Succinate dehydrogenase-deficient tumors: diagnostic advances and clinical implications

Breast Cancer Risk and Management in the Endocrine Clinic: A Comprehensive Review

OBJECTIVE

This review seeks to provide endocrine clinicians with a comprehensive analysis of breast cancer risk, diagnostic modalities and management strategies in women with endocrine disorders, with particular emphasis on the influence of metabolic factors such as diabetes and obesity, and the role of Menopausal Hormone Therapy (MHT).

DESIGN

The review examines a spectrum of endocrine disorders commonly encountered in clinical practice, including Multiple Endocrine Neoplasia Types 1 (MEN1), 2 (MEN2) and 4 (MEN4), Von Hippel-Lindau syndrome (VHL), Pheochromocytoma and Paraganglioma (PPGL), Acromegaly, Hyperprolactinaemia, Polycystic Ovary Syndrome (PCOS), Congenital Adrenal Hyperplasia (CAH), Turner Syndrome, alongside metabolic conditions such as diabetes and obesity and the effects of MHT. The review critically appraises each disorder's association with breast cancer risk, screening implications and therapeutic management.

PATIENTS

This analysis focuses on women with the aforementioned endocrine and metabolic disorders, assessing their specific breast cancer risk profiles, informed by the latest clinical evidence and molecular insights.

MEASUREMENTS

The review comprehensively evaluates current evidence-based approaches to screening, diagnostic accuracy and treatment in this patient cohort. Emphasis is placed on the metabolic derangements, hormonal influences and genetic predispositions that modulate breast cancer risk, providing disorder-specific recommendations for individualised care.

RESULTS

The findings indicate a significantly elevated breast cancer risk in patients with MEN1, necessitating early initiation of MRI screening by age 40. In MEN2, emerging evidence suggests that combining RET inhibitors with endocrine therapy may yield clinical benefits, although further research is needed to validate this approach. The breast cancer risk associated with MEN4 and VHL syndromes, while documented, remains less well-characterised, requiring further investigation. Diabetes and obesity are confirmed as major modifiable risk factors, particularly in postmenopausal women, where hyperinsulinemia and metabolic dysfunction contribute to increased incidence and poorer outcomes, notably in triple-negative breast cancer (TNBC). The role of MHT, particularly combined oestrogen-progestogen therapy, is strongly associated with increased breast cancer risk, particularly for hormone receptor-positive malignancies, necessitating cautious use and personalised treatment planning. In contrast, oestrogen-only MHT appears to confer a reduced risk in women post-hysterectomy. For patients with PCOS, CAH and Turner Syndrome, while definitive evidence of elevated breast cancer risk is lacking, individualised screening strategies and careful hormone therapy management remain essential due to the complex interplay of hormonal and metabolic factors.

CONCLUSIONS

The review highlights the need for personalised breast cancer screening and management protocols in women with endocrine and metabolic disorders. For high-risk groups such as MEN1 patients, early initiation of MRI screening is warranted. In women with diabetes and obesity, targeted interventions addressing hyperinsulinemia and metabolic dysfunction are critical to mitigating their increased cancer risk. The association between MHT and breast cancer underscores the importance of individualised risk stratification in hormone therapy administration, particularly in women with predisposing genetic or endocrine conditions. Enhanced surveillance tailored to the unique risk profiles of endocrine disorder patients will facilitate early detection and improve clinical outcomes. However, further large-scale studies are necessary to refine these associations and develop robust, evidence-based guidelines.

Tricarboxylic Acid Cycle Relationships with Non-Metabolic Processes: A Short Story with DNA Repair and Its Consequences on Cancer Therapy Resistance

Metabolic changes involving the tricarboxylic acid (TCA) cycle have been linked to different non-metabolic cell processes. Among them, apart from cancer and immunity, emerges the DNA damage response (DDR) and specifically DNA damage repair. The oncometabolites succinate, fumarate and 2-hydroxyglutarate (2HG) increase reactive oxygen species levels and create pseudohypoxia conditions that induce DNA damage and/or inhibit DNA repair. Additionally, by influencing DDR modulation, they establish direct relationships with DNA repair on at least four different pathways. The AlkB pathway deals with the removal of N-alkylation DNA and RNA damage that is inhibited by fumarate and 2HG. The MGMT pathway acts in the removal of O-alkylation DNA damage, and it is inhibited by the silencing of the MGMT gene promoter by 2HG and succinate. The other two pathways deal with the repair of double-strand breaks (DSBs) but with opposite effects: the FH pathway, which uses fumarate to help with the repair of this damage, and the chromatin remodeling pathway, in which oncometabolites inhibit its repair by impairing the homologous recombination repair (HRR) system. Since oncometabolites inhibit DNA repair, their removal from tumor cells will not always generate a positive response in cancer therapy. In fact, their presence contributes to longer survival and/or sensitization against tumor therapy in some cancer patients.

A highly malignant succinate dehydrogenase A‑deficient renal cell carcinoma with bone metastasis misdiagnosed as hereditary leiomyomatosis and renal cell carcinoma: A case report

Succinate dehydrogenase (SDH)-deficient renal cell carcinoma (RCC) is an autosomal dominant syndrome caused by heterozygous pathogenic germline variants of the SDH gene. SDH mutations are associated with an increased risk of developing RCC, although studies describing SDH-deficient RCC are currently limited. The present study reported a case of SDH-deficient RCC with high malignancy and rare bone metastasis. The patient was diagnosed with a right renal mass through B-mode ultrasound imaging and showed a carcinoma embolus in the right renal vein and inferior vena cava through kidney contrast-enhanced computed tomography. A whole-body bone scan showed radionuclide accumulation in the upper end of the left humerus, which indicated possible pathological bone destruction. As a result, surgical resection was performed. The postoperative pathology indicated a high-grade RCC and although the specific classification remained uncertain, hereditary leiomyomatosis and RCC was suspected. Subsequently, a germline mutation of the succinate dehydrogenase complex flavoprotein subunit A gene was identified through high-throughput sequencing (c.1A>G, p. Met1?) and immunohistochemistry demonstrated the loss of succinate dehydrogenase complex flavoprotein subunit B expression. Postoperatively, the patient underwent radiotherapy and targeted therapy. After 6 months of follow-up treatment, there was no indication of recurrence or metastasis on thoracoabdominal CT and whole-body bone scintigraphy. Based on the present report, germline screening should potentially be encouraged in early-onset patients as family history or pathological results may not provide sufficient information for the early, differential diagnosis of SDH-deficient RCC.

Regulation of tumor metabolism by post translational modifications on metabolic enzymes

Metabolic reprogramming is a hallmark of cancer development, progression, and metastasis. Several metabolic pathways such as glycolysis, tricarboxylic acid (TCA) cycle, lipid metabolism, and glutamine catabolism are frequently altered to support cancer growth. Importantly, the activity of the rate-limiting metabolic enzymes in these pathways are specifically modulated in cancer cells. This is achieved by transcriptional, translational, and post translational regulations that enhance the expression, activity, stability, and substrate sensitivity of the rate-limiting enzymes. These mechanisms allow the enzymes to retain increased activity supporting the metabolic needs of rapidly growing tumors, sustain their survival in the hostile tumor microenvironments and in the metastatic lesions. In this review, we primarily focused on the post translational modifications of the rate-limiting enzymes in the glucose and glutamine metabolism, TCA cycle, and fatty acid metabolism promoting tumor progression and metastasis.

SDHA Germline Mutations in SDH-Deficient GISTs: A Current Update

Loss of function of the succinate dehydrogenase complex characterizes 20–40% of all KIT/PDGFRA-negative GIST. Approximately half of SDH-deficient GIST patients lack SDHx mutations and are caused by a hypermethylation of the SDHC promoter, which causes the repression of SDHC transcription and depletion of SDHC protein levels through a mechanism described as epimutation. The remaining 50% of SDH-deficient GISTs have mutations in one of the SDH subunits and SDHA mutations are the most common (30%), with consequent loss of SDHA and SDHB protein expression immunohistochemically. SDHB, SDHC, and SDHD mutations in GIST occur in only 20–30% of cases and most of these SDH mutations are germline. More recently, germline mutations in SDHA have also been described in several patients with loss of function of the SDH complex. SDHA-mutant patients usually carry two mutational events at the SDHA locus, either the loss of the wild type allele or a second somatic event in compound heterozygosis. This review provides an overview of all data in the literature regarding SDHA-mutated GIST, especially focusing on the prevalence of germline mutations in SDH-deficient GIST populations who harbor SDHA somatic mutations, and offers a view towards understanding the importance of genetic counselling for SDHA-variant carriers and relatives.

The Classic, the Trendy, and the Refashioned: A Primer for Pathologists on What Is New in Familial Endocrine Tumor Syndromes

Familial endocrine tumor syndromes are continuously expanding owing to the growing role of genetic testing in routine clinical practice. Pathologists are usually the first on the clinical team to encounter these syndromes at their initial presentation; thus, recognizing them is becoming more pivotal in routine pathology practice to help in properly planning management and further family testing. Our increasing knowledge about them is reflected in the newer syndromes included in the new World Health Organization classification and in the evolving discovery of new endocrine tumors and new familial associations. In many of these syndromes, the clinical features and co-occurrence of multiple neoplasia are the only clues (multiple endocrine neoplasia syndromes). In other syndromes, specific morphologic findings (pituitary blastoma and DICER1 syndrome, cribriform morular thyroid carcinoma, and AFP syndrome) and available ancillary studies (SDHB in SDH-deficient tumor syndromes) can aid pathologists. The aim of this review is to provide a primer on recent updates on familial endocrine tumor syndromes and related tumors, focusing on recent classification changes or tumor syndromes where a clearer role for pathologists is at play.

Clinicopathological characteristics of patients with carotid body tumor with cervical lymph node metastasis: A retrospective study of 10 cases and review of the literature

Carotid body tumor (CBT), also known as carotid body chemoreceptor tumor or nonchromaffin paraganglioma, originates from the chemoreceptor behind the common carotid artery bifurcation in the carotid sheath. Most CBTs are benign. Malignant CBT (MCBT) is extremely rare, and cervical lymph node metastasis (CLNM) is usually regarded as a manifestation of malignant behavior. The association between CLNM, pathological features of the primary lesion, clinical manifestations, and prognosis deserves further investigation. The clinical materials of 133 patients with CBT who underwent total resection of the primary tumor and concomitant selective neck dissection (SND) from February 2002 to June 2018 in a single center were reviewed. Postoperative histopathology confirmed CLNM in 10 cases (10/133); clinical manifestations, pathological and imaging characteristics, and treatment outcome data were reviewed and analyzed. The average patient age was 50.5 years, with a female sex tendency (7/10). The mean and median follow-up periods of all cases were 6.9 years and 7 years, respectively. Nine patients (9/10) survived; one patient died of multiple systemic metastases 10 months after surgery when the tumor metastasized to the bilateral breast and other organs in an orderly manner. None of the patients had local recurrence, but postoperative residual lesions were detected by computer-aided 3-dimensional (3D) visualization computerized tomography in one (1/10). Most CBT cases with CLNM displayed adverse features, especially in patients without distant metastases. Immunohistochemically, the patient with distant metastases was negative for S-100, synaptophysin (Syn), and succinate dehydrogenase B (SDHB) expression. Most patients with CBT with CLNM have a good prognosis. Breast metastasis is an exceedingly rare manifestation of MCBT. Despite some association between clinical biological and histological malignancies in CBT with CLNM, the association seems to be vague in cases involving distant metastasis. The combination of certain immunohistochemical indicators (S-100, Syn, and SDHB) might be valuable for predicting the occurrence of distant metastasis. Computer-aided 3D visualization technology might be helpful for the diagnosis and postoperative follow-up of MCBT. Simultaneous SND can remove potentially metastatic lymph nodes and facilitate diagnosis and treatment.

Impaired oxygen-sensitive regulation of mitochondrial biogenesis within the von Hippel-Lindau syndrome

Mitochondria are the main consumers of oxygen within the cell. How mitochondria sense oxygen levels remains unknown. Here we show an oxygen-sensitive regulation of TFAM, an activator of mitochondrial transcription and replication, whose alteration is linked to tumours arising in the von Hippel-Lindau syndrome. TFAM is hydroxylated by EGLN3 and subsequently bound by the von Hippel-Lindau tumour-suppressor protein, which stabilizes TFAM by preventing mitochondrial proteolysis. Cells lacking wild-type VHL or in which EGLN3 is inactivated have reduced mitochondrial mass. Tumorigenic VHL variants leading to different clinical manifestations fail to bind hydroxylated TFAM. In contrast, cells harbouring the Chuvash polycythaemia VHL^R200W mutation, involved in hypoxia-sensing disorders without tumour development, are capable of binding hydroxylated TFAM. Accordingly, VHL-related tumours, such as pheochromocytoma and renal cell carcinoma cells, display low mitochondrial content, suggesting that impaired mitochondrial biogenesis is linked to VHL tumorigenesis. Finally, inhibiting proteolysis by targeting LONP1 increases mitochondrial content in VHL-deficient cells and sensitizes therapy-resistant tumours to sorafenib treatment. Our results offer pharmacological avenues to sensitize therapy-resistant VHL tumours by focusing on the mitochondria.

Increased expression of Nrf2 and elevated glucose uptake in pheochromocytoma and paraganglioma with SDHB gene mutation

Background

Pheochromocytomas (PCC) and paragangliomas (PGL) are catecholamine-producing neuroendocrine tumors. According to the World Health Organization Classification 2017, all PCC/PGL are considered to have malignant potential. There is growing evidence that PCC/PGL represent a metabolic disease that leads to aerobic glycolysis. Cellular energy metabolism involves both transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) and succinate dehydrogenase (SDH) subtypes, but the association of these substances with PCC/PGL is largely unknown.

Methods

We investigated SDHB gene mutation and protein expressions for SDHB and Nrf2 in surgical specimens from 29 PCC/PGL. We also assessed preoperative maximum standard glucose uptake (SUVmax) on [¹⁸F]fluorodeoxy-glucose positron emission tomography and mRNA levels for Nrf2.

Results

Among 5 PCC/PGL with a PASS Score ≥ 4 or with a moderately to poorly differentiated type in the GAPP Score, 4 were metastatic and found to be SDHB mutants with homogeneous deletion of SDHB protein. SDHB mutants showed a higher expression of Nrf2 protein and a higher preoperative SUVmax than non-SDHB mutants with a PASS < 4 or a well-differentiated GAPP type. Furthermore, protein expression of Nrf2 was positively associated with preoperative SUVmax. The Nrf2 mRNA level positively correlated with malignant phenotype, higher expression for Nrf2 protein and SDHB gene mutant, but negatively correlated with expression for SDHB protein. There was also a positive correlation between Nrf2 mRNA level and SUVmax.

Conclusion

These results suggest that activation of Nrf2 and elevated metabolism play roles in PCC/PGL with malignant potential that have SDHB gene mutation and SDHB deficiency.

SDH-deficient renal cell carcinoma: A case report associated with a novel germline mutation

The highly syndromic nature of succinate dehydrogenase-deficient RCCs constitutes their active surveillance and molecular profiling the alpha and omega.

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.

Radiologic-Pathologic Correlation of Primary Retroperitoneal Neoplasms

An earlier incorrect version of this article appeared in print. The online version is correct.

Single nucleotide variants of succinate dehydrogenase A gene in renal cell carcinoma

Succinate dehydrogenase (SDH)-deficient renal cell carcinoma (RCC) is mainly associated with a mutation in the SDHB gene and sometimes with mutations in the SDHC or SDHD genes. However, only three cases of succinate dehydrogenase A (SDHA)-deficient RCC have been reported, and the relation between SDHA mutations and RCC has not been clarified. This study assessed the role of SDHA gene mutations in human RCC. We investigated SDHA/B/C/D gene mutations in 129 human RCCs. Targeted next-generation sequencing and direct Sanger sequencing revealed single nucleotide variants (SNVs) of the SDHA gene with amino acid sequence variations in 11/129 tumors, while no SDHB/C/D gene mutations were found. Tumor cells with SNVs of the SDHA gene were characterized by eosinophilic cytoplasm and various patterns of proliferation. Immunohistochemistry examination found that the 11 tumors with SNVs of the SDHA gene showed significant reduction of SDHA protein and SDHB protein expression compared to the 19 tumors without SDHA or SDHB mutations (both P < .0001). Western blotting showed a greater decrease in the expression of SDHA and SDHB proteins in the 11 tumors with SNVs of the SDHA gene than in the 19 tumors without (both P < .0001). There was a positive correlation between SDHA and SDHB protein levels (P < .0001). On immunohistochemistry and Western blotting, the 11 tumors with SNVs of the SDHA gene had higher protein expression for nuclear factor E2-related factor 2 (Nrf2) compared to the 19 tumors without the mutation (P < .01). These observations suggest that SDHA gene mutations might be associated with a subset of RCC.

Mitochondria: A Galaxy in the Hematopoietic and Leukemic Stem Cell Universe

Mitochondria are the main fascinating energetic source into the cells. Their number, shape, and dynamism are controlled by the cell’s type and current behavior. The perturbation of the mitochondrial inward system via stress response and/or oncogenic insults could activate several trafficking molecular mechanisms with the intention to solve the problem. In this review, we aimed to clarify the crucial pathways in the mitochondrial system, dissecting the different metabolic defects, with a special emphasis on hematological malignancies. We investigated the pivotal role of mitochondria in the maintenance of hematopoietic stem cells (HSCs) and their main alterations that could induce malignant transformation, culminating in the generation of leukemic stem cells (LSCs). In addition, we presented an overview of LSCs mitochondrial dysregulated mechanisms in terms of (1) increasing in oxidative phosphorylation program (OXPHOS), as a crucial process for survival and self-renewal of LSCs,(2) low levels of reactive oxygen species (ROS), and (3) aberrant expression of B-cell lymphoma 2 (Bcl-2) with sustained mitophagy. Furthermore, these peculiarities may represent attractive new “hot spots” for mitochondrial-targeted therapy. Finally, we remark the potential of the LCS metabolic effectors to be exploited as novel therapeutic targets.

An Algorithmic Immunohistochemical Approach to Define Tumor Type and Assign Site of Origin

Immunohistochemistry represents an indispensable complement to an epidemiology and morphology-driven approach to tumor diagnosis and site of origin assignment. This review reflects the state of my current practice, based on 15-years' experience in Pathology and a deep-dive into the literature, always striving to be better equipped to answer the age old questions, "What is it, and where is it from?" The tables and figures in this manuscript are the ones I "pull up on the computer" when I am teaching at the microscope and turn to myself when I am (frequently) stuck. This field is so exciting because I firmly believe that, through the application of next-generation immunohistochemistry, we can provide better answers than ever before. Specific topics covered in this review include (1) broad tumor classification and associated screening markers; (2) the role of cancer epidemiology in determining pretest probability; (3) broad-spectrum epithelial markers; (4) noncanonical expression of broad tumor class screening markers; (5) a morphologic pattern-based approach to poorly to undifferentiated malignant neoplasms; (6) a morphologic and immunohistochemical approach to define 4 main carcinoma types; (7) CK7/CK20 coordinate expression; (8) added value of semiquantitative immunohistochemical stain assessment; algorithmic immunohistochemical approaches to (9) "garden variety" adenocarcinomas presenting in the liver, (10) large polygonal cell adenocarcinomas, (11) the distinction of primary surface ovarian epithelial tumors with mucinous features from metastasis, (12) tumors presenting at alternative anatomic sites, (13) squamous cell carcinoma versus urothelial carcinoma, and neuroendocrine neoplasms, including (14) the distinction of pheochromocytoma/paraganglioma from well-differentiated neuroendocrine tumor, site of origin assignment in (15) well-differentiated neuroendocrine tumor and (16) poorly differentiated neuroendocrine carcinoma, and (17) the distinction of well-differentiated neuroendocrine tumor G3 from poorly differentiated neuroendocrine carcinoma; it concludes with (18) a discussion of diagnostic considerations in the broad-spectrum keratin/CD45/S-100-"triple-negative" neoplasm.

Pathologic Considerations in Gastroenteropancreatic Neuroendocrine Tumors

This review serves as a primer on contemporary neuroendocrine neoplasm classification, with an emphasis on gastroenteropancreatic well-differentiated neuroendocrine tumors. Topics discussed include general features of neuroendocrine neoplasms, general neuroendocrine marker immunohistochemistry, the distinction of well-differentiated neuroendocrine tumor from pheochromocytoma/paraganglioma and other diagnostic mimics and poorly differentiated neuroendocrine carcinoma from diagnostic mimics, the concepts of differentiation and grade and the application of Ki-67 immunohistochemistry to determine the latter, the various WHO classifications of neuroendocrine neoplasms including the 2019 WHO classification of gastroenteropancreatic tumors, organ-specific considerations for gastroenteropancreatic well-differentiated neuroendocrine tumors, immunohistochemistry to determine site of origin in metastatic well-differentiated neuroendocrine tumor of occult origin, immunohistochemistry in the distinction of well-differentiated neuroendocrine tumor G3 from large cell neuroendocrine carcinoma, and, finally, required and recommended reporting elements for biopsies and resections of gastroenteropancreatic neuroendocrine epithelial neoplasms.

Immunohistochemistry in the diagnosis and classification of neuroendocrine neoplasms: what can brown do for you?

This review is based on a presentation given at the Hans Popper Hepatopathology Society companion meeting at the 2019 United States and Canadian Academy of Pathology Annual Meeting. It presents updates on the diagnosis and classification of neuroendocrine neoplasms, with an emphasis on the role of immunohistochemistry. Neuroendocrine neoplasms often present in liver biopsies as metastases of occult origin. Specific topics covered include 1. general features of neuroendocrine neoplasms, 2. general neuroendocrine marker immunohistochemistry, with discussion of the emerging marker INSM1, 3. non-small cell carcinoma with (occult) neuroendocrine differentiation, 4. the WHO Classification of neuroendocrine neoplasms, with discussion of the 2019 classification of gastroenteropancreatic neoplasms, 5. use of Ki-67 immunohistochemistry, 6. immunohistochemistry to assign site of origin in neuroendocrine metastasis of occult origin, 7. immunohistochemistry to distinguish well-differentiated neuroendocrine tumor G3 from poorly differentiated neuroendocrine carcinoma, 8. lesions frequently misdiagnosed as well-differentiated neuroendocrine tumor, and 9. required and recommended data elements for biopsies and resections with associated immunohistochemical stains. Next-generation immunohistochemistry, including lineage-restricted transcription factors (e.g., CDX2, islet 1, OTP, SATB2) and protein correlates of molecular genetic events (e.g., p53, Rb), is indispensable for the accurate diagnosis and classification of these neoplasms.

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.

Genetic and epigenetic alterations of SDH genes in patients with sporadic succinate dehydrogenase-deficient gastrointestinal stromal tumors

This study aimed to investigate the association of SDH gene mutations and promoter methylation with succinate dehydrogenase-deficient gastrointestinal stromal tumors (SDH-deficient GISTs) and to further discuss the potential molecular mechanisms underlying SDHB expression loss in these tumors. First, a total of 26 patients with SDH-deficient GISTs were selected by identifying the loss of SDHB protein expression and wild-type for KIT and PDGFRa mutations. Then SDH gene mutations and promoter methylation were detected by DNA sequencing and methylation-specific polymerase chain reaction, respectively, and the clinical and pathological data of SDH-deficient GISTs patients were collected and analyzed accordingly. The results of genetic testing demonstrated that 38.46% (10/26) of these patients harbored mutations in SDHB, SDHC, and SDHD genes (3 cases with double mutations). Besides, aberrant promoter methylation of SDH genes was detected in 10 out of 26 cases (38.46%), including 8 cases in SDHA gene, 3 cases in SDHB gene, 1 case in both SDHA and SDHB genes. It is suggested that SDH gene mutations and promoter methylation may contribute to the loss of SDH protein expression in sporadic SDH-deficient GISTs. This study indicated that the genetic and epigenetic alterations of SDH genes may occur during tumor formation.

Paragangliomas in Carney-Stratakis Syndrome

Carney-Stratakis Syndrome (CSS) comprises of paragangliomas (PGLs) and gastrointestinal stromal tumors (GISTs). Several of its features overlap with Carney Triad (CT) - PGLs, GISTs, and pulmonary chondromas. CSS has autosomal dominant inheritance, incomplete penetrance, and greater relative frequency of PGL over GISTs. The PGLs in CSS are multicentric and GISTs are multifocal in all the patients, suggesting an inherited susceptibility and associating the two manifestations. In this review, we highlight the clinical, pathological, and molecular characteristics of CSS, along with its diagnostic and therapeutic implications.

Succinate Dehydrogenase-Deficient Renal Cell Carcinoma

Succinate dehydrogenase (SDH)-deficient renal cell carcinoma is a recently recognized distinct subtype of renal cell carcinoma in the 2016 World Health Organization classification. It is associated with SDH gene germline mutations, which also cause paraganglioma/pheochromocytoma, gastrointestinal stromal tumor, and pituitary adenoma. The tumor most commonly presents in young adulthood. The tumors are arranged in solid nests or in tubules and frequently show cystic change. The tumors are composed of cuboidal to oval cells with round nuclei, dispersed chromatin, and inconspicuous nucleoli. The cytoplasm is eosinophilic or flocculent but not truly oncocytic. The most distinctive histologic feature is the presence of cytoplasmic vacuoles or inclusions. Loss of SDH subunit B immunostaining is needed for a definite diagnosis. The prognosis is good for low-grade tumors but worse for tumors with high-grade nuclei, sarcomatoid change, or coagulative necrosis. Long-term follow-up is indicated.

SDH-deficient renal cell carcinoma associated with biallelic mutation in succinate dehydrogenase A: comprehensive genetic profiling and its relation to therapy response

Succinate dehydrogenase (SDH)-deficient renal cell carcinoma (RCC) is a rare RCC subtype that is caused by biallelic mutation of one of the four subunits of the SDH complex (SDHA, B, C, and D) and results in inactivation of the SDH enzyme. Here we describe a case of genetically characterized SDH-deficient RCC caused by biallelic (germline plus somatic) SDHA mutations. SDHA pathogenic variants were detected using comprehensive genomic profiling and SDH absence was subsequently confirmed by immunohistochemistry. Very little is known regarding the genomic context of SDH-deficient RCC. Interestingly we found genomic amplifications commonly observed in RCC but there was an absence of additional variants in common cancer driver genes. Prior to genetic testing a PD-1 inhibitor treatment was administered. However, following the genetic results a succession of tyrosine kinase inhibitors were administered as targeted treatment options and we highlight how the genetic results provide a rationale for their effectiveness. We also describe how the genetic results benefited the patient by empowering him to adopt dietary and lifestyle changes in accordance with knowledge of the mechanisms of SDH-related tumorigenesis.

Modern Pathologic Diagnosis of Renal Oncocytoma

Oncocytoma is a well-defined benign renal tumor, with classic gross and histologic features, including a tan or mahogany-colored mass with central scar, microscopic nested architecture, bland cytology, and round, regular nuclei with prominent central nucleoli. As a result of variations in this classic appearance, difficulty in standardizing diagnostic criteria, and entities that mimic oncocytoma, such as eosinophilic variant chromophobe renal cell carcinoma and succinate dehydrogenase-deficient renal cell carcinoma, pathologic diagnosis remains a challenge. This review addresses the current state of pathologic diagnosis of oncocytoma, with emphasis on modern diagnostic markers, areas of controversy, and emerging techniques for less invasive diagnosis, including renal mass biopsy and advanced imaging.

SDHD promoter mutations are rare events in cutaneous melanomas but SDHD protein expression is downregulated in advanced cutaneous melanoma

BACKGROUND

SDHD promoter mutations were reported in 4-10% of cutaneous melanomas. The advanced clinico-pathological and patient survival association with SDHD mutation and/or expression in cutaneous melanoma remains controversial.

OBJECTIVES

To evaluate the presence of SDHD promoter mutations and SDHD protein expression in a melanoma series and its possible association with prognosis and survival of the patients.

METHODS

We assessed SDHD promoter status in cutaneous melanomas (CM), ocular melanomas (OM) and melanoma cell lines, and the expression of SDHD protein by immunohistochemistry in CM and OM, and by western blot in melanoma cell lines. We explored the putative association between SDHD protein expression and clinico-pathological and prognostic parameters of melanoma.

RESULTS

We detected 2% of SDHD promoter mutations in CM, but none in OM and cell lines. SDHD protein expression was present in all CM, in OM and in all CM and OM derived cell lines analysed. A significant association between lower SDHD mean protein expression and presence of ulceration and higher pT stage was found.

CONCLUSIONS

SDHD promoter mutation seems to be a rare event in CM but SDHD lower expression might associate with worst prognostic features in CM.

Renal cell carcinoma with TFE3 translocation and succinate dehydrogenase B mutation

Translocation renal cell carcinoma and succinate dehydrogenase (SDH)-deficient renal cell carcinoma are now recognized as specific renal tumor types in the World Health Organization (WHO) classification. Both have limited immunohistochemical positivity for epithelial markers, and the spectrum of morphology continues to widen for both of these entities. We identified four renal cell carcinomas with positive TFE3 immunohistochemical staining and negative SDHB staining. The patients (2F, 2M) ranged in age from 19 to 65 years. All tumors were composed, at least in part, of eosinophilic cells. Cytoplasmic inclusions, prominent nucleoli, and mitotic figures were seen in three tumors. Psammoma bodies were also present in two tumors. Using immunohistochemistry, a broad spectrum of commonly used renal tumor markers yielded nonspecific, limited positivity, including uniformly positive reactions for PAX8 but negative results for cathepsin K and HMB45. Fluorescence in situ hybridization results showed the presence of TFE3 gene rearrangement in all four tumors, and molecular analysis revealed SDHB mutations in neoplastic cells of three tumors. In one case, the same SDHB mutation was confirmed in the adjacent non-neoplastic tissue. We report for the first time the presence of both TFE3 translocation and SDHB mutation in the same tumor.

Adrenal Tumors in Adults

Although most adrenal tumors are not diagnostic dilemmas, there are cases that are challenging. This may be due to the tissue provided, for example fragmented tissue received in the setting of morcellation, or it may be due to inherently challenging histology, such as in cases with equivocal features of malignancy. Additionally, much has been learned about the molecular alterations of adrenal tumors, especially pheochromocytomas. Many of these alterations represent germline mutations with significant clinical implications for patients and their families. The aim of this review is to provide an overview of the most common adrenal tumors in adults so that pathologists can tackle these interesting tumors.

Molecular genetics and immunohistochemistry characterization of uncommon and recently described renal cell carcinomas

Renal cell carcinoma (RCC) compromises multiple types and has been emerging dramatically over the recent several decades. Advances and consensus have been achieved targeting common RCCs, such as clear cell carcinoma, papillary RCC and chromophobe RCC. Nevertheless, little is known on the characteristics of several newly-identified RCCs, including clear cell (tubulo) papillary RCC, Xp11 translocation RCC, t(6;11) RCC, succinate dehydrogenase (SDH)-deficient RCC, acquired cystic disease-associated RCC, hereditary leiomyomatosis RCC syndrome-associated RCC, ALK translocation RCC, thyroid-like follicular RCC, tubulocystic RCC and hybrid oncocytic/chromophobe tumors (HOCT). In current review, we will collect available literature of these newly-described RCCs, analyze their clinical pathologic characteristics, discuss their morphologic and immunohistologic features, and finally summarize their molecular and genetic evidences. We expect this review would be beneficial for the understanding of RCCs, and eventually promote clinical management strategies.

Succinate dehydrogenase B: a new prognostic biomarker in clear cell renal cell carcinoma

Succinate dehydrogenase B (SDHB) is a mitochondrial enzyme complex subunit. Loss of SDHB protein expression has been found to correlate with SDHx gene mutations. Little is known about its expression in subtypes of renal cell carcinoma (RCC) and whether it is a prognostic indicator. Four hundred fifty renal epithelial neoplasms were analyzed for SDHB, comprising clear cell RCC (CCRCC) (n = 240), papillary RCC (n = 84), chromophobe RCC (n = 49), renal oncocytoma (n = 47), clear cell papillary RCC (CCPRCC) (n = 19), and von Hippel-Lindau (VHL)-associated CCPRCC-like tumors (n = 11). Succinate dehydrogenase B expression was graded based upon staining intensity using a 4-tiered system (0-3+), in which 3+ was strongest and complete absence was 0. Neoplasms were further categorized based upon staining extent into SDHB weak (1+-2+) and strong (3+). Succinate dehydrogenase B was strongly preserved in 131 (55%) of 240 CCRCCs, 84 (100%) of 84 papillary RCCs, 49 (100%) of 49 chromophobe RCCs, 1 (5%) of 19 CCPRCC, 5 (45%) of 11 VHL-associated CCPRCC-like tumors, and 47 (100%) of 47 renal oncocytomas. The remaining 109 CCRCCs, 18 CCPRCCs, and 6 VHL-associated CCPRCC-like tumors had weak but preserved SDHB. Succinate dehydrogenase B expression in CCRCCs with high International Society of Urological Pathology nucleolar grade (G3-G4) correlated significantly with survival (log-rank, P = .0004). Succinate dehydrogenase B is variably expressed in RCCs with clear cell morphology and strongly preserved in most other neoplasms. Therefore, weak staining, particularly in clear neoplasms, should not be misinterpreted as negative. Finally, SDHB expression in CCRCCs with high nucleolar grade (G3-G4) is significantly associated with survival, indicating it may be both a diagnostic and prognostic marker in RCC.

Succinate dehydrogenase-deficient gastrointestinal stromal tumors

Most gastrointestinal stromal tumors (GISTs) are characterized by KIT or platelet-derived growth factor alpha (PDGFRA) activating mutations. However, there are still 10%-15% of GISTs lacking KIT and PDGFRA mutations, called wild-type GISTs (WT GISTs). Among these so-called WT GISTs, a small subset is associated with succinate dehydrogenase (SDH) deficiency, known as SDH-deficient GISTs. In addition, GISTs that occur in Carney triad and Carney-Stratakis syndrome represent specific examples of SDH-deficient GISTs. SDH-deficient GISTs locate exclusively in the stomach, showing predilection for children and young adults with female preponderance. The tumor generally pursues an indolent course and exhibits primary resistance to imatinib therapy in most cases. Loss of succinate dehydrogenase subunit B expression and overexpression of insulin-like growth factor 1 receptor (IGF1R) are common features of SDH-deficient GISTs. In WT GISTs without succinate dehydrogenase activity, upregulation of hypoxia-inducible factor 1α may lead to increased growth signaling through IGF1R and vascular endothelial growth factor receptor (VEGFR). As a result, IGF1R and VEGFR are promising to be the novel therapeutic targets of GISTs. This review will update the current knowledge on characteristics of SDH-deficient GISTs and further discuss the possible mechanisms of tumorigenesis and clinical management of SDH-deficient GISTs.

Succinate dehydrogenase-deficient renal cell carcinoma: detailed characterization of 11 tumors defining a unique subtype of renal cell carcinoma

Patients with germline mutation of succinate dehydrogenase (SDH) subunit genes are prone to develop paraganglioma, gastrointestinal stromal tumor, and rarely renal cell carcinoma (RCC). However, SDH-deficient RCC is not yet widely recognized. We identified such tumors by distinctive morphology and confirmed absence of immunohistochemical staining for SDHB. Immunohistochemical features were evaluated using a panel of antibodies to renal tumor antigens. Targeted next-generation sequencing was performed on DNA extracted from paraffin-embedded tissue. Eleven tumors were identified from 10 patients, 22-72 years of age (median 40). Two patients had paragangliomas, 1 bilateral SDH-deficient RCC, and 1 contralateral oncocytoma. Grossly, tumors were tan or red-brown, 2-20 cm in diameter (median 4.25 cm). Fuhrman grade was 2 (n=10) or 3 (n=1). Stage was pT1a-pT2b. One patient developed widespread metastases 16 years after nephrectomy and died of disease 6 years later. All tumors were composed of uniform eosinophilic cells containing vacuoles or flocculent cytoplasmic inclusions. Architecture was primarily solid; entrapped renal tubules and intratumoral mast cells were common. By immunohistochemistry, tumor cells were negative for SDHB (11/11) and rarely SDHA (1/11). Labeling was uniformly positive for PAX8 and kidney-specific cadherin and absent for KIT, RCC, and carbonic anhydrase IX. Staining for broad-spectrum epithelial markers was often negative or focal (positive staining for AE1/AE3 in 4/10, CAM5.2 3/7, CK7 1/11, EMA 10/10). By sequencing, SDHB mutation and loss of the second allele were present in 5/6 tumors; the SDHA-deficient tumor showed no SDHB abnormality. SDH-deficient RCC is a unique neoplasm that is capable of progression, often harboring SDHB mutation. A monomorphic oncocytic renal tumor with solid architecture, cytoplasmic inclusions of flocculent material, and intratumoral mast cells should prompt evaluation of SDH status, as it may have implications for screening the patient and relatives. Negative immunohistochemistry for KIT and heterogeneous labeling for epithelial antigens are other supportive features.

Gastrointestinal stromal tumor - an evolving concept

Gastrointestinal stromal tumors (GISTs) are the most frequent mesenchymal tumors of the gastrointestinal tract. The discovery that these tumors, formerly thought of smooth muscle origin, are indeed better characterized by specific activating mutation in genes coding for the receptor tyrosine kinases (RTKs) CKIT and PDGFRA and that these mutations are strongly predictive for the response to targeted therapy with RTK inhibitors has made GISTs the typical example of the integration of basic molecular knowledge in the daily clinical activity. The information on the mutational status of these tumors is essential to predict (and subsequently to plan) the therapy. As resistant cases are frequently wild type, other possible oncogenic events, defining other "entities," have been discovered (e.g., succinil dehydrogenase mutation/dysregulation, insuline growth factor expression, and mutations in the RAS-RAF-MAPK pathway). The classification of disease must nowadays rely on the integration of the clinico-morphological characteristics with the molecular data.

WHO classification of soft tissue tumours: an update based on the 2013 (4th) edition

The fourth edition of the World Health Organization (WHO) Classification of Tumours of Soft Tissue and Bone was published in February 2013, and serves to provide an updated classification scheme and reproducible diagnostic criteria for pathologists. Given the relative rarity of soft tissue tumours and the rapid rate of immunohistochemical and genetic/molecular developments (not infrequently facilitating recognition of new tumour entities), this updated text edited by a consensus group is important for both practising pathologists and oncologists. The 2013 WHO classification includes several changes in soft tissue tumour classification, including several new entities (e.g., pseudomyogenic haemangioendothelioma, haemosiderotic fibrolipomatous tumour, and acral fibromyxoma), three newly included sections for gastrointestinal stromal tumours, nerve sheath tumours, and undifferentiated/unclassified soft tissue tumours, respectively, various 'reclassified' tumours, and a plethora of new genetic and molecular data for established tumour types that facilitate better definition and are useful as diagnostic tools. This article briefly outlines these updates based on the 2013 WHO classification of soft tissue tumours.

Telomerase reverse transcriptase promoter mutations in tumors originating from the adrenal gland and extra-adrenal paraganglia

Hotspot mutations in the promoter of the telomerase reverse transcriptase (TERT) gene have been recently reported in human cancers and proposed as a novel mechanism of telomerase activation. To explore TERT promoter mutations in tumors originating from the adrenal gland and extra-adrenal paraganglia, a set of 253 tumors (38 adrenocortical carcinomas (ACCs), 127 pheochromocytomas (PCCs), 18 extra-adrenal paragangliomas (ea PGLs), 37 head and neck PGLs (HN PGLs), and 33 peripheral neuroblastic tumors) was selected along with 16 human neuroblastoma (NBL) and two ACC cell lines to assess TERT promoter mutations by the Sanger sequencing method. All mutations detected were confirmed by a SNaPshot assay. Additionally, 36 gastrointestinal stromal tumors (GISTs) were added to explore an association between TERT promoter mutations and SDH deficiency. TERT promoter mutations were found in seven out of 289 tumors and in three out of 18 human cell lines; four C228T mutations in 38 ACCs (10.5%), two C228T mutations in 18 ea PGLs (11.1%), one C250T mutation in 36 GISTs (2.8%), and three C228T mutations in 16 human NBL cell lines (18.75%). No mutation was detected in PCCs, HN PGLs, neuroblastic tumors as well as ACC cell lines. TERT promoter mutations preferentially occurred in a SDH-deficient setting (P=0.01) being present in three out of 47 (6.4%) SDH-deficient tumors vs zero out of 171 (0%) SDH-intact tumors. We conclude that TERT promoter mutations occur in ACCs and ea PGLs. In addition, preliminary evidence indicates a potential association with the acquisition of TERT promoter mutations in SDH-deficient tumors.

Hereditary Pheochromocytoma

INTRODUCTION

Pheochromocytomas (PHEO) and paragangliomas (PGL) are rare neuroendocrine tumors with an estimated occurrence of 2 to 5 patients per million per year and an incidence of about 1 per 100 000 in the general population. These tumors may arise sporadically or be associated to various syndromes, namely multiple endocrine neoplasia type 2, neurofibromatosis type 1, Von Hippel-Lindau syndrome, and hereditary paraganglioma-pheochromocytoma syndromes.

OBJECTIVES

This article aims to review the current epidemiology, pathogenesis, clinical presentation, and genetic aspects of syndromes associated with hereditary PHEO/PGL.

METHODS

The literature research, conducted at PubMed database, included review articles, published from February 2009 to February 2014, written in English or Portuguese, using as query: "Hereditary AND Pheochromocytoma."

CONCLUSION

These tumors can be part of a myriad hereditary conditions that are not yet fully understood. Nevertheless, important systemic symptoms and even fatal outcomes can occur. Knowledge of these hereditary conditions can ensure a more efficient detection, treatment, and even prevention of these neuroectodermal tumors, thus new tests and studies should be conducted.

Succinate dehydrogenase deficient gastrointestinal stromal tumors (GISTs) - a review

Loss of function of the succinate dehydrogenase complex characterizes a rare group of human tumors including some gastrointestinal stromal tumors, paragangliomas, renal carcinomas, and pituitary adenomas, and these can all be characterized as SDH-deficient tumors. Approximately 7.5% of gastric gastrointestinal stromal tumors are SDH-deficient and not driven by KIT/PDGFRA mutations, as are most other GISTs. The occurrence of SDH-deficient GISTs is restricted to stomach, and they typically occur in children and young adults representing a spectrum of clinical behavior from indolent to progressive. Slow progression is a common feature even after metastatic spread has taken place, and many patients live years with metastases. SDH-deficient GISTs have characteristic morphologic features including multinodular gastric wall involvement, often multiple separate tumors, common lymphovascular invasion, and occasional lymph node metastases. Diagnostic is the loss of succinate dehydrogenase subunit B (SDHB) from the tumor cells and this can be practically assessed by immunohistochemistry. SDHA is lost in cases associated with SDHA mutations. Approximately half of the patients have SDH subunit gene mutations, often germline and most commonly A (30%), and B, C or D (together 20%), with both alleles inactivated in the tumor cells according to the classic tumor suppressor gene model. Half of the cases are not associated with SDH-mutations and epigenetic silencing of the SDH complex is the possible pathogenesis. Extensive genomic methylation has been observed in these tumors, which is in contrast with other GISTs. SDH-loss causes succinate accumulation and activation of pseudohypoxia signaling via overexpression of HIF-proteins. Activation of insulin-like growth factor 1-signaling is also typical of these tumors. SDH-deficient GISTs are a unique group of GISTs with an energy metabolism defect as the key oncogenic mechanism. This article is part of a Directed Issue entitled: Rare Cancers.

Points to consider in the clinical use of NGS panels for mitochondrial disease: an analysis of gene inclusion and consent forms

Mitochondrial next generation sequencing (NGS) panels offer single-step analysis of the numerous nuclear genes involved in the structure, function, and maintenance of mitochondria. However, the complexities of mitochondrial biology and genetics raise points for consideration in clinical use of these tests. To understand the current status of mitochondrial genetic testing, we assessed the gene offerings and consent forms of mitochondrial NGS panels available from seven US-based clinical laboratories. The NGS panels varied markedly in number of genes (101-1204 genes), and the proportion of genes causing "classic" mitochondrial diseases and their phenocopies ranged widely between labs (18 %-94 % of panel contents). All panels included genes not associated with classic mitochondrial diseases (6 %-28 % of panel contents), including genes causing adult-onset neurodegenerative disorders, cancer predisposition, and other genetic syndromes or inborn errors of metabolism. Five of the panels included genes that are not listed in OMIM to be associated with a disease phenotype (5 %-49 % of panel contents). None of the consent documents reviewed had options for patient preference regarding receipt of incidental findings. These findings raise points of discussion applicable to mitochondrial diagnostics, but also to the larger arenas of exome and genome sequencing, including the need to consider the boundaries between clinical and research testing, the necessity of appropriate informed consent, and the responsibilities of clinical laboratories and clinicians. Based on these findings, we recommend careful evaluation by laboratories of the genes offered on NGS panels, clear communication of the predicted phenotypes, and revised consent forms to allow patients to make choices about receiving incidental findings. We hope that our analysis and recommendations will help to maximize the considerable clinical utility of NGS panels for the diagnosis of mitochondrial disease.

Novel uses of immunohistochemistry in the diagnosis and classification of soft tissue tumors

Immunohistochemistry plays a key role in the diagnosis of soft tissue tumors. Until recently, however, the primary purpose of immunohistochemistry in this context was simply to attempt to demonstrate a line of differentiation. Unfortunately, most traditional markers (predominantly directed against cytoplasmic determinants) show relatively limited specificity. Over the last decade or so, much more specific immunohistochemical markers for soft tissue tumors have been developed. This review will provide an update of some of the most useful new diagnostic markers, which are significantly changing clinical practice for surgical pathologists, separated into three general categories: (1) lineage-restricted transcription factors, (2) protein correlates of molecular alterations, and (3) diagnostic markers identified by gene expression profiling.

Non-pheochromocytoma (PCC)/paraganglioma (PGL) tumors in patients with succinate dehydrogenase-related PCC-PGL syndromes: a clinicopathological and molecular analysis

OBJECTIVE

Although the succinate dehydrogenase (SDH)-related tumor spectrum has been recently expanded, there are only rare reports of non-pheochromocytoma/paraganglioma tumors in SDHx-mutated patients. Therefore, questions still remain unresolved concerning the aforementioned tumors with regard to their pathogenesis, clinicopathological phenotype, and even causal relatedness to SDHx mutations. Absence of SDHB expression in tumors derived from tissues susceptible to SDH deficiency is not fully elucidated.

DESIGN AND METHODS

Three unrelated SDHD patients, two with pituitary adenoma (PA) and one with papillary thyroid carcinoma (PTC), and three SDHB patients affected by renal cell carcinomas (RCCs) were identified from four European centers. SDHA/SDHB immunohistochemistry (IHC), SDHx mutation analysis, and loss of heterozygosity analysis of the involved SDHx gene were performed on all tumors. A cohort of 348 tumors of unknown SDHx mutational status, including renal tumors, PTCs, PAs, neuroblastic tumors, seminomas, and adenomatoid tumors, was investigated by SDHB IHC.

RESULTS

Of the six index patients, all RCCs and one PA displayed SDHB immunonegativity in contrast to the other PA and PTC. All immunonegative tumors demonstrated loss of the WT allele, indicating bi-allelic inactivation of the germline mutated gene. Of 348 tumors, one clear cell RCC exhibited partial loss of SDHB expression.

CONCLUSIONS

These findings strengthen the etiological association of SDHx genes with pituitary neoplasia and provide evidence against a link between PTC and SDHx mutations. Somatic deletions seem to constitute the second hit in SDHB-related renal neoplasia, while SDHx alterations do not appear to be primary drivers in sporadic tumorigenesis from tissues affected by SDH deficiency.

The International Society of Urological Pathology (ISUP) Vancouver Classification of Renal Neoplasia

The classification working group of the International Society of Urological Pathology consensus conference on renal neoplasia was in charge of making recommendations regarding additions and changes to the current World Health Organization Classification of Renal Tumors (2004). Members of the group performed an exhaustive literature review, assessed the results of the preconference survey and participated in the consensus conference discussion and polling activities. On the basis of the above inputs, there was consensus that 5 entities should be recognized as new distinct epithelial tumors within the classification system: tubulocystic renal cell carcinoma (RCC), acquired cystic disease-associated RCC, clear cell (tubulo) papillary RCC, the MiT family translocation RCCs (in particular t(6;11) RCC), and hereditary leiomyomatosis RCC syndrome-associated RCC. In addition, there are 3 rare carcinomas that were considered as emerging or provisional new entities: thyroid-like follicular RCC; succinate dehydrogenase B deficiency-associated RCC; and ALK translocation RCC. Further reports of these entities are required to better understand the nature and behavior of these highly unusual tumors. There were a number of new concepts and suggested modifications to the existing World Health Organization 2004 categories. Within the clear cell RCC group, it was agreed upon that multicystic clear cell RCC is best considered as a neoplasm of low malignant potential. There was agreement that subtyping of papillary RCC is of value and that the oncocytic variant of papillary RCC should not be considered as a distinct entity. The hybrid oncocytic chromophobe tumor, which is an indolent tumor that occurs in 3 settings, namely Birt-Hogg-Dubé Syndrome, renal oncocytosis, and as a sporadic neoplasm, was placed, for the time being, within the chromophobe RCC category. Recent advances related to collecting duct carcinoma, renal medullary carcinoma, and mucinous spindle cell and tubular RCC were elucidated. Outside of the epithelial category, advances in our understanding of angiomyolipoma, including the epithelioid and epithelial cystic variants, were considered. In addition, the apparent relationship between cystic nephroma and mixed epithelial and stromal tumor was discussed, with the consensus that these tumors form a spectrum of neoplasia. Finally, it was thought that the synovial sarcoma should be removed from the mixed epithelial and mesenchymal category and placed within the sarcoma group. The new classification is to be referred to as the International Society of Urological Pathology Vancouver Classification of Renal Neoplasia.

Succinate dehydrogenase deficiency is associated with decreased 5-hydroxymethylcytosine production in gastrointestinal stromal tumors: implications for mechanisms of tumorigenesis

Gastrointestinal stromal tumors (GISTs) usually harbor activating mutations in KIT or PDGFRA, which promote tumorigenesis through activation of growth factor receptor signaling pathways. Around 15% of GISTs in adults and >90% in children lack such mutations ('wild-type' GISTs). Most gastric wild-type GISTs show loss of function of the Krebs cycle enzyme complex succinate dehydrogenase (SDH). However, the mechanism by which SDH deficiency drives tumorigenesis is unclear. Loss of SDH leads to succinate accumulation, which is thought to inhibit α-ketoglutarate-dependent dioxygenase enzymes, such as the TET family of DNA hydroxylases. TET proteins catalyze the conversion of 5-methylcytosine to 5-hydroxymethylcytosine (5-hmC), which is required for subsequent DNA demethylation. Thus, TET-mediated 5-hmC production alters global DNA methylation patterns and may thereby influence gene expression. We investigated 5-hmC levels in a cohort of genotyped GISTs to determine whether loss of SDH was associated with inhibition of TET activity. 5-hmC levels were examined via immunohistochemistry in a cohort of 30 genotyped GISTs, including 10 SDH-deficient tumors (5 SDHA mutant; 1 SDHB mutant; 1 SDHC mutant; 3 unknown), 14 tumors with KIT mutations (10 in exon 11; 3 in exon 9; 1 in exon 17), and 6 tumors with PDGFRA mutations (all in exon 18). Staining for 5-hmC was negative in 9 of 10 (90%) SDH-deficient GISTs, 3 of 14 (21%) KIT-mutant GISTs, and 1 of 6 (17%) PDGFRA-mutant GISTs. The other SDH-deficient GIST showed weak staining for 5-hmC. Thus, 5-hmC was absent in nearly all SDH-deficient GISTs. These findings suggest that SDH deficiency may promote tumorigenesis through accumulation of succinate and inhibition of dioxygenase enzymes. Inhibition of TET activity may, in turn, alter global DNA methylation and gene expression in SDH-deficient tumors.

Succinate dehydrogenase expression in breast cancer

The aim of this study was to investigate succinate dehydrogenase (SDH) expression in breast cancer according to breast cancer molecular subtype using immunohistochemistry and to assess the clinical implications of SDH expression. Immunohistochemical staining for ER, PR, HER-2, Ki-67, HIF-1α, SDHA, and SDHB was performed on tissue microarrays of 721 breast cancers. According to the immunohistochemistry results for ER, PR, HER-2, and Ki-67 and fluorescence in situ hybridization (FISH) results for HER-2, breast cancer molecular subtypes were classified into luminal A, luminal B, HER-2, and triple-negative breast cancer (TNBC). HER-2 subtype breast cancers most frequently showed high-level expression of SDHA in tumor cells, while the luminal A subtype most frequently showed low or negative expression of SDHA in tumor cells (P = 0.032). Stromal SDHB expression rate was highest in HER-2 subtype and lowest in TNBC (P < 0.001). SDHA-negative breast cancers were associated with younger age at diagnosis (P = 0.012), and SDHB-negative breast cancers with lower histologic grade (P = 0.044) and lower Ki-67 labeling index (LI) (P = 0.046). Tumor phenotypes according to the SDH status were SDHA(+)/SDHB(+) > SDHA(-)/SDHB(-) > SDHA(-)/SDHB(+) > SDHA(+)/SDHB(-) in order of frequency. The stromal phenotypes were SDHA(-)/SDHB(-) > SDHA(+)/SDHB(+) > SDHA(-)/SDHB(+) > SDHA(+)/SDHB(-). In conclusion, loss of SDHA or SDHB expression was observed in about 3% of breast cancers in this study. Low SDH expression status in breast tumor cells was associated with younger age at diagnosis and low-grade histology.