Carney triad can be (rarely) associated with germline succinate dehydrogenase defects

Identifying and managing rare subtypes of gastrointestinal stromal tumors

INTRODUCTION

A subset of gastrointestinal stromal tumors (GISTs) lacks the common mutations in KIT/PDGFRa genes. This is a rare and heterogeneous group of challenging GISTs due to their diversity and absence of sensitivity to the tyrosine kinase inhibitor (TKI) imatinib.

AREAS COVERED

In this manscript, we review the pathogenesis, natural history, diagnostic features and management of KIT/PDGFRa wild-type (WT) GISTs, including SDH-deficient GISTs, GISTs with mutations in the RAS/RAF pathway, and quadruple WT GISTs which lack mutations in either KIT/PDGFRa and SDH genes or components of the RAS/RAF pathway, and syndromic GISTs as well as GISTs with rare KIT/PDGFRa mutations.

EXPERT OPINION

Patients should be managed in reference centers. There has been progress in the understanding of the biology of these GISTs, and promising therapeutic targets have been identified. In SDH-deficient GISTs, the TKI olverembatinib has shown encouraging clinical activity but requires further clinical validation, while the HIF2a inhibitor bezultifan and temozolomide alone or in combination with the death receptor agonist 5 are under clinical investigation. Targeting the RAS/RAF pathway in RAS/RAF-mutated GISTs warrants evaluation in clinical trials. Rare molecular alterations in quadruple WT GISTs require investigation for their oncogenic potential. Collaborative research and patient advocacy is critical for these extremely rare tumors.

Case report: A safeguard in the sea of variants of uncertain significance: a case study on child with high risk neuroblastoma and acute myeloid leukemia

The increased availability of genetic technologies has significantly improved the detection of novel germline variants conferring a predisposition to tumor development in patients with malignant disease. The identification of variants of uncertain significance (VUS) represents a challenge for the clinician, leading to difficulties in decision-making regarding medical management, the surveillance program, and genetic counseling. Moreover, it can generate confusion and anxiety for patients and their family members. Herein, we report a 5-year-old girl carrying a VUS in the Succinate Dehydrogenase Complex Subunit C (SHDC) gene who had been previously treated for high-risk neuroblastoma and subsequently followed by the development of secondary acute myeloid leukemia. In this context, we describe how functional studies can provide additional insight on gene function determining whether the variant interferes with normal protein function or stability.

[Mesenchymal tumors and tumor-like lesions of the gastrointestinal tract: an overview]

Mesenchymal tumors and tumor-like lesions of the gastrointestinal (GI) tract are uncommon. They vary from reactive tumefactive lesions and benign neoplasms to highly aggressive sarcomas. Among them, GI stromal tumors (GISTs) are most common, followed, with less frequency, by smooth muscle and neurogenic tumors. The major challenge resides in correctly identifying GISTs and providing a comprehensive report (including risk assessment and genotyping) that represents the basis for an optimized surgical-oncological treatment and/or adjuvant therapy. On the other hand, the challenge of benign lesions is to find a good name (well understandable and reproducible diagnostic term) that helps avoid diagnostic ambiguity and prognostic uncertainty so that overprognostication and overtreatment can be prevented. Moreover, several recently described genetically defined benign and malignant entities need be correctly diagnosed due to their special "targeted" therapeutic options and to further characterize their clinicopathological and biological properties in the future. These recent entities include aggressive epithelioid inflammatory myofibroblastic sarcoma (ALK-RANBP2-driven), malignant gastrointestinal neuroectodermal tumor (EWSR1-ATF1/CREB-related), NTRK-rearranged neoplasms, and, most recently, colorectal NUTM1-rearranged sarcomas. This review highlights the major clinicopathological features of gastrointestinal mesenchymal lesions in light of recent developments.

Carney's triad in an adult male from a tertiary care center in India: a case report

BACKGROUND

Carney's triad is a rare syndrome comprising gastrointestinal stromal tumor, extra-adrenal paraganglioma, and pulmonary chondroma along with newer additions of adrenal adenoma and esophageal leiomyoma. The triad is completely manifest in only 25-30% cases, with most patients presenting with two out of three parts of the syndrome. Wild-type succinate-dehydrogenase-deficient gastric gastrointestinal stromal tumor forms the most common component of Carney's triad and is usually multicentric and multifocal. It usually demonstrates indolent behavior and resistance to imatinib; hence, the management remains predominantly surgical. Pulmonary chondromas are commonly unilateral and multiple with slow-growing nature, which allows for conservative management. Adrenocortical adenomas are found in 20% of patients and are usually detected as incidentalomas.

CASE PRESENTATION

A 49-year-old Asian male presented with upper gastrointestinal bleed and was diagnosed with multiple gastric succinate-dehydrogenase-deficient gastrointestinal stromal tumors. On evaluation, he was found to have left pulmonary chondroma and non-secretory adrenal adenoma, thus completing the Carney's triad. He underwent surgery with sleeve gastrectomy and excision of the antral tumor nodule, while the adrenal and pulmonary tumors have been under close follow-up.

CONCLUSION

Literature regarding Carney's triad is scarce, especially from the Indian setting. Our report aims to highlight the various manifestations of this syndrome with emphasis on management of wild-type succinate-dehydrogenase-deficient gastrointestinal stromal tumor. Radical gastric surgeries do not offer a survival advantage in this condition; hence, more conservative modalities of resection can be adopted.

Approach to the Patient With Adrenal Incidentaloma

Adrenal tumors are commonly discovered incidentally on cross-sectional abdominal imaging performed for reasons other than adrenal mass. Incidence of adrenal tumors increased 10-fold in the past 2 decades, with most diagnosed in older adults. In any patient with a newly discovered adrenal mass, determining whether the adrenal mass is malignant and whether it is hormonally active is equally important to guide the best management. Malignancy is diagnosed in 5% to 8% of patients with adrenal tumors, with a higher risk in young patients, if history of extra-adrenal malignancy, in those with large adrenal tumors with indeterminate imaging characteristics, and in bilateral adrenal tumors. Although overt hormone excess is uncommon in adrenal incidentalomas, mild autonomous cortisol secretion can be diagnosed in up to 30% to 50% of patients. Because autonomous cortisol secretion is associated with increased cardiovascular morbidity and metabolic abnormalities, all patients with adrenal incidentalomas require work up with dexamethasone suppression test. Management of adrenal tumors varies based on etiology, associated comorbidities, and patient's preference. This article reviews the current evidence on the diagnosis and evaluation of patients with adrenal mass and focuses on management of the most common etiologies of adrenal incidentalomas.

SDHC Methylation Pattern in Patients With Carney Triad

Carney triad is a multitumor syndrome affecting almost exclusively young women in a nonfamilial setting, which manifests by multifocal gastric gastrointestinal stromal tumors, paragangliomas, and pulmonary chondroma. The Carney triad-associated tumors are characterized by a deficiency of the mitochondrial succinate dehydrogenase enzymatic complex. Recently, it has been observed that the deficiency results from epigenetic silencing of the SDHC gene by its promoter hypermethylation. To elucidate anatomic distribution of SDHC promoter methylation in Carney triad patients and thus to shed some light on the possible natural development of this epigenetic change, both neoplastic and available non-neoplastic tissues of 3 patients with Carney triad were tested for hypermethylation at the SDHC promoter site. SDHC promoter hypermethylation was proven in all tumors studied. Lack of SDHC epigenetic silencing in the non-neoplastic lymphoid and duodenal tissue (ie, tissues not involved in the development of Carney triad-associated tumors) together with the finding of SDHC promoter hypermethylation in the non-neoplastic gastric wall favors the hypothesis of postzygotic somatic mosaicism as the biological background of Carney triad; it also offers an explanation of the multifocality of gastrointestinal stromal tumors of the stomach occurring in this scenario as well. However, the precise mechanism responsible for the peculiar organ-specific distribution of Carney triad-associated tumors is still unknown.

What Have We Learned from Molecular Biology of Paragangliomas and Pheochromocytomas?

Recent advances in molecular genetics and genomics have led to increased understanding of the aetiopathogenesis of pheochromocytomas and paragangliomas (PPGLs). Thus, pan-genomic studies now provide a comprehensive integrated genomic analysis of PPGLs into distinct molecularly defined subtypes concordant with tumour genotypes. In addition, new embryological discoveries have refined the concept of how normal paraganglia develop, potentially establishing a developmental basis for genotype-phenotype correlations for PPGLs. The challenge for modern pathology is to translate these scientific discoveries into routine practice, which will be based largely on histopathology for the foreseeable future. Here, we review recent progress concerning the cell of origin and molecular pathogenesis of PPGLs, including pathogenetic mechanisms, genetic susceptibility and molecular classification. The current roles and tools of pathologists are considered from a histopathological perspective, including differential diagnoses, genotype-phenotype correlations and the use of immunohistochemistry in identifying hereditary predisposition and validating genetic variants of unknown significance. Current and potential molecular prognosticators are also presented with the hope that predictive molecular biomarkers will be integrated into risk stratification scoring systems to assess the metastatic potential of these intriguing neoplasms and identify potential drug targets.

New insights into the clinical management of advanced gastrointestinal stromal tumors

INTRODUCTION

90% of gastrointestinal stromal tumors (GISTs) harbor an activating mutation in the KIT or PDGFRα oncogene, and these are known to confer imatinib sensitivity.

AREAS COVERED

The author reviews the data regarding the current management of GIST, mechanisms of resistance to imatinib, and new drugs currently in clinical development and provides his unique perspectives on the subject matter.

EXPERT OPINION

Several studies have shown that the response to imatinib in GIST patients mainly depends on the mutational status of KIT or PDGFRα. Moreover, most, if not all, patients treated with imatinib for advanced GIST will develop a secondary progressive disease under the treatment. In most cases, such progressions are the result of acquired resistance due to the occurrence of secondary c-KIT mutations, especially in GISTs with primary exon 11 mutations. Sunitinib and regorafenib are inhibitors of multiple tyrosine kinases, including KIT, PDGFRα, PDGFRβ, and VEGFRs, and are approved for the management of imatinib- and imatinib/sunitinib-refractory GIST patients, respectively. Clearly, better knowledge of the molecular mechanisms underlying the resistance to imatinib as well as the development of a new class of broad-spectrum tyrosine kinase inhibitors such as avapritinib and ripretinib will provide new individualized therapeutic strategies for GIST patients.

Therapeutic Potential of PI3K/AKT/mTOR Pathway in Gastrointestinal Stromal Tumors: Rationale and Progress

Gastrointestinal stromal tumor (GIST) originates from interstitial cells of Cajal (ICCs) in the myenteric plexus of the gastrointestinal tract. Most GISTs arise due to mutations of KIT and PDGFRA gene activation, encoding the receptor tyrosine kinase (RTK). The clinical use of the RTK inhibitor imatinib has significantly improved the management of GIST patients; however, imatinib resistance remains a challenge. The phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathway is a critical survival pathway for cell proliferation, apoptosis, autophagy and translation in neoplasms. Constitutive autophosphorylation of RTKs has an impact on the activation of the PI3K/AKT/mTOR pathway. In several preclinical and early-stage clinical trials PI3K/AKT/mTOR signaling inhibition has been considered as a promising targeted therapy strategy for GISTs. Various inhibitory drugs targeting different parts of the PI3K/AKT/mTOR pathway are currently being investigated in phase I and phase II clinical trials. This review highlights the progress for PI3K/AKT/mTOR-dependent mechanisms in GISTs, and explores the relationship between mTOR downstream signals, in particular, eukaryotic initiation factors (eIFs) and the development of GISTs, which may be instrumental for identifying novel therapeutic targets.

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.

Evolutionarily conserved susceptibility of the mitochondrial respiratory chain to SDHI pesticides and its consequence on the impact of SDHIs on human cultured cells

Succinate dehydrogenase (SDH) inhibitors (SDHIs) are used worldwide to limit the proliferation of molds on plants and plant products. However, as SDH, also known as respiratory chain (RC) complex II, is a universal component of mitochondria from living organisms, highly conserved through evolution, the specificity of these inhibitors toward fungi warrants investigation. We first establish that the human, honeybee, earthworm and fungal SDHs are all sensitive to the eight SDHIs tested, albeit with varying IC₅₀ values, generally in the micromolar range. In addition to SDH, we observed that five of the SDHIs, mostly from the latest generation, inhibit the activity of RC complex III. Finally, we show that the provision of glucose ad libitum in the cell culture medium, while simultaneously providing sufficient ATP and reducing power for antioxidant enzymes through glycolysis, allows the growth of RC-deficient cells, fully masking the deleterious effect of SDHIs. As a result, when glutamine is the major carbon source, the presence of SDHIs leads to time-dependent cell death. This process is significantly accelerated in fibroblasts derived from patients with neurological or neurodegenerative diseases due to RC impairment (encephalopathy originating from a partial SDH defect) and/or hypersensitivity to oxidative insults (Friedreich ataxia, familial Alzheimer’s disease).

Germline c.1A>C heterozygous pathogenic variant in SDHA reported for the first time in a young adult with a gastric gastrointestinal stromal tumour (GIST): a case report

Background

Gastrointestinal stromal tumors (GISTs) represent the most frequent mesenchymal tumor of the gastrointestinal tract. Less than 5% of them seem to be hereditary, being succinate dehydrogenase complex (SDHx) deficient disorders and neurofibromatosis type 1 the more related inherited conditions. Wild type (WT) KIT and PDGFRα GISTs constitute a clue for a hypothetical underlying germline condition.

Case presentation

We present a case of a 20 years old female diagnosed of a gastric WT GIST who developed hepatic metastases during her clinical course. No significant or typical phenotypic features suggestive of a specific syndrome were detected by physical examination. Also, her family history seemed to be irrelevant, since no other cases of GISTs, paragangliomas or pheochromocytomas were reported. Her paternal grandfather died as a consequence of a pituitary adenoma. In light of the age of tumor presentation and somatic features of gastric GIST, we performed genetic testing of SDHx genes. Analysis obtained from peripheral blood sample revealed the presence, in heterozygous state, of the c.1A > C; p.(Met1?) pathogenic variant in the SDHA.

Conclusions

To the best of our knowledge, this is the first published report in which the c.1A > C; p.(Met1?) pathogenic variant in the SDHA is associated with a GIST. SDHA pathogenic variants increase the risk of paraganglioma, pheochromocytoma, GIST, pituitary adenoma and renal cancer in an autosomal dominant inherited condition named paraganglioma syndrome type 5. The absence of family history of tumors in SDHA pathogenic variants carriers could be related to its low penetrance. All patients diagnosed with WT GISTs should be referred to a hereditary cancer genetic counseling unit regardless of the age at presentation or the absence of a suspicious family history.

Pheochromocytoma and paraganglioma: implications of germline mutation investigation for treatment, screening, and surveillance

OBJECTIVE

Paraganglioma (PGL) and pheochromocytoma (PCC) are rare neuroendocrine tumors that were considered to be predominantly sporadic. However, with the identification of novel susceptibility genes over the last decade, it is currently estimated that up to 40% of cases can occur in the context of a hereditary syndrome. We aimed to characterize PGL/PCC families to exemplify the different scenarios in which hereditary syndromes can be suspected and to emphasize the importance for patients and their families of making an opportune genetic diagnosis.

MATERIALS AND METHODS

Retrospective analysis of patients diagnosed with PGL/PCC. Germline mutations were studied using next-generation sequencing panels including SDHA, SDHB, SDHC and SDHD. Clinical data were collected from clinical records, and all patients received genetic counseling.

RESULTS

We describe 4 families with PGL/PCC and germline mutations in SDH complex genes. 2 families have SDHB mutations and 2 SDHD mutations. The clinical presentation of the patients and their families was heterogeneous, with some being atypical according to the literature.

CONCLUSIONS

PGL/PCC are more commonly associated with a germline mutation than any other cancer type, therefore, all individuals with these types of tumors should undergo genetic risk evaluation. NGS multigene panel testing is a cost-effective approach given the overlapping phenotypes. Individuals with germline mutations associated with PGL/PCC should undergo lifelong clinical, biochemical and imaging surveillance and their families should undergo genetic counseling. For all these reasons, it is critical that all medical staff can suspect and diagnose these inherited cancer predisposition syndromes.

SDHC epi-mutation testing in gastrointestinal stromal tumours and related tumours in clinical practice

The enzyme succinate dehydrogenase (SDH) functions in the citric acid cycle and loss of function predisposes to the development of phaeochromocytoma/paraganglioma (PPGL), wild type gastrointestinal stromal tumour (wtGIST) and renal cell carcinoma. SDH-deficient tumours are most commonly associated with a germline SDH subunit gene (SDHA/B/C/D) mutation but can also be associated with epigenetic silencing of the SDHC gene. However, clinical diagnostic testing for an SDHC epimutation is not widely available. The objective of this study was to investigate the indications for and the optimum diagnostic pathways for the detection of SDHC epimutations in clinical practice. SDHC promoter methylation analysis of 32 paraffin embedded tumours (including 15 GIST and 17 PPGL) was performed using a pyrosequencing technique and correlated with SDHC gene expression. SDHC promoter methylation was identified in 6 (18.7%) tumours. All 6 SDHC epimutation cases presented with SDH deficient wtGIST and 3/6 cases had multiple primary tumours. No case of constitutional SDHC promoter hypermethylation was detected. Whole genome sequencing of germline DNA from three wtGIST cases with an SDHC epimutation, did not reveal any causative sequence anomalies. Herein, we recommend a diagnostic workflow for the detection of an SDHC epimutation in a service setting.

Clinical Diagnosis of Gastrointestinal Stromal Tumor (GIST): From the Molecular Genetic Point of View

Gastrointestinal stromal tumors (GISTs) originating from the interstitial cells of Cajal are mesenchymal tumors of the gastrointestinal tract and have been found to harbor c-KIT mutations and KIT (CD117) expression since 1998. Later, PDGFRA mutations, SDH alterations, and other drive mutations were identified in GISTs. In addition, more and more protein markers such as DOG1, PKCθ were found to be expressed in GISTs which might help clinicians diagnose CD117-negative GISTs. Therefore, we plan to comprehensively review the molecular markers and genetics of GISTs and provide clinicians useful information in diagnostic and therapeutic strategies of GISTs. Twenty years after the discovery of KIT in GISTs, the diagnosis of GISTs became much more accurate by using immunohistochemical (IHC) panel (CD117/DOG1) and molecular analysis (KIT/PDGFRA), both of which constitute the gold standard of diagnosis in GISTs. The accurately molecular diagnosis of GISTs guides clinicians to precision medicine and provides optimal treatment for the patients with GISTs. Successful treatment in GISTs prolongs the survival of GIST patients and causes GISTs to become a chronic disease. In the future, the development of effective treatment for GISTs resistant to imatinib/sunitinib/regorafenib and KIT/PDGFRA-WT GISTs will be the challenge for GISTs.

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.

Preferential MGMT methylation could predispose a subset of KIT/PDGFRA-WT GISTs, including SDH-deficient ones, to respond to alkylating agents

BACKGROUND

Succinate dehydrogenase (SDH)-deficient gastrointestinal stromal tumors (GISTs) constitute a small KIT/PDGFRA-WT GIST subgroup featuring DNA methylation which, although pervasive, appears nevertheless not randomly distributed. Although often indolent, these tumors are mostly chemorefractory in aggressive cases. Promoter methylation-induced O⁶-methylguanine DNA methyltransferase (MGMT) inactivation improves the efficacy of alkylating agents in gliomas, colorectal cancer and diffuse large B cell lymphoma. MGMT methylation has been found in some GISTs, without determining SDH status. Thirty-six GISTs were enrolled in past sarcoma trials testing alkylating agents, with negative results. Nevertheless, a possible effect on MGMT-methylated GISTs could have escaped detection, since tested GISTs were neither selected by genotype nor investigated for SDH; MGMT was studied in two cases only, revealing baseline activity; these trials were performed prior to the adoption of Choi criteria, the most sensitive for detecting GIST responses to therapy. Under these circumstances, we investigated whether MGMT methylation is preferentially found in SDH-deficient cases (identified by SDHB immunohistochemistry) by analyzing 48 pathogenetically heterogeneous GISTs by methylation-specific PCR, as a premise for possible investigations on the use of alkylating drugs in these tumors.

RESULTS

Nine GISTs of our series were SDH-deficient, revealing significantly enriched in MGMT-methylated cases (6/9-67%-, vs. 6/39-15%- of SDH-proficient GISTs; p = 0.004). The pathogenetically heterogeneous KIT/PDGFRA-WT GISTs were also significantly MGMT-methylated (11/24-46%-, vs. 1/24-4%- of KIT/PDGFRA-mutant cases, p = 0.002).

CONCLUSIONS

A subset of KIT/PDGFRA-WT GISTs, including their largest pathogenetically characterized subgroup (i.e., SDH-deficient ones), is preferentially MGMT-methylated. This finding could foster a reappraisal of alkylating agents for treating malignant cases occurring among these overall chemorefractory tumors.

An update on adrenal endocrinology: significant discoveries in the last 10 years and where the field is heading in the next decade

The last 10 years have produced an amazing number of significant discoveries in the field of adrenal endocrinology. The development of the adrenal gland was linked to specific molecules. Cortisol-producing lesions were associated mostly with defects of the cyclic AMP (cAMP) signaling pathway, whereas aldosterone-producing lesions were found to be the result of defects in aldosterone biosynthesis or the potassium channel KCNJ5 and related molecules. Macronodular adrenal hyperplasia was linked to ARMC5 defects and new genes were found to be involved in adrenocortical cancer (ACC). The succinate dehydrogenase (SDH) enzyme was proven to be the most important molecular pathway involved in pheochromocytomas, along with several other genes. Adrenomedullary tumors are now largely molecularly elucidated. Unfortunately, most of these important discoveries have yet to produce new therapeutic tools for our patients with adrenal diseases: ACC in its advanced stages remains largely an untreatable disorder and malignant pheochromocytomas are equally hard to treat. Thus, the challenge for the next 10 years is to translate the important discoveries of the previous decade into substantial advances in the treatment of adrenal disorders and tumors.

65 YEARS OF THE DOUBLE HELIX: Endocrine tumour syndromes in children and adolescents

As medicine is poised to be transformed by incorporating genetic data in its daily practice, it is essential that clinicians familiarise themselves with the information that is now available from more than 50 years of genetic discoveries that continue unabated and increase by the day. Endocrinology has always stood at the forefront of what is called today 'precision medicine': genetic disorders of the pituitary and the adrenal glands were among the first to be molecularly elucidated in the 1980s. The discovery of two endocrine-related genes, GNAS and RET, both identified in the late 1980s, contributed greatly in the understanding of cancer and its progression. The use of RET mutation testing for the management of medullary thyroid cancer was among the first and one of most successful applications of genetics in informing clinical decisions in an individualised manner, in this case by preventing cancer or guiding the choice of tyrosine kinase inhibitors in cancer treatment. New information emerges every day in the genetics or system biology of endocrine disorders. This review goes over most of these discoveries and the known endocrine tumour syndromes. We cover key genetic developments for each disease and provide information that can be used by the clinician in daily practice.

Succinate dehydrogenase (SDH) deficiency, Carney triad and the epigenome

In this report, we review the relationship between succinate dehydrogenase (SDH) deficiency and the epigenome, especially with regards to two clinical conditions. Carney triad (CT) is a very rare disease with synchronous or metachronous occurrence of at least three different tumor entities; gastric gastrointestinal stromal tumor (GIST), paraganglioma (PGL), and pulmonary chondroma. This condition affects mostly females and it is never inherited. Another disease that shares two of the tumor components of CT, namely GIST and PGL is the Carney-Stratakis syndrome (CSS) or dyad. CSS affects both genders during childhood and adolescence. We review herein the main clinical features and molecular mechanisms behind those two syndromes that share quite a bit of similarities, but one is non-hereditary (CT) whereas the other shows an autosomal-dominant, with incomplete penetrance, inheritance pattern (CSS). Both CT and CSS are caused by the deficiency of the succinate dehydrogenase (SDH) enzyme. The key difference between the two syndromes is the molecular mechanism that causes the SDH deficiency. Most cases of CT show down-regulation of SDH through site-specific hyper-methylation of the SDHC gene, whereas CSS cases carry inactivating germline mutations within one of the genes coding for the SDH subunits A, B, C, or D (SDHA, SDHB, SDHC, and SDHD). There is only partial overlap between the two conditions (there are a few patients with CT that have SDH subunit mutations) but both lead to increased methylation of the entire genome in the tumors associated with them. Other tumors (outside CT and CSS) that have SDH deficiency are associated with increased methylation of the entire genome, but only in CT there is site-specific methylation of the SDHC gene. These findings have implications for diagnostics and the treatment of patients with these, often metastatic tumors.

The role of metabolic enzymes in mesenchymal tumors and tumor syndromes: genetics, pathology, and molecular mechanisms

The discovery of mutations in genes encoding the metabolic enzymes isocitrate dehydrogenase (IDH), succinate dehydrogenase (SDH), and fumarate hydratase (FH) has expanded our understanding not only of altered metabolic pathways but also epigenetic dysregulation in cancer. IDH1/2 mutations occur in enchondromas and chondrosarcomas in patients with the non-hereditary enchondromatosis syndromes Ollier disease and Maffucci syndrome and in sporadic tumors. IDH1/2 mutations result in excess production of the oncometabolite (D)-2-hydroxyglutarate. In contrast, SDH and FH act as tumor suppressors and genomic inactivation results in succinate and fumarate accumulation, respectively. SDH deficiency may result from germline SDHA, SDHB, SDHC, or SDHD mutations and is found in autosomal-dominant familial paraganglioma/pheochromocytoma and Carney-Stratakis syndrome, describing the combination of paraganglioma and gastrointestinal stromal tumor (GIST). In contrast, patients with the non-hereditary Carney triad, including paraganglioma, GIST, and pulmonary chondroma, usually lack germline SDH mutations and instead show epigenetic SDH complex inactivation through SDHC promoter methylation. Inactivating FH germline mutations are found in patients with hereditary leiomyomatosis and renal cell cancer (HLRCC) syndrome comprising benign cutaneous/uterine leiomyomas and renal cell carcinoma. Mutant IDH, SDH, and FH share common inhibition of α-ketoglutarate-dependent oxygenases such as the TET family of 5-methylcytosine hydroxylases preventing DNA demethylation, and Jumonji domain histone demethylases increasing histone methylation, which together inhibit cell differentiation. Ongoing studies aim to better characterize these complex alterations in cancer, the different clinical phenotypes, and variable penetrance of inherited and sporadic cancer predisposition syndromes. A better understanding of the roles of metabolic enzymes in cancer may foster the development of therapies that specifically target functional alterations in tumor cells in the future. Here, the physiologic functions of these metabolic enzymes, the mutational spectrum, and associated functional alterations will be discussed, with a focus on mesenchymal tumor predisposition syndromes.

Classification of gastrointestinal stromal tumor syndromes

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract, thought to derive from neoplastic outgrowth of the interstitial cells of Cajal. Building on recent advances in recognition, classification and diagnosis, the past two decades have seen a changing paradigm with molecular diagnostics and targeted therapies. KIT and PDGFRA mutations account for 85-90% of GIST carcinogenesis. However, the remaining 10-15% of GISTs, which until recently were called KIT/PDGFRA wild-type GISTs, have been found to have one of the several mutations, including in the SDHA, B, C, D, BRAF and NF1 genes. Though most of such GISTs are sporadic, a number of families with high incidence rates of GISTs and other associated clinical manifestations have been reported and found to harbor germline mutations in KIT, PDGFRA, SDH subunits and NF1 The goal of this review is to describe the mutations, clinical manifestations and therapeutic implications of syndromic and inherited GISTs in light of recent studies of their clinicopathologic range and pathogenesis.

Gastrointestinal Stromal Tumors: The GIST of Precision Medicine

The discovery of activated KIT mutations in gastrointestinal (GI) stromal tumors (GISTs) in 1998 triggered a sea change in our understanding of these tumors and has ushered in a new paradigm for the use of molecular genetic diagnostics to guide targeted therapies. KIT and PDGFRA mutations account for 85-90% of GISTs; subsequent genetic studies have led to the identification of mutation/epimutation of additional genes, including the succinate dehydrogenase (SDH) subunit A, B, C, and D genes. This review focuses on integrating findings from clinicopathologic, genetic, and epigenetic studies, which classify GISTs into two distinct clusters: an SDH-competent group and an SDH-deficient group. This development is important since it revolutionizes our current management of affected patients and their relatives, fundamentally, based on the GIST genotype.

When should genetic testing be performed in patients with neuroendocrine tumours?

Neuroendocrine tumours (NETs) are a heterogenous group of tumours arising from neuroendocrine cells in several sites around the body. They include tumours of the gastroenteropancreatic system, phaeochromocytoma and paraganglioma and medullary thyroid cancer. In recent years, it has become increasingly apparent that a number of these tumours arise as a result of germline genetic mutations and are inherited in an autosomal dominant pattern. The number of genes implicated is increasing rapidly. Identifying which patients are likely to have a germline mutation enables clinicians to counsel patients adequately about their future disease risk, and allows for earlier detection of at-risk patients through family screening. The institution of screening and surveillance programmes may in turn lead to a major shift in presentation patterns for some of these tumours. In this review, we examine the features which may lead a clinician to suspect that a patient may have an inherited cause of a NET and we outline which underlying conditions should be suspected. We also discuss what type of screening may be appropriate in a variety of situations.

Imaging of Intrathoracic Paragangliomas

Intrathoracic paragangliomas are uncommon and only represent 1%-2% of paragangliomas. They are most commonly found in mediastinal compartments (aortopulmonary window or posterior mediastinum). Computed tomography, magnetic resonance, and specific nuclear medicine radiotracers are routinely used to characterize these lesions and help exclude other more common conditions. Selective angiography is currently used for preoperative embolization and mapping of the vascular supply before surgical resection, rather than for diagnostic purposes alone.

Paragangliomas of the Head and Neck: An Overview from Diagnosis to Genetics

Paragangliomas (PGL) develop from the parasympathetic system in the head and neck (HN) and arise primarily in four distinct areas: Carotid body, vagal, middle ear, and larynx. Globally, the diagnosis and morphologic features are the same regardless of anatomic site, however the incidence, frequency of genetic alterations/syndromes and differential diagnosis vary. It is now recognized that nearly 40% of all HN PGLs are hereditary, including a significant subset without a known family history. Now pathologists are central to the evaluation for diagnosis and further management of patients with HNPGLs. Specifically, SDHB immunohistochemical evaluation is an excellent screening tool to detect tumors with alterations in the SDH family of genes that represent the majority of hereditary cases in HNPGL. Similarly, SDHB immunohistochemical analysis allows for screening of PGL syndrome associated tumors (gastrointestinal stromal tumor (GIST), renal cell carcinoma (RCC), and pituitary adenomas) that have now been linked by their overlapping gene alterations. Awareness of the spectrum of these syndromes, and their associated tumors, positions the pathologist to augment patient care and surveillance.

Update from the 4th Edition of the World Health Organization Classification of Head and Neck Tumours: Paragangliomas

Updated editions of The World Health Organization Classification of Tumours Pathology & Genetics for both Head and Neck Tumours and Tumours of Endocrine Organs took place in 2016 based on consensus conferences. These editions present unification of concepts in paragangliomas and highlight expanding knowledge of their etiology. There is a major emphasis in the new bluebooks on familial/syndromic paragangliomas, representing ~40% of all head and neck paragangliomas. Ancillary use of immunohistochemical evaluation, specifically of SDHB, allows the pathologist to screen for a large subset of these potentially hereditary cases. In addition, similarly to other neuroendocrine tumors, paragangliomas are now considered to represent a continuum of risk, and are assessed in terms of risk stratification. Tumors with SDHB mutations pose the highest risk for metastasis. There is currently no validated or endorsed histologic grading system. Paragangliomas remain tumors of undetermined biologic potential and should not be termed benign.

Mitochondrial Complex II: At the Crossroads

Mitochondrial complex II (CII), also called succinate dehydrogenase (SDH), is a central purveyor of the reprogramming of metabolic and respiratory adaptation in response to various intrinsic and extrinsic stimuli and abnormalities. In this review we discuss recent findings regarding SDH biogenesis, which requires four known assembly factors, and modulation of its enzymatic activity by acetylation, succinylation, phosphorylation, and proteolysis. We further focus on the emerging role of both genetic and epigenetic aberrations leading to SDH dysfunction associated with various clinical manifestations. This review also covers the recent discovery of the role of SDH in inflammation-linked pathologies. Conceivably, SDH is a potential target for several hard-to-treat conditions, including cancer, that remains to be fully exploited.

Hamartomas from head to toe: an imaging overview

Hamartomas are tumours composed of mesenchymal tissues such as cartilage, fat, connective tissue and smooth muscle and can be found in virtually any organ system. These masses commonly develop sporadically, but are also seen in certain syndromes such as tuberous sclerosis or Carney triad. While their imaging appearance varies depending on the organ they arise from, findings are usually unique and a diagnosis can be confidently made. Radiologists must be aware of the clinical and imaging presentations of these lesions with the particular goal of avoiding unnecessary studies or invasive procedures. Furthermore, knowledge of common syndromic entities is crucial, as the radiologist may be the first to suggest the diagnosis.

Bronchial Paraganglioma with SDHB Deficiency

Though most paragangliomas arise as sporadic tumors, the recent advantages in the genetic screening revealed that about 30 % of paragangliomas are linked to hereditary mutations, such as those involving SDH genes. A 22-year-old woman carrying a left main bronchus tumor underwent surgery in our institution. Her past medical history included a GIST without KIT or PDGFRA mutation. The histological examination revealed a nested proliferation of medium-sized cells expressing neuroendocrine markers (chromogranin A and synaptophysin). The neoplastic cells failed to express SDHB gene product. These findings led us to the final diagnosis of bronchial paraganglioma in the setting of Carney-Stratakis syndrome. Bronchial paragangliomas are exceedingly rare tumors with polymorphous clinical presentation, and usually benign clinical course. Though most paragangliomas are sporadic, some tumors are associated with specific hereditary disease, especially those occurring in young patients or in combination with other neoplasms.

An unusual case of incomplete Carney triad: an 18-year-old girl suffering from multiple benign tumors

Carney triad is a rare syndrome that involves gastrointestinal stromal tumor (GIST), pulmonary chondroma and extra-adrenal paraganglioma. Patients presenting GIST and pulmonary chondroma account for 72.7% of all incomplete Carney triad cases. Clinically, it is mainly diagnosed by radiological images and pathological results. Some studies have elucidated the pathogenesis of Carney triad. Surgical resection is the preferred treatment for Carney triad. Generally speaking, the prognosis of patients with Carney triad has been satisfied. According to current reports, the rate of 40-year survival is up to 73%. The case reports an 18-year-old girl suffering from pulmonary chondroma and posterior mediastinal paraganglioma, simultaneously with pulmonary hamartoma, breast fibroma and lower limb chondroma.

Molecular subtypes of gastrointestinal stromal tumors and their prognostic and therapeutic implications

Gastrointestinal stromal tumors (GISTs) are composed of various molecular subtypes, with differing prognostic and predictive relevance. Previously, tumors lacking mutations in the KIT and PDGFRA genes have been designated as 'wild-type' GISTs; however, they represent a heterogeneous group currently undergoing further subclassification. Primary and secondary resistance to imatinib poses a significant clinical challenge, therefore ongoing research is trying to evaluate mechanisms to overcome resistance. Thorough understanding of the prognostic and predictive relevance of different genetic subtypes of GIST can guide clinical decision-making both in the adjuvant and the metastatic setting. Further work is required to identify tailored therapies for specific subgroups of GISTs wild-type for KIT and PDGFRA mutations and to identify predictive factors of resistance to currently approved systemic therapies.

Syndromic gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasms of gastrointestinal tract. They feature heterogeneous triggering mechanisms, implying relevant clinical differences. The vast majority of GISTs are sporadic tumors. Rarely, however, GIST-prone syndromes occur, mostly depending on heritable GIST predisposing molecular defects involving the entire organism. These conditions need to be properly identified in order to plan appropriate diagnostic, prognostic and therapeutic procedures. Clinically, GIST-prone syndromes must be thought of whenever GISTs are multiple and/or associated with accompanying signs peculiar to the background tumorigenic trigger, either in single individuals or in kindreds. Moreover, syndromic GISTs, individually considered, tend to show distinctive features depending on the underlying condition. When applicable, genotyping is usually confirmatory. In GIST-prone conditions, the prognostic features of each GIST, defined according to the criteria routinely applied to sporadic GISTs, combine with the characters proper to the background syndromes, defining peculiar clinical settings which challenge physicians to undertake complex decisions. The latter concern preventive therapy and single tumor therapy, implying possible surgical and molecularly targeted options. In the absence of specific comprehensive guidelines, this review will highlight the traits characteristic of GIST-predisposing syndromes, with particular emphasis on diagnostic, prognostic and therapeutic implications, which can help the clinical management of these rare diseases.