Effects and safety of ¹³¹I-metaiodobenzylguanidine (MIBG) radiotherapy in malignant neuroendocrine tumors: results from a multicenter observational registry

Effective treatments for malignant neuroendocrine tumors are under development. While iodine-131 metaiodobenzylguanidine (¹³¹I-MIBG) radiotherapy has been used in the treatment of malignant neuroendocrine tumors, there are few studies evaluating its therapeutic effects and safety in a multicenter cohort. In the current study, we sought to evaluate the effects and safety of ¹³¹I-MIBG therapy for conditions including malignant pheochromocytoma and paraganglioma within a multicenter cohort. Forty-eight malignant neuroendocrine tumors (37 pheochromocytoma and 11 paraganglioma) from four centers underwent clinical ¹³¹I-MIBG radiotherapy. The tumor responses were observed before and 3 to 6 months after the ¹³¹I-MIBG radiotherapy in accordance with RECIST criteria. We also evaluated the data for any adverse effects. The four centers performed a total of 87 ¹³¹I-MIBG treatments on 48 patients between January 2000 and March 2009. Of the treatments, 65 were evaluable using RECIST criteria. One partial response (PR), 40 stable disease (SD), and 9 progressive disease (PD) in malignant pheochromocytoma were observed after each treatment. Fourteen SD and one PD-were observed in paraganglioma. Patients with normal hypertension (systolic blood pressure (BP) > 130 mmHg) showed significantly reduced systolic BP after the initial follow-up (n=10, 138.1±8.2 to 129.5±13.5 mmHg, P=0.03). In adult neuroendocrine tumors with a treatment-basis analysis, there were side effects following 41 treatments (47.1%) and most of them (90.2%) were minor. In this multicenter registry, PR or SD was achieved in 84.6% of the treatment occasions in adult neuroendocrine tumors through ¹³¹I-MIBG radiotherapy. This indicated that most of the ¹³¹I-MIBG radiotherapy was performed safely without significant side effects.

Succinate-to-fumarate ratio as a new metabolic marker to detect the presence of SDHB/D-related paraganglioma: initial experimental and ex vivo findings

Pheochromocytomas (PHEOs) and paragangliomas (PGLs; extra-adrenal tumors) are rare neuroendocrine chromaffin cell tumors with a hereditary background in about 30%-35%. Those caused by succinate dehydrogenase subunit B (SDHB) germline mutations are associated with a high metastatic potential and ultimately higher patient mortality. Succinate dehydrogenase converts succinate to fumarate, uniquely linking the Krebs cycle and oxidative phosphorylation. SDH mutations result in the accumulation of succinate associated with various metabolic disturbances and the shift to aerobic glycolysis in tumor tissue. In the present study, we measured succinate and fumarate levels in mouse pheochromocytoma (MPC) and mouse tumor tissue (MTT) cells and in 10 apparently sporadic, 10 SDHB-, 5 SDHD-, and 2 neurofibromatosis 1-related PHEOs/PGLs and plasma samples using mass spectrometry. We found that the succinate-to-fumarate ratio was significantly higher in the SDHB- and SDHD-related PGLs than in apparently sporadic and neurofibromatosis 1-related PHEOs/PGLs (P = .0376). To further support our data, we silenced SDHB expression in MPC and MTT cells and evaluated the succinate and fumarate levels. Compared with control samples, SDHB-silenced MTT cells also showed an increase in the succinate-to-fumarate ratio (MTT cells: 2.45 vs 7.53), similar to the findings in SDHB-related PGLs. The present findings for the first time demonstrate a significantly increased succinate-to-fumarate ratio in SDHB/D-related PGLs and thus suggest this ratio may be used as a new metabolic marker for the detection of SDHB/D-related PHEOs/PGLs.

Pulmonary gangliocytic paraganglioma: a case report and review of the literature

Gangliocytic paraganglioma (GP) is a rare histologic type of neuroendocrine tumors. We report a case of pulmonary GP in a 29-year-old male presenting with an asymptomatic endobronchial nodule. Grossly, the tumor showed a 4.0x3.8x3.5 cm well-defined nodule with yellowish cut surface. Microscopically, the tumor was composed of three distinct cellular types: epithelioid cells, ganglion-like cells and spindle cells. Meanwhile, transitional cells, having morphologic features between ganglion-like and epithelioid cells, were also presented. The epithelioid cells arranged in various morphologic architectures, including Zellballen, papillary, cystic and microcystic pattern. The epithelioid cells were positive for AE1/AE3, CAM 5.2, chromogranin A and synaptophysin. Ganglion-like cells showed immunoreactivity for chromogranin A and synaptophysin. A few ganglion-like cells were also positive for AE1/AE3 and/or CAM 5.2. The spindle cells were positive for S-100 protein and neurofilament. The transitional cells showed a similar immunohistochemical profile to the epithelioid cells. The authors believe stem cell theory is a reasonable explanation for the origin of GP. GP probably originate from some kind of mucosa associated stem cell which can differentiate into diverse cellular lineages.

Usefulness of negative and weak-diffuse pattern of SDHB immunostaining in assessment of SDH mutations in paragangliomas and pheochromocytomas

This is a confirmatory study about usefulness of SDHB and SDHA immunostaining in assessment of SDH mutations in paragangliomas and pheochromocytomas. Paraganglioma/pheochromocytoma syndrome (PGL/PCC syndrome) consists of different entities, associated with germline mutations in five different genes: SDHD, SDHAF2, SDHC, SDHA and SDHB. It has been suggested that negative immunostaining of SDHB can be taken as an indicator of the presence of a mutation in one of the five SDH genes. We have performed SDHB and SDHA immunohistochemical staining in a series of paragangliomas and pheochromocytomas from 64 patients. The patients had been previously checked for mutations in SDHD, SDHC and SDHB, but also for mutation in RET and VHL. All 14 patients with SDH mutations (9 with SDHB and 5 with SDHD mutations) exhibited negative or weak-diffuse SDHB staining pattern in tumour tissue, whereas cells of the 23 RET mutated and 8 VHL mutated tumours showed a positive SDHB immunostaining. Sixteen of the patients that did not exhibit a mutation in any gene showed positive SDHB immunostaining in tumour tissue, while only three of the patients without mutation exhibited negative staining. All patients exhibited positive pattern of SDHA immunostaining. The results confirm the value of SDHB immunohistochemical status in assessment of germline mutations in PGL/PCC syndrome.

A new specific succinate-glutamate metabolomic hallmark in SDHx-related paragangliomas

Paragangliomas (PGLs) are frequently associated with germline mutations in genes involved in energy metabolism. The purpose of the present study was to assess whether the tumor metabolomic profile of patients with hereditary and apparently sporadic PGLs enables the distinction of different subtypes of tumors. Twenty-eight unrelated patients with a histological diagnosis of PGLs were included in the present study. Twelve had germline mutations in SDHx genes (5 SDHB, 7 SDHD), 6 VHL, and 10 were apparently sporadic. Intact tumor samples from these patients (one per patient) were evaluated with ¹H high-resolution magic angle spinning (HRMAS) NMR spectroscopy. SDHx-related tumors were characterized by an increase in succinate levels in comparison to other tumor subtypes (p = 0.0001 vs VHL and p = 0.000003 vs apparently sporadic). Furthermore, we found significantly lower values of glutamate in SDHx-related tumors compared to other subtypes (p = 0.0007 vs VHL and p = 0.003 vs apparently sporadic). Moreover, SDHx-tumors also exhibited lower values of ATP/ADP/AMP (p = 0.01) compared to VHL. VHL tumors were found to have the highest values of glutathione (GSH) compared to other tumors. Based on 4 metabolites (succinate, glutamate, GSH, and ATP/ADP/AMP), tumors were accurately distinguished from the other ones on both 3- and 2-class PLS-DA models. The present study shows that HRMAS NMR spectroscopy is a very promising method for investigating the metabolomic profile of various PGLs. The present data suggest the existence of a specific succinate-glutamate hallmark of SDHx PGLs. The relevance of such a metabolomic hallmark is expected to be very useful in designing novel treatment options as well as improving the diagnosis and follow-up of these tumors, including metastatic ones.

Overexpression of the insulin-like growth factor 1 receptor (IGF-1R) is associated with malignancy in familial pheochromocytomas and paragangliomas

CONTEXT

Pheochromocytomas and paragangliomas (pheo/pgl) are neuroendocrine tumours derived from chromaffin cells. Although mostly benign, up to 26% of pheo/pgl will undergo malignant transformation. Reliable histological signs to differentiate benign pheo/pgl from malignant tumours are currently lacking. Increased IGF-1R expression has been shown during progression to metastatic phenotypes of several types of cancer.

OBJECTIVE

To analyse the distribution and expression of the IGF-1R in pheo/pgl of different genetic origin and degree of malignancy.

MEASUREMENTS

We studied the expression of the IGF-1R protein by immunohistochemistry, in 40 primary tumours from patients with pheo/pgl from different genetic aetiology (11 of 29 metastatic/nonmetastatic diseases).

RESULTS

We found a strong association between increased expression of IGF-1R and malignant behaviour regardless of the age at diagnosis and the genetic aetiology. IGF-1R labelling was mostly weak in primary tumours from patients with nonmetastatic pheo/pgl. Conversely, intense IGF-1R labelling was predominant in cases of pheo/pgl with confirmed metastatic disease. The risk of metastases was 11·7 times higher if tumour IGF-1R labelling was intense independently of age at diagnosis. The probability of remaining free of metastases was higher in patients with pheo/pgl scored weak for IGF-1R at 60 months and more than twofold higher at 120 months of follow-up than in patients with intense IGF-1R labelling in their primary tumours.

CONCLUSIONS

Our results strongly suggest that IGF-1R is associated with malignancy in familial pheo/pgl and that IGF-1R expression in the primary tumour might be a useful tool to detect those patients harbouring pheo/pgl who have an increased risk of metastasis.

Identification of somatic VHL gene mutations in sporadic head and neck paragangliomas in association with activation of the HIF-1α/miR-210 signaling pathway

CONTEXT

Head and neck paragangliomas (HNPGLs) arise from parasympathetic paraganglias and 35% to 45% are hereditary caused by mutations in succinate dehydrogenase (SDH) genes. The connection between SDH and tumor development is unclear. The most accepted hypothesis proposes a central role for the pseudohypoxic (pHx) pathway activated by hypoxia-inducible factor (HIF). Paradoxically, we showed that activation of HIF in HNPGLs is restricted to a subset of HNPGLs lacking SDH mutations. These tumors overexpress HIF-1α protein and target genes and the HIF-inducible microRNA miR-210 (pHx-HNPGLs).

OBJECTIVE

The present study aimed at unraveling the SDH-independent mechanisms involved in the activation of HIF in HNPGLs.

DESIGN

The VHL gene was analyzed in 53 tumors by gene sequencing, multiplex-ligation-dependent probe amplification, and quantitative PCR. The miR-210, HIF-1α, and CA9 levels were used as markers of the pHx gene signature. Meta-analysis of the transcriptome of pHx-HNPGLs was performed using the Oncomine platform. Assays in cells lacking functional pVHL and HIF-1α were performed to analyze the role of pVHL/HIF-1α on miR-210 expression.

RESULTS

We identified, for the first time, somatic VHL mutations in HNPGLs. These were found in 2 of 4 pHx-HNPGLs with concomitant loss of heterozygosity in one of them; but not in non-pHx-HNPGLs. Meta-analysis of the transcriptome of pHx-HNPGLs revealed that these tumors are highly related to clear cell renal cell carcinoma. Cell-based assays showed that loss of pVHL lead to upregulation of miR-210 mainly via HIF-1α activation.

CONCLUSIONS

VHL, involved in tumorigenesis of PGLs and clear cell renal cell carcinomas, may be an important player in the pathogenesis of sporadic HNPGLs via activation of an HIF-1α/miR-210 pHx pathway.

Paraganglioma of the vulva: a case report and review of the literature

Paraganglioma is a neuroendocrine neoplasm, which is extremely rare in the vulva and only one case has been reported. Here we present a case of vulvar paraganglioma in a 48-year-old woman and a literature review. The patient found a lump located in the genitals below the symphysis pubis 3 months before presentation when she complained that the lump was increasing in size. A 3.2 cm x 2.3 cm x 1.5 cm nodule was excised from subcutaneous soft tissue in the vulva. Microscopy showed a diversity of cell morphologies and structures in the rich vascular network of the tumor separated the chief cells into round cell nests (Zellballen pattern). Some areas of the tumor presented epithelioid and spindle-shaped cells with increased cell density and indistinct structural characteristics. Hyaline degeneration of collagen fibers or mucoid degeneration was found in tumor interstitium. Immunohistochemical staining showed diffused expression of synaptophysin in the chief cells, focal expression of S-100 protein in the sustentacular cells and high expression of CD34 in the vascular components. Based on morphological and immunohistochemical results, a rare paraganglioma of the vulva was diagnosed.

Phospho-mTOR is not upregulated in metastatic SDHB paragangliomas

BACKGROUND

Pheochromocytomas (PCCs)/paragangliomas (PGLs) are neuroendocrine tumours that may cause arrhythmia and death if untreated. Treatment for patients with metastatic tumours is lacking. As new PCC/PGL susceptibility genes are discovered that are associated with the mTOR pathway, treatment targets focusing on this pathway are being intensively explored.

DESIGN

Twenty-one human PCC/PGLs were analysed from two tertiary care centres. Immunohistochemistry (IHC) analysis was performed for phospho-mTOR (pmTOR), phospho-S6K (pS6K), phosphoinositide 3-kinase (PI3K), phospho-4EBP1 (p4EBP1), HIF1α and MIB-1 in 6 metastatic SDHB PCC/PGLs, 15 nonmetastatic PCC/PGLs, (including 1 TMEM127 PCC and 1 nonmetastatic SDHB PGL) and 6 normal adrenal medullas. The product of the intensity of stain and percentage of cells stained was calculated as an H score.

RESULTS

Using a two-sample t-test and paired t-test, pmTOR and pS6K had significantly higher H scores in nonmetastatic PCC/PGLs than in metastatic SDHB PCC/PGLs. HIF1α had significantly higher H scores in metastatic SDHB PCC/PGLs compared with nonmetastatic PCC/PGLs and normal adrenal medulla. No difference in H scores was seen with p4EBP1, PI3K and MIB-1 when comparing metastatic SDHB PCC/PGLs and nonmetastatic PCC/PGLs. Significantly higher difference in pS6K was seen in normal adrenal medullas compared to nonmetastatic PCC/PGLs and metastatic SDHB PCC/PGLs.

CONCLUSION

The present results suggest that the use of mTOR inhibitors alone for metastatic SDHB PCC/PGLs may not achieve good therapeutic efficacy in patients.

Plasma levels of free metanephrines and 3-methoxytyramine indicate a higher number of biochemically active HNPGL than 24-h urinary excretion rates of catecholamines and metabolites

CONTEXT

A substantial number of patients with head and neck paragangliomas (HNPGLs) have biochemically active tumors, evidenced by increased urinary excretion of catecholamines and metabolites, including 3-methoxytyramine (3MT). It is unclear whether plasma levels of these parameters are more sensitive to detect biochemical activity in HNPGL patients than urinary excretion rates.

OBJECTIVE

To compare plasma free levels vs urinary excretion rates of deconjugated 3MT and combined metanephrines (MNs) in patients with HNPGL.

PATIENTS AND METHODS

We included 124 consecutive patients with HNPGL for screening of catecholamine excess by measurement of 24-h urinary excretion rates of deconjugated (nor)metanephrine, (nor)epinephrine, dopamine, vanillylmandelic acid, 3MT, and plasma free levels of (nor)metanephrine and 3MT.

RESULTS

Plasma free 3MT levels were increased in 35 of the 124 patients (28%), whereas 24-h urinary excretion of deconjugated 3MT was increased in 30 patients (24%) (P=0.13). Plasma free MN levels were increased in seven patients (6%) and urinary deconjugated MN levels in six patients (5%) (P=1.00). Plasma free normetanephrine (NMN) levels were increased in seven patients (6%), and five patients had increased urinary excretion of deconjugated NMN (4%) (P=0.69). Plasma free combined MN levels (NMN, MN, and 3MT) were increased in 41 patients (33%), whereas 24-h urinary excretion rates of deconjugated combined MNs were increased in 33 patients (27%, P<0.05).

CONCLUSIONS

The combined levels of free MNs and free 3MT in plasma indicate a higher number of biochemically active HNPGLs than the 24-h urinary excretion rates of these markers.

Primary paraganglioma of thyroid gland: a clinicopathologic and immunohistochemical analysis of three cases with a review of the literature

Thyroid paraganglioma is an extremely rare tumor and frequently mistaken for other thyroid neoplasms. Increased awareness of its potential presentation in thyroid and its characteristic features is essential for avoiding diagnostic and therapeutic pitfalls. We describe here three additional cases of primary thyroid paraganglioma and analyze their clinical findings and pathological characteristics. Patients included two women and one man presenting with asymptomatic thyroid nodules. Radiological examinations were nonspecific and none had been diagnosed correctly before surgery. On intraoperative frozen section consultation they were all misdiagnosed as carcinomas, either primary or metastatic. However, the permanent sections showed features consistent with paraganglioma. Of note, two cases displayed extension into adjacent thyroid tissues, one of which exhibited increased mitotic activity, confluent tumor necrosis and vascular invasion. Immunohistochemically, the neoplastic chief cells expressed chromogranin, synaptophysin, neuron-specific enolase and CD56, whereas the sustentacular cells were highlighted by S100 protein. All three patients were well with normal hormone secretion, without local recurrence or distant metastasis at last follow-up (range 10-47 months). We further reviewed the literature to summarize the characteristics of this distinctive entity. Albeit being very rare, paraganglioma should be included in the differential diagnosis of hypervascular thyroidal neoplasms. Accurate diagnosis relies on the histopathogical findings and adjunctive immunohistochemcial studies. To date, all the reported cases have pursued a benign course. Although atypical features seem to have no association with clinical behavior, long time postoperative surveillance with biochemical screening of hormone secretion, cervical ultrasonography and whole-body CT scan is recommended.

Genotype-specific abnormalities in mitochondrial function associate with distinct profiles of energy metabolism and catecholamine content in pheochromocytoma and paraganglioma

PURPOSE

Pheochromocytomas and paragangliomas (PGL) are neuroendocrine tumors of sympathetic and parasympathetic paraganglia. This study investigated the relationships between genotype-specific differences in mitochondrial function and catecholamine content in PGL tumors.

EXPERIMENTAL DESIGN

Respiratory chain enzyme assays and (1)H-nuclear magnetic resonance (NMR) spectroscopy at 500 MHz were conducted on homogenates of 35 sporadic PGLs and 59 PGLs from patients with hereditary mutations in succinate dehydrogenase subunits B and D (SDHB, SDHD), succinate dehydrogenase assembly factor 2, von Hippel-Lindau (VHL), rearranged during transfection (RET), neurofibromatosis type 1 (NF1), and myc-associated factor X.

RESULTS

In SDHx-related PGLs, a significant decrease in complex II activity (P < 0.0001) and a significant increase in complex I, III, and IV enzyme activities were observed when compared to sporadic, RET, and NF1 tumors. Also, a significant increase in citrate synthase (P < 0.0001) enzyme activity was observed in SDHx-related PGLs when compared to sporadic-, VHL-, RET-, and NF1-related tumors. An increase in succinate accumulation (P < 0.001) and decrease in ATP/ADP/AMP accumulation (P < 0.001) was observed when compared to sporadic PGLs and PGLs of other genotypes. Positive correlations (P < 0.01) were observed between respiratory chain complex II activity and total catecholamine content and ATP/ADP/AMP and total catecholamine contents in tumor tissues.

CONCLUSIONS

This study for the first time establishes a relationship between determinants of energy metabolism, like activity of respiratory chain enzyme complex II, ATP/ADP/AMP content, and catecholamine content in PGL tumors. Also, this study for the first time successfully uses NMR spectroscopy to detect catecholamines in PGL tumors and provides ex vivo evidence for the accumulation of succinate in PGL tumors with an SDHx mutation.

A comprehensive next generation sequencing-based genetic testing strategy to improve diagnosis of inherited pheochromocytoma and paraganglioma

CONTEXT

Pheochromocytomas and paragangliomas are notable for a high frequency of inherited cases, many of which present as apparently sporadic tumors.

OBJECTIVE

The objective of this study was to establish a comprehensive next generation sequencing (NGS)-based strategy for the diagnosis of patients with pheochromocytoma and paraganglioma by testing simultaneously for mutations in MAX, RET, SDHA, SDHB, SDHC, SDHD, SDHAF2, TMEM127, and VHL.

DESIGN

After the methodology for the assay was designed and established, it was validated on DNA samples with known genotype and then patients were studied prospectively.

SETTING

The study was performed in a diagnostic genetics laboratory.

PATIENTS

DNA samples from 205 individuals affected with adrenal or extraadrenal pheochromocytoma/head and neck paraganglioma (PPGL/HNPGL) were analyzed. A proof-of-principle study was performed using 85 samples known to contain a variant in 1 or more of the genes to be tested, followed by prospective analysis of an additional 120 samples.

MAIN OUTCOME MEASURES

We assessed the ability to use an NGS-based method to perform comprehensive analysis of genes implicated in inherited PPGL/HNPGL.

RESULTS

The proof-of-principle study showed that the NGS assay and analysis gave a sensitivity of 98.7%. A pathogenic mutation was identified in 16.6% of the prospective analysis cohort of 120 patients.

CONCLUSIONS

A comprehensive NGS-based strategy for the analysis of genes associated with predisposition to PPGL and HNPGL was established, validated, and introduced into diagnostic service. The new assay provides simultaneous analysis of 9 genes and allows more rapid and cost-effective mutation detection than the previously used conventional Sanger sequencing-based methodology.

Somatic mutations in H-RAS in sporadic pheochromocytoma and paraganglioma identified by exome sequencing

CONTEXT

Up to 60% of pheochromocytoma (PCC) and paraganglioma (PGL) are associated with either somatic or germline mutations in established PCC and PGL susceptibility loci. Most unexplained cases are characterized by an increased activity of the RAS/RAF/ERK signaling pathway. Mutations in RAS subtypes H, K, and N are common in human cancers; however, previous studies have been inconsistent regarding the mutational status of RAS in PCC and PGL.

OBJECTIVES

The aim of this study was to identify novel disease causing genes in PCC and PGL tumors.

DESIGN, SETTING, AND PARTICIPANTS

Four benign and sporadic PCC and PGL tumors were subjected to whole exome sequencing using the Illumina HiSeq Platform. Sequences were processed by CLC genomics 4.9 bioinformatics software and the acquired list of genetic variants was filtered against the Catalogue of Somatic Mutations in Cancer database. Findings were validated in an additional 78 PCC and PGL tumor lesions.

RESULTS

Exome sequencing identified 2 cases with somatic mutations in the H-RAS. In total, 6.9% (n = 4/58) of tumors negative for mutations in major PCC and PGL loci had mutations in H-RAS: G13R, Q61K, and Q61R. There were 3 PCC and 1 PGL; all had sporadic presentation with benign tumor characteristics and substantial increases in norepinephrine and/or epinephrine. H-RAS tumors were exclusively found in male patients (P = .007).

CONCLUSIONS

We identified recurrent somatic H-RAS mutations in pheochromocytoma and paraganglioma. Tumors with H-RAS mutations had activation of the RAS/RAF/ERK signaling pathway and were associated with male PCC patients having benign and sporadic disease characteristics. H-RAS could serve as a prognostic and predictive marker as well as a novel therapeutic target.

Genetics of pheochromocytoma and paraganglioma syndromes: new advances and future treatment options

PURPOSE OF REVIEW

To summarize the recent advances in the genetics of pheochromocytoma and paraganglioma (PHEO/PGL), focusing on the new susceptibility genes and dividing PHEOs/PGLs into two groups based on their transcription profile.

RECENT FINDINGS

Recently, TMEM127, MYC-associated factor X, and hypoxia-inducible factor (HIF) 2α have been described in the pathogenesis of PHEOs/PGLs. Thus, now about 30-40% of these tumors are linked to the germline mutations, which also include mutations in the VHL, RET, NF1, SDHx, and SDHAF2 genes. Furthermore, PHEOs/PGLs have been divided into two groups, cluster 1 (SDHx/VHL) and cluster 2 (RET/NF1), based on the transcription profile revealed by genome-wide expression microarray analysis.

SUMMARY

PHEOs/PGLs are the most inherited tumors among (neuro)endocrine tumors. Future approaches in genetics, including whole-genome sequencing, will allow the discovery of additional PHEO/PGL susceptibility genes. The current division of PHEOs/PGLs into cluster 1 and 2 provides us with additional knowledge related to the pathogenesis of these tumors, including the introduction of new treatment options for patients with metastatic PHEOs/PGLs. New discoveries related to the role of the HIF-1/HIF-2α genes in the pathogenesis of almost all inherited PHEOs/PGLs may call for a new regrouping of these tumors and discoveries of new treatment targets.

First report of bilateral pheochromocytoma in the clinical spectrum of HIF2A-related polycythemia-paraganglioma syndrome

CONTEXT

Molecular genetic research has so far resulted in the identification of 10 well-characterized susceptibility genes for hereditary pheochromocytoma (PHEO) or paraganglioma (PGL). Recently, a new syndrome characterized by multiple PGLs and somatostatinomas associated with congenital polycythemia due to somatic mutations in HIF2A has been reported.

OBJECTIVE

The aim of the study was to define the genetic defect in a new case of bilateral PHEO and multiple PGLs associated with congenital polycythemia.

PATIENT

A female patient presented with neonatal polycythemia (treated by phlebotomies, 1 session approximately every 4 mo), mildly enlarged cerebral ventricles, and bilateral PHEO and multiple PGLs. There was no family history of any neuroendocrine tumor or polycythemia. Surgical removal of the tumors only temporarily normalized plasma erythropoietin (Epo) levels and discontinued phlebotomies. No germline mutations were initially detected in the SDHB, SDHC, SDHD, VHL, and PHD2 genes, known to be associated with polycythemia. The PHEOs presented with a typical noradrenergic biochemical phenotype.

RESULTS

A heterozygous missense mutation (c.1589C>T) was identified in exon 12 of HIF2A, resulting in an alanine 530 substitution in the HIF-2α protein with valine (A530V). This somatic mutation was detected in the tissue from 1 PHEO and 1 PGL, with no HIF2A germline mutation found. This mutation led to stabilization of HIF-2α and hence a gain-of-function phenotype, as in previously published studies.

CONCLUSION

This case represents the first association of a somatic HIF2A gain-of-function mutation with PHEO and congenital polycythemia, and it alerts physicians to perform proper genetic screening in patients presenting with multiple norepinephrine-producing PHEOs and polycythemia. This report also extends the previous findings of a new syndrome of only multiple PGLs, somatostatinomas, and polycythemia to multiple PHEOs.

Disomy as the genetic underlying mechanisms of loss of heterozigosity in SDHD-paragangliomas

CONTEXT

Succinate dehydrogenase complex, subunit D (SDHD) mutations cause pheochromocytoma/paraganglioma syndrome. SDHD, located at chromosome 11q23, shows a parent-of-origin effect because the disease is observed almost exclusively when the mutation is transmitted from the father, although some cases of maternal transmission have been reported. Several hypotheses have been proposed for this peculiar inheritance pattern, but the underlying mechanisms have not yet been clearly elucidated.

OBJECTIVE

The objective of the study was to explain the parent-of-origin effect in a family, mainly affected by paternally transmitted paragangliomas, and with a maternally transmitted renal tumor.

PATIENTS

Peripheral blood DNA from 15 carriers and 7 tumor DNA samples from SDHD-p.Trp5* carriers were studied.

METHODS

We conducted mutation genotyping and microsatellite marker analysis in germline and tumor DNA and methylation status analysis in tumor DNA by methylation-specific multiplex ligation-dependent probe amplification.

RESULTS

Mutation genotyping and microsatellite marker analysis demonstrated loss of heterozygosity of the wild-type allele (maternal) in all studied tumors, except the renal tumor, which lost the mutated allele (maternal), and the prostate tumor, which had no loss of heterozygosity. The methylation-specific multiplex ligation-dependent probe amplification demonstrated that the methylation profile corresponded exclusively to the paternal chromosome without genomic loss, suggesting paternal uniparental disomy as the mechanism underlying the parent-of-origin effect in this SDHD family.

CONCLUSIONS

The paternal uniparental disomy involves the loss of maternally imprinted cell cycle regulators and the overexpression of paternally imprinted growth activators, leading to tumorigenesis in this syndrome.

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 therapeutic approaches for metastatic pheochromocytoma and paraganglioma: focus on SDHB tumors

As a result of intense genetic studies of families with specific mutations, the road to better therapeutic intervention for pheochromocytoma (PHEOs) and parangangliomas (PGLs) has more recently become populated with several promising molecular targets. Consequently a change in paradigm from a previous view on nonspecific therapy has shifted towards more selective molecular targeted therapies. In particular, malignant PHEOs/PGLs, more specifically the tumors that result from mutations in succinate dehydrogenase subunit B (SDHB), are a clear concern, and novel therapies should be developed to address this problem. Here we summarize current and future therapeutic approaches.

Mitochondrial complex II and genomic imprinting in inheritance of paraganglioma tumors

Germ line heterozygous mutations in the structural subunit genes of mitochondrial complex II (succinate dehydrogenase; SDH) and the regulatory gene SDHAF2 predispose to paraganglioma tumors which show constitutive activation of hypoxia inducible pathways. Mutations in SDHD and SDHAF2 cause highly penetrant multifocal tumor development after a paternal transmission, whereas maternal transmission rarely, if ever, leads to tumor development. This transmission pattern is consistent with genomic imprinting. Recent molecular evidence supports a model for tissue-specific imprinted regulation of the SDHD gene by a long range epigenetic mechanism. In addition, there is evidence of SDHB mRNA editing in peripheral blood mononuclear cells and long-term balancing selection operating on the SDHA gene. Regulation of SDH subunit expression by diverse epigenetic mechanisms implicates a crucial dosage-dependent role for SDH in oxygen homeostasis. This article is part of a Special Issue entitled: Respiratory complex II: Role in cellular physiology and disease.

Role of hypoxia and HIF2α in development of the sympathoadrenal cell lineage and chromaffin cell tumors with distinct catecholamine phenotypic features

Hypoxia has wide-ranging impact in normal physiology and disease processes. This stimulus evokes changes in gene expression mediated by transcription factors termed hypoxia-inducible factors (HIFs) that affect numerous processes: angiogenesis, cell survival, cellular metabolism, stem cell self-renewal and multipotency, migration, invasiveness, and metastatic progression in tumor cells. Over the past decade, increasing numbers of reports have emerged documenting differential roles of HIF1α and HIF2α in these processes. In cells of the sympathoadrenal lineage, both HIFs differentially mediate influences of hypoxia on catecholamine synthesis and secretion, but HIF2α signaling has particularly prominent functions in regulating developmental processes of growth and differentiation. This chapter discusses the role of HIF2α and HIF1α in the context of the development, phenotypic features, and functions of chromaffin cells. Moreover, current knowledge about tumor formation in cells of the sympathoadrenal lineage, leading to catecholamine-producing pheochromocytomas and paragangliomas, is analyzed in the light of the HIF2α signaling network.

The evolution in the use of MIBG scintigraphy in pheochromocytomas and paragangliomas

Radioiodinated metaiodobenzylguanidine (MIBG) was developed in the late 1970's, at the Michigan University Medical Center, for imaging of the adrenal medulla and its diseases. Soon after, MIBG was shown to depict a wide range of tumors of neural crest origin other than pheochromocytomas/paragangliomas (Pheo/PGL) with the result that its use rapidly spread to many countries. After more than 30 years of clinical application, MIBG continues to be the most widespread radiopharmaceutical for the functional imaging of Pheo/PGL in spite of the emergent role of PET agents for detection of these tumors. In this paper we review the evolution in the use of MIBG over more than 30 years of experimental and clinical applications, with particular focus on the uptake mechanisms, pharmacokinetics, biodistribution and drug interaction as well as on clinical studies in Pheo/PGL also in comparison to other gamma-emitters tracers and PET radiopharmaceuticals.

Identification of a signaling axis HIF-1α/microRNA-210/ISCU independent of SDH mutation that defines a subgroup of head and neck paragangliomas

BACKGROUND

Head and neck paragangliomas (HNPGLs) are rare tumors associated with the parasympathetic nervous system. Most are sporadic, but about one third result from germline mutations in succinate dehydrogenase (SDH) genes (SDHB, SDHC, SDHD, SDHA, or SDHAF2). Although a molecular connection between SDH dysfunction and tumor development is still unclear, the most accepted hypothesis proposes a central role of the pseudohypoxic pathway. SDH dysfunction induces abnormal stabilization of the hypoxia-inducible factors (HIFs) that regulate target genes involved in proliferation, apoptosis, angiogenesis, and metabolism. The involvement of these pathways in the development of sporadic HNPGLs is presently unknown.

OBJECTIVE

To get some insights into the hypoxic/pseudohypoxic molecular basis of HNPGLs, we attempted to define the gene, microRNA (miRNA), and HIF-1α expression patterns that distinguish tumors from normal paraganglia tissue.

DESIGN

Genome microarray and TaqMan low-density arrays were used to analyze gene and miRNA expression, respectively, in 17 HNPGL tumor tissues and three normal human carotid bodies. Twelve HNPGLs were used for validation of data. HIF-1α, SDHB, and iron-sulfur cluster scaffold protein (ISCU) protein expression was analyzed by immunohistochemistry.

RESULTS

We found activation of a canonical HIF-1α-related gene expression signaling only in a subset of HNPGLs from patients that did not harbor germline or somatic SDH mutations. The pseudohypoxic signature consisted in the overexpression of both HIF-1α-target genes and the HIF-1α-inducible miRNA, miR-210, and down-regulation of the miR-210 target gene, ISCU1/2. A decreased level of the iron-sulfur-containing protein SDHB was found by immunohistochemical analysis performed in two of these tumors.

CONCLUSIONS

Collectively, this study unveiled a putative signaling axis of HIF-1α/miRNA-210/ISCU in a subset of HNPGLs that could have an impact on SDHB protein stability by a mechanism independent of SDH mutations, thus providing a foundation to better understand the functional interplay between HIF, miR-210, and mitochondria and its relevance in the pathogenesis of HNPGLs.

Gene expression profiles of phaeochromocytomas with ERBB2 overexpression reveal a new molecular mechanism tumourigenicity

OBJECTIVE

Phaeochromocytomas (PHEO) and functional paragangliomas (PGLs) are catecholamine-secreting neuroendocrine tumours. Although most PHEO/PGLs are benign, 10-35% present as (or develop into) malignant tumours with a poor prognosis. Overexpression of ERBB2 (v-erb-b2 erythroblastic leukaemia viral oncogene homologue 2) has been reported to be associated with malignant PHEO. We used gene expression profiling of PHEO/PGLs to gain a better understanding of the tumourigenic pathways associated with ERBB2.

METHODS

We used the Affymetrix Gene Chip U133 Plus 2·0 genome-wide gene expression cDNA microarray of 18 PHEO/PGLs (12 benign and six malignant, divided into two groups depending on ERBB2 expression levels) to analyse the gene expression patterns.

RESULTS

Unsupervised hierarchical cluster analysis of transcription profiles of 18 samples identified two dominant expression clusters corresponding to samples belonging to the ERBB2+ and ERBB2- groups. According to the gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) databases, the differentially expressed genes were classified into diverse functional categories and signalling pathways. In particular, the focal adhesion signalling pathway showed significant differences between the groups; specifically, the FAK-Src-MAPK pathway was prominently activated in the ERBB2+ group.

CONCLUSIONS

In summary, ERBB2+ PHEO/PGLs have a distinct expression pattern compared with the ERBB2- group. The focal adhesion signalling pathway may participate in ERBB2-induced tumourigenesis in PHEO/PGLs.