Asymptomatic Succinate Dehydrogenase Mutation Carriers

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.

Clinical consensus guideline on the management of phaeochromocytoma and paraganglioma in patients harbouring germline SDHD pathogenic variants

Patients with germline SDHD pathogenic variants (encoding succinate dehydrogenase subunit D; ie, paraganglioma 1 syndrome) are predominantly affected by head and neck paragangliomas, which, in almost 20% of patients, might coexist with paragangliomas arising from other locations (eg, adrenal medulla, para-aortic, cardiac or thoracic, and pelvic). Given the higher risk of tumour multifocality and bilaterality for phaeochromocytomas and paragangliomas (PPGLs) because of SDHD pathogenic variants than for their sporadic and other genotypic counterparts, the management of patients with SDHD PPGLs is clinically complex in terms of imaging, treatment, and management options. Furthermore, locally aggressive disease can be discovered at a young age or late in the disease course, which presents challenges in balancing surgical intervention with various medical and radiotherapeutic approaches. The axiom-first, do no harm-should always be considered and an initial period of observation (ie, watchful waiting) is often appropriate to characterise tumour behaviour in patients with these pathogenic variants. These patients should be referred to specialised high-volume medical centres. This consensus guideline aims to help physicians with the clinical decision-making process when caring for patients with SDHD PPGLs.

A need to tailor surveillance based on family history: describing a highly penetrant familial paraganglioma kindred with an SDHD pathogenic variant

Pathogenic variants (PVs) in the SDHD gene increase risk for paragangliomas (PGL)/pheochromocytomas, renal cell carcinomas, and gastrointestinal stromal tumors. Penetrance in individuals with SDHD PVs varies in reported research from 40-70%, and there is limited evidence of specific genotype risks. This study aims to characterize a multi-generational family with SDHD p.Trp43* PVs and potential genotype-phenotype considerations for surveillance. Individuals with a paternally inherited SDHD p.Trp43*(c.129G > A) PV were identified. Genetic, medical and family histories were abstracted, including clinical characteristics, tumor histories, and treatment approaches. Eleven individuals with the SDHD PV in the same kindred were diagnosed with 41 SDHx-related tumors across all family members. Eight individuals developed 27 head and neck PGL of varying origins, and seven individuals developed tumors outside of the head and neck region. Many individuals had multiple tumors, and age of first tumor diagnosis ranged from age 10 to age 45 years old. Individuals with SDHD p.Trp43* variants may have higher risks for SDHx related tumors than other SDHD variants. Prioritizing identification of at-risk individuals and initiating surveillance tailored to family history is recommended given the rate of multiple tumors found in one familial branch of individuals under 18 years old. Individuals with strong family histories of PGL at young ages with this PV will benefit from tailored surveillance recommendations.

Molecular genetic testing in the management of pituitary disease

OBJECTIVE

Most pituitary tumours occur sporadically without a genetically identifiable germline abnormality, a small but increasing proportion present with a genetic defect that predisposes to pituitary tumour development, either isolated (e.g., aryl hydrocarbon receptor-interacting protein, AIP) or as part of a tumour-predisposing syndrome (e.g., multiple endocrine neoplasia (MEN) type 1, Carney complex, McCune-Albright syndrome or pituitary tumour and paraganglioma association). Genetic alterations in sporadic pituitary adenomas may include somatic mutations (e.g., GNAS, USP8). In this review, we take a practical approach: which genetic syndromes should be considered in case of different presentation, such as tumour type, family history, age of onset and additional clinical features of the patient.

DESIGN

Review of the recent literature in the field of genetics of pituitary tumours.

RESULTS

Genetic testing in the management of pituitary disease is recommended in a significant minority of the cases. Understanding the genetic basis of the disease helps to identify patients and at-risk family members, facilitates early diagnosis and therefore better long-term outcome and opens up new pathways leading to tumorigenesis.

CONCLUSION

We provide a concise overview of the genetics of pituitary tumours and discuss the current challenges and implications of these genetic findings in clinical practice.

Succinate: A Serum Biomarker of SDHB-Mutated Paragangliomas and Pheochromocytomas

CONTEXT

Pheochromocytomas and paragangliomas (PPGL) are rare neuroendocrine tumors that are frequently associated with succinate dehydrogenase (SDH) germline mutations. When mutated, SDH losses its function, thus leading to succinate accumulation.

OBJECTIVE

In this study, we evaluated serum succinate levels as a new metabolic biomarker in SDHx-related carriers.

METHODS

Retrospective monocentric study of 88 PPGL patients (43 sporadic, 35 SDHB, 10 SDHA/C/D), 17 tumor-free familial asymptomatic carriers (13 SDHB, 4 SDHC/D), and 60 healthy controls. Clinical, biological, and imaging data were reviewed. Serum succinate levels (n = 280) were quantified by an ultra-performance liquid chromatography coupled to a tandem mass spectrometry method and correlated to SDHx mutational status, disease extension, and other biological biomarkers.

RESULTS

Serum succinate levels > 7 μM allowed identification of tumor-free asymptomatic SDHB-mutated cases compared to a healthy control group (100% specificity; 85% sensitivity). At PPGL diagnosis, SDHB-mutated patients had a significantly increased median succinate level (14 μM) compared to sporadic patients (8 μM) (P < 0.01). Metastatic disease extension was correlated to serum succinate levels (r = 0.81). In the SDHB group, patients displaying highest tumor burdens showed significant increased succinate levels compared to the sporadic group (P < 0.0001).

CONCLUSIONS

In this pilot study, we showed that serum succinate level is an oncometabolic biomarker that should be useful to identify SDHB-related carriers. Succinate levels are also a marker of metabolic tumor burden in patients with a metastatic PPGL and a potential marker of treatment response and follow-up.

Radiologic screening and surveillance in hereditary cancers

Hereditary cancer syndromes comprise an important subset of cancers caused by pathogenic germline mutations that can affect various organ systems. Radiologic screening and surveillance for solid tumors has emerged as a critical component of patient management in permitting early cancer detection. Although imaging surveillance may be tailored for organ-specific cancer risks, surveillance protocols frequently utilize whole-body MRI or PET/CT because of their ability to identify neoplasms in different anatomic regions in a single exam. In this review, we discuss the basic tenets of imaging screening and surveillance strategies in these syndromes, highlighting the more common neoplasms and their associated multimodality imaging findings.

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Pathogenic germline mutations in hereditary cancers cause early-onset distinctive tumors in an organ-specific pattern.

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Geneticist, oncologist, and radiologist coordination facilitates syndrome-appropriate screening and surveillance strategies.

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WB-MRI is a promising comprehensive non-ionizing screening/surveillance modality but with sparse prospective survival data.

Screening of a Large Cohort of Asymptomatic SDHx Mutation Carriers in Routine Practice

CONTEXT

When an SDHx mutation is identified in a patient with a pheochromocytoma (PCC) or a paraganglioma (PGL), predictive genetic testing can detect mutation carriers that would benefit from screening protocols.

OBJECTIVE

To define the tumor detection rate in a large cohort of asymptomatic SDHX mutation carriers.

DESIGN AND SETTING

Retrospective multicentric study in 6 referral centers.

PATIENTS

Between 2005 and 2019, 249 asymptomatic SDHx (171 SDHB, 31 SDHC, 47 SDHD) mutation carriers, with at least 1 imaging work-up were enrolled.

RESULTS

Initial work-up, including anatomical (98% of subjects [97-100% according to center]) and/or functional imaging (67% [14-90%]) detected 48 tumors in 40 patients. After a negative initial work-up, 124 patients benefited from 1 to 9 subsequent follow-up assessments (mean: 1.9 per patient), with a median follow-up time of 5 (1-13) years. Anatomical (86% [49-100 %]) and/or functional imaging (36% [7-60 %]) identified 10 new tumors (mean size: 16 mm [4-50]) in 10 patients. Altogether, 58 tumors (55 paraganglioma [PGL], including 45 head and neck PGL, 2 pheochromocytoma [PCC], 1 gastrointestinal stromal tumor [GIST]), were detected in 50 patients (22 [13%] SDHB, 1 [3.2%] SDHC, and 27 [57%] SDHD), with a median age of 41 years old [11-86], 76% without catecholamine secretion and 80% during initial imaging work-up.

CONCLUSIONS

Imaging screening enabled detection of tumors in 20% of asymptomatic SDHx mutation carriers, with a higher detection rate in SDHD (57%) than in SDHB (13%) and SDHC (3%) mutation carriers, arguing for a gene-by-gene approach. Prospective studies using well-defined protocols are needed to obtain strong and useful data.

Large Retroperitoneal Paraganglioma Associated with Germline Mutation of the Succinate Dehydrogenase Gene

Paragangliomas (PGLs) are rare neural tumors that can be benign or malignant and often associated with familial syndromes. We present a case of a 23-year-old male with a large retroperitoneal PGL found incidentally during the workup of elevated liver enzymes. After surgical excision, the patient was found to have an autosomal dominant mutation in the succinate dehydrogenase B (SDHB) gene, which when compared to sporadic PGLs or other familial syndromes is associated with a higher risk of tumor recurrence, occult metastasis, and development of other cancers. The patient’s first-degree relatives were recommended to undergo screening for the genetic mutation.

Co-existent Epicardial Paraganglioma and Anterior Mediastinal Thymoma

Thymoma and paraganglioma are known causes of mediastinal masses, the latter being extremely rare. Thymomas arise from remnant thymic tissue in the anterior mediastinum; whereas, thoracic paragangliomas arise from para-aortic or para-vertebral sympathetic chain ganglion (derivatives of embryonic neural crest) in the middle or posterior mediastinum. We report a case of a middle-aged woman with two mediastinal masses, originally believed to be a single tumor or primary malignancy with adjacent metastasis on Computed Tomography (CT) that were further delineated with Magnetic Resonance Imaging (MRI) and [68Ga]-DOTA-(Tyr3)-octreotate (DOTA-TATE) Positron Emission Tomography-Computed Tomography (PET-CT) and surgical pathology as two distinct entities: left epicardial paraganglioma and anterior mediastinal thymoma. A comprehensive discussion of both entities is included.

The genetic basis of isolated mitochondrial complex II deficiency

Mitochondrial complex II (succinate:ubiquinone oxidoreductase) is the smallest complex of the oxidative phosphorylation system, a tetramer of just 140 kDa. Despite its diminutive size, it is a key complex in two coupled metabolic pathways - it oxidises succinate to fumarate in the tricarboxylic acid cycle and the electrons are used to reduce FAD to FADH₂, ultimately reducing ubiquinone to ubiquinol in the respiratory chain. The biogenesis and assembly of complex II is facilitated by four ancillary proteins, all of which are autosomally-encoded. Numerous pathogenic defects have been reported which describe two broad clinical manifestations, either susceptibility to cancer in the case of single, heterozygous germline variants, or a mitochondrial disease presentation, almost exclusively due to bi-allelic recessive variants and associated with an isolated complex II deficiency. Here we present a compendium of pathogenic gene variants that have been documented in the literature in patients with an isolated mitochondrial complex II deficiency. To date, 61 patients are described, harbouring 32 different pathogenic variants in four distinct complex II genes: three structural subunit genes (SDHA, SDHB and SDHD) and one assembly factor gene (SDHAF1). Many pathogenic variants result in a null allele due to nonsense, frameshift or splicing defects however, the missense variants that do occur tend to induce substitutions at highly conserved residues in regions of the proteins that are critical for binding to other subunits or substrates. There is phenotypic heterogeneity associated with defects in each complex II gene, similar to other mitochondrial diseases.

Pediatric applications of Dotatate: early diagnostic and therapeutic experience

In recent years, new somatostatin receptor agents (SSTRs) have become available for diagnostic imaging and therapy in neuroendocrine tumors. The novel SSTR ligand DOTA-DPhel-Tyr3-octreotate (Dotatate) in particular can be linked with ⁶⁸Gallium for diagnostic imaging purposes, and with the β-emitter ¹⁷⁷Lutetium for radiotherapy in the setting of neuroendocrine tumors. Dotatate imaging offers distinct advantages in the evaluation of neuroendocrine tumors compared to standard techniques, including greater target-to-background ratio and lesion conspicuity, high sensitivity/specificity, improved spatial resolution with positron emission tomography (PET)/CT or PET/MR, and decreased radiation exposure. Although currently off-label in pediatrics, Dotatate theranostics in children are being explored, most notably in the setting of neuroblastoma and hereditary neuroendocrine syndromes. This article provides a multicenter case series of Dotatate imaging and therapy in pediatric patients in order to highlight the spectrum of potential clinical applications.

Pediatric pheochromocytoma: current status of diagnostic imaging and treatment procedures

PURPOSE OF REVIEW

To provide an overview of relevant data available and updated recommendations for management of pediatric patients with pheochromocytoma (PCC).

RECENT FINDINGS

Much of the available data surrounding pediatric PCC is in the form of case reports and case series. With the accumulation of data over time, pediatric PCC does in fact differ significantly from not only what is known in the adult population, but also from classic teaching. Pediatric patients are much more likely to have a hereditary predisposition as well as aggressive and malignant disease. Much of the recent literature focuses on defining these genetic syndromes in order to provide recommendations for screening and genetic counseling. Other recent advances center around developing treatments for metastatic disease. Timely diagnosis with plasma metanephrines and cross-sectional imaging, and appropriate preoperative medical optimization followed by surgical resection remain the center of treatment.

SUMMARY

Although rare and adult principles are applied to pediatric PCC, genetic testing plays a pivotal role in management of children, adolescents and young adults with PCC.

Pheochromocytoma and paraganglioma-an update on diagnosis, evaluation, and management

Pheochromocytomas and paragangliomas (PPGLs) generally grouped together are rare catecholamine-secreting endocrine tumors. Symptoms of catecholamine excess are non-specific and therefore a high index of suspicion in children with sustained hypertension, family history of endocrine tumors, or features of syndromes associated with PPGLs leads to a timely diagnosis and treatment. Free metanephrines in the plasma or 24-h urine are the preferred tests to establish catecholamine excess. Considerations for false-positive conditions improve diagnostic yield and accuracy. Functional imaging, targeting either specific cell membrane transporters or vesicular catecholamine transport systems, is indicated for incidental lesions suspicious for PPGLs with inconclusive biochemical testing, assessment of regional extension or multifocality, and exclusion of metastases. Surgery is the mainstay of treatment for PPGLs. Preoperatively, sequential use of alpha adrenergic receptor blockade and volume expansion followed by beta blockade is mandatory to reduce intraoperative intravascular instability and blood pressure fluctuation due to tumor manipulation. Since genetic mutations have been reported in tumor susceptibility genes in nearly 50% of patients with PPGLs, genetic counselling and testing should be considered in all patients with a confirmed tumor.

Current management of succinate dehydrogenase-deficient gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are increasingly recognized as having diverse biology. With the development of tyrosine kinase inhibitors molecularly matched to oncogenic KIT and PDGFRA mutations, GISTs have become a quintessential model for precision oncology. However, about 5-10% of GIST lack these driver mutations and are deficient in succinate dehydrogenase (SDH), an enzyme that converts succinate to fumarate. SDH deficiency leads to accumulation of succinate, an oncometabolite that promotes tumorigenesis. SDH-deficient GISTs are clinically unique in that they generally affect younger patients and are associated with GIST-paraganglioma hereditary syndrome, also known as Carney-Stratakis Syndrome. SDH-deficient GISTs are generally resistant to tyrosine-kinase inhibitors, the standard treatment for advanced or metastatic GIST. Thus, surgical resection is the mainstay of treatment for localized disease, but recurrence is common. Clinical trials are currently underway investigating systemic agents for treatment of advanced SDH-deficient GIST. However, further studies are warranted to improve our understanding of SDH-deficient GIST disease biology, natural history, surgical approaches, and novel therapeutics.

Tinnitus With Unexpected Spanish Roots: Head and Neck Paragangliomas Caused by SDHAF2 Mutation

It is estimated that up to 40% of all head and neck paragangliomas (HNPGL) have a hereditary background with the most common mutations being found in the succinate dehydrogenase (SDH) genes. SDHAF2 mutation leads to the rare paraganglioma syndrome 2. The authors present the case of a 15-year-old male patient with 2, non-secretory HNPGLs, presenting with left-sided, pulsatile tinnitus, and hearing loss. Imaging led to the suspicion of a jugulotympanic paraganglioma on the left, as well as a carotid body tumor on the right. After resection of the jugulotympanic tumor, histology confirmed the presence of a paraganglioma; immunohistochemistry furthermore suggested a loss of SDHB expression. Genetic testing revealed a rare germline, loss-of-function mutation in the SDHAF2 gene, previously described to cause hereditary paraganglioma syndrome 2. Twenty months after the first operation, the patient underwent a resection of the right carotid body paraganglioma. Plasma-free metanephrines/catecholamines always remained within the reference range; the patient is under regular follow-up, and his relatives will be screened. Our findings emphasize the relevance of genetic testing in patients with HNPGL, also with negative family history, especially when the patients present at a young age and with multiple lesions.

Brown adipose activation and reversible beige coloration in adipose tissue with multiple accumulations of 18F-fluorodeoxyglucose in sporadic paraganglioma: A case report

In pheochromocytoma/paraganglioma, nontumorous high 18F-fluorodeoxyglucose accumulations are observed in both beige and brown adipose tissues. Recognizing this feature of 18F-fluorodeoxyglucose accumulation can help physicians make precise diagnoses and help them avoid the pitfalls of a false-positive 18F-fluorodeoxyglucose positron emission tomography result, preventing unnecessary interventions.

An analysis of surveillance screening for SDHB-related disease in childhood and adolescence

Objective Phaeochromocytomas (PCC) and paragangliomas (PGL) are rare in children. A large proportion of these are now understood to be due to underlying germline mutations. Here we focus on succinate dehydrogenase subunit B (SDHB) gene mutation carriers as these tumours carry a high risk of malignant transformation. There remains no current consensus with respect to optimal surveillance for asymptomatic carriers and those in whom the presenting tumour has been resected. Method We undertook a retrospective analysis of longitudinal clinical data of all children and adolescents with SDHB mutations followed up in a single UK tertiary referral centre. This included index cases that pre-dated the introduction of surveillance screening and asymptomatic carriers identified through cascade genetic testing. We also conducted a literature review to inform a suggested surveillance protocol for children and adolescents harbouring SDHB mutations. Results Clinical outcomes of a total of 38 children are presented: 8 index cases and 30 mutation-positive asymptomatic carriers with 175 patient years of follow-up data. Three of the eight index cases developed metachronous disease and two developed metastatic disease. Of the 30 asymptomatic carriers, 3 were found to have PGLs on surveillance screening. Conclusions Surveillance screening was well tolerated in our paediatric cohort and asymptomatic paediatric subjects. Screening can identify tumours before they become secretory and/or symptomatic, thereby facilitating surgical resection and reducing the chance of distant spread. We propose a regular screening protocol commencing at age 5 years in this at-risk cohort of patients.

Can subunit-specific phenotypes guide surveillance imaging decisions in asymptomatic SDH mutation carriers?

OBJECTIVE

With the discovery that familial phaeochromocytoma and paraganglioma syndrome can be caused by mutations in each subunit of the succinate dehydrogenase enzyme (SDH), has come the recognition that mutations in the individual subunits have their own distinct natural histories. Increased genetic screening is leading to the identification of increasing numbers of, mostly asymptomatic, gene mutation carriers and the implementation of screening strategies for these individuals. Yet there is, to date, no international consensus regarding screening strategies for asymptomatic carriers.

DESIGN

A comprehensive PubMed search from 1/1/2000 to 28/2/2018 was undertaken using multiple search terms and subsequently a manual review of references in identified papers to identify all clinically relevant cases and cohorts. In this review, the accumulated, published experience of phenotype and malignancy risks of individual SDH subunits is analysed. Where possible screening results for asymptomatic SDH mutation carriers have been analysed separately to define the penetrance in asymptomatic carriers (asymptomatic penetrance).

RESULTS

The combined data confirms that "asymptomatic penetrance" is highest for SDHD and when there is penetrance, the most likely site to develop a PGL is head and neck (SDHD) and extra-adrenal abdominal (SDHB). However, the risk in SDHB carriers of developing HNPGL is also high (35.5%) and a PCC is low (15.1%), and in SDHD carriers there is a high risk of developing a PCC (35.8%) or abdominal PGL (9.4%) and a small, but significant risk at other sympathetic sites. The data suggest that the risk of malignant transformation is the same for both PCC and extra-adrenal abdominal PGLs (30%-35%) in SDHB carriers. In SDHD carriers, the risk of malignant transformation was highest in HNPGLs (7.5%) and similar for sympathetic sites (3.8%-5.2%).

CONCLUSIONS

Using this data, we suggest surveillance screening of asymptomatic carriers can be tailored to the underlying SDH subunit and review possible surveillance programmes.

Succinate dehydrogenase mutations: paraganglioma imaging and at-risk population screening

Paragangliomas are rare vascular tumours of the autonomic nervous system. They can be classified as sympathetic or parasympathetic. Sympathetic paragangliomas, which include phaeochromocytomas, tend to be functional and symptomatic. Parasympathetic paragangliomas are usually non-functional and may present with mass effect. Forty percent of paragangliomas are linked to genetic syndromes, most commonly due to mutations of the succinate dehydrogenase (SDH) enzyme complex and are collectively known as paraganglioma syndromes, of which five are described. Genetic testing is recommended for all patients, and their first-degree relatives, diagnosed with paragangliomas. When SDH mutations are discovered, biochemical screening and imaging surveillance is indicated. There is currently no consensus on imaging surveillance protocols. Most advocate full-body imaging, but the choice of technique and frequency varies. If paragangliomas are demonstrated, functional imaging to look for synchronous tumours or metastases is indicated. 2-[¹⁸F]-fluoro-2-deoxy-d-glucose (¹⁸F-FDG) positron-emission tomography (PET)-computed tomography (CT) is the technique of choice for metastatic evaluation, but [¹²³I]-metaiodobenzylguanidine or [¹¹¹In]-DTPA-octreotide scintigraphy are also utilised. Current research into emerging positron-emitting radiolabelled somatostatin analogues have yielded promising results, which is likely to be reflected in future guidelines. As genetic testing becomes increasingly prevalent, the need to answer the remaining questions regarding surveillance imaging is paramount.

[Hereditary pheochromocytoma and paraganglioma: screening and follow-up strategies in asymptomatic mutation carriers]

The management of pheochromocytoma and paraganglioma has deeply evolved over the last years due to the discovery of novel genes of susceptibility, especially SDHx, MAX and TMEM127. While the modalities of diagnosis and management of patients presenting with hereditary pheochromocytoma and paraganglioma are now well defined, screening and follow-up strategies for asymptomatic mutation carriers remain a matter of debate. This raises major questions as these asymptomatic patients will require a lifelong follow-up. The aim of this review is an attempt to give insights on the optimal screening and follow-up strategies of asymptomatic carriers of SDHx, MAX and TMEM127 mutations, with additional thoughts on the forensic and psychological aspects of the management of such patients with rare diseases.