DIAGNOSIS of ENDOCRINE DISEASE: SDHx mutations: beyond pheochromocytomas and paragangliomas

The Molecular Classification of Pheochromocytomas and Paragangliomas: Discovering the Genomic and Immune Landscape of Metastatic Disease

Pheochromocytomas (PCCs) and paragangliomas (PGLs, together PPGLs) are the most hereditary tumors known. PPGLs were considered benign, but the fourth edition of the World Health Organisation (WHO) classification redefined all PPGLs as malignant neoplasms with variable metastatic potential. The metastatic rate differs based on histopathology, genetic background, size, and location of the tumor. The challenge in predicting metastatic disease lies in the absence of a clear genotype-phenotype correlation among the more than 20 identified genetic driver variants. Recent advances in molecular clustering based on underlying genetic alterations have paved the way for improved cluster-specific personalized treatments. However, despite some clusters demonstrating a higher propensity for metastatic disease, cluster-specific therapies have not yet been widely adopted in clinical practice. Comprehensive genomic profiling and transcriptomic analyses of large PPGL cohorts have identified potential new biomarkers that may influence metastatic potential. It appears that no single biomarker alone can reliably predict metastatic risk; instead, a combination of these biomarkers may be necessary to develop an effective prediction model for metastatic disease. This review evaluates current guidelines and recent genomic and transcriptomic findings, with the aim of accurately identifying novel biomarkers that could contribute to a predictive model for mPPGLs, thereby enhancing patient care and outcomes.

Genetic diagnosis in acromegaly and gigantism: From research to clinical practice

It is usually considered that only 5% of all pituitary neuroendocrine tumours are due to inheritable causes. Since this estimate was reported, however, multiple genetic defects driving syndromic and nonsyndromic somatotrophinomas have been unveiled. This heterogeneous genetic background results in overlapping phenotypes of GH excess. Genetic tests should be part of the approach to patients with acromegaly and gigantism because they can refine the clinical diagnoses, opening the possibility to tailor the clinical conduct to each patient. Even more, genetic testing and clinical screening of at-risk individuals have a positive impact on disease outcomes, by allowing for the timely detection and treatment of somatotrophinomas at early stages. Future research should focus on determining the actual frequency of novel genetic drivers of somatotrophinomas in the general population, developing up-to-date disease-specific multi-gene panels for clinical use, and finding strategies to improve access to modern genetic testing worldwide.

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.

International initiative for a curated SDHB variant database improving the diagnosis of hereditary paraganglioma and pheochromocytoma

BACKGROUND

SDHB is one of the major genes predisposing to paraganglioma/pheochromocytoma (PPGL). Identifying pathogenic SDHB variants in patients with PPGL is essential to the management of patients and relatives due to the increased risk of recurrences, metastases and the emergence of non-PPGL tumours. In this context, the 'NGS and PPGL (NGSnPPGL) Study Group' initiated an international effort to collect, annotate and classify SDHB variants and to provide an accurate, expert-curated and freely available SDHB variant database.

METHODS

A total of 223 distinct SDHB variants from 737 patients were collected worldwide. Using multiple criteria, each variant was first classified according to a 5-tier grouping based on American College of Medical Genetics and NGSnPPGL standardised recommendations and was then manually reviewed by a panel of experts in the field.

RESULTS

This multistep process resulted in 23 benign/likely benign, 149 pathogenic/likely pathogenic variants and 51 variants of unknown significance (VUS). Expert curation reduced by half the number of variants initially classified as VUS. Variant classifications are publicly accessible via the Leiden Open Variation Database system (https://databases.lovd.nl/shared/genes/SDHB).

CONCLUSION

This international initiative by a panel of experts allowed us to establish a consensus classification for 223 SDHB variants that should be used as a routine tool by geneticists in charge of PPGL laboratory diagnosis. This accurate classification of SDHB genetic variants will help to clarify the diagnosis of hereditary PPGL and to improve the clinical care of patients and relatives with PPGL.

The epigenetic-metabolic interplay in gliomagenesis

Although tumourigenesis occurs due to genetic mutations, the role of epigenetic dysregulations in cancer is also well established. Epigenetic dysregulations in cancer may occur as a result of mutations in genes encoding histone/DNA-modifying enzymes and chromatin remodellers or mutations in histone protein itself. It is also true that misregulated gene expression without genetic mutations in these factors could also support tumour initiation and progression. Interestingly, metabolic rewiring has emerged as a hallmark of cancer due to gene mutations in specific metabolic enzymes or dietary/environmental factors. Recent studies report an intricate cross-talk between epigenetic and metabolic reprogramming in cancer. This review discusses the role of epigenetic and metabolic dysregulations and their cross-talk in tumourigenesis with a special focus on gliomagenesis. We also discuss the role of recently developed human embryonic stem cells/induced pluripotent stem cells-derived organoid models of gliomas and how these models are proving instrumental in uncovering human-specific cellular and molecular complexities of gliomagenesis.

A Multicenter Epidemiological Study on Second Malignancy in Non-Syndromic Pheochromocytoma/Paraganglioma Patients in Italy

No studies have carried out an extensive analysis of the possible association between non-syndromic pheochromocytomas and paragangliomas (PPGLs) and other malignancies. To assess >the risk of additional malignancy in PPGL, we retrospectively evaluated 741 patients with PPGLs followed-up in twelve referral centers in Italy. Incidence of second malignant tumors was compared between this cohort and Italian patients with two subsequent malignancies. Among our patients, 95 (12.8%) developed a second malignant tumor, which were mainly prostate, colorectal and lung/bronchial cancers in males, breast cancer, differentiated thyroid cancer and melanoma in females. The standardized incidence ratio was 9.59 (95% CI 5.46-15.71) in males and 13.21 (95% CI 7.52-21.63) in females. At multivariable analysis, the risk of developing a second malignant tumor increased with age at diagnosis (HR 2.50, 95% CI 1.15-5.44, p = 0.021 for 50-59 vs. <50-year category; HR 3.46, 95% CI 1.67-7.15, p < 0.001 for >60- vs. <50-year). In patients with available genetic evaluation, a positive genetic test was inversely associated with the risk of developing a second tumor (HR 0.25, 95% CI 0.10-0.63, p = 0.003). In conclusion, PPGLs patients have higher incidence of additional malignant tumors compared to the general population who had a first malignancy, which could have an impact on the surveillance strategy.

Molecular characterization of DICER1-mutated pituitary blastoma

Pituitary blastoma (PitB) has recently been identified as a rare and potentially lethal pediatric intracranial tumor. All cases that have been studied molecularly possess at least one DICER1 pathogenic variant. Here, we characterized nine pituitary samples, including three fresh frozen PitBs, three normal fetal pituitary glands and three normal postnatal pituitary glands using small-RNA-Seq, RNA-Seq, methylation profiling, whole genome sequencing and Nanostring® miRNA analyses; an extended series of 21 pituitary samples was used for validation purposes. These analyses demonstrated that DICER1 RNase IIIb hotspot mutations in PitBs induced improper processing of miRNA precursors, resulting in aberrant 5p-derived miRNA products and a skewed distribution of miRNAs favoring mature 3p over 5p miRNAs. This led to dysregulation of hundreds of 5p and 3p miRNAs and concomitant dysregulation of numerous mRNA targets. Gene expression analysis revealed PRAME as the most significantly upregulated gene (500-fold increase). PRAME is a member of the Retinoic Acid Receptor (RAR) signaling pathway and in PitBs, the RAR, WNT and NOTCH pathways are dysregulated. Cancer Hallmarks analysis showed that PI3K pathway is activated in the tumors. Whole genome sequencing demonstrated a quiet genome with very few somatic alterations. The comparison of methylation profiles to publicly available data from ~ 3000 other central nervous system tumors revealed that PitBs have a distinct methylation profile compared to all other tumors, including pituitary adenomas. In conclusion, this comprehensive characterization of DICER1-related PitB revealed key molecular underpinnings of PitB and identified pathways that could potentially be exploited in the treatment of this tumor.

SDHx and Non-Chromaffin Tumors: A Mediastinal Germ Cell Tumor Occurring in a Young Man with Germline SDHB Mutation

Background: Mutations in genes encoding one of the subunits of succinate dehydrogenase (SDH) are involved in pheochromocytoma (PHEO) and paraganglioma (PGL) development. Over the last few years, such mutations have also been associated with non-chromaffin tumors. However, immunohistochemistry (IHC) on the tumor tissue and a study on the loss of heterozygosity (LOH) aimed at demonstrating the pathogenic role of SDHx genes have only been employed in a few cases. Case report: We describe the case of a 19-year-old Caucasian man with a germline SDHB mutation, who presented with acne vulgaris resistant to medical treatment. His follow-up for chromaffin tumors was negative, while hormonal tests revealed suppressed gonadotropins with testosterone in the upper range of normality and elevated β-human chorionic gonadotropin (β-hCG). At the whole-body enhanced CT scan, a mediastinal lesion suggestive of a germ cell tumor (GCT) was detected. ¹⁸FDG-PET (fluorodeoxyglucose-positron emission tomography) imaging showed low glucose metabolism at the mediastinal site. Surgical removal of the mass was uneventful. Pathology confirmed the diagnosis of GCT consisting of cystic teratoma (95%) and seminoma (5%). IHC for SDHB showed normal protein expression, and genetic analysis of the tumor tissue revealed the absence of SDHB LOH. Normalization of the hormonal tests and acne attenuation were achieved after surgery. Conclusion: We report an incidental association of a germinal SDHB mutation and mediastinal GCT in a young Caucasian man. Our paper highlights the importance of IHC and genetic analysis in confirming the etiologic role of SDHx genes in nonchromaffin tumors, thus excluding incidental associations.

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.

Clinical and Molecular Update on Genetic Causes of Pituitary Adenomas

Pituitary adenomas are benign tumors with variable functional characteristics that can have a significant impact on patients. The majority arise sporadically, but an inherited genetic susceptibility is increasingly being recognized. Recent advances in genetics have widened the scope of our understanding of pituitary tumorigenesis. The clinical and genetic characteristics of pituitary adenomas that develop in the setting of germline-mosaic and somatic GNAS mutations (McCune-Albright syndrome and sporadic acromegaly), germline MEN1 mutations (multiple endocrine neoplasia type 1), and germline PRKAR1A mutations (Carney complex) have been well described. Non-syndromic familial cases of isolated pituitary tumors can occur as familial isolated pituitary adenomas (FIPA); mutations/deletions of the AIP gene have been found in a minority of these. Genetic alterations in GPR101 have been identified recently as causing X-linked acro-gigantism (X-LAG) leading to very early-onset pediatric gigantism. Associations of pituitary adenomas with other tumors have been described in syndromes like multiple endocrine neoplasia type 4, pheochromocytoma-paraganglioma with pituitary adenoma association (3PAs) syndrome and some of their genetic causes have been elucidated. The genetic etiologies of a significant proportions of sporadic corticotropinomas have recently been identified with the discovery of USP8 and USP48 mutations. The elucidation of genetic and molecular pathophysiology in pituitary adenomas is a key factor for better patient management and effective follow-up.

3P association (3PAs): Pituitary adenoma and pheochromocytoma/paraganglioma. A heterogeneous clinical syndrome associated with different gene mutations

BACKGROUND

Pituitary adenomas (PA) associated with pheochromocytomas/paragangliomas (Pheo/PGL), also known as "the three P association" or "3PAs" could be the results of coincidence, but new evidence supports a common pathogenic mechanism in some patients. Our aim is to report the clinical data, surgical outcome, genetic findings of a large case series and review the current knowledge on this topic.

METHODS AND RESULTS

In a retrospective multicentre study, we compiled 10 patients with PAs (6 new unreported cases). Six patients were female with mean age of 51.6 ± 18.0 years. PA were: 6 acromegaly, 3 prolactinoma and 1 non-functioning PA (NFPA). Among the Pheo/PGL, 7 patients had a single tumour (4 Pheo and 3 PGL) and 3 patients had multiple or bilateral disease (2 PGL and 1 Pheo). Patients with GH-secreting PA and NFPA underwent surgery, while patients with prolactinoma received medical treatment (one patient required surgery). Unilateral adrenalectomy was carried out in all single Pheo and a bilateral procedure was performed in the patient with bilateral tumour. A single tumour was resected in two patients with multiple PGL. We found 3 germline pathogenic mutations: 2 in SDHB (c.166-170delCCTCA and a gross deletion involving exon 1) and 1 SDHD (p.P81L exon 3). Two variants of uncertain significance: 1 in MEN1 (c.1618C > T; p.Pro540Ser) and 1 in RET (c.2556C > G, p.Ile852Met), and finally a RET^M918T somatic mutation in a Pheo tissue.

CONCLUSION

We actively suggest considering the possibility of hereditary disease in all cases with 3PA and performing a complete genetic study.

Pheochromocytoma, paragangliomas, and pituitary adenoma: An unusual association in a patient with an SDHD mutation. Case report

RATIONALE

Pituitary adenomas and paragangliomas are both rare endocrine diseases. Paragangliomas (PGL)/pheochromocytomas (PHEO) are part of an inherited syndrome in about 30% to 40% of cases. Among familial cases, mutations of the succinate dehydrogenase (SDH) subunit genes (succinate dehydrogenase subunit [SDH]B, SDHC, SDHD, succinate dehydrogenase subunit AF2 [SDHAF2] , and SDHA) are the most common cause.

PATIENT CONCERNS

We here report a 31-year-old patient with a known SDHD mutation whose disease has been revealed by a left PHEO during childhood and who presented at age 29 years a large paraganglioma of the right jugular foramen, a concomitant PHEO of the left adrenal and 2 retroperitoneal paragangliomas. A pituitary incidentaloma was found during investigations on a fluorodeoxyglucose (FDG)-positron emission tomography (PET) (FDG-PET).

DIAGNOSIS

A pituitary magnetic resonance imaging (MRI) confirmed the presence of a 14 mm pituitary macroadenoma. The pituitary function was normal except for hypogonadotropic hypogonadism. On examination of the fundus, a diagnosis of Pseudo Foster-Kennedy syndrome was made due to a venous compression of the right jugular vein caused by the paraganglioma (PGL). The pituitary adenoma was not compressive to the optic chiasm.

INTERVENTIONS

A treatment with acetazolamide was started in order to improve intracranial hypertension. The patient couldn't benefit of a surgical approach for the paraganglioma of the right jugular foramen; the patient has been treated with stereotactic radiosurgery (Gamma Knife).

OUTCOMES

The most recent MRI revealed that the right jugular foramen PGL is stable and the latest visual assessment demonstrated stability despite a recent reduction in acetazolamide dosage. A surveillance by MRI of the pituitary adenoma has been planned.

LESSONS

The association of a pituitary adenoma to paragangliomas within a same patient is very uncommon and raises the question of related physiopathological mechanisms.

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.

The loss of succinate dehydrogenase B expression is frequently identified in hemangioblastoma of the central nervous system

Succinate dehydrogenase (SDH) is a mitochondrial enzyme that plays an important role in both the Krebs cycle and the electron transport chain. SDH inactivation is associated with tumorigenesis in certain types of tumor. SDH consists of subunits A, B, C and D (SDHA, SDHB, SDHC, and SDHD, respectively). Immunohistochemistry for SDHB is a reliable method for detecting the inactivation of SDH by mutations in SDHA, SDHB, SDHC, SDHD and SDH complex assembly factor 2 (SDHAF2) genes with high sensitivity and specificity. SDHB immunohistochemistry has been used to examine the inactivation of SDH in various types of tumors. However, data on central nervous system (CNS) tumors are very limited. In the present study, we investigated the loss of SDHB immunoexpression in 90 cases of CNS tumors. Among the 90 cases of CNS tumors, only three cases of hemangioblastoma showed loss of SDHB immunoexpression. We further investigated SDHB immunoexpression in 35 cases of hemangioblastoma and found that 28 (80%) showed either negative or weak-diffuse pattern of SDHB immunoexpression, which suggests the inactivation of SDH. Our results suggest that SDH inactivation may represent an alternative pathway in the tumorigenesis of hemangioblastoma.

The Role of Immunohistochemistry and Molecular Analysis of Succinate Dehydrogenase in the Diagnosis of Endocrine and Non-Endocrine Tumors and Related Syndromes

Succinate dehydrogenase (SDH) is an enzyme complex, composed of four protein subunits, that plays a role in both the citric acid cycle and the electron transport chain. The genes for SDHA, SDHB, SDHC, and SDHD are located in the nuclear DNA, and mutations in these genes have initially been described in paragangliomas (PGL) and pheochromocytomas (PCC), which are relatively rare tumors derived from the autonomic nervous system and the adrenal medulla, respectively. Patients with SDH mutations, that are almost exclusively in the germline, are frequently affected by multiple PGL and/or PCC. In addition, other tumors have been associated with SDH mutations as well, including gastrointestinal stromal tumors, SDH-deficient renal cell carcinoma, and pituitary adenomas. Immunohistochemistry for SDHB and SDHA has been shown to be a valuable additional tool in the histopathological analysis of these tumors, and can be considered as a surrogate marker for molecular analysis. In addition, SDHB immunohistochemistry is relevant in the decision-making whether a genetic sequence variant represents a pathogenic mutation or not. In this review, we highlight the current knowledge of the physiologic and pathologic role of the SDH enzyme complex and its involvement in endocrine and non-endocrine tumors, with an emphasis on the applicability of immunohistochemistry.

Familial paraganglioma due to a novel SDHB mutation: familial phenotypic heterogeneity and a potentially novel manifestation

Non-paraganglioma (PGL) tumors are rare manifestations of familial PGL syndromes. Primary hyperparathyroidism has not been described in PGL syndromes. We present a 36-year-old man with a history of right carotid body tumor at 24 years and an abdominal PGL at 31 years of age. At 35 years, he developed hypercalcemia (serum Ca 2.65–2.72 mmol/l), and high parathyroid hormone of 92–131 ng/l (normal range, 15–65) and a Tc99 Sestamibi scan showed a single parathyroid adenoma which was confirmed on histopathological examination of parathyroidectomy. Recently, he was diagnosed with a left glomus jugulare which has not been operated on yet. His family history is strongly positive for PGLs. Genetic testing revealed a novel SDHB mutation (p.K137E) but the phenotype and penetrance were variable in different family members.

[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.