Different expression of catecholamine transporters in phaeochromocytomas from patients with von Hippel-Lindau syndrome and multiple endocrine neoplasia type 2

New Biology of Pheochromocytoma and Paraganglioma

Pheochromocytomas and paragangliomas continue to be defined by significant morbidity and mortality despite their several recent advances in diagnosis, localization, and management. These adverse outcomes are largely related to mass effect as well as catecholamine-induced hypertension, tachyarrhythmias and consequent target organ damage, acute coronary syndromes, and strokes (ischemic and hemorrhagic stroke). Thus, a proper understanding of the physiology and pathophysiology of these tumors and recent advances are essential to affording optimal care. These major developments largely include a redefinition of metastatic behavior, a novel clinical categorization of these tumors into 3 genetic clusters, and an enhanced understanding of catecholamine metabolism and consequent specific biochemical phenotypes. Current advances in imaging of these tumors are shifting the paradigm from poorly specific anatomical modalities to more precise characterization of these tumors using the advent and development of functional imaging modalities. Furthermore, recent advances have revealed new molecular events in these tumors that are linked to their genetic landscape and, therefore, provide new therapeutic platforms. A few of these prospective therapies translated into new clinical trials, especially for patients with metastatic or inoperable tumors. Finally, outcomes are ever-improving as patients are cared for at centers with cumulative experience and well-established multidisciplinary tumor boards. In parallel, these centers have supported national and international collaborative efforts and worldwide clinical trials. These concerted efforts have led to improved guidelines collaboratively developed by healthcare professionals with a growing expertise in these tumors and consequently improving detection, prevention, and identification of genetic susceptibility genes in these patients.

A Case of 123I-Metaiodobenzylguanidine Scintigraphy-Negative Pheochromocytoma with a Tumor-Developing Mutation in the RET Gene

Pheochromocytoma (PCC) is rare catecholamine-producing endocrine tumor that metastasizes in approximately 10% of cases. As a functional imaging of PCC, 123I-metaiodobenzylguanidine (MIBG) scintigraphy was established, and some cases of PCC exhibit negative accumulation on MIBG scintigraphy, indicating a high risk of metastasis. Additionally, germline genetic variants of PCC are evident in approximately 30% of cases, although the genotype-phenotype correlation in PCC, especially the association between genetic mutations and MIBG scintigraphy, remains unclear. A 33-year-old man was admitted to our hospital for further examination for hypertension. He was diagnosed with sporadic PCC, and left adrenalectomy was performed. The adrenal tumor was negative on MIBG scintigraphy. Histology of the tumor revealed a moderately differentiated PCC. Target gene testing revealed a mutation in RET (c.2071G > A). This mutation has been reported to be a tumor-developing gene involved in the pathogenesis of PCC. Moreover, the RET mutation is the only gene mutation reported in a previous study of PCC with negative results on MIBG scintigraphy, except for the SDHB gene mutation, which is a common mutation in metastatic PCC. Correctively, the present RET gene mutation may be associated to MIBG-scintigraphy negative PCC and its pathophysiology. Clinicians should follow such cases more cautiously in clinical practice.

Vesicular monoamine transporters expression in pheochromocytomas and paragangliomas according to scintigraphy and positron emission tomography behavior

BACKGROUND

The expression of vesicular catecholamine transporters (VMAT1 and 2) in pheochromocytomas (PHEOs) and paragangliomas (PGLs) and the possible relationships with [18F]FDOPA PET/CT and [123I]MIBG scintigraphy uptake are unknown. Our purpose was to investigate possible correlations of either VMAT1 and VMAT2 expression with the functional imaging in patients with PHEOs and PGLs.

METHODS

An observational 3-year time study was performed by enrolling 31 consecutive patients with PHEO (N.=17) or PGL (N.=14). They underwent the same diagnostic work-up; moreover, [123I]MIBG SPECT/CT (N.=20) and [18F]FDOPA PET/CT (N.=14) were performed in a subset of patients. After surgery, routine histology and semiquantitative analysis of VMAT1/VMAT2 immunoreactivity were carried out in all cases.

RESULTS

VMAT1 immunoreactivity was found in all tumors, but two PHEOs. VMAT1 immunoreactivity was higher in PGLs than in PHEOs, though at not significant extent. Elevated VMAT2 immunoreactivity score was present in all but two negative tumors. Normal [123I]-MIBG uptake was independent from VMAT1/2 immunoreactivity. Patients undergoing [18F]FDOPA PET/CT showed a high score level of both VMATs and were detected by the technique in all cases.

CONCLUSIONS

VMAT1 and VMAT2 are highly expressed in most tumors, though VMAT1 immunoreactivity is apparently prevalent in PGLs as compared to PHEOs. Presence and expression of VMAT1 and VMAT2 are not limiting factors for MIBG uptake. The status of VMAT expression might help to understand why the more frequently used radiotracers do not always have the expected diagnostic performance. Finally, the present study points out the importance of developing new radiotracers with higher sensitivity, specificity and accuracy consequently reducing healthcare costs.

Pheochromocytoma Multisystem Crisis: A Case Study

INTRODUCTION

Known as the "great mimic," pheochromocytoma is rare and difficult to diagnose. When a pheochromocytoma begins to cause end-organ damage, it becomes pheochromocytoma multisystem crisis, an even more rare and deadly diagnosis.

CLINICAL FINDINGS

N.R., a 63-year old man, presented to the emergency department 1 day after receiving a cortisone injection for a nondisplaced wrist fracture. His chief concern was a "racing heart and chest pressure." N.R. was admitted to the telemetry unit after routine electrocardiography showed atrial fibrillation and elevated blood pressure. Symptoms quickly progressed, and N.R. was transferred to the intensive care unit where he received noninvasive positive pressure ventilation.

DIAGNOSIS

A computed tomography scan revealed a 7-cm right intra-adrenal mass, and an echocardiogram showed a markedly reduced ejection fraction. N.R. received a preliminary diagnosis of pheochromocytoma multisystem crisis, although confirmatory laboratory test results were pending. N.R. became progressively more hemodynamically unstable and his respiratory status worsened, and by the end of hospital day 2 he had been intubated and was receiving multiple vasoactive medications intravenously. On hospital day 7, N.R. was transferred to a facility for definitive surgical intervention.

CONCLUSION

This case represents the importance of timely interventions by nursing staff, clear communication between staff on different shifts, and real-time education by physicians to nursing staff. This collaborative milieu empowered nurses to use their experience and critical thinking to make clinical decisions in providing care.

Intricacies of the Molecular Machinery of Catecholamine Biosynthesis and Secretion by Chromaffin Cells of the Normal Adrenal Medulla and in Pheochromocytoma and Paraganglioma

The adrenal medulla is composed predominantly of chromaffin cells producing and secreting the catecholamines dopamine, norepinephrine, and epinephrine. Catecholamine biosynthesis and secretion is a complex and tightly controlled physiologic process. The pathways involved have been extensively studied, and various elements of the underlying molecular machinery have been identified. In this review, we provide a detailed description of the route from stimulus to secretion of catecholamines by the normal adrenal chromaffin cell compared to chromaffin tumor cells in pheochromocytomas. Pheochromocytomas are adrenomedullary tumors that are characterized by uncontrolled synthesis and secretion of catecholamines. This uncontrolled secretion can be partly explained by perturbations of the molecular catecholamine secretory machinery in pheochromocytoma cells. Chromaffin cell tumors also include sympathetic paragangliomas originating in sympathetic ganglia. Pheochromocytomas and paragangliomas are usually locally confined tumors, but about 15% do metastasize to distant locations. Histopathological examination currently poorly predicts future biologic behavior, thus long term postoperative follow-up is required. Therefore, there is an unmet need for prognostic biomarkers. Clearer understanding of the cellular mechanisms involved in the secretory characteristics of pheochromocytomas and sympathetic paragangliomas may offer one approach for the discovery of novel prognostic biomarkers for improved therapeutic targeting and monitoring of treatment or disease progression.

Hemodynamic instability during percutaneous ablation of extra-adrenal metastases of pheochromocytoma and paragangliomas: a case series

Background

Surgical manipulation of pheochromocytomas and paragangliomas (PPGLs) may induce large hemodynamic oscillations due to catecholamine release. Little is known regarding hemodynamic instability during percutaneous ablation of PPGLs. We examined intraprocedural hemodynamic variability and postoperative complications related to percutaneous ablation of extra-adrenal metastases of PPGL.

Methods

From institutional PPGL registry we identified patients undergoing ablation of extra-adrenal PPGL metastases from January 1, 2000, through December 31, 2016. We reviewed medical records for clinical characteristics and hospital outcomes. Tumors were categorized as functional or nonfunctional based on preprocedural fractionated catecholamine and metanephrine profiles.

Results

Twenty-one patients (14 female [67%]) underwent 38 ablations. Twenty-four ablations were performed in patients with functional metastatic lesions, and 14 were in nonfunctional lesions. Intraprocedural use of potent vasodilators for hypertension was higher for patients with functional tumors (P = 0.02); use of vasopressors for hypotension was similar for functional and nonfunctional tumors (P = 0.74). Mean (±SD) intraprocedural blood pressure range (maximum–minimum blood pressure) during 38 procedures was greater for functional than nonfunctional tumors [systolic: 106 (±48) vs 64 (±30) mm Hg, P = 0.005; diastolic: 58 (±22) vs 35 (±14) mm Hg, P = 0.002; mean arterial: 84 (±43) vs 47 (±29) mm Hg, P = 0.007]. Complications included 5 unplanned intensive care unit admissions (3 for precautionary monitoring, 1 for recalcitrant hypotension, and 1 for hypertensive crisis), 1 case of postoperative bleeding, and 1 death.

Conclusions

Substantial hemodynamic instability may develop during ablation of functional and nonfunctional PPGL metastases. When anesthesia is provided for ablation of metastatic PPGLs in radiology suites, preparation for hemodynamic management should match standards used for surgical resection.

Perioperative outcomes of syndromic paraganglioma and pheochromocytoma resection in patients with von Hippel-Lindau disease, multiple endocrine neoplasia type 2, or neurofibromatosis type 1

BACKGROUND

Pheochromocytoma and/or paraganglioma associated with neurofibromatosis type 1, multiple endocrine neoplasia type 2A, and von Hippel-Lindau disease have different catecholamine biochemical phenotypes. We examined perioperative outcomes of pheochromocytoma/paraganglioma resection in 3 syndromic forms.

METHODS

Retrospective review of patients undergoing resection of syndromic pheochromocytoma/paraganglioma from 2000 through 2016.

RESULTS

Eighty-one patients underwent pheochromocytoma/paraganglioma resection (multiple endocrine neoplasia type 2A, n = 36; neurofibromatosis type 1, n = 26; von Hippel-Lindau disease, n = 19). Tumor size differed across groups; patients with neurofibromatosis type 1 and von Hippel-Lindau disease had the largest tumors (P = .017). Larger tumor volumes correlated with higher urine 24-hour total metanephrine (r = 0.94, P < .001; r = 0.67, P = .033; and r = 0.89, P < .001 for multiple endocrine neoplasia type 2A, von Hippel-Lindau disease, and neurofibromatosis type 1, respectively). High adrenergic secretion (24-hour urine metanepinephrine) was found in neurofibromatosis type 1 (median, 861 μg/24 h), similar to that found in multiple endocrine neoplasia type 2A (median, 809 μg/24 h). The highest noradrenergic secretion (24-hour urine normetanephrine) occurred with von Hippel-Lindau disease (median, 4,598 μg/24 h), followed by neurofibromatosis type 1 and multiple endocrine neoplasia type 2A (median, 1,607 and 923 μg/24 h, respectively). The highest graded complications occurred among patients with neurofibromatosis type 1 (P = .036). However, when comparing postoperative outcomes across 3 groups in those who had laparoscopic resection, there was no significant difference (P = .955).

CONCLUSION

Patients with neurofibromatosis type 1 had the most volatile intraoperative hemodynamic course and more severe postoperative complications. These complications are related to large tumors associated with abundant catecholamine secretion and the fact that a high proportion underwent open resection. Among only patients who underwent laparoscopic procedures, there were no differences in postoperative outcomes across syndromic groups.

Functional Imaging of Paragangliomas with an Emphasis on Von Hippel-Lindau-Associated Disease: A Mini Review

Few reports have presented data and results on functional (i.e., nuclear medicine) imaging of paragangliomas and pheochromocytomas (PGLs/PHEOs) for von Hippel-Lindau (VHL) patients. Nuclear medicine localization modalities for chromaffin tumors can be specific or nonspecific. Specific methods make use of the expression of the human norepinephrine transporter (hNET) and vesicular monoamine transporters (VMATs) by these tumors. These permit the use of radiolabeled ligands that enter the synthesis and storage pathway of catecholamines. Nonspecific methods are not related to the synthesis, uptake, or storage of catecholamines but make use of the tumors' high glucose metabolism or expression of somatostatin receptors. Consensuses and guidelines suggest that metastatic and sporadic PHEOs/PGLs in VHL patients (as in patients with chromaffin tumors of yet unknown genotype) should be evaluated first with ¹⁸F-dihydroxyphenylalanine (¹⁸F-DOPA) positron emission tomography/computed tomography (PET/CT). The functional imaging of second choice is ¹²³I-metaiodobenzylguanidine (¹²³I-MIBG) for PHEOs in VHL patients. ¹²³I-MIBG, ⁶⁸Ga-DOTATATE/DOTATOC/DOTANOC PET/CT, or ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET/CT can be a second choice of functional imaging for PGLs in VHL patients.

Metabologenomics of Phaeochromocytoma and Paraganglioma: An Integrated Approach for Personalised Biochemical and Genetic Testing

The tremendous advances over the past two decades in both clinical genetics and biochemical testing of chromaffin cell tumours have led to new considerations about how these aspects of laboratory medicine can be integrated to improve diagnosis and management of affected patients. With germline mutations in 15 genes now identified to be responsible for over a third of all cases of phaeochromocytomas and paragangliomas, these tumours are recognised to have one of the richest hereditary backgrounds among all neoplasms. Depending on the mutation, tumours show distinct differences in metabolic pathways that relate to or even directly impact clinical presentation. At the same time, there has been improved understanding about how catecholamines are synthesised, stored, secreted and metabolised by chromaffin cell tumours. Although the tumours may not always secrete catecholamines it has become clear that almost all continuously produce and metabolise catecholamines. This has not only fuelled changes in laboratory medicine, but has also assisted in recognition of genotype-biochemical phenotype relationships important for diagnostics and clinical care. In particular, differences in catecholamine and energy pathway metabolomes can guide genetic testing, assist with test interpretation and provide predictions about the nature, behaviour and imaging characteristics of the tumours. Conversely, results of genetic testing are important for guiding how routine biochemical testing should be employed and interpreted in surveillance programmes for at-risk patients. In these ways there are emerging needs for modern laboratory medicine to seamlessly integrate biochemical and genetic testing into the diagnosis and management of patients with chromaffin cell tumours.

I-131 Metaiodobenzylguanidine Therapy of Pheochromocytoma and Paraganglioma

Pheochromocytomas and paragangliomas are rare tumors arising from chromaffin cells. Available therapeutic modalities consist of chemotherapy, tyrosine kinase inhibitors, and I-131 metaiodobenzylguanidine (MIBG). I-131 MIBG is taken up via specific receptors and localizes into many but not all pheochromocytomas and paragangliomas. Because these tumors are rare, most therapy studies are retrospective presentations of clinical experience. Numerous retrospective studies and a few prospective studies have shown favorable responses in this disease, including symptomatic, biochemical, and objective responses. In this report, we review the experience of using I-131 MIBG therapy for targeting pheochromocytoma and paragangliomas.

Laparoscopic adrenalectomy for pheochromocytoma-does size matter? A single surgeon comparative study

Background

Surgical difficulty in laparoscopic adrenalectomy for pheochromocytoma increases with tumor size. We compared single surgeon outcomes of laparoscopic adrenalectomy for pheochromocytomas in patients with tumors smaller or greater than 4 cm to assess safety of the procedure.

Methods

A retrospective review was performed of laparoscopic adrenalectomies for pheochromocytoma by a single surgeon over a 3-year period. All patients underwent lateral transperitoneal surgery. Operative and outcome data was retrieved and compared for tumors >4 cm versus smaller tumors.

Results

We performed 28 laparoscopic adrenalectomies on 24 patients including four simultaneous bilateral surgeries. Fifteen tumors were greater than 4 cm in size (mean 6.3 cm) while 13 were smaller (mean 2.9 cm). Both groups had similar operating time (138 vs. 116 min; P=0.2) and blood loss (181 vs. 143 mL; P=0.41). The small tumor group had four Clavien-Dindo grade 1 and one grade 3a complication while the large tumor group had three grade 1 complications. There were no conversions to open surgery. Eighteen patients (75%) did not require any anti-hypertensive medications post-operatively.

Conclusions

Tumor size does not impact outcomes of laparoscopic adrenalectomy for pheochromocytomas. Larger tumors are associated with similar operative time, blood loss and complications as smaller ones.

Anesthetic considerations on adrenal gland surgery

Adrenal gland surgery needs a multidisciplinary team including endocrinologist, radiologist, anesthesiologist, and surgeon. The indications for adrenal gland surgery include hormonal secreting and non-hormonal secreting tumors. Adrenal hormonal secreting tumors present to the anesthesiologist unique challenges requiring good preoperative evaluation, perioperative hemodynamic control, corrections of all electrolytes and metabolic abnormalities, a detailed and careful anesthetic strategy, overall knowledge about the specific diseases, control and maintaining of postoperative adrenal function, and finally a good collaboration with other involved colleagues. This review will focus on the endocrine issues, as well as on the above-mentioned aspects of anesthetic management during hormone secreting adrenal gland tumor resection.

Genotype and tumor locus determine expression profile of pseudohypoxic pheochromocytomas and paragangliomas

Pheochromocytomas (PHEOs) and paragangliomas (PGLs) related to mutations in the mitochondrial succinate dehydrogenase (SDH) subunits A, B, C, and D, SDH complex assembly factor 2, and the von Hippel-Lindau (VHL) genes share a pseudohypoxic expression profile. However, genotype-specific differences in expression have been emerging. Development of effective new therapies for distinctive manifestations, e.g., a high rate of malignancy in SDHB- or predisposition to multifocal PGLs in SDHD patients, mandates improved stratification. To identify mutation/location-related characteristics among pseudohypoxic PHEOs/PGLs, we used comprehensive microarray profiling (SDHB: n = 18, SDHD-abdominal/thoracic (AT): n = 6, SDHD-head/neck (HN): n = 8, VHL: n = 13). To avoid location-specific bias, typical adrenal medulla genes were derived from matched normal medullas and cortices (n = 8) for data normalization. Unsupervised analysis identified two dominant clusters, separating SDHB and SDHD-AT PHEOs/PGLs (cluster A) from VHL PHEOs and SDHD-HN PGLs (cluster B). Supervised analysis yielded 6937 highly predictive genes (misclassification error rate of 0.175). Enrichment analysis revealed that energy metabolism and inflammation/fibrosis-related genes were most pronouncedly changed in clusters A and B, respectively. A minimum subset of 40 classifiers was validated by quantitative real-time polymerase chain reaction (quantitative real-time polymerase chain reaction vs. microarray: r = 0.87). Expression of several individual classifiers was identified as characteristic for VHL and SDHD-HN PHEOs and PGLs. In the present study, we show for the first time that SDHD-HN PGLs share more features with VHL PHEOs than with SDHD-AT PGLs. The presented data suggest novel subclassification of pseudohypoxic PHEOs/PGLs and implies cluster-specific pathogenic mechanisms and treatment strategies.

Current and future anatomical and functional imaging approaches to pheochromocytoma and paraganglioma

After establishing a biochemical diagnosis, pheochromocytomas and extra-adrenal paragangliomas (PPGLs) can be localized using different anatomical and functional imaging modalities. These include computed tomography, magnetic resonance imaging, single-photon emission computed tomography (SPECT) using 123I-metaiodobenzylguanidine or 111In-DTPA-pentetreotide, and positron emission tomography (PET) using 6-[18F]-fluorodopamine (18F-FDA), 6-[18F]-fluoro-l-3,4-dihydroxyphenylalanine (18F-DOPA), and 2-[18F]-fluoro-2-deoxy-d-glucose. We review the currently available data on the performance of anatomical imaging, SPECT, and PET for the detection of (metastatic) PPGL as well as parasympathetic head and neck paragangliomas. We show that there appears to be no 'gold-standard' imaging technique for all patients with (suspected) PPGL. A tailor-made approach is warranted, guided by clinical, biochemical, and genetic characteristics. In the current era of a growing number of PET tracers, PPGL imaging has moved beyond tumor localization towards functional characterization of tumors.

Usefulness of [18F]-DA and [18F]-DOPA for PET imaging in a mouse model of pheochromocytoma

PURPOSE

To evaluate the usefulness of [(18)F]-6-fluorodopamine ([(18)F]-DA) and [(18)F]-L-6-fluoro-3,4-dihydroxyphenylalanine ([(18)F]-DOPA) positron emission tomography (PET) in the detection of subcutaneous (s.c.) and metastatic pheochromocytoma in mice; to assess the expression of the norepinephrine transporter (NET) and vesicular monoamine transporters 1 and 2 (VMAT1 and VMAT2), all important for [(18)F]-DA and [(18)F]-DOPA uptake. Furthermore, to compare tumor detection by micro-computed tomography (microCT) to magnetic resonance imaging (MRI) in individual mouse.

METHODS

SUV(max) values were calculated from [(18)F]-DA and [(18)F]-DOPA PET, tumor-to-liver ratios (TLR) were obtained and expression of NET, VMAT1 and VMAT2 was evaluated.

RESULTS

[(18)F]-DA detected less metastatic lesions compared to [(18)F]-DOPA. TLR values for liver metastases were 2.26-2.71 for [(18)F]-DOPA and 1.83-2.83 for [(18)F]-DA. A limited uptake of [(18)F]-DA was found in s.c. tumors (TLR = 0.22-0.27) compared to [(18)F]-DOPA (TLR = 1.56-2.24). Overall, NET and VMAT2 were expressed in all organ and s.c. tumors. However, s.c. tumors lacked expression of VMAT1. We confirmed [(18)F]-DA's high affinity for the NET for its uptake and VMAT1 and VMAT2 for its storage and retention in pheochromocytoma cell vesicles. In contrast, [(18)F]-DOPA was found to utilize only VMAT2.

CONCLUSION

MRI was superior in the detection of all organ tumors compared to microCT and PET. [(18)F]-DOPA had overall better sensitivity than [(18)F]-DA for the detection of metastases. Subcutaneous tumors were localized only with [(18)F]-DOPA, a finding that may reflect differences in expression of VMAT1 and VMAT2, perhaps similar to some patients with pheochromocytoma where [(18)F]-DOPA provides better visualization of lesions than [(18)F]-DA.

Phaeochromocytoma: a catecholamine and oxidative stress disorder

The WHO classification of endocrine tumors defines pheochromocytoma as a tumor arising from chromaffin cells in the adrenal medulla - an intra-adrenal paraganglioma. Closely related tumors of extra-adrenal sympathetic and parasympathetic paraganglia are classified as extra-adrenal paragangliomas. Almost all pheochromocytomas and paragangliomas produce catecholamines. The concentrations of catecholamines in pheochromocytoma tissues are enormous, potentially creating a volcano that can erupt at any time. Significant eruptions result in catecholamine storms called "attacks" or "spells". Acute catecholamine crisis can strike unexpectedly, leaving traumatic memories of acute medical disaster that champions any intensive care unit. A very well-defined genotype-biochemical phenotype relationship exists, guiding proper and cost-effective genetic testing of patients with these tumors. Currently, the production of norepinephrine and epinephrine is optimally assessed by the measurement of their O-methylated metabolites, normetanephrine or metanephrine, respectively. Dopamine is a minor component, but some paragangliomas produce only this catecholamine or this together with norepinephrine. Methoxytyramine, the O-methylated metabolite of dopamine, is the best biochemical marker of these tumors. In those patients with equivocal biochemical results, a modified clonidine suppression test coupled with the measurement of plasma normetanephrine has recently been introduced. In addition to differences in catecholamine enzyme expression, the presence of either constitutive or regulated secretory pathways contributes further to the very unique mutation-dependent catecholamine production and release, resulting in various clinical presentations. Oxidative stress results from a significant imbalance between levels of prooxidants, generated during oxidative phosphorylation, and antioxidants. The gradual accumulation of prooxidants due to metabolic oxidative stress results in proto-oncogene activation, tumor suppressor gene inactivation, DNA damage, and genomic instability. Since the mitochondria serves as the main source of prooxidants, any mitochondrial impairment leads to severe oxidative stress, a major outcome of which is tumor development. In terms of cancer pathogenesis, pheochromocytomas and paragangliomas represent tumors where the oxidative phosphorylation defect due to the mutation of succinate dehydrogenase is the cause, not a consequence, of tumor development. Any succinate dehydrogenase pathogenic mutation results in the shift from oxidative phosphorylation to aerobic glycolysis in the cytoplasm (also called anaerobic glycolysis if hypoxia is the main cause of such a shift). This phenomenon, also called the Warburg effect, is well demonstrated by a positive [18F]-fluorodeoxyglycose positron emission tomography scan. Microarray studies, genome-wide association studies, proteomics and protein arrays, metabolomics, transcriptomics, and bioinformatics approaches will remain powerful tools to further uncover the pathogenesis of these tumors and their unique markers, with the ultimate goal to introduce new therapeutic options for those with metastatic or malignant pheochromocytoma and paraganglioma. Soon oxidative stress will be tightly linked to a multistep cancer process in which the mutation of various genes (perhaps in a logistic way) ultimately results in uncontrolled growth, proliferation, and metastatic potential of practically any cell. Targeting the mTORC, IGF-1, HIF and other pathways, topoisomerases, protein degradation by proteosomes, balancing the activity of protein kinases and phosphatases or even synchronizing the cell cycle before any exposure to any kind of therapy will soon become a reality. Facing such a reality today will favor our chances to "beat" this disease tomorrow.

New imaging approaches to phaeochromocytomas and paragangliomas

Formerly used concepts for phaeochromocytomas and paragangliomas have been challenged by recent discoveries that at least 24% of tumours are familial and thereby often multiple in various locations throughout the body. Furthermore, tumours are often malignant and perhaps more aggressive if associated with SDHB gene mutations. Some paragangliomas are clinically silent and may present only with dopamine hypersecretion. In the current era where CT and MRI are more commonly used, tumours are more often found as incidentalomas and MRI may be less specific for phaeochromocytoma and paraganglioma than previously thought. Because of unique tumour characteristics (e.g. the presence of cell membrane and intracellular vesicular norepinephrine transporters) these tumours were 'born' to be imaged by means of specific functional imaging approaches. Moreover, additional recent discoveries related to apoptosis, hypoxia, acidosis, anaerobic glycolysis and angiogenesis, often disturbed in tumour cells, open new options and challenges to specifically image phaeochromocytomas and paragangliomas and possibly link those results to their pathophysiology, genotypic alterations and metastatic potential. Functional imaging, especially represented by positron emission tomography (PET), offers an excellent approach by which tumour-specific processes can be detected, evaluated and seen in the context of tumour-specific behaviour and its genetic signature. In this review, we address the recent developments in new functional imaging modalities for phaeochromocytoma and paraganglioma and provide the reader with suggested imaging approaches in various phaeochromocytomas and paragangliomas of sympathetic origin. Current imaging algorithms of head and neck parasympathetic paragangliomas are not discussed. Finally, this review outlines some future perspectives of functional imaging of these tumours.

Risk Factors for Hemodynamic Instability during Surgery for Pheochromocytoma

BACKGROUND

Surgery on pheochromocytoma carries a risk for hemodynamic (HD) instability. The aim of this study was to identify preoperative risk factors for intraoperative HD instability. In addition, efficacy of pretreatment with the alpha-adrenergic receptor (alpha) antagonists phenoxybenzamine (PXB) and doxazosin (DOX) was compared with respect to reduction of intraoperative HD instability.

METHODS

Seventy-three patients operated in Erasmus Medical Center between 1995 and 2007 were included. Parameters studied were catecholamine type and concentration, tumor diameter, mean arterial pressure (MAP) before and after (MAP(alpha)) pretreatment with alpha-antagonist, postural fall in blood pressure (BP) after pretreatment, type of alpha-blockade, type of operation, and presence of a familial polytumor syndrome. HD instability was assessed by measuring the number and time period MAP was below 60 mm Hg and systolic BP (SBP) was above 160 mm Hg.

RESULTS

A correlation was found between the intraoperative time periods of SBP above 160 mm Hg and plasma norepinephrine levels (r = 0.23; P < 0.05), tumor diameter (r = 0.36; P < 0.01), and postural BP fall (r = 0.30; P < 0.05). MAP at presentation and after alpha-blockade above 100 mm Hg (BP, 130/85 mm Hg) was related to more and longer episodes with a SBP above 160 mm Hg (P < 0.01). Type of operation or alpha-blockade and presence of a familial polytumor syndrome were not related to intraoperative HD instability. Postoperative MAP was lower in the DOX group than in the PXB group (P < 0.05).

CONCLUSION

Risk factors for HD instability during surgery for pheochromocytoma include a high plasma NE concentration, larger tumor size, more profound postural BP fall after alpha-blockade, and a MAP above 100 mm Hg (130/85 mm Hg). Efficacy for preventing HD instability was identical for PXB and DOX.

Comparison of 18F-fluoro-L-DOPA, 18F-fluoro-deoxyglucose, and 18F-fluorodopamine PET and 123I-MIBG scintigraphy in the localization of pheochromocytoma and paraganglioma

CONTEXT

Besides (123)I-metaiodobenzylguanidine (MIBG), positron emission tomography (PET) agents are available for the localization of paraganglioma (PGL), including (18)F-3,4-dihydroxyphenylalanine (DOPA), (18)F-fluoro-2-deoxy-D-glucose ((18)F-FDG), and (18)F-fluorodopamine ((18)F-FDA).

OBJECTIVE

The objective of the study was to establish the optimal approach to the functional imaging of PGL and examine the link between genotype-specific tumor biology and imaging.

DESIGN

This was a prospective observational study.

INTERVENTION

There were no interventions.

PATIENTS

Fifty-two patients (28 males, 24 females, aged 46.8 +/- 14.2 yr): 20 with nonmetastatic PGL (11 adrenal), 28 with metastatic PGL (13 adrenal), and four in whom PGL was ruled out; 22 PGLs were of the succinate dehydrogenase subunit B (SDHB) genotype.

MAIN OUTCOME MEASURES

Sensitivity of (18)F-DOPA, (18)F-FDG, and (18)F-FDA PET, (123)I-MIBG scintigraphy, computed tomography (CT), and magnetic resonance imaging (MRI) for the localization of PGL were measured.

RESULTS

Sensitivities for localizing nonmetastatic PGL were 100% for CT and/or MRI, 81% for (18)F-DOPA PET, 88% for (18)F-FDG PET/CT, 78% for (18)F-FDA PET/CT, and 78% for (123)I-MIBG scintigraphy. For metastatic PGL, sensitivity in reference to CT/MRI was 45% for (18)F-DOPA PET, 74% for (18)F-FDG PET/CT, 76% for (18)F-FDA PET/CT, and 57% for (123)I-MIBG scintigraphy. In patients with SDHB metastatic PGL, (18)F-FDA and (18)F-FDG have a higher sensitivity (82 and 83%) than (123)I-MIBG (57%) and (18)F-DOPA (20%).

CONCLUSIONS

(18)F-FDA PET/CT is the preferred technique for the localization of the primary PGL and to rule out metastases. Second best, equal alternatives are (18)F-DOPA PET and (123)I-MIBG scintigraphy. For patients with known metastatic PGL, we recommend (18)F-FDA PET in patients with an unknown genotype, (18)F-FDG or (18)F-FDA PET in SDHB mutation carriers, and (18)F-DOPA or (18)F-FDA PET in non-SDHB patients.

Biochemically silent abdominal paragangliomas in patients with mutations in the succinate dehydrogenase subunit B gene

CONTEXT

Patients with adrenal and extra-adrenal abdominal paraganglioma (PGL) almost invariably have increased plasma and urine concentrations of metanephrines, the O-methylated metabolites of catecholamines. We report four cases of biochemically silent abdominal PGL, in which metanephrines were normal despite extensive disease.

OBJECTIVE

Our objective was to identify the mechanism underlying the lack of catecholamine hypersecretion and metabolism to metanephrines in biochemically silent PGL.

DESIGN

This is a descriptive study.

SETTING

The study was performed at a referral center.

PATIENTS

One index case and three additional patients with large abdominal PGL and metastases but with the lack of evidence of catecholamine production, six patients with metastatic catecholamine-producing PGL and a mutation of the succinate dehydrogenase subunit B (SDHB) gene, and 136 random patients with catecholamine-producing PGL were included in the study.

MAIN OUTCOME MEASURES

Plasma, urine, and tumor tissue concentrations of catecholamines and metabolites were calculated with electron microscopy and tyrosine hydroxylase immunohistochemistry.

RESULTS

All four patients with biochemically silent PGL had an underlying SDHB mutation. In the index case, the tumor tissue concentration of catecholamines (1.8 nmol/g) was less than 0.01% that of the median (20,410 nmol/g) for the 136 patients with catecholamine-producing tumors. Electron microscopy showed the presence of normal secretory granules in all four biochemically silent PGLs. Tyrosine hydroxylase immunoreactivity was negligible in the four biochemically silent PGLs but abundant in catecholamine-producing PGLs.

CONCLUSIONS

Patients with SDHB mutations may present with biochemically silent abdominal PGLs due to defective catecholamine synthesis resulting from the absence of tyrosine hydroxylase. Screening for tumors in patients with SDHB mutations should not be limited to biochemical tests of catecholamine excess.

Differential expression of the regulated catecholamine secretory pathway in different hereditary forms of pheochromocytoma

Pheochromocytomas in patients with von Hippel-Lindau (VHL) syndrome and multiple endocrine neoplasia type 2 (MEN 2) differ in the types and amounts of catecholamines produced and the resulting signs and symptoms. We hypothesized the presence of different processes of catecholamine release reflecting differential expression of components of the regulated secretory pathway among the two types of hereditary tumors. Differences in catecholamine secretion from tumors in patients with VHL syndrome (n = 47) and MEN 2 (n = 32) were examined using measurements of catecholamines in tumor tissue, urine, and plasma, the last of which was under baseline conditions in all subjects and in a subgroup of patients who received intravenous glucagon to provoke catecholamine release. Microarray and proteomics analyses, quantitative PCR, and Western blotting were used to assess expression of tumor tissue secretory pathway components. The rate constant for baseline catecholamine secretion was 20-fold higher in VHL than in MEN 2 tumors (0.359 +/- 0.094 vs. 0.018 +/- 0.009 day(-1)), but catecholamine release was responsive only to glucagon in MEN 2 tumors. Compared with tumors from MEN 2 patients, those from VHL patients were characterized by reduced expression of numerous components of the regulated secretory pathway (e.g., SNAP25, syntaxin, rabphilin 3A, annexin A7, calcium-dependent secretion activator). The mutation-dependent differences in expression of secretory pathway components indicate a more mature regulated secretory pathway in MEN 2 than VHL tumors. These data provide a unique mechanistic link to explain how variations in the molecular machinery governing exocytosis may contribute to clinical differences in the secretion of neurotransmitters or hormones and the subsequent presentation of a disease.

Development of differential diagnosis for benign and malignant pheochromocytomas

Unlike common malignant tumors, malignant pheochromocytomas cannot be definitely diagnosed using histological features. This unique nature of pheochromocytomas provides a valuable model that may promote the investigation of the mechanism of other common malignant tumors where similar frameworks are not available. Studies on malignant pheochromocytomas should benefit not only the individuals with pheochromocytomas but those with other tumors. A review on the development of differentiating diagnosis between malignant and benign pheochromocytomas in imaging studies, biological fluid examinations, pathological examinations, molecular markers and genome studies, was updated in the hopes of guiding the next studies of pheochromcytomas.

Preoperative management of the pheochromocytoma patient

Pheochromocytomas are rare neuroendocrine tumors with a highly variable clinical presentation, but they most commonly present as spells of headaches, sweating, palpitations, and hypertension. Patients with pheochromocytoma may develop complicated and potentially lethal cardiovascular and other complications, especially in the setting of diagnostic or interventional procedures (e.g. upon induction of anesthesia or during surgery). The serious and potentially lethal nature of such complications is due to the potent effect of paroxysmal release of catecholamines. Because this warrants prompt diagnosis and treatment, the physician should be aware of the clinical manifestations and complications of catecholamine excess and be able to provide proper preoperative management to minimize catecholamine-related pre-, intra-, and postoperative adverse events. The following clinical scenario and discussion aim to enhance the knowledge of the physician regarding the behavior of pheochromocytoma and to outline current approaches to comprehensive preoperative management of patients suffering from this tumor.

Superiority of fluorodeoxyglucose positron emission tomography to other functional imaging techniques in the evaluation of metastatic SDHB-associated pheochromocytoma and paraganglioma

PURPOSE

Germline mutations of the gene encoding subunit B of the mitochondrial enzyme succinate dehydrogenase (SDHB) predispose to malignant paraganglioma (PGL). Timely and accurate localization of these aggressive tumors is critical for guiding optimal treatment. Our aim is to evaluate the performance of functional imaging modalities in the detection of metastatic lesions of SDHB-associated PGL.

PATIENTS AND METHODS

Sensitivities for the detection of metastases were compared between [18F]fluorodopamine ([18F]FDA) and [18F]fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET), iodine-123- (123I) and iodine-131 (131I) -metaiodobenzylguanidine (MIBG), 111In-pentetreotide, and Tc-99m-methylene diphosphonate bone scintigraphy in 30 patients with SDHB-associated PGL. Computed tomography (CT) and magnetic resonance imaging (MRI) served as standards of reference.

RESULTS

Twenty-nine of 30 patients had metastatic lesions. In two patients, obvious metastatic lesions on functional imaging were missed by CT and MRI. Sensitivity according to patient/body region was 80%/65% for 123I-MIBG and 88%/70% for [18F]FDA-PET. False-negative results on 123I-MIBG scintigraphy and/or [18F]FDA-PET were not predicted by genotype or biochemical phenotype. [18F]FDG-PET yielded a by patient/by body region sensitivity of 100%/97%. At least 90% of regions that were false negative on 123I-MIBG scintigraphy or [18F]FDA-PET were detected by [18F]FDG-PET. In two patients, 111In-pentetreotide scintigraphy detected liver lesions that were negative on other functional imaging modalities. Sensitivities were similar before and after chemotherapy or 131I-MIBG treatment, except for a trend toward lower post- (60%/41%) versus pretreatment (80%/65%) sensitivity of 123I-MIBG scintigraphy.

CONCLUSION

With a sensitivity approaching 100%, [18F]FDG-PET is the preferred functional imaging modality for staging and treatment monitoring of SDHB-related metastatic PGL.

Neuropeptide Y expression in phaeochromocytomas: relative absence in tumours from patients with von Hippel-Lindau syndrome

Phaeochromocytomas are rare neuroendocrine tumours that produce catecholamines and numerous secretory proteins and peptides, including neuropeptide Y (NPY), a vasoactive peptide with influences on blood pressure. The production of catecholamines and NPY by phaeochromocytomas is highly variable. This study examined influences of hereditary factors and differences in catecholamine production on tumour expression of NPY, as assessed by quantitative PCR, enzyme immunoassay and immunohistochemistry. Phaeochromocytomas included hereditary adrenaline-producing tumours (adrenergic phenotype) in multiple endocrine neoplasia type 2 (MEN 2), predominantly noradrenaline-producing tumours (noradrenergic phenotype) in von Hippel-Lindau (VHL) syndrome, and other adrenergic and noradrenergic tumours where there was no clear hereditary syndrome. NPY levels in phaeochromocytomas from VHL patients were lower (P<0.0001) than in those from MEN 2 patients for both mRNA (84-fold difference) and the peptide (99-fold difference). These findings were supported by immunohistochemistry. NPY levels were also lower in VHL tumours than in those where there was no hereditary syndrome. Relative absence of expression of NPY in phaeochromocytomas from VHL patients when compared with other groups appears to be largely independent of differences in catecholamine production and is consistent with a unique phenotype in VHL syndrome.

Transcriptional regulation of phenylethanolamine N-methyltransferase in pheochromocytomas from patients with von Hippel-Lindau syndrome and multiple endocrine neoplasia type 2

Pheochromocytomas in multiple endocrine neoplasia type 2 (MEN-2) express phenylethanolamine N-methyltransferase (PNMT), the enzyme that catalyzes conversion of norepinephrine to epinephrine, whereas those in von Hippel-Lindau (VHL) syndrome do not. Consequently, pheochromocytomas in MEN-2 produce epinephrine, whereas those in VHL syndrome produce mainly norepinephrine. This study examined whether transcription factors known to regulate expression of PNMT explain the different tumor phenotypes in these syndromes. Quantitative polymerase chain reaction (PCR) and Western blotting were used to assess levels of mRNA and protein for the glucocorticoid receptor, early growth response 1 (Egr-1), the Sp1 transcription factor (Sp1), and MYC-associated zinc finger protein (MAZ) in 6 MEN-2 and 13 VHL tumors. Results were cross-checked with data obtained using microarray gene expression profiling in a further set of 10 MEN-2 and 12 VHL tumors. Pheochromocytomas in MEN-2 and VHL syndrome did not differ in expression of the glucocorticoid receptor, Egr-1, Sp1, or MAZ as assessed by quantitative PCR and Western blotting. Microarray data also indicated no relevant differences in expression of the glucocorticoid receptor, Egr-1, MAZ, and the AP2 transcription factor. Thus, our results do not support a role for the above transcription factors in determining differences in expression of PNMT in pheochromocytomas from patients with VHL syndrome and MEN-2. Microarray analysis, however, did indicate differences in expression of genes involved in neural crest cell lineage and chromaffin cell development, consistent with differential survival of PNMT-expressing cells in the two syndromes.

The norepinephrine transporter and pheochromocytoma

Pheochromocytomas are rare neuroendocrine tumors of chromaffin cell origin that synthesize and secrete excess quantities of catecholamines and other vasoactive peptides. Pheochromocytomas also express the norepinephrine transporter (NET), a molecule that is used clinically as a means of incorporating radiolabelled substrates such as 131I-MIBG (iodo-metaiodobenzylguanidine) into pheochromocytoma tumor cells. This allows the diagnostic localization of these tumors and, more recently, 131I-MIBG has been used in trials in the treatment of pheochromocytoma, potentially giving rise to NET as a therapeutic target. However, because of varying levels or activities of the transporter, the ability of 131I-MIBG to be consistently incorporated into tumor cells is limited, and therefore various strategies to increase NET functional activity are being investigated, including the use of traditional chemotherapeutic agents such as cisplatin or doxorubicin. Other aspects of NET discussed in this short review include the regulation of the transporter and how novel protein-protein interactions between NET and structures such as syntaxin 1A may hold the key to innovative ways to increase the therapeutic value of 131I-MIBG.