Succinate Dehydrogenase Complex Iron Sulfur Subunit B (SDHB) Immunohistochemistry in Pheochromocytoma, Head and Neck Paraganglioma, Thoraco-Abdomino-Pelvic Paragangliomas: Is It a Good Idea to Use in Routine Work?

BACKGROUND: In this study, we aimed to detect Succinate Dehydrogenase Complex Iron Sulfur Subunit B (SDHB) frequency in paragangliomas and pheochromocytomas (PPGL) with immunohistochemistry; compare with Pheochromacytoma of the Adrenal Gland Scaled Score (PASS) classification and analyse the differences between pheochromocytoma (Pheo), head-neck paragangliomas (HNPGL) and thoraco-abdominal-pelvic paraganglioma (TAPPGL) sub-groups. METHODS: A total 114 PPGL cases (73 HNPGL, 15 TAPPGL and 27 Pheo belonging to 112 cases) are included. Immunohistochemically, SDHB and Ki-67 are investigated and malignancy risks are determined by PASS classification. Results are assessed statistically with chi-square test and p <0,01 is considered significant. RESULTS: SDHB mutations are observed in 20 of 114 (17.54 %) PPGL cases, 3 (11,12%) of which is Pheo, 12 (16,44) is HNPGL, and 5 (35,71%) is TAPPGL (P <0,02). While 15/82 (18,29%) cases with SDHB mutations do not have a malignancy potential according to PASS classification, 5/32 (15,63%) cases has (p=0,73). TAPPGL, HNPGL and Pheo sub-groups have a significant difference between SDHB expression (p <0,02), malignancy potential according to PASS classification (p <0,0001) and Ki-67 proliferation index (p <0,0001). CONCLUSION: To identify patients for molecular pathological examination, routine application of SDHB immunohistochemistry to PPGL tumors are suggested especially in HNPGLs.

Succinate Mediates Tumorigenic Effects via Succinate Receptor 1: Potential for New Targeted Treatment Strategies in Succinate Dehydrogenase Deficient Paragangliomas.

Paragangliomas and pheochromocytomas (PPGLs) are chromaffin tumors associated with severe catecholamine-induced morbidities. Surgical removal is often curative. However, complete resection may not be an option for patients with succinate dehydrogenase subunit A-D (SDHx) mutations. SDHx mutations are associated with a high risk for multiple recurrent, and metastatic PPGLs. Treatment options in these cases are limited and prognosis is dismal once metastases are present. Identification of new therapeutic targets and candidate drugs is thus urgently needed. Previously, we showed elevated expression of succinate receptor 1 (SUCNR1) in SDHB PPGLs and SDHD head and neck paragangliomas. Its ligand succinate has been reported to accumulate due to SDHx mutations. We thus hypothesize that autocrine stimulation of SUCNR1 plays a role in the pathogenesis of SDHx mutation-derived PPGLs. We confirmed elevated SUCNR1 expression in SDHx PPGLs and after SDHB knockout in progenitor cells derived from a human pheochromocytoma (hPheo1). Succinate significantly increased viability of SUCNR1-transfected PC12 and ERK pathway signaling compared to control cells. Candidate SUCNR1 inhibitors successfully reversed proliferative effects of succinate. Our data reveal an unrecognized oncometabolic function of succinate in SDHx PPGLs, providing a growth advantage via SUCNR1.

MITOCHONDRIA: Succinate dehydrogenase subunit B-associated phaeochromocytoma and paraganglioma.

Phaeochromocytomas and paragangliomas are rare neuroendocrine tumours. So far, over 20 causative genes have been identified, of which the most frequent and strongest indicator for malignancies are mutations in succinate dehydrogenase subunit B. No curative therapy is available for patients with metastases resulting in poor prognosis. Therapy development has been hindered by lack of suitable model systems. The succinate dehydrogenase complex is located in the inner membrane of the mitochondria and plays a crucial role in the oxidative phosphorylation chain and the tricarboxylic acid-cycle. Succinate dehydrogenase deficiency results in accumulation of the oncometabolite succinate inducing hypoxia inducible factor stabilization, deoxyribonucleic acid and histone methylation inhibition, and impaired production of adenosine triphosphate. It remains unknown which combination of pathways and/or triggers are decisive for metastases development. In this review, the role of mitochondria in malignant succinate dehydrogenase subunit B-associated phaeochromocytomas and paragangliomas and implications for mitochondria as therapeutic target are discussed.

Clinical characteristics and outcomes of SDHB-related pheochromocytoma and paraganglioma in children and adolescents.

PURPOSE: Pheochromocytomas/paragangliomas (PHEOs/PGLs) are rare in children with only a few SDHB mutation-related cases. Previous studies on children were conducted in small cohorts. This large set of pediatric patients provides robust data in the evaluation of clinical outcomes. METHODS: Sixty-four pediatric PHEO/PGL patients with SDHB germline mutations were included in the present study. The clinical presentation, disease course, and survival rate were evaluated. RESULTS: Thirty-eight males and 26 females were diagnosed with PHEO/PGL at a median age of 13 years. The majority of patients displayed norepinephrine hypersecretion and 73.44% initially presented with a solitary tumor. Metastases developed in 70% of patients at the median age of 16 years and were mostly diagnosed first 2 years and in years 12-18 post-diagnosis. The presence of metastases at the time of diagnosis had a strong negative impact on survival in males but not in females. The estimated 5-, 10-, and 20-year survival rates were 100%, 97.14%, and 77.71%, respectively. CONCLUSION: The present report has highlighted several important aspects in the management of pediatric patients with SDHB mutations associated-PHEO/PGL. Initial diagnostic evaluation of SDHB mutation carriers should be started at age of 5-6 years with initial work-up focusing on abdominal region. Thorough follow-up is crucial first 2 years post-diagnosis and more frequent follow-ups are needed in years 10-20 post-diagnosis due to the increased risk of metastases. Although this age group developed metastasis as early as 5 years from diagnosis, we have shown that the overall 20-year prognosis and survival are good.

Molecular pathogenesis of tumorigenesis caused by succinate dehydrogenase defect.

Succinate dehydrogenase (SDH), also named as complex II or succinate:quinone oxidoreductases (SQR) is a critical enzyme in bioenergetics and metabolism. This is because the enzyme is located at the intersection of oxidative phosphorylation and tricarboxylic acid cycle (TCA); the two major pathways involved in generating energy within cells. SDH is composed of 4 subunits and is assembled through a multi-step process with the aid of assembly factors. Not surprisingly malfunction of this enzyme has marked repercussions in metabolism leading to devastating tumors such as paraganglioma and pheochromocytoma. It is already known that mutations in the genes encoding subunits lead to tumorigenesis, but recent discoveries have indicated that mutations in the genes encoding the assembly factors also contribute to tumorigenesis. The mechanisms of pathogenesis of tumorigenesis have not been fully understood. However, a multitude of signaling pathways including succinate signaling was determined. We, here discuss how defective SDH may lead to tumor development at the molecular level and describe how yeast, as a model system, has contributed to understanding the molecular pathogenesis of tumorigenesis resulting from defective SDH.

Imaging Features of Succinate Dehydrogenase-deficient Pheochromocytoma-Paraganglioma Syndromes.

Pheochromocytoma (PC) and paraganglioma (PGL) are rare neuroendocrine tumors that occur throughout the body from the base of the skull to the pelvis. Sympathetic catecholamine-secreting tumors may be associated with hyperadrenergic symptoms and long-term morbidity if they are untreated. Typically biochemically silent, head and neck PGLs may result in cranial nerve palsies and symptoms due to localized mass effect. Tumors can arise sporadically or as part of an inheritable PC-PGL syndrome. Up to 40% of tumors are recognized to be associated with germline mutations in an increasing array of susceptibility genes, including those that appear to arise sporadically. Most commonly, up to 25% of all PC-PGLs are associated with mutations in one of the succinate dehydrogenase (SDH) enzyme subunit genes. The resulting familial PC-PGL syndrome varies according to the affected enzyme subunit (most commonly SDHB and SDHD mutations) with respect to tumor prevalence, location, age of onset, and risk of malignancy. Patients with SDH enzyme mutations have increased lifetime risk of developing multifocal tumors and malignancy. Early recognition of individuals at high risk, genetic testing, screening of family members, and lifelong surveillance programs are recommended, but not without health, economic, and psychologic implications. Anatomic and functional imaging is key to diagnosis, staging, treatment planning, and lifelong surveillance of these individuals. Radiologists must be aware of the imaging appearance of these varied tumors.©RSNA, 2019.

Expression of PDK1 in malignant pheochromocytoma as a new promising potential therapeutic target.

PURPOSE: Phosphoinositide-dependent kinase 1 (PDK1) is highly expressed in many solid tumors. And several studies have demonstrated that PDK1 has been an emerging and promising target for anti-cancer therapies. However, the role of PDK1 has not been studied so far in malignant pheochromocytoma (PCC). METHODS: In this study, immunohistochemical staining was performed to investigate the protein level of PDK1 in 63 PCC tissue samples, of which 49 were benign and 14 were malignant. In addition, we evaluated the effect of inhibition of PDK1 with siRNA on cell growth, apoptosis and invasive capacity in PC12 cells and identified the underlying mechanisms. RESULTS: We found that PDK1 was overexpressed in malignant PCC tissues, and knockdown of PDK1 with siRNA significantly inhibited cell proliferation, increased apoptosis induction, and attenuated cell migration and invasive capacity in PC12 cells. We also showed that knockdown of PDK1 significantly reduced the phosphorylation of Akt at threonine 308 (p-Akt T308) but did not alter the serine phosphorylation of Akt on the S473 site (p-Akt S473). Furthermore, we found that the p-Akt expression was noticeably decreased after knockdown of PDK1, but the t-Akt expression did not show a significant decrease. CONCLUSION: We have demonstrated for the first time that PDK1 is overexpressed in human malignant PCC and plays an important role in the malignant biological behaviors of PC12 cell. Specifically, we have revealed that knockdown of PDK1 could attenuate activation of the Akt signaling. These data suggest that PDK1 could be a new promising potential therapeutic target in human cancer treatment for malignant PCC.

Diagnostic Investigation of Lesions Associated with Succinate Dehydrogenase Defects.

The mitochondrial enzyme succinate dehydrogenase (SDH) acts as a tumor suppressor. Biallelic inactivation of one of the genes encoding for SDH subunits (collectively named SDHx) leads to complete loss of the protein function and the development of diverse group of tumors. Pheochromocytomas-paragangliomas are the prime example of hereditary tumors caused by SDH deficiency. In this review, we discuss the roles of imaging examinations, and illustrate new insights into genotype-imaging phenotype relationships.

An Update on the Histology of Pheochromocytomas: How Does it Relate to Genetics?

Pheochromocytomas are rare neuroendocrine tumors of the adrenal gland, whereas any extra-adrenal tumor with similar histology is designated as paraganglioma. These tumors have a very high rate of germline mutations in a large number of genes, up to 35% to 40%, frequently predisposing for other tumors as well. Therefore, they represent a phenomenal challenge for treating physicians. This review focuses on pheochromocytomas only, with special attention to gross and microscopic clues to the diagnosis of genetic syndromes, including the role of succinate dehydrogenase subunit A and subunit B immunohistochemistry as surrogate markers for genetic analysis in the field of succinate dehydrogenase subunit gene mutations.

Catecholamine-Synthesizing Enzymes in Pheochromocytoma and Extraadrenal Paraganglioma.

In chromaffin cells, tyrosine hydroxylase (TH), aromatic L-amino acid decarboxylase (AADC), dopamine ß-hydroxylase (DBH), and phenylethanolamine N-methyltransferase (PNMT) are mainly involved in catecholamine synthesis. In this study, we evaluated the association between the status of catecholamine-synthesizing enzymes and histopathological features of pheochromocytoma and extraadrenal paraganglioma with special emphasis upon their postoperative clinical behavior. Immunohistochemical evaluation of TH, DBH, AADC, PNMT, Ki 67, and S-100 was performed in 29 pheochromocytoma and 10 extraadrenal paraganglioma and one lymph node harboring metastatic pheochromocytoma. Among these cases, metastasis was subsequently developed in three cases. Urinary normetanephrine (U-NM) levels were significantly higher in clinical metastatic cases than non-metastatic ones. Ki 67 labeling index was significantly higher in both clinical metastatic cases and the Adrenal Gland Scaled Score (PASS) score of ≧ 4 cases than PASS < 4 cases, although this score was originally used in pheochromocytoma. H-score of AADC and DBH were significantly lower in PASS ≧ 4 cases than those with < 4 cases, and in the cases associated with intratumoral necrosis (n = 4), the presence of spindle shaped tumor cells (n = 4), and large nests of cells or diffuse growth (n = 5). Lower status of intratumoral AADC could be related to poor differentiation of tumor cells in both catecholamine production and morphology and could be related to aggressive biological behavior of both pheochromocytoma and extraadrenal paraganglioma.

Continued Tumor Reduction of Metastatic Pheochromocytoma/Paraganglioma Harboring Succinate Dehydrogenase Subunit B Mutations with Cyclical Chemotherapy.

Patients harboring germline mutations in the succinate dehydrogenase complex subunit B (SDHB) gene present with pheochromocytomas and paragangliomas (PPGL) that are more likely malignant and clinically aggressive. The combination chemotherapy cyclophosphamide, vincristine, and dacarbazine (CVD) was retrospectively evaluated in patients with SDHB-associated metastatic PPGL.Query Twelve metastatic PPGL patients harboring SDHB mutations/polymorphisms with undetectable SDHB immunostaining were treated with CVD. CVD therapy consisted of 750 mg/m2 cyclophosphamide with 1.4 mg/m2 vincristine on day 1 and 600 mg/m2 dacarbazine on days 1 and 2, every 21-28 days. Treatment outcome was determined by RECIST criteria as well as determination of response duration and progression-free and overall survivals. A median of 20.5 cycles (range 4-41) was administered. All patients had tumor reduction (12-100% by RECIST). Complete response was seen in two patients, while partial response was observed in 8. The median number of cycles to response was 5.5. Median duration of response was 478 days, with progression-free and overall survivals of 930 and 1190 days, respectively. Serial [18F]-fluorodeoxyglucose positron emission tomography and computed tomography imaging demonstrated continued incremental reduction in maximal standardized uptake values (SUVmax) values in 26/30 lesions. During treatment administration, the median SUV decreased from > 25 to < 6, indicating the efficacy of chemotherapy over a prolonged period of time. Prolonged therapy results in continued incremental tumor reduction, and is consistent with persistent drug sensitivity. CVD chemotherapy is recommended to be considered part of the initial management in patients with metastatic SDHB-related PPGL.

PKA activity exacerbates hypoxia-induced ROS formation and hypoxic injury in PC-12 cells.

Hypoxia is a primary factor in many pathological conditions. Hypoxic cell death is commonly attributed to metabolic failure and oxidative injury. cAMP-dependent protein kinase A (PKA) is activated in hypoxia and regulates multiple enzymes of the mitochondrial electron transport chain, thus may be implicated in cellular energy depletion and hypoxia-induced cell death. Wild type (WT) PC-12 cells and PKA activity-deficient 123.7 PC-12 cells were exposed to 3, 6, 12 and 24h hypoxia (0.1% or 5% O2). Hypoxia, at 24h 0.1% O2, induced cell death and increased reactive oxygen species (ROS) in WT PC-12 cells. Despite lower ATP levels in normoxic 123.7 cells than in WT cells, hypoxia only decreased ATP levels in WT cells. However, menadione-induced oxidative stress similarly affected both cell types. While mitochondrial COX IV expression remained consistently higher in 123.7 cells, hypoxia decreased COX IV expression in both cell types. N-acetyl cysteine antioxidant treatment blocked hypoxia-induced WT cell death without preventing ATP depletion. Transient PKA catα expression in 123.7 cells partially restored hypoxia-induced ROS but did not alter ATP levels or COX IV expression. We conclude that PKA signaling contributes to hypoxic injury, by regulating oxidative stress rather than by depleting ATP levels. Therapeutic strategies targeting PKA signaling may improve cellular adaptation and recovery in hypoxic pathologies.

Composite Pheochromocytoma/Paraganglioma-Ganglioneuroma: A Clinicopathologic Study of Eight Cases with Analysis of Succinate Dehydrogenase.

Ganglioneuromas represent the most well-differentiated spectrum of neoplasia arising from the sympathetic nervous system, while neuroblastomas represent the most poorly differentiated counterpart, and ganglioneuroblastomas represent intermediate stages of differentiation. Small series of cases have documented the co-occurrence of ganglioneuroma with a pheochromocytoma (Pheo)/paraganglioma (PGL) component. We report the clinicopathologic features of eight such cases, diagnosed between 2003 and 2015 with a mean follow-up of 22 months (1-47), which were evaluated for syndrome associations, SDHB expression, and clinical outcome. Mutations of the succinate dehydrogenase (SDH) complex subunits (A, B, C, D, and SDHAF2) have been implicated in predicting metastatic behavior and in identifying possible paraganglioma syndromes. The proliferative index was calculated by manual quantification of Ki-67-positive cells at selected hot-spots using ImageJ (NIH). In our series, composite Pheo/PGL-ganglioneuromas predominantly involved the adrenal gland (Pheo 7, PGL 1). The cases had an equal gender distribution (males 4, females 4), with a mean age at diagnosis of 67 years (range 53 to 86 years), an average size of 5.2 cm (range 2 to 8.2 cm), an average weight of 49.3 g (7.8 to 144.7 g, n = 6), and the majority were functionally active (7 of 8, 88%). The mean Ki67 proliferation rate was 2% (range 0.3 to 3%), and all cases retained SDHB expression (8/8, 100%). No patient (0/8, 0%) developed metastatic disease on follow-up. One patient had a retroperitoneal composite PGL-ganglioneuroma in the setting of neurofibromatosis type 1. No recurrent disease or other associations were identified. In our study, composite Pheo/PGL-ganglioneuromas predominantly affected the adrenal gland in older patients, showed no loss of SDHB, and no disease recurrence was identified.

Protective Effect of Quercetin against Oxidative Stress-Induced Cytotoxicity in Rat Pheochromocytoma (PC-12) Cells.

Oxidative stress has been implicated in the pathogenesis of many kinds of neurodegenerative disorders, particularly Parkinson's disease. Quercetin is a bioflavonoid found ubiquitously in fruits and vegetables, and has antioxidative activity. However, the underlying mechanism of the antioxidative effect of quercetin in neurodegenerative diseases has not been well explored. Here, we investigated the antioxidative effect and underlying molecular mechanisms of quercetin on PC-12 cells. We found that PC-12 cells pretreated with quercetin exhibited an increased cell viability and reduced lactate dehydrogenase (LDH) release when exposed to hydrogen peroxide (H2O2). The significantly-alleviated intracellular reactive oxygen species (ROS), malondialdehyde (MDA), and lipoperoxidation of the cell membrane of PC-12 cells induced by H2O2 were observed in the quercetin pretreated group. Furthermore, quercetin pretreatment markedly reduced the apoptosis of PC-12 cells and hippocampal neurons. The inductions of antioxidant enzyme catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) in PC-12 cells exposed to H2O2 were significantly reduced by preatment with quercetin. In addition, quercetin pretreatment significantly increased Bcl-2 expression, and reduced Bax, cleaved caspase-3 and p53 expressions. In conclusion, this study demonstrated that quercetin exhibited a protective effect against oxidative stress-induced apoptosis in PC-12 cells. Our findings suggested that quercetin may be developed as a novel therapeutic agent for neurodegenerative diseases induced by oxidative stress.

Analysis of SDHAF3 in familial and sporadic pheochromocytoma and paraganglioma.

BACKGROUND: Germline mutations in genes encoding subunits of succinate dehydrogenase (SDH) are associated with the development of pheochromocytoma (PC) and/or paraganglioma (PGL). As assembly factors have been identified as playing a role in maturation of individual SDH subunits and assembly of the functioning SDH complex, we hypothesized that SDHAF3 variants may be associated with PC/PGL and functionality of SDH. METHODS: DNA was extracted from the blood of 37 individuals (from 23 families) with germline SDH mutations and 18 PC/PGL (15 sporadic, 3 familial) and screened for mutations using a custom gene panel, containing SDHAF3 (SDH assembly factor 3) as well as eight known PC/PGL susceptibility genes. Molecular and functional consequences of an identified sequence variant of SDHAF3 were assessed in yeast and mammalian cells (HEK293). RESULTS: Using massively parallel sequencing, we identified a variant in SDHAF3, c.157 T > C (p.Phe53Leu), associated with increased prevalence in familial and sporadic PC/PGL (6.6%) when compared to normal populations (1.2% [1000 Genomes], p = 0.003; 2.1% [Exome Aggregation Consortium], p = 0.0063). In silico prediction tools suggest this variant is probably damaging to protein function, hence we assessed molecular and functional consequences of the resulting amino acid change (p.Phe53Leu) in yeast and human cells. We showed that introduction of SDHAF3 p.Phe53Leu into Sdh7 (ortholog of SDHAF3 in humans) null yeast resulted in impaired function, as observed by its failure to restore SDH activity when expressed in Sdh7 null yeast relative to WT SDHAF3. As SDHAF3 is involved in maturation of SDHB, we tested the functional impact of SDHAF3 c.157 T > C and various clinically relevant SDHB mutations on this interaction. Our in vitro studies in human cells show that SDHAF3 interacts with SDHB (residues 46 and 242), with impaired interaction observed in the presence of the SDHAF3 c.157 T > C variant. CONCLUSIONS: Our studies reveal novel insights into the biogenesis of SDH, uncovering a vital interaction between SDHAF3 and SDHB. We have shown that SDHAF3 interacts directly with SDHB (residue 242 being key to this interaction), and that a variant in SDHAF3 (c.157 T > C [p.Phe53Leu]) may be more prevalent in individuals with PC/PGL, and is hypomorphic via impaired interaction with SDHB.

MicroRNA-15b-5p targets ERK1 to regulate proliferation and apoptosis in rat PC12 cells.

MicroRNAs (miRNAs) play an important role in multiple biological processes, and many miRNAs have been shown to regulate cell proliferation and apoptosis. In this study, we investigated the role of miR-15b-5p in cell proliferation and apoptosis in PC12 cells. We found that overexpression of miR-15b-5p could decrease cell proliferation and induce apoptosis and cytotoxic activities in PC12 cells. Bioinformatics analysis and luciferase activities assays showed that miR-15b-5p might target extracellular signal-regulated kinase 1 (ERK1) by binding to its 3'-untranslated region (3'-UTR). Moreover, we also found that overexpression of ERK1 could attenuate the effects of miR-15b-5p in PC12 cells. Finally, our results suggest that miR-15b-5p might inhibit cell proliferation and induce apoptosis in PC12 cells by targeting ERK1.

MicroRNA 183 family profiles in pheochromocytomas are related to clinical parameters and SDHB expression.

This study aims to examine the expression profiles of the miR-183 cluster (miR-96/182/183) in pheochromocytoma. Pheochromocytoma tissues were prospectively collected from 50 patients with pheochromocytoma. Expression of miR-183 cluster members and SDHB protein expression were analyzed in these tissues by quantitative real-time polymerase chain reaction and immunohistochemistry, respectively. The expression of miR-183 cluster members in pheochromocytomas was correlated with the clinical and pathological parameters of these patients. The expression levels of miR-183 cluster members were predominantly downregulated or deleted in pheochromocytoma. Low expression or deletion of miR-96 was predominantly noted in younger patients with pheochromocytoma (<50 years, P=.01). Female patients in the study group showed marked deletion of miR-182 (P=.05). Deletion of the cluster was also associated with SDHB protein expression in pheochromocytoma. Moreover, patients with low miR-183 cluster expression had a slightly better survival rate when compared with patients with high expression. To conclude, the findings indicate a role for miR-183 cluster members in the pathogenesis and clinical progression of pheochromocytoma.

Potential Pitfalls of SDH Immunohistochemical Detection in Paragangliomas and Phaeochromocytomas Harbouring Germline SDHx Gene Mutation.

BACKGROUND/AIM: Germline mutations in any of the succinate dehydrogenase (SDH) genes result in destabilization of the SDH protein complex and loss of SDHB expression at immunohistochemistry. SDHA is lost together with SDHB in SDHA-mutated tumours, but its expression is retained in tumours with other SDH mutations. We investigated whether SDHA/SDHB immunohistochemistry is able to identify SDH-related tumours in a retrospective case series of phaeochromocytomas (PCCs) and paragangliomas (PGLs). MATERIALS AND METHODS: SDHA and SDHB immunostaining was performed in 13 SDH gene-mutated tumours (SDHB: n=3; SDHC: n=1; SDHD: n=9) and 16 wild-type tumours. Protein expression by western blot analysis and enzymatic activity were also assessed. RESULTS: Tumours harbouring SDH gene mutations demonstrated a significant reduction in enzymatic activity and protein expression when compared to wild-type tumours. SDHB immunostaining detected 76.9% of SDH mutated PCCs/PGLs (3/3 SDHB-mutated samples; 1/1 SDHC-mutated sample; 6/9 SDHD-mutated samples). In three SDHD-related tumours with the same mutation (p.Pro81Leu), positive (n=2) or weakly diffuse (n=1) SDHB staining was observed. All wild-type PCCs/PGLs exhibited SDHB immunoreactivity, while immunostaining for SDHA was positive in 93.8% cases and weakly diffuse in one (6.2%). SDHA protein expression was preserved in all tumours with mutations. CONCLUSION: SDHA and SDHB immunohistochemistry should be interpreted with caution, due to possible false-positive or false-negative results, and ideally in the setting of quality assurance provided by molecular testing. In SDHD mutation, weak non-specific cytoplasmic staining occurs commonly, and this pattern of staining can be difficult to interpret with certainty.

A rare missense variant in RET exon 8 in a Portuguese family with atypical multiple endocrine neoplasia type 2A.

BACKGROUND AND OBJECTIVE: Multiple Endocrine Neoplasia type 2 (MEN2) is a rare genetic disorder characterized by medullary thyroid carcinoma (MTC), pheochromocytoma and primary hyperparathyroidism. MEN2 is an autosomal dominant syndrome caused by mutations in the RET proto-oncogene. In the vast majority of patients, the mutations are localized in exons 10, 11 and 13-15 of the RET gene. Rare variants located in exon 8 were recently identified but their clinical significance remains unclear. DESIGN AND METHODS: We studied two sisters presenting with pheochromocytoma as the first tumor. One of the sisters was diagnosed with a right pheochromocytoma at the age of 44 and at age 53 she developed an invasive left pheochromocytoma with no other endocrine neoplasia. The other sister was diagnosed with a left pheochromocytoma at age 50 and at age 64 she had a right phemochromocytoma and MTC. Neither of the two sisters presented evidence of primary hyperparathyroidism. Mutations of the RET proto-oncogene were investigated by DNA sequencing. RESULTS: We detected a germline missense variant in RET exon 8 (p.Cys531Arg) in both sisters. The p.Cys531Arg variant was not present in a third 50-year-old sister who has remained to date clinically unaffected. CONCLUSION: This is the first case showing the p.Cys531Arg variant in RET exon 8 co-segregating with family members affected by a syndrome reminiscent of MEN2A. Our results suggest that this variant has a specific genotype-phenotype correlation as it is associated with the development of pheochromocytoma before the onset of MTC.