Molecular mechanisms of RET receptor-mediated oncogenesis in multiple endocrine neoplasia 2.

Multiple endocrine neoplasia type 2 is an inherited cancer syndrome characterized by tumors of thyroid and adrenal tissues. Germline mutations of the REarranged during Transfection (RET) proto-oncogene, leading to its unregulated activation, are the underlying cause of this disease. Multiple endocrine neoplasia type 2 has been a model in clinical cancer genetics, demonstrating how knowledge of the genetic basis can shape the diagnosis and treatment of the disease. Here, we discuss the nature and effects of the most common recurrent mutations of RET found in multiple endocrine neoplasia type 2. Current understanding of the molecular mechanisms of RET mutations and how they alter the structure and function of the RET protein leading to its aberrant activation, and the effects on RET localization and signaling are described.

Hemorrhagic shock as the initial manifestation of pheochromocytoma: report of a sequential management strategy.

OBJECTIVE: To describe a patient presenting with hemorrhagic shock attributable to bleeding pheochromocytomas and the sequential management strategy used for treating this patient. METHODS: We summarize the clinical presentation, diagnostic work-up, surgical management, and pathologic features of our patient and review the pertinent literature. RESULTS: A 38-year-old man with multiple endocrine neoplasia type 2A and bilateral pheochromocytomas presented initially with nearly fatal retroperitoneal and intraperitoneal hemorrhage rather than the characteristic hypertensive paroxysms. After lifesaving operative intervention and a 5-month period of rehabilitation and convalescence, the patient underwent bilateral retroperitoneoscopic adrenalectomy as definitive treatment. Thus, the abdomen that had been operated on multiple times because of hemorrhage was left undisturbed, and the patient had a successful recovery. CONCLUSION: Near-fatal intraperitoneal hemorrhage is a very rare initial manifestation of pheochromocytoma. Our current patient with bilateral pheochromocytomas presented in this dramatic manner. This case shows that a sequential management strategy of damage-control surgical treatment followed by future resection of the tumors after appropriate a-adrenergic blockade is a safe and effective therapeutic option.

Successful kidney transplantation in a patient with multiple endocrine neoplasia type 2A syndrome: case study.

We present the case of a 37-year-old patient diagnosed with multiple endocrine neoplasia type 2A (MEN 2A) syndrome, as confirmed by genetic tests, who underwent the transplantation of a kidney from a cadaveric donor. MEN 2A, a hereditary autosomal dominant syndrome, is caused by the mutation of the RET proto-oncogene. In almost all patients this syndrome, is characterized by the occurrence of medullary thyroid cancer and pheochromocytoma; in some individuals also hyperparathyroidism. The available literature has not documented a kidney transplantation performed in Poland for this indication.

Clinical and prognostic implications of the genetic diagnosis of hereditary NET syndromes in asymptomatic patients.

Neuroendocrine tumors (NETs) can be sporadic or they can arise in complex hereditary syndromes. Patients with hereditary NETs can be identified before the development of tumors by performing genetic screenings. The aim of the study was to evaluate the clinical and prognostic impact of a preclinical genetic screening in subjects with hereditary NET syndromes. 46 subjects referred for hereditary NET syndrome [22 MEN1, 12 MEN2, 12 Familial Paragangliomatosis (FPGL)] were enrolled and divided in 2 groups (group A, 20 subjects with clinical appearance of NET before the genetic diagnosis; group B, 26 subjects with genetic diagnosis of hereditary NET syndromes before the clinical appearance of NETs). The main outcome measures were severity of disease, prognosis, and survival. The rate of surgery for MEN1-, MEN2-, FPGL4-related tumors was 90% in group A and 35% in group B (p<0.01). Both symptoms related to tumors and symptoms related to therapies were significantly less frequent in group B than in group A (p<0.05). Tumor stage was locally advanced or metastatic in 50% of group A and in no one of group B (p<0.01). The mortality rate was 25% in group A and 0% in group B (p<0.05). An early genetic screening for hereditary NET syndromes results in an improvement in clinical presentation and morbidity. A potential impact of the genetic screening on the mortality rate of these subjects is suggested and needs to be investigated in further and more appropriate studies.

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.

Hemodynamic instability during resection of pheochromocytoma in MEN versus non-MEN patients.

OBJECTIVE: Hemodynamic (HD) instability still underlies difficulties during pheochromocytoma resection. Little is known about HD instability in patients with multiple endocrine neoplasia (MEN) type 2-related pheochromocytoma. Our aim was to assess differences in HD during pheochromocytoma resection between MEN2 and non-MEN patients. In addition, we sought to identify risk factors for intraoperative HD instability. DESIGN: Retrospective cohort study. METHODS: A total of 22 MEN2 and 34 non-MEN patients underwent 61 pheochromocytoma resections at the University Medical Center Utrecht between 2000 and 2010. All MEN2-related pheochromocytomas were diagnosed by annual screening. HD instability was assessed by measuring the frequency of hypotensive (mean arterial blood pressure (MABP) <60  mmHg) and/or hypertensive (systolic arterial blood pressure (SABP) >200  mmHg) episodes. RESULTS: Compared with non-MEN patients, MEN2 patients were younger at diagnosis, had less symptoms, lower hormone levels, and smaller tumors. Intraoperatively, MEN2 patients had a similar frequency of hypertensive episodes (1.3 vs 1.9, P=0.162, 95% confidence interval (CI): -6.7 to 35.4) and a similar maximum SABP (200 vs 220  mmHg, P=0.180, 95% CI: -9.7 to 50.5). However, MEN2 patients experienced less frequent (1.04 vs 2.6, P=0.003, 95% CI: 0.57 to 2.6) and less severe hypotensive episodes after tumor resection (lowest MABP: 52.5 vs 45.6  mmHg, P=0.015, 95% CI: -12.6 to 1.16). Tumor size was an independent risk factor for HD instability for the total group after multivariate analysis. CONCLUSION: MEN2 patients with pheochromocytoma, despite their smaller tumors, do not distinguish themselves from non-MEN patients in terms of hypertensive episodes during pheochromocytoma resection. Therefore, pretreatment with α- and ß-blockade remains the standard of care in MEN2-related as well as in non-MEN-related pheochromocytomas.

Pheochromocytoma and medullary thyroid carcinoma in a pregnant multiple endocrine neoplasia-2A patient.

OBJECTIVE: We describe a rare combination of pheochromocytoma and medullary thyroid carcinoma (MTC) during pregnancy. METHODS: Twenty-three-years old lady, primigravida, was detected to be hypertensive at 12 weeks of gestation and was found to have left adrenal mass on routine obstetric scan. She had a goitre on examination which was proven to be MTC on fine needle aspiration cytology. Twenty-four hours urinary vanillyl mandelic acid and serum calcitonin levels were elevated. After adequate α and ß blockade she underwent left adrenalectomy during second trimester of gestation with no significant perioperative complications. Twelve days later she underwent total thyroidectomy. RESULTS: Adrenal mass was confirmed to be pheochromocytoma while MTC was confirmed in the thyroidectomy specimen. Post-operatively, she was normotensive and delivered a healthy female baby at term. Both mother and the baby tested positive for germline RET mutation (C634W) in exon 11. CONCLUSION: We describe a rare case of pregnant multiple endocrine neoplasia-2A patient with pheochromocytoma and MTC.

Parathyroid hormone-dependent hypercalcemia.

The past fifteen years have resulted in great progress in our understanding of the pathogenesis and pathophysiology of hypercalcemic disorders occurring either sporadically or in a familial setting. This paper briefly reviews the clinically most important new knowledge on sporadic and hereditary forms of parathyroid hormone-dependent hypercalcemic disorders, with special emphasis on familial syndromes such as multiple endocrine neoplasia type 1 and type 2A, hyperparathyroidism-jaw tumor syndrome, familial isolated hyperparathyroidism, familial hypocalciuric hypercalcemia and neonatal severe primary hyperparathyroidism. In addition, the authors briefly present the most important clinical characteristics of 141 patients with parathyroid hormone-dependent hypercalcemia, including index patients of 18 families with hereditary disorders, diagnosed in a Hungarian endocrine center between 1997 and 2007.

Characterization of the largest kindred with MEN2A due to a Cys609Ser RET mutation.

RET codon 609 point mutations are rare and may predispose to aggressive medullary thyroid carcinoma (MTC). In a kindred with 15 carriers of the Cys609Ser RET mutation we observed no MTC before 17 years of age, no lymph node metastases before 30 years and no distant metastases before 60 years. Two patients developed pheochromocytoma and one had primary hyperparathyroidism as the first sign of the syndrome. In conclusion, at variance from what already known, in this large kindred the Cys609Ser RET mutation predispose to a scarcely aggressive, highly penetrant MTC and a low penetrance of pheochromocytoma and primary hyperparathyroidism.

Long term parathyroid function following total parathyroidectomy with autotransplantation in adult patients with MEN2A.

While there is no doubt that total thyroidectomy is necessary for medullary thyroid carcinoma (MTC) in multiple endocrine neoplasia type 2A (MEN2A) patients, there is still controversy regarding the management of the parathyroid glands. Although most, but not all, endocrine surgeons leave normal-appearing parathyroid glands in situ during thyroid surgery for MEN2A, we have employed total parathyroidectomy with autotransplantation. Between 1994 and 2006, 12 MEN2A patients underwent therapeutic total or completion thyroidectomy and lymph nodes dissection at least in the central compartment for MTC. Total or completion parathyroidectomy with autotransplantation was performed concurrently with above-mentioned surgery. All patients were over 25 years old, and the median age was 48.5 years. There were 5 males and 7 females from 8 families. The average number of transplanted parathyroid glands was 3. Serum calcium and intact PTH levels have been maintained during the median follow up of 107 months in all patients except for one who of died of advanced MTC one year after surgery. Total parathyroidectomy with autotransplantation at the time of primary surgery for MTC, i.e. total thyroidectomy with bilateral central neck dissection, is a feasible approach for managing the risk of hyperparathyroidism.

MEN1 clinical background.

Multiple endocrine neoplasia Type 1 (MEN1) is a rare hereditary tumor syndrome predisposing to tumor development in several endocrine organs. Its major manifestations include hyperparathyroidism, tumors of endocrine pancreas and pituitary. Beside these three, several other endocrine (adrenocortical, foregut carcinoid) and nonendocrine (lipoma, angiofibroma, collagenoma, ependymoma, meningioma) tumors have been described to be associated with this syndrome. Both familial and sporadic forms of the disease are known. The diagnosis of MEN1 can be established if two of the three major manifestations are found in the same patient, whereas the diagnosis of familial MEN1 requires one MEN1 patient and a first degree relative with at least one MEN1 manifestation. MEN1 is transmitted as an autosomal dominant trait with high penetrance, approaching 95-100% by the age of 60. Both benign (parathyroid, anterior pituitary) and malignant (gastrinoma, glucagonoma) lesions may develop in MEN1 patients. Regular surveillance of MEN1 gene mutation carriers is necessary to reveal disease manifestations. Several diagnostic modalities can be used to screen for and to examine MEN1-related tumors. The therapy of MEN1-associated tumors requires specific approach in some cases, as multiple tumors and recurrence is frequently observed.

RET signaling in endocrine tumors: delving deeper into molecular mechanisms.

The rearranged during transfection (RET) proto-oncogene encodes a receptor tyrosine kinase that is implicated in the development of endocrine tumors of the thyroid and adrenal glands. In humans, activating RET mutations are found in the inherited cancer syndrome multiple endocrine neoplasia 2 and in sporadic medullary and papillary thyroid carcinomas. The specific type and location of RET mutations are strongly correlated with the disease phenotype and have both diagnostic and prognostic value. Recent advances in the molecular characterization of the RET receptor and its mutants have begun to define the mechanisms underlying the transforming ability of the different RET mutant forms. This information has revealed key functional features of these mutant proteins that distinguish the different clinically recognized mutations and provide clues as to the functional origins of the phenotypes associated with specific RET mutations. The elucidation of molecular mechanisms involved in RET-mediated transformation is a key step in the development of much needed therapeutics that target RET's oncogenic properties. Recent advances have begun to provide a deeper understanding of the receptor's function, and dysfunction, in human tumors that may guide this process.

Molecular pathogenesis of MEN2-associated tumors.

Although the gene responsible for multiple endocrine neoplasia type 2 (MEN2) was discovered many years ago, the exact mechanisms of tumor development in patients affected with RET germline mutations remain unknown. In vitro studies have certain pitfalls, one of which is the use of cell culture systems such as the NIH3T3 cells, in which RET usually is not expressed in contrast to the in vivo situation. Recent data suggest that an overrepresentation of mutant RET as a 'second hit' event might trigger tumorigenesis. However, alterations in other genes might contribute to this overrepresentation of RET or impact on MEN 2-related tumor development through completely different mechanisms and pathways. The final goal of further elucidating the natural history and pathogenesis of MEN2-related tumors should be the chance to offer patients with RET germline mutations an optimal cancer prevention (e.g. codon specific recommendations for prophylactic thyroidectomy) and treatment program, especially for metastatic medullary thyroid carcinoma for which presently no effective therapy other than surgery exists.

Multiple endocrine neoplasia type 2.

Multiple endocrine neoplasia type 2 (MEN 2) is an autosomal dominant inherited cancer syndrome. Predisposition to MEN 2 is caused by germline mutations of the RET proto-oncogene on chromosome 10q11.2 [1]. There are three clinically distinct forms of MEN 2 syndrome -- MEN 2A, familial medullary thyroid carcinoma (FMTC), and MEN 2B. In all of these subtypes, medullary thyroid carcinoma (MTC) is a key. MEN 2A is the most common subtype of MEN 2. Clinical features of the MEN 2A syndrome include medullary thyroid carcinoma (MTC) and/or C-cell hyperplasia (CCH) in almost all affected individuals, pheochromocytoma (approximately 50%) and hyperparathyroidism (HPT) (15-30%). MEN type 2B is the most aggressive of the MEN 2 variants and accounts for approximately 5% of all cases of MEN 2. MEN 2B is similar to MEN 2A but is characterized by the earlier onset of the disease and by developmental abnormalities. In FMTC, the third form of MEN 2, MTC is the only clinical feature. Introduced in recent years and still developing genetic testing of individuals at highest hereditary risk of MEN 2 syndrome holds the possibility of early detection and improved treatment and prognosis.

Multiple endocrine neoplasia syndrome: genetic basis for clinical management.

PURPOSE OF REVIEW: Multiple endocrine neoplasia (MEN) types 1 and 2 are rare hereditary cancer syndromes expressing a variety of mainly endocrine neoplasias. Improved understanding of the molecular and clinical genetics associated with these lesions will likely enhance the diagnosis and treatment of patients with these diseases. RECENT FINDINGS: The MEN1 gene causing MEN1 is a tumor suppressor gene and seems to act as a regulator of the transcriptional machinery. Novel genetic and diagnostic modalities tend to identify neoplastic lesions at an earlier stage, potentially improving outcome and quality of life. Improved understanding of genotype-phenotype correlations in MEN2, caused by a mutation in the RET oncogene, may enable a more individualized treatment for these patients. SUMMARY: Recent advances in molecular pathology, diagnosis, and management of patients with MEN1 and MEN2 are reviewed.

Chromaffin cell mitogenesis by neurturin and glial cell line-derived neurotrophic factor.

Neurturin and glial cell line-derived neurotrophic factor are novel mitogens for normal adult rat chromaffin cells in vitro. These neurotrophic factors differ from the previously described adult chromaffin cell mitogens, nerve growth factor and basic fibroblast growth factor, in that their effects are potentiated by depolarization and activation of protein kinase C. Neurturin and glial cell line-derived neurotrophic factor signal via the receptor tyrosine kinase, ret, but may also act independently of ret. Both depolarization and phorbol esters act synergistically with neurturin to up-regulate ret protein expression in chromaffin cell cultures, suggesting a mechanism for potentiation of mitogenesis. However, a direct role for ret in mitogenesis has not been established. Stimulation by neurturin causes increased phosphorylation of extracellular signal-regulated kinases 1 and 2 in cultured chromaffin cells, and mitogenesis is prevented by inhibitors of their phosphorylation. Inhibitors of phosphatidylinositol 3-kinase also prevent mitogenesis. The present findings suggest the hypothesis that neurotrophic factors and neurally derived signals might cooperatively regulate chromaffin cell proliferation in vivo in the rat. In addition, trans-synaptic stimulation might provide a route by which epigenetic factors could influence the development of adrenal medullary hyperplasia in humans with hereditary multiple endocrine neoplasia syndromes 2A and 2B by affecting expression and/or activation of ret.