Biochemical Diagnosis and Localization of Pheochromocytoma: Can We Reach a Consensus?

Tumor metabolism in pheochromocytomas: clinical and therapeutic implications

Pheochromocytomas and paragangliomas (PPGLs) have emerged as one of the most common endocrine tumors. It epitomizes fascinating crossroads of genetic, metabolic, and endocrine oncology, providing a canvas to explore the molecular intricacies of tumor biology. Predominantly rooted in the aberration of metabolic pathways, particularly the Krebs cycle and related enzymatic functionalities, PPGLs manifest an intriguing metabolic profile, highlighting elevated levels of oncometabolites like succinate and fumarate, and furthering cellular malignancy and genomic instability. This comprehensive review aims to delineate the multifaceted aspects of tumor metabolism in PPGLs, encapsulating genetic factors, oncometabolites, and potential therapeutic avenues, thereby providing a cohesive understanding of metabolic disturbances and their ramifications in tumorigenesis and disease progression. Initial investigations into PPGLs metabolomics unveiled a stark correlation between specific genetic mutations, notably in the succinate dehydrogenase complex (SDHx) genes, and the accumulation of oncometabolites, establishing a pivotal role in epigenetic alterations and hypoxia-inducible pathways. By scrutinizing voluminous metabolic studies and exploiting technologies, novel insights into the metabolic and genetic aspects of PPGLs are perpetually being gathered elucidating complex interactions and molecular machinations. Additionally, the exploration of therapeutic strategies targeting metabolic abnormalities has burgeoned harboring potential for innovative and efficacious treatment modalities. This review encapsulates the profound metabolic complexities of PPGLs, aiming to foster an enriched understanding and pave the way for future investigations and therapeutic innovations in managing these metabolically unique tumors.

Fluorescence-guided minimally-invasive resection of abdominal paragangliomas using indocyanine green

This retrospective study explores the utility of near-infrared (NIR) fluorescence imaging with indocyanine green (ICG) in enhancing the intraoperative identification and guidance for the resection of abdominal paragangliomas. They can be challenging to detect during minimally invasive surgery, due to their anatomical location, varying size and similar appearance in regard to their surrounding tissue. Patients with suspected abdominal paragangliomas planned for a minimally-invasive resection were included. As part of standard of care they received single intravenous dose of 5 mg ICG after abdominal exploration. NIR fluorescence imaging of the anatomical region of the suspected lesion was performed immediately following intravenous administration, to assess fluorescence signals, intraoperative identification, and histopathological correlation. Out of five resected suspicious lesions, four were imaged with NIR fluorescence, pathology confirming four as paragangliomas, the latter turned out to be an adrenal adenoma. NIR fluorescence identified all four lesions, surpassing the limitations of white-light visualization. Homogeneous fluorescence signals appeared 30-60 s post-ICG administration, which lasted up to 30 min. The study demonstrates the feasibility and potential clinical value of fluorescence-guided minimally-invasive resections of abdominal paragangliomas using a single intravenous ICG dose. These findings support the scientific basis for routine use of ICG-fluorescence-guided surgery in challenging anatomical cases, providing valuable assistance in lesion detection and resection.

[Comparison of the effectiveness of various methods for determining the level of metanephrines in the diagnosis of pheochromocytomas]

BACKGROUND

Pheochromocytoma (PHEO) is a tumor from the chromaffin tissue of the adrenal medulla, capable of hyperproduction of catecholamines. The increased production of hormones by the tumor leads to catecholamine crises, which have a pathological effect on all organs and systems. In the primary diagnosis of pheochromocytomas, it is important to determine the level of the metabolite of catecholamines - metanephrines. Currently, in clinical practice, various methods are used to determine the level of this metabolite: in blood plasma or in urine, total or only free form, fractionated analysis or unfractionated.

AIM

Comparison of the effectiveness of various methods for determining the level of metanephrines for the diagnosis of pheochromocytomas.

MATERIALS AND METHODS

A retrospective single-center cohort study was conducted on a sample of patients who were initially operated on for adrenal neoplasm at the Pirogov St. Petersburg State University High Medical Technology Clinic from November 2007 to December 2022 and who passed analysis to determine the level of blood or urine metanephrins before surgical treatment. The results of tests for metanephrine and tumor size were evaluated.

RESULTS

1088 patients with adrenal neoplasms who underwent surgical treatment were examined, of which 348 had histologically confirmed the presence of pheochromocytoma. Four types of metanephrine assays were compared: free fractionated plasma metanephrines (232 patients), unfractionated daily urine metanephrines (431 patients), fractionated total daily urine metanephrines (427 patients) and fractionated free daily urine metanephrines (178 patients). The greatest sensitivity was demonstrated by the analysis of free fractionated plasma methanephrines (95.4%). Unlike others, the sensitivity of this analysis did not decrease in the group of patients with small pheochromocytomas (3 cm or less). The greatest specificity was demonstrated by the analysis of unfractionated metanephrines in daily urine (97.8%), with the lowest sensitivity among all tests (67.6%). The study of fractionated total daily urine metanephrins showed good results of sensitivity and specificity, only slightly inferior to the best indicators, and the analysis of free daily urine metanephrins demonstrated unexpectedly low efficiency. There is a positive correlation between the level of metanephrine in the blood and the size of the tumor.

CONCLUSION

Based on the data obtained, the preferred assays for the primary diagnosis of pheochromocytoma can be considered the determination of fractionated free plasma metanephrines and fractionated total daily urine metanephrines, which is consistent with relevant clinical recommendations. It was found that the size of the tumor correlates with the severity of an increase in the level of metanephrins determined by any of the described methods.

Management of pheochromocytomas and paragangliomas: Review of current diagnosis and treatment options

Pheochromocytomas (PCCs) are rare neuroendocrine tumors derived from the chromaffin cells of the adrenal medulla. When these tumors have an extra-adrenal location, they are called paragangliomas (PGLs) and arise from sympathetic and parasympathetic ganglia, particularly of the para-aortic location. Up to 25% of PCCs/PGLs are associated with inherited genetic disorders. The majority of PCCs/PGLs exhibit indolent behavior. However, according to their affiliation to molecular clusters based on underlying genetic aberrations, their tumorigenesis, location, clinical symptomatology, and potential to metastasize are heterogenous. Thus, PCCs/PGLs are often associated with diagnostic difficulties. In recent years, extensive research revealed a broad genetic background and multiple signaling pathways leading to tumor development. Along with this, the diagnostic and therapeutic options were also expanded. In this review, we focus on the current knowledge and recent advancements in the diagnosis and treatment of PCCs/PGLs with respect to the underlying gene alterations while also discussing future perspectives in this field.

Adrenal bleeding due to pheochromocytoma - A call for algorithm

BACKGROUND

Adrenal hemorrhage is a rare, usually life-threating complication. The most common neoplasm resulting in spontaneous adrenal bleeding is pheochromocytoma and it accounts for nearly 50% of cases. Currently, the recommendations for the diagnosis and management of patients with adrenal bleeding due to pheochromocytoma are unavailable.

MATERIALS AND METHODS

We performed a database search for all pheochromocytoma patients, diagnosed and treated from 2005 to 2021 in tertiary endocrinology center. 206 patients were identified, 183 with complete data were included in the analysis. We investigated clinicopathological characteristics, treatment and outcomes of hemorrhagic pheochromocytoma cases and characterize our approach to perioperative diagnosis and medical management. Finally our experiences and data from previously published articles concerning adrenal hemorrhage were analyzed to propose a diagnostic and therapeutic algorithm for hemorrhagic pheochromocytomas.

RESULTS

In the whole group, seven patients (4 men and 3 women) with adrenal bleeding were found, (3.8%). Median patient's age was 49 years (range: 36-78 years). The most common manifestation of adrenal bleeding was acute abdominal pain (5/7). Two patients developed shock. Hormonal assessment was performed in five patients, based on 24-hour urinary fractionated metanephrines with urinary 3-methoxytyramine. Normetanephrine was elevated in all patients, metanephrine and 3-methoxytyramine - in four cases (4/5). Most patients (6/7) had symptoms suggesting pheochromocytoma before hemorrhage - most commonly paroxysmal hypertension (4/7). One patient died, before the diagnosis of adrenal bleeding was made. Diagnostic imaging performed in six out of seven patients revealed adrenal tumor, with median largest diameter equal to 7.4 cm (range: 5-11 cm). Five patients had elective surgery, in one case an urgent surgery was performed. In all cases the diagnosis of pheochromocytoma was confirmed in postoperative histopathology or in autopsy. The perioperative survival rate was 85.7%.

CONCLUSIONS

Diagnosis of pheochromocytoma should be always considered in patients with adrenal bleeding, especially with accompanying abdominal pain, hemodynamic shock and previous history of pheochromocytoma-associated symptoms. Lack of proper diagnosis of pheochromocytoma before surgery is associated with an additional perioperative risk. To improve the decision making in this life-threatening clinical situation, based on our results and literature data, we proposed a diagnostic and treatment algorithm.

Recurrence Rate of Sporadic Pheochromocytomas After Curative Adrenalectomy: A Systematic Review and Meta-analysis

BACKGROUND

Evidence on follow-up duration for patients with sporadic pheochromocytomas is absent, and current guidelines of the European Society of Endocrinology, American Association of Clinical Endocrinologists and Endocrine Surgeons, and the Endocrine Society are ambiguous about the appropriate duration of follow-up. The aim of this systematic review and meta-analysis is to evaluate the recurrence rate of sporadic pheochromocytomas after curative adrenalectomy.

MATERIALS AND METHODS

A literature search in PubMed, Embase, and the Cochrane Library was performed. A study was eligible if it included a clear report on the number of sporadic patients, recurrence rate, and follow-up duration. Studies with an inclusion period before 1990, <2 years of follow-up, <10 patients, and unclear data on the sporadic nature of pheochromocytomas were excluded. A meta-analysis on recurrence was performed provided that the heterogeneity was low (I2 < 25%) or intermediate (I2 26-75%). Hozo's method was used to calculate weighted mean follow-up duration and weighted time to recurrence with combined standard deviations (SDs).

RESULTS

A total of 13 studies, including 430 patients, were included in the synthesis. The meta-analysis results describe a pooled recurrence rate after curative surgery of 3% (95% confidence interval: 2-6%, I2 = 0%), with a weighted mean time to recurrence of 49.4 months (SD = 30.7) and a weighted mean follow-up period of 77.3 months (SD = 32.2).

CONCLUSIONS

This meta-analysis shows a very low recurrence rate of 3%. Prospective studies, including economical and health effects of limited follow-up strategies for patients with truly sporadic pheochromocytomas should be considered.

Measurements of Plasma-Free Metanephrines by Immunoassay Versus Urinary Metanephrines and Catecholamines by Liquid Chromatography with Amperometric Detection for the Diagnosis of Pheochromocytoma/Paraganglioma

Studies conflict concerning the use of enzyme immunoassays (EIA) for plasma free metanephrines (P-MNs) vs. other methods for pheochromocytoma/paraganglioma (PPGL) diagnosis. We compared commercially available EIAs for P-MNs with high-pressure liquid chromatography (HPLC) for 24 h-urinary MNs (U-MNs) and -catecholamines (U-CATs). 943 (565 female, 378 male) patients (54 PPGL, 889 Non-PPGL) were studied. Simultaneous measurements of all parameters analyzed at the central lab of our university hospital was mandatory for inclusion. Sensitivity of P-MNs (94.4%) was similar to that of U-MNs (100%), and both were higher than of U-CATs (77.8%), specificity of P-MNs (100%) higher than of U-MNs (73.6%), and similar to U-CATs (99.8%). With the recently proposed downward adjusted ULN of P-MNs to correct for the reported negative bias of the EIAs sensitivity (98.1%) raised non-significantly, but specificity decreased significantly (94.8%). Areas under receiver-operating characteristic curves indicated comparable diagnostic performance of P-MNs (0.989) vs. U-MNs (0.995), both better than U-CATs (0.956). In summary, the EIAs to measure P-MNs performed similarly to U-MNs by HPLC, and both better than U-CATs by HPLC. The post-test probability of PPGL given a positive test result was best for P-MNs, and higher than for the other pairs of analytes. Downward corrections of ULN of P-MNs did not improve test performances.

Abdominal Ultrasound in the Detection of an Incidental Paraganglioma

Paraganglioma is a tumor that originates from neuroendocrine cells of the sympathetic or parasympathetic systems. Patients may suffer from headaches, palpitations, diaphoresis, and hypertension due to catecholamine excess or symptoms from the mass effect of the tumor. In the absence of typical symptoms of catecholamine excess, the diagnosis of a nonfunctional paraganglioma is often delayed. Herein, we report a case of a 63-year-old female patient with a nonfunctional paraganglioma which is an accidental finding during investigation of a fever. Abdominal ultrasonography incidentally detected this lesion as a complex, solid, cystic mass in the left suprarenal retroperitoneum.

Pheochromocytoma: An approach to diagnosis

Pheochromocytomas are rare neuroendocrine chromaffin-derived tumors that arise within the adrenal medulla. They are usually benign, but if not diagnosed or if left untreated, they can have devastating consequences. Clinical consideration of the diagnosis is paramount, as they may have protean manifestations, and a high index of suspicion is essential if serious consequences are to be avoided. An accurate biochemical diagnosis is crucial for the management of these patients: either plasma or urinary metanephrines are both highly sensitive and specific if correctly employed, but knowledge of pre- and post-analytic interference is essential. Diagnostic imaging with cross-sectional CT and/or MRI offers high sensitivity in their detection, but lack specificity. The introduction of PET/CT/MR has led to a dramatic improvement in the localization of both pheochromocytomas and paragangliomas, together with the increasing availability of new functional imaging radionuclides. Optimal investigation and accurate diagnosis is best achieved at 'centers of excellence' with expert multidisciplinary teams.

Correlation between urinary fractionated metanephrines in 24-hour and spot urine samples for evaluating the therapeutic effect of metyrosine: a subanalysis of a multicenter, open-label phase I/II study

We recently conducted an open-label phase I/II study to evaluate the efficacy and safety of preoperative and chronic treatment with metyrosine (an inhibitor of catecholamine synthesis) in pheochromocytoma/paraganglioma (PPGL) in Japan. We compared creatinine-corrected metanephrine fractions in spot urine and 24-hour urine samples (the current standard for the screening and diagnosis of PPGLs) from 16 patients to assess the therapeutic effect of metyrosine. Percent changes from baseline in urinary metanephrine (uMN) or normetanephrine (uNMN) were compared between spot and 24-hour urine samples. Mean percent changes in uMN or uNMN in spot and 24-hour urine were -26.36% and -29.27%, respectively. The difference in the percent change from baseline between uMN or uNMN in spot and 24-hour urine was small (-2.90%). The correlation coefficient was 0.87 for percent changes from baseline between uMN or uNMN measured in spot and 24-hour urine. The area under the receiver operator characteristic (ROC) curve of uMN or uNMN measured in spot urine vs. 24-hour urine (reference standard) to assess the efficacy of metyrosine treatment was 0.93. Correlations and ROCs between 24-hour urinary vanillylmandelic acid, adrenaline, and noradrenaline and 24-hour uMN or uNMN were similar to those between spot uMN or uNMN and 24-hour uMN or uNMN. No large difference was observed between spot and 24-hour urine for the assessment of metyrosine treatment by quantifying uMN or uNMN in Japanese patients with PPGLs. These results suggest that spot urine samples may be useful in assessing the therapeutic effect of metyrosine.

Current Management of Pheochromocytoma/Paraganglioma: A Guide for the Practicing Clinician in the Era of Precision Medicine

Pheochromocytomas and paragangliomas (PCC/PGLs) are rare, mostly catecholamine-producing neuroendocrine tumors of the adrenal gland (PCCs) or the extra-adrenal paraganglia (PGL). They can be separated into three different molecular clusters depending on their underlying gene mutations in any of the at least 20 known susceptibility genes: The pseudohypoxia-associated cluster 1, the kinase signaling-associated cluster 2, and the Wnt signaling-associated cluster 3. In addition to tumor size, location (adrenal vs. extra-adrenal), multiplicity, age of first diagnosis, and presence of metastatic disease (including tumor burden), other decisive factors for best clinical management of PCC/PGL include the underlying germline mutation. The above factors can impact the choice of different biomarkers and imaging modalities for PCC/PGL diagnosis, as well as screening for other neoplasms, staging, follow-up, and therapy options. This review provides a guide for practicing clinicians summarizing current management of PCC/PGL according to tumor size, location, age of first diagnosis, presence of metastases, and especially underlying mutations in the era of precision medicine.

Peptide Receptor Radionuclide Therapy as a Novel Treatment for Metastatic and Invasive Phaeochromocytoma and Paraganglioma

At present there is no clinical guideline or standardised protocol for the treatment of metastatic or invasive phaeochromocytoma and paraganglioma (collectively known as PPGL) due to the rarity of the disease and the lack of prospective studies or extended national databases. Prognosis is mainly determined by genetic predisposition, tumour burden, rate of disease progression, and location of metastases. For patients with progressive or symptomatic disease that is not amenable to surgery, there are various palliative treatment options available. These include localised therapies including radiotherapy, radiofrequency, or cryoablation, as well as liver-directed therapies for those patients with hepatic metastases (e.g., transarterial chemoembolisation) and systemic therapies including chemotherapy or molecular targeted therapies. There is currently intense research interest in the value of radionuclide therapy for neuroendocrine tumours, including phaeochromocytoma and paraganglioma, with either iodine-131 (131I)-radiolabelled metaiodobenzylguanidine or very recently peptide receptor radionuclide therapy (PRRT), and the most important contemporary clinical studies will be highlighted in this review. The studies to date suggest that PRRT may induce major clinical, biochemical, and radiological changes, with 177Lu-DOTATATE being most efficacious and presenting less toxicity than 90Y-DOTATATE. Newer combination therapies with combined radioisotopes, or combinations with chemotherapeutic agents, also look promising. Given the favourable efficacy, logistic, and safety profiles, we believe that PRRT will probably become the standard treatment for inoperable metastatic PPGL in the near future, but we await data from definitive randomised controlled trials to understand its role.

Metastatic Phaeochromocytoma: Spinning Towards More Promising Treatment Options

Phaeochromocytomas (PCC) and paragangliomas (PGL) are rare tumours arising from the chromaffin cells of the adrenal medulla (PCC) or the paraganglia located outside the adrenal gland (PGL). However, their incidence is likely to be underestimated; around 10% of all PCC/PGL are metastatic, with higher metastatic potential of PGLs compared to PCCs. If benign, surgery is the treatment of choice, but if metastatic, therapy is challenging. Here we review the currently existing therapy options for metastatic PCCs/PGLs including conventional chemotherapy (the original Averbuch scheme, but updated), radiopharmaceutical treatments (¹³¹I-MIBG, ⁹⁰Y- and ¹⁷⁷Lu-DOTATATE) and novel targeted therapies (anti-angiogenic tyrosine kinase inhibitors and mTORC1 inhibitors), emphasising future therapeutic approaches (HIF-2α and PARP inhibitors, temozolomide alone, metronomic temozolomide, somatostatin analogues) based on the oncogenic signalling pathways related to three different clusters comprising more than 20 well-characterised PCC/PGL susceptibility genes. We suggest that targeted combination therapies including repurposed agents may offer more effective future options worthy of exploration.

Development and validation of liquid chromatography-tandem mass spectrometry method for quantification of plasma metanephrines for differential diagnosis of adrenal incidentaloma

High-resolution imaging techniques have increased the detection rate of adrenal incidentaloma. We developed a method of liquid chromatography-tandem mass spectrometry (LC-MS/MS) for detection of plasma free metanephrine (MN) and normetanephrine (NMN) and evaluated its analytical performance and clinical efficacy in differential diagnosis of adrenal incidentaloma. After solid-phase extraction, chromatographic isolation of the analytes and internal standard was achieved by column elution in the LC-MS/MS system. The analytes were detected in multiple-reaction monitoring mode by using positive electrospray ionization: MN, transition m/z 180.1→165.1; NMN, m/z 166.1→134.1. This method was validated for linearity, precision, accuracy, lower limits of quantification and detection, extraction recovery, and the matrix effect. Plasma concentrations of MN and NMN of 14 patients with pheochromocytoma were compared with those of 17 healthy volunteers, 10 patients with essential hypertension, and 60 patients with adrenal adenoma. The assay's linear range was 0.04-50.0 and 0.08-100.0 nmol/L for MN and NMN, respectively. Assay imprecision was 1.86-7.50%. The accuracy ranged from -7.50% to 2.00%, and the mean recovery of MN and NMN was within the range 71.5-95.2%. Our LC-MS/MS method is rapid, accurate, and reliable and useful for differential diagnosis of adrenal incidentaloma.

Phaeochromocytoma and Paraganglioma

Phaeochromocytomas and paragangliomas are relatively uncommon tumours which may be manifest in many ways, specifically as sustained or paroxysmal hypertension, episodes of palpitations, sweating, headache and anxiety, or increasingly as an incidental finding. Recent studies have shown that an increasing number are due to germline mutations. This review concentrates on the diagnosis, biochemistry and treatment of these fascinating tumours.

Diagnosing phaeochromocytoma/paraganglioma in a patient presenting with critical illness: biochemistry versus imaging

Phaeochromocytomas and paragangliomas (PPGLs) are revealed by acute cardiovascular complications involving end-organ damage in up to 20% of cases, a presentation associated with particularly high risk for mortality. Among such cases, PPGLs should be considered in patients with unexplained left ventricular failure, multi-organ failure, hypertensive crises or shock. The diagnosis of PPGL commonly relies on measurements of metanephrines in plasma or urine. However, acute critical illness is usually associated with sympathoadrenal activation. Thus, levels of metanephrines in patients in an acute emergency or intensive care setting, whether treated or not with vasoactive drugs, usually cannot be used to reliably diagnose PPGL. Delays in provision of diagnostic test results, particularly when these require 24-h urine collections, may also be incompatible for any need for rapid decisions on patient management or therapeutic interventions. The acute emergency situation therefore represents one exception to the rule where imaging studies to search for a PPGL may be undertaken without biochemical evidence of a catecholamine-producing tumour.

Analysis of laboratory data of 155 patients with pheochromocytoma-paraganglioma syndrome diagnosed during the past 20 years

Introduction: Laboratory diagnosis of pheochromocytoma-paraganglioma syndrome has been markedly improved during the past two decades. Aim: Retrospective assessment of diagnostic utility of urinary catecholamines and their metabolites as well as serum chromogranin A in 155 patients diagnosed at the 2nd Department of Medicine, Semmelweis University. Method: Urinary catecholamines and metabolites were measured using high-performance liquid chromatography with electrochemical detection in 155 patients with pheochromocytoma-paraganglioma (of whom 28.4% had hereditary background) and in 170 non-pheochromocytoma patients used as controls. Serum chromogranin A was measured by immunoradiometry. Results: Sensitivity (93.2%) and specificity (87.0%) of urinary fractionated metanephrines were higher than those of urinary catecholamines (90.9% vs. 85.7%, respectively) and serum chromogranin A (88.7% and 77.5%, respectively). Urinary normetanephrine and serum chromogranin A correlated positively with tumor size (r = 0.552, p<0.0001 and r = 0.618, p<0.0001, respectively). Conclusions: These data confirm the diagnostic utility of urinary catecholamines and their metabolites. Urinary normetanephrine and serum chromogranin A may help to estimate tumour mass and probably tumour progression. Orv. Hetil., 2015, 156(16), 626–635.

Penetrance and clinical features of pheochromocytoma in a six-generation family carrying a germline TMEM127 mutation

CONTEXT

The phenotype of familial pheochromocytoma (PHEO) associated with germline TMEM127 mutations (TMEM127-related PHEO) has not been clearly defined.

OBJECTIVE

This study aimed to investigate the penetrance, full phenotypic spectrum and effectiveness of clinical/genetic screening in TMEM127-related PHEO.

DESIGN, SETTING, AND PARTICIPANTS

Clinical and genetic screening, and genetic counseling were offered to 151 individuals from a six-generation family carrying a TMEM127 germline mutation in a referral center.

INTERVENTION AND MAIN OUTCOME MEASURES

TMEM127 genetic testing was offered to at-risk relatives and clinical surveillance for pheochromocytoma was performed in mutation-positive carriers.

RESULTS

Forty seven individuals carried the c.410-2A>C TMEM127 mutation. Clinical data were obtained from 34 TMEM127-mutation carriers followed up for 8.7 ± 8.1 years (range, 1-20 y). Pheochromocytoma was diagnosed in 11 carriers (32%) at a median age of 43 years. In nine patients, symptoms started at 29 years (range, 10-55 y) and two cases were asymptomatic. Tumors were multicentric in five (45%) and bilateral in five (45%) patients. Six patients (54%) had at least one adrenomedullary nodule less than 10 mm. No paragangliomas, distant metastases, or other manifestations were detected. Cumulative penetrance of pheochromocytoma was 0% at 0-20 years, 3% at 21-30 years, 15% at 31-40 years, 24% at 41-50 years, and 32% at 51-65 years. The youngest case was diagnosed at 22 years and the earliest symptoms were reported at age 10.

CONCLUSIONS

Tumor multicentricity, nodular adrenomedullary hyperplasia, and the occurrence of symptoms more than a decade earlier than the age at diagnosis are novel findings in TMEM127-related PHEO. The high penetrance of pheochromocytoma in this condition validates the benefits of genetic testing of at-risk relatives. We thus recommend that TMEM127 genetic testing should be offered to at-risk individuals at age 22 years and mutation carriers should undergo clinical surveillance annually.

Radioimmunoassay of free plasma metanephrines for the diagnosis of catecholamine-producing tumors

BACKGROUND

The determination of plasma metanephrines (MNs) provides a highly sensitive test for the diagnosis of catecholamine producing tumors. Chromatographic determinations with electrochemical or mass spectrometric detections are the methods of choice, but immunological assays have been developed. This study evaluated the clinical performances of a radioimmunoassay for free MNs in plasma.

METHODS

MNs, normetanephrine (NMN) and metanephrine (MN) and catecholamines, norepinephrine (NE) and epinephrine (E) were determined in plasma and urine of 533 patients suspected of catecholamine producing tumor. Urinary and plasma catecholamines and urinary MNs were determined by HPLC using amperometric detection. Plasma MNs were purified by solid phase chromatography and quantified by a specific radioimmunoassay.

RESULTS

Fifty-nine patients had tumors (13 paraganglioma and 46 pheochromocytoma) and the diagnosis was excluded in 474 patients. Receiver operator characteristic curves have identified optimal thresholds at 100 pg/mL for plasma NMN (sensitivity 96.6% and specificity 95.8%) and 70 pg/mL for plasma MN (sensitivity 61.0% and specificity 96.8%). These cut-off values were lower than those suggested by the manufacturer (170 and 100 pg/mL, respectively). The sensitivity of combined MNs was similar in plasma (100%) and urine (98%) but higher than that of urinary catecholamines (85%, p<0.001). The specificity of combined MNs in plasma (95%) was higher than urinary MNs (85%, p<0.001) and plasma catecholamines (75%, p<0.001).

CONCLUSIONS

Plasma-free and urinary-total MNs have a better discriminative power than catecholamines in the diagnosis of catecholamines producing tumors. Using these established cut-offs, measurement of plasma-free MN by radioimmunoassay represents an effective alternative to chromatographic methods.

Pheochromocytoma: pitfalls in the biochemical evaluation

The current work-up of a patient suspected to have a pheochromocytoma starts with the measurement of plasma or urine metanephrines. Notably, up to a quarter of these patients will have a false positive result. When the plasma or urine metanephrines are less than the 4-fold upper limit of normal, clinicians struggle between the fear of missing a potentially fatal condition and ordering costly follow up tests. In many cases, ordering unnecessary imaging studies may only increase the level of patient anxiety. This article will review various physiologic factors, pathologic conditions and medications that may influence the levels of catecholamines and their metabolites yielding false positive or false negative results. Acquiring familiarity with these conditions as well as interfering medications will equip clinicians with better interpretation skills of the biochemical tests.

Reference intervals for plasma free metanephrines with an age adjustment for normetanephrine for optimized laboratory testing of phaeochromocytoma

BACKGROUND

Measurements of plasma normetanephrine and metanephrine provide a useful diagnostic test for phaeochromocytoma, but this depends on appropriate reference intervals. Upper cut-offs set too high compromise diagnostic sensitivity, whereas set too low, false-positives are a problem. This study aimed to establish optimal reference intervals for plasma normetanephrine and metanephrine.

METHODS

Blood samples were collected in the supine position from 1226 subjects, aged 5-84 y, including 116 children, 575 normotensive and hypertensive adults and 535 patients in whom phaeochromocytoma was ruled out. Reference intervals were examined according to age and gender. Various models were examined to optimize upper cut-offs according to estimates of diagnostic sensitivity and specificity in a separate validation group of 3888 patients tested for phaeochromocytoma, including 558 with confirmed disease.

RESULTS

Plasma metanephrine, but not normetanephrine, was higher (P < 0.001) in men than in women, but reference intervals did not differ. Age showed a positive relationship (P < 0.0001) with plasma normetanephrine and a weaker relationship (P = 0.021) with metanephrine. Upper cut-offs of reference intervals for normetanephrine increased from 0.47 nmol/L in children to 1.05 nmol/L in subjects over 60 y. A curvilinear model for age-adjusted compared with fixed upper cut-offs for normetanephrine, together with a higher cut-off for metanephrine (0.45 versus 0.32 nmol/L), resulted in a substantial gain in diagnostic specificity from 88.3% to 96.0% with minimal loss in diagnostic sensitivity from 93.9% to 93.6%.

CONCLUSIONS

These data establish age-adjusted cut-offs of reference intervals for plasma normetanephrine and optimized cut-offs for metanephrine useful for minimizing false-positive results.

Updated and new perspectives on diagnosis, prognosis, and therapy of malignant pheochromocytoma/paraganglioma

Malignant pheochromocytomas/paragangliomas are rare tumors with a poor prognosis. Malignancy is diagnosed by the development of metastases as evidenced by recurrences in sites normally devoid of chromaffin tissue. Histopathological, biochemical, molecular and genetic markers offer only information on potential risk of metastatic spread. Large size, extraadrenal location, dopamine secretion, SDHB mutations, a PASS score higher than 6, a high Ki-67 index are indexes for potential malignancy. Metastases can be present at first diagnosis or occur years after primary surgery. Measurement of plasma and/or urinary metanephrine, normetanephrine and metoxytyramine are recommended for biochemical diagnosis. Anatomical and functional imaging using different radionuclides are necessary for localization of tumor and metastases. Metastatic pheochromocytomas/paragangliomas is incurable. When possible, surgical debulking of primary tumor is recommended as well as surgical or radiosurgical removal of metastases. I-131-MIBG radiotherapy is the treatment of choice although results are limited. Chemotherapy is reserved to more advanced disease stages. Recent genetic studies have highlighted the main pathways involved in pheochromocytomas/paragangliomas pathogenesis thus suggesting the use of targeted therapy which, nevertheless, has still to be validated. Large cooperative studies on tissue specimens and clinical trials in large cohorts of patients are necessary to achieve better therapeutic tools and improve patient prognosis.

Diagnostic tests and biomarkers for pheochromocytoma and extra-adrenal paraganglioma: from routine laboratory methods to disease stratification

The laboratory workup of patients with pheochromocytoma and extra-adrenal paraganglioma (PPGLs) has traditionally focused on biochemical measurements of tumor secretory products or their metabolites, with ultimate diagnosis resting on routine histopathology and immunohistochemistry. While such testing remains important, the needs to distinguish potentially metastatic from benign tumors and to identify tumors with a hereditary basis have stimulated searches for additional means to stratify patients according to risk of metastasis or presence of a particular mutation. Biomarkers based on traditional biochemical tests, such as profiles of catecholamine metabolites and granin-derived peptides, provide utility for both purposes, while novel biomarkers are being identified by proteomic and transcriptomic studies, the latter including microRNA expression profiling. Histopathological scoring methods for predicting metastatic potential, such as the Pheochromocytoma of the Adrenal Gland Scaled Score (PASS), are limited by poor interobserver concordance, discrepant results between studies and incomplete knowledge of how scores relate to genotype. Immunohistochemical staining for succinate dehydrogenase (SDH) subunit B to triage patients for genetic testing of SDH subunit genes illustrates the growing importance of pathology as an adjunct to genetic testing for disease stratification. Although considerable effort has been expended on microarray-based platforms to identify biomarkers of malignancy, as yet, none of those proposed have been demonstrated to reliably discriminate malignant from benign disease any better than the PASS. Because of the heterogeneity of PPGLs and variable time between first appearance of tumors and identification of metastases, any prospective study to establish prognostic efficacy requires large numbers of patients and extended follow-up.

Pheochromocytoma and pregnancy: a deceptive connection

A pheochromocytoma in a pregnant patient is one of the most threatening medical conditions for mother, fetus, and physician. Although extraordinarily rare with a frequency of 0.002% of all pregnancies, this tumor is notorious for its devastating consequences. As in non-pregnant patients, the signs and symptoms are quite variable but not specific, with hypertension being one of the most prominent signs. Confusion with the much more prevalent forms of pregnancy-related hypertension is the main cause of overlooking the diagnosis. If undiagnosed, maternal and fetal mortality is around 50%. Conversely, early detection and proper treatment during pregnancy decrease the maternal and fetal mortality to <5 and 15% respectively. For the biochemical diagnosis, plasma or urinary metanephrines are the tests of first choice since they have a nearly maximal negative predictive value. For reliable localization, only magnetic resonance imaging is suitable, with a sensitivity of more than 90%. When the tumor is diagnosed in the first 24 weeks of gestation, it should be removed by laparoscopic adrenalectomy after 10-14 days of medical preparation with the same drugs as in non-pregnant patients. If the tumor is diagnosed in the third trimester, the patient should be managed until the fetus is viable using the same drug regimen as for regular surgical preparation. Cesarean section with tumor removal in the same session or at a later stage is then preferred since vaginal delivery is possibly associated with higher mortality. Despite all technical diagnostic and therapeutic progress over the last decades, the key factor for further reduction of maternal and fetal mortality is early awareness and recognition of the potential presence of a pheochromocytoma in a pregnant patient with hypertension.

Pheochromocytoma - update on disease management

Pheochromocytomas are rare endocrine tumors that can present insidiously and remain undiagnosed until death or onset of clear manifestations of catecholamine excess. They are often referred to as one of the 'great mimics' in medicine. These tumors can no longer be regarded as a uniform disease entity, but rather as a highly heterogeneous group of chromaffin cell neoplasms with different ages of onset, secretory profiles, locations, and potential for malignancy according to underlying genetic mutations. These aspects all have to be considered when the tumor is encountered, thereby enabling optimal management for the patient. Referral to a center of specialized expertise for the disease should be considered wherever possible. This is not only important for surgical management of patients, but also for post-surgical follow up and screening of disease in patients with a hereditary predisposition to the tumor. While preoperative management has changed little over the last 20 years, surgical procedures have evolved so that laparoscopic resection is the standard of care and partial adrenalectomy should be considered in all patients with a hereditary condition. Follow-up testing is essential and should be recommended and ensured on a yearly basis. Managing such patients must now also take into account possible underlying mutations and the appropriate selection of genes for testing according to disease presentation. Patients and family members with identified mutations then require an individualized approach to management. This includes consideration of distinct patterns of biochemical test results during screening and the appropriate choice of imaging studies for tumor localization according to the mutation and associated differences in predisposition to adrenal, extra-adrenal and metastatic disease.

Evil lurks in the heart of man: cardiac paraganglioma presenting as recurrent dyspnoea and chronic cough

A man in his 60s presents with chronic dyspnoea and cough for 3 years. EKG and nuclear stress test were not diagnostic. An echocardiogram revealed moderate pericardial effusion. His symptoms improved with ibuprofen temporarily and a repeat echocardiogram showed resolution of the effusion. However, when his symptoms recurred, re-imaging showed a large intracardiac tumour causing right ventricular outflow obstruction. Subsequent histological examination revealed metastatic paraganglioma. He was found to carry a germline mutation in the SDHB gene which is associated with higher malignant risk. Knowledge of his underlying mutation allowed the patient and his family to receive appropriate gene-specific counselling and surveillance.

Malignant pheochromocytomas and paragangliomas: a diagnostic challenge

INTRODUCTION

Malignant pheochromocytomas (PCCs) and paragangliomas (PGLs) are rare disorders arising from the adrenal gland, from the glomera along parasympathetic nerves or from paraganglia along the sympathetic trunk. According to the WHO classification, malignancy of PCCs and PGLs is defined by the presence of metastases at non-chromaffin sites distant from that of the primary tumor and not by local invasion. The overall prognosis of metastasized PCCs/PGLs is poor. Surgery offers currently the only change of cure. Preferably, the discrimination between malignant and benign PCCs/PGLs should be made preoperatively.

METHODS

This review summarizes our current knowledge on how benign and malignant tumors can be distinguished.

CONCLUSION

Due to the rarity of malignant PCCs/PGLs and the obvious difficulties in distinguishing benign and malignant PCCs/PGLs, any patient with a PCC/PGL should be treated in a specialized center where a multidisciplinary setting with specialized teams consisting of radiologists, endocrinologist, oncologists, pathologists and surgeons is available. This would also facilitate future studies to address the existing diagnostic and/or therapeutic obstacles.

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 and emerging syndromes due to neuroendocrine tumors

Neuroendocrine tumors (NETs) are rare, slow-growing neoplasms characterized by their ability to store and secrete different peptides and neuroamines. Some of these substances cause specific clinical syndromes whereas others are not associated with specific syndromes or symptom complexes. NETs usually have episodic expression that makes diagnosis difficult, erroneous, and often late. For these reasons a high index of suspicion is needed, and it is important to understand the pathophysiology of each tumor to decide which biochemical markers are more useful and when they should be used.

Catecholamine metabolomic and secretory phenotypes in phaeochromocytoma

Phaeochromocytomas and paragangliomas (PPGLs) are highly heterogeneous tumours with variable catecholamine biochemical phenotypes and diverse hereditary backgrounds. This analysis of 18 catecholamine-related plasma and urinary biomarkers in 365 patients with PPGLs and 846 subjects without PPGLs examined how catecholamine metabolomic profiles are impacted by hereditary background and relate to variable hormone secretion. Catecholamine secretion was assessed in a subgroup of 156 patients from whom tumour tissue was available for measurements of catecholamine contents. Among all analytes, the free catecholamine O-methylated metabolites measured in plasma showed the largest tumour-related increases relative to the reference group. Patients with tumours due to multiple endocrine neoplasia type 2 and neurofibromatosis type 1 (NF1) showed similar catecholamine metabolite and secretory profiles to patients with adrenaline-producing tumours and no evident hereditary background. Tumours from these three patient groups contained higher contents of catecholamines, but secreted the hormones at lower rates than tumours that did not contain appreciable adrenaline, the latter including PPGLs due to von Hippel-Lindau (VHL) and succinate dehydrogenase (SDH) gene mutations. Large increases of plasma dopamine and its metabolites additionally characterised patients with PPGLs due to the latter mutations, whereas patients with NF1 were characterised by large increases in plasma dihydroxyphenylglycol and dihydroxyphenylacetic acid, the deaminated metabolites of noradrenaline and dopamine. This analysis establishes the utility of comprehensive catecholamine metabolite profiling for characterising the distinct and highly diverse catecholamine metabolomic and secretory phenotypes among different groups of patients with PPGLs. The data further suggest developmental origins of PPGLs from different populations of chromaffin cell progenitors.

Incidental and metastatic adrenal masses

In the last decades discoveries of adrenal masses incidentally during the course of diagnostic procedures for unrelated disorders (incidentalomas) have become progressively more frequent. The clinician in this position must answer two main questions: Is the mass benign or malignant?, and To what extent is the adrenal secretion altered? To come to a clinical decision, several diagnostic tools need to be engaged, starting with an accurate and correct radiological evaluation and a hormonal assessment of the adrenal function. When necessary, other diagnostic procedures such as functional imaging and fine-needle biopsy (FNB) can be considered in selected cases. Surgical removal is recommended for clinically relevant hypersecretory masses, as well as for masses suspected to be malignant. Most frequently, adrenal incidentalomas (AIs) are represented by benign cortical adenomas, a subset of which causes a mild hypercortisolism, known as subclinical Cushing's syndrome (SCS). The criteria to define this syndrome, as well as its treatment, are still debated and controversial. AIs that are not surgically removed should be re-examined in time to exclude a supervening increase in size or function. Follow-up criteria have not been established. Laparoscopic surgery is the recommended procedure to remove benign masses. The surgical procedure for adrenal malignancies is still debated.

Failure to diagnose phaeochromocytoma preoperatively: a case report and review of diagnostic criteria

We present a case in which phaeochromocytoma was not diagnosed preoperatively despite extensive investigation. There was significant haemodynamic instability during surgery. We review current diagnostic criteria with a view to reducing such a risk in future.

Urinary catecholamine and metanephrine to creatinine ratios in dogs with hyperadrenocorticism or pheochromocytoma, and in healthy dogs

BACKGROUND

Urinary catecholamines and metanephrines are used for the diagnosis of pheochromocytoma (PHEO) in dogs. Hyperadrenocorticism (HAC) is an important differential diagnosis for PHEO.

OBJECTIVES

To measure urinary catecholamines and metanephrines in dogs with HAC.

ANIMALS

Fourteen dogs with HAC, 7 dogs with PHEO, and 10 healthy dogs.

METHODS

Prospective clinical trial. Urine was collected during initial work-up in the hospital; in dogs with HAC an additional sample was taken at home 1 week after discharge. Parameters were measured using high-pressure liquid chromatography and expressed as ratios to urinary creatinine concentration.

RESULTS

Dogs with HAC had significantly higher urinary epinephrine, norepinephrine and normetanephrine to creatinine ratios than healthy dogs. Urinary epinephrine, norepinephrine, and metanephrine to creatinine ratios did not differ between dogs with HAC and dogs with PHEO, whereas the urinary normetanephrine to creatinine ratio was significantly higher (P= .011) in dogs with PHEO (414, 157.0-925.0, median, range versus (117.5, 53.0-323.0). Using a cut-off ratio of 4 times the highest normetanephrine to creatinine ratio measured in controls, there was no overlap between dogs with HAC and dogs with PHEO. The variables determined in urine samples collected at home did not differ from those collected in the hospital.

CONCLUSION AND CLINICAL IMPORTANCE

Dogs with HAC might have increased concentrations of urinary catecholamines and normetanephrine. A high concentration of urinary normetanephrine (4 times normal), is highly suggestive of PHEO.

The North American Neuroendocrine Tumor Society consensus guideline for the diagnosis and management of neuroendocrine tumors: pheochromocytoma, paraganglioma, and medullary thyroid cancer

Pheochromocytomas, intra-adrenal paraganglioma, and extra-adrenal sympathetic and parasympathetic paragangliomas are neuroendocrine tumors derived from adrenal chromaffin cells or similar cells in extra-adrenal sympathetic and parasympathetic paraganglia, respectively. Serious morbidity and mortality rates associated with these tumors are related to the potent effects of catecholamines on various organs, especially those of the cardiovascular system. Before any surgical procedure is done, preoperative blockade is necessary to protect the patient against significant release of catecholamines due to anesthesia and surgical manipulation of the tumor. Treatment options vary with the extent of the disease, with laparoscopic surgery being the preferred treatment for removal of primary tumors. Medullary thyroid cancer (MTC) is a malignancy of the thyroid C cells or parafollicular cells. Thyroid C cells elaborate a number of peptides and hormones, such as calcitonin, carcinoembryonic antigen, and chromogranin A. Some or all of these markers are elevated in patients with MTC and can be used to confirm the diagnosis as well as to follow patients longitudinally for recurrence. Medullary thyroid cancer consists of a spectrum of diseases that ranges from extremely indolent tumors that are stable for many years to aggressive types associated with a high mortality rate. Genetic testing for RET mutations has allowed identification of familial cases and prophylactic thyroidectomy for cure. The only curative treatment is complete surgical resection.

Phaeochromocytoma: diagnostic challenges for biochemical screening and diagnosis

The aim of this article is to provide knowledge of the origin of catecholamines and metabolites so that there can be an informed approach to the methods for biochemical screening for a possible phaeochromocytoma; The article includes a review of catecholamine and metadrenaline metabolism, with methods used in biochemical screening. In the adrenal medulla and a phaeochromocytoma, catecholamines continuously leak from chromaffin granules into the cytoplasm and are converted to metadrenalines. For a phaeochromocytoma to become biochemically detectable, metnoradrenaline secretion needs to rise fourfold, whereas noradrenaline secretion needs to rise 15-fold. The prevalence of a sporadic phaeochromocytoma is low; therefore false-positive results exceed true-positive results. Assay sensitivity is high because it is important not to miss a possible phaeochromocytoma. The use of urine or plasma fractionated metadrenalines as the first-line test has been recommended due to improved sensitivity. A negative result excludes a phaeochromocytoma. Only after a sporadic phaeochromocytoma has been diagnosed biochemically is it cost effective to request imaging. Sensitivities and specificities of the assays differ according to pre-test probabilities of the presence of a phaeochromocytoma, with hereditary and incidentalomas having a higher pre-test probability than sporadic phaeochromocytoma. In conclusion, in screening for a possible phaeochromocytoma, biochemical investigations should be completed first to exclude or establish the diagnosis. The preferred biochemical screening test is fractionated metadrenalines, including methoxytyramine so as not to miss dopamine-secreting tumours.

SDH-related pheochromocytoma and paraganglioma

Pheochromocytoma and paraganglioma are rare tumors of adrenals as well as the sympathetic and parasympathetic paraganglia. Clinical presentation of these tumors depends on localization, secretory profile and malignant potential. Four distinct syndromes--PGL1-4--are related to mutations in the succinate dehydrogenase gene--mitochondrial complex involved in electron transfer and Krebs cycle. Here we describe etiology, genetics, as well as clinical aspects of SDH-related tumors. We also describe recent discoveries in HIF-related pathway of tumorigenesis and mutations in new SDH-related genes that have improved our understanding of this disease.

Tachyarrythmias with elevated cardiac enzymes in Münchausen syndrome

We report the case of a woman with Münchausen syndrome who surreptitiously injected epinephrine causing recurrent ventricular tachyarrhythmias accompanied by dramatically high plasma levels of epinephrine and normal norepinephrine levels.

Chemically induced pheochromocytomas in rats: mechanisms and relevance for human risk assessment

Pheochromocytomas are tumors originating from chromaffin cells of the adrenal medulla, which have been observed in numerous carcinogenicity studies. The authors have evaluated pheochromocytoma concurrence with other effects and the possible mechanisms, in order to assess the relevance of such data for the classification of carcinogenic effects and their relevance to humans. The evaluation revealed that pheochromocytomas occur with relatively higher frequency in male rats, especially when the following conditions are involved: hypoxia, uncoupling of oxidative phosphorylation, disturbance in calcium homeostasis, and disturbance of the hypothalamic endocrine axis. The underlying biochemical mechanisms suggest that other substances that interfere with these biochemical endpoints also produce pheochromocytomas. Such endpoints include enzymes involved in catecholamine synthesis, receptor tyrosine kinase (RET), hypoxia-inducible factor (HIF), succinate dehydrogenase, fumarate hydratase, and pyruvate dehydrogenase. To date, there is no indication that the substances inducing pheochromocytomas in animal experiments also induce corresponding tumors in humans. Because the mechanisms of action identified in rats are to be expected in humans, pheochromocytomas may be induced after exposure conditions similar to those used in the animal studies. Whether hereditary mutations represent a risk factor in humans is not clear. Pheochromocytomas that occur in animal experiments currently appear to have little relevance for conditions at the work place. When sufficiently documented and evaluated, such secondary pheochromocytomas are not relevant for classification and human risk assessment.

Pheochromocytoma and paraganglioma

Pheochromocytoma is a very special kind of tumor full of duplicity. On the one hand it represents its own microworld with unique clinical, biochemical and pathological features, while on the other it constitutes a tremendously significant part of whole body system, playing a vital role for practically every organ system. It has a very special character - sometimes like a child it can be sweet and predictable, while at times it can behave like a deadly wild beast, crashing and tearing everything on its path in a fierce rage. It also consists of the amazingly intelligent neuroendocrine cells that possess a magical ability to make miraculous substances of many kinds. But most of all, it is a system that is able to drive our curiosity and the itch of "Cogito, ergo sum" to limitless depths and year by year it still amazes us with new and unexpected discoveries that move our understanding of multiple pathways and metabolic events closer to the ultimate truth. Recent discoveries of succinate dehydrogenase (SHD) and prolyl hydroxylase (PHD) mutations, for example, propelled our understanding of neuroendocrine tumorigenesis as a whole, as well as physiology of mitochondrial respiratory chain and phenomenon of pseudohypoxia in particular. Good old discoveries make their way from dusty repositories to shine with new meaning, appropriate for the current level of knowledge. This acquired wisdom makes us better physicians - knowing the specific expression makeup of catecholamine transporters, GLUTs and SRIFs allows for better tailored imaging and therapeutic manipulations. There are still long ways to go, keeping in mind that pheochromocytoma is but so very special, and we are optimistic and expect many great things to come.