Pheochromocytoma: recommendations for clinical practice from the First International Symposium. October 2005

The First International Symposium on Pheochromocytoma, held in October 2005, included discussions about developments concerning these rare catecholamine-producing tumors. Recommendations were made during the symposium for biochemical diagnosis, localization, genetics, and treatment. Measurement of plasma or urinary fractionated metanephrines, the most accurate screening approach, was recommended as the first-line test for diagnosis; reference intervals should favor sensitivity over specificity. Localization studies should only follow reasonable clinical evidence of a tumor. Preoperative pharmacologic blockade of circulatory responses to catecholamines is mandatory. Because approximately a quarter of tumors develop secondary to germ-line mutations in any one of five genes, mutation testing should be considered; however, it is not currently cost effective to test every gene in every patient. Consideration of tumor location, presence of multiple tumors, presence of metastases, and type of catecholamine produced is useful in deciding which genes to test. Inadequate methods to distinguish malignant from benign tumors and a lack of effective treatments for malignancy are important problems requiring further resolution.

Hypoglycemia due to ectopic release of insulin from a paraganglioma

Insulin-secreting pancreatic tumors and insulin-like growth hormone-secreting non-islet cell tumors can cause hypoglycemia. However, insulin-releasing paraganglioma or pheochromocytoma has almost never been reported. A 67-year-old female patient was admitted to our hospital because of headache, palpitation, perspiration, faintness, frequent sense of hunger and absent-mindedness. These intermittent symptoms had begun approximately a year before admission. On physical examination, she had high blood pressure of 150/90 mm Hg. Hormonal studies demonstrated increased urinary norepinephrine levels, and hyperinsulinemic hypoglycemia was confirmed while the patient was symptomatic. Abdominal MRI revealed a retroperitoneal mass measuring 4.5 cm in the pancreatic region. She was treated with an alpha-blocking agent to control blood pressure preceding the removal of the mass. Histopathological diagnosis was paraganglioma, and immunohistochemically insulin staining in the neoplastic cells was demonstrated. Her blood pressure normalized and hypoglycemia relieved after the operation. The patient did not have recurrence of hypoglycemia after a year of follow-up. Paraganglioma is a rare tumor of the neural crest, and co-secretion of insulin and catecholamines has been reported only by a single case report in the literature. The present patient is another case with this co-secretion.

A case of catecholamine and glucocorticoid excess syndrome due to a corticotropin-secreting paraganglioma

We present a case of a 61-year-old female patient with ectopic corticotropin (ACTH) syndrome, hypopituitarism, and catecholamine excess due to a paraganglioma at the inferior pole of the left kidney. In this article we discuss the hormonal findings in the patient and its consequences, the pitfalls of the endocrine workup, and the results of our immunohistological and molecular studies in more detail.

Expression of HIF-1alpha, HIF-2alpha (EPAS1), and their target genes in paraganglioma and pheochromocytoma with VHL and SDH mutations

CONTEXT

Activation of the hypoxia-inducible transcription factors HIF-1 and HIF-2 and a HIF-independent defect in developmental apoptosis have been implicated in the pathogenesis of pheochromocytoma (PCC) associated with VHL, SDHB, and SDHD mutations.

OBJECTIVE

Our objective was to compare protein (HIF-1alpha, EPAS1, SDHB, JunB, CCND1, CD34, CLU) and gene (VEGF, BNIP3) expression patterns in VHL and SDHB/D associated tumors.

RESULTS

Overexpression of HIF-2 was relatively more common in VHL than SDHB/D PCC (12 of 13 vs. 14 of 20, P = 0.02), whereas nuclear HIF-1 staining was relatively more frequent in SDHB/D PCC (19 of 20 vs. 13 of 16, P = 0.04). In addition, CCND1 and VEGF expression (HIF-2 target genes) was significantly higher in VHL than in SDHB/D PCC. These findings suggest that VHL inactivation leads to preferential HIF-2 activation and CCND1 expression as described previously in VHL-defective renal cell carcinoma cell lines but not in other cell types. These similarities between the downstream consequences of VHL inactivation and HIF dysregulation in renal cell carcinoma and PCC may explain how inactivation of the ubiquitously expressed VHL protein results in susceptibility to specific tumor types. Both VHL and SDHB/D PCC demonstrated reduced CLU and SDHB expression. SDHB PCC are associated with a high risk of malignancy, and expression of (proapototic) BNIP3 was significantly lower in SDHB than VHL PCC.

CONCLUSION

Although inactivation of VHL and SDHB/D may disrupt similar HIF-dependent and HIF-independent signaling pathways, their effects on target gene expression are not identical, and this may explain the observed clinical differences in PCC and associated tumors seen with germline VHL and SDHB/D mutations.

High frequency of SDHB germline mutations in patients with malignant catecholamine-producing paragangliomas: implications for genetic testing

CONTEXT

Adrenal and extraadrenal paragangliomas are tumors of chromaffin cells that are usually benign but that may also develop into malignant disease. Mutations of the gene for succinate dehydrogenase subunit B (SDHB) are associated with a high risk of malignancy, but establishing the precise contribution requires relatively large numbers of patients with well-defined malignancy.

OBJECTIVE

We assessed the prevalence of SDHB mutations in a series of patients with malignant paraganglioma.

DESIGN

SDHB mutation testing was carried out in 44 consecutive patients with malignant paraganglioma. Clinical characteristics of patients with malignant disease due to SDHB mutations were compared with those without mutations.

RESULTS

Pathogenic SDHB mutations were found in 13 of the 44 patients (30%). Close to one third of patients had metastases originating from an adrenal primary tumor, compared with a little over two thirds from an extraadrenal tumor. Among the latter patients, the frequency of SDHB mutations was 48%.

CONCLUSION

This study establishes that missense, nonsense, frameshift, and splice site mutations of the SDHB gene are associated with about half of all malignancies originating from extraadrenal paragangliomas. The high frequency of SDHB germline mutations among patients with malignant disease, particularly when originating from an extraadrenal paraganglioma, may justify a high priority for SDHB germline mutation testing in these patients.

Suprasellar and intrasellar paragangliomas

Neoplasms of the sellar region are entities with a large differential diagnosis. Although paraganglionic cells have not been demonstrated in the pituitary or adjacent structures, the existence of sellar region paragangliomas is well-documented. To elucidate, in this area the nature of these unusual tumors is relatively difficult. Clinical history, physical examination, radiographic investigation as well as intraoperative gross observation are the same as those of sellar meningioma or pituitary adenoma. Immunohistochemistry, using neuroendocrine markers and electron microscopy are the two definitive diagnostic methods to differentiate among these entities. The clinical management, the possible pathogenesis of the tumor, the importance of immunohistochemistry in making the diagnosis and the clinical outcome of these patients are discussed.

Basic fibroblast growth factor and fibroblastic growth factor receptor-1 may contribute to head and neck paraganglioma development by an autocrine or paracrine mechanism

Paragangliomas are hypervascular tumors arising from neural crest-derived paraganglia that are associated with the autonomic nerve system. Mutations in genes coding for subunits of mitochondrial complex II are associated with hereditary paragangliomas, and it has been suggested that these mutations result in a pseudohypoxic signal triggering tumorigenesis. Fibroblastic growth factors are hypoxia-inducible angiogenic stimuli that are involved in the angiogenesis and tumorigenesis of several neoplasms. It has been demonstrated that basic fibroblastic growth factor (bFGF) is a survival factor for cultured chief cells of the carotid body, capable of inducing proliferation. To examine the role of this growth factor in paragangliomas, we studied the immunohistochemical expression of bFGF and its high affinity receptor fibroblastic growth factor receptor 1 (FGFR1) in 7 normal carotid bodies and in 33 head and neck paragangliomas, including 2 malignant cases and their metastases. Immunohistochemical expression of bFGF and FGFR1 in tumors was confirmed by real-time polymerase chain reaction. FGFR1 was moderately present in carotid bodies, and there was strong and significantly enhanced cytoplasmatic staining of FGFR1 in all paragangliomas. Chief cells in carotid bodies and tumors showed strong cytoplasmatic staining for bFGF. The results indicate that FGFR1 and bFGF may contribute to the development of head and neck paragangliomas.

Primary cutaneous paraganglioma of the scalp

Paragangliomas are neuroendocrine tumors that arise in relation to the sympathetic or parasympathetic ganglia of the autonomic nervous system. Rarely, they are reported in unusual locations such as the urinary bladder, prostate, and uterus. Herein, we report a case of primary cutaneous paraganglioma of the scalp in a child. The tumor was studied histologically, immunohistochemically, and ultrastructurally. This case might represent an aberrant migration of neural crest cells in their descent toward the branchial arches. In addition, it highlights the complex interaction of the neural crest and branchial arches/clefts during embryogenesis.

Epidermal growth factor receptor expression and activation in neuroendocrine tumours

Epidermal growth factor receptor (EGFR) is expressed in many cancers and is associated with poor prognosis. EGFR activation pathways have been well characterised using tumour cell lines and are known to involve EGFR activation through autophosphorylation. Phosphorylation of downstream signalling molecules, such as ERK1/2 (extra-cellular regulated kinase 1 and 2) and PKB/Akt (protein kinase B), leads to enhanced tumour cell survival and proliferation. Although EGFR expression has been determined in neuroendocrine tumour tissue, its activation and subsequent effects on the downstream signalling molecules, ERK1/2 and Akt, have not been studied. We therefore planned to determine the role of EGFR in neuroendocrine tumours (NETs) by determining its pattern of expression and activation, and the subsequent activation of downstream signalling molecules ERK1/2 and Akt. Paraffin-embedded tumour tissue was available from 98 patients with NETs (39 foregut, 42 midgut, four hindgut, five paragangliomas, and four of unknown origin). Immunohistochemical evaluation was performed for the expression of EGFR, p-EGFR, p-Akt, and p-ERK1/2. Ninety-six percent of tumour samples were positive for EGFR expression; 63% were positive for activated EGFR; 76% were positive for activated Akt; and 96% were positive for activated ERK1/2. Importantly, the histological score for the activation of Akt and ERK1/2 correlated with the histological score for activated EGFR. These data provide a rationale for considering EGFR inhibitors in the treatment of NETs. Additionally, direct inhibition of Akt and ERK1/2 may provide further therapeutic options in the treatment of NETs in the future.

Corticotropin-producing pulmonary gangliocytic paraganglioma associated with Cushing's syndrome

Gangliocytic paraganglioma (GP) is an unusual tumor in the wide spectrum of neuroendocrine neoplasms. The biologic behavior and histogenesis of this tumor is uncertain because, despite its benign histologic features, there have been reports of metastases to regional lymph nodes and distant metastases. Although most of these tumors have been reported in the duodenum, examples of GP arising in extra-ampullary sites have been well documented. Herein, we report the case of a lung GP corticotropin producing and presenting as Cushing's syndrome. After removal of the tumor, there was a significant drop in cortisol and corticotropin levels. To our knowledge, this is the first report of a GP causing Cushing's syndrome.

Sclerosing Paraganglioma

Nineteen cases of a distinctive variant of paraganglioma characterized by extensive collagen deposition resulting in a pattern of growth that resembled an invasive malignant neoplasm are described. The patients were 3 men and 16 women, 32 to 69 years of age (mean, 50.5 years). The tumors were located in the carotid body region, parapharyngeal region, and mediastinum. Tumor size ranged from 2 to 6 cm in greatest diameter. Grossly, the tumors were described as rubbery to firm, tan-red, and with extensive areas of sclerosis. Histologic examination showed nests and cords of tumor cells separated by broad bands of fibrous tissue. The tumor cells ranged from round to polygonal with abundant cytoplasm to elongated spindle cells with scant cytoplasm. Nuclear cytomegaly was present focally enhancing the atypical appearance of the tumor cell population in 17 cases. Mitoses were sparse (<1 x 10 HPF), and there was no evidence of necrosis in any of the cases. Foci of vascular and perineural invasion were present in 2 and 4 cases, respectively. The most striking morphologic feature was the presence of irregular cords and bands of hyalinized fibrous tissue that compartmentalized the lesion into irregular nests, islands, or cords of tumor cells, imparting them with an infiltrative appearance. All the tumors showed positive immunostaining for chromogranin, synaptophysin, and monoclonal neuron specific enolase. S-100 protein stains identified a sustentacular cell network, whereas cytokeratin AE1/AE3 was negative in all cases. Clinical follow-up in 14 cases, ranging from 2 months to 20 years (mean follow-up, 6.6 years) showed evidence of local recurrence in 2 cases and the development of a separate tumor in the contralateral neck in 1 case. The remainder of patients were free of recurrence or metastasis following simple local excision. Because of the prominent sclerosis, a diagnosis of an invasive malignant neoplasm was initially considered in the majority of cases. Sclerosing paraganglioma should be included in the differential diagnosis of sclerosing lesions of the head and neck region and mediastinum. Appropriate immunohistochemical stains may be of aid for establishing the correct diagnosis.

Composite paraganglioma-ganglioneuroma of the urinary bladder

Presented herein is the case of a 73-year-old man, complaining of dysuria, who had a composite paraganglioma-ganglioneuroma of the urinary bladder (CPGUB). At cystoscopy a submucosal tumor was found in the urinary bladder and resected after transurethral biopsy. The levels of serum catecholamine and 24 h urinary excretion of catecholamine and vanillylmandelic acid were elevated. Grossly, the resected tumor, measuring 4 x 3 x 2.5 cm, had a brownish cut surface with no necrosis and hemorrhage. Histologically, the tumor had alternating cellular and fibrous areas. The cellular areas consisted of polygonal cells, arranged in well-defined nests (Zellballen) and positive for Grimelius staining, with abundant amphophilic to acidophilic cytoplasm, occasionally containing eosinophilic hyaline globules and brown pigments. Although the nuclei of several polygonal cells were bizarre, mitoses and vascular invasion were not found. Fibrous areas consisted of spindle cells, resembling Schwann cell, admixed with ganglionic cells. To the authors' knowledge, only four cases of CPGUB have been reported in the English-language literature. Detailed reported cases and the present case showed no malignant features, such as extra-bladder infiltration and metastasis, and no recurrence in the short length of follow up. Accumulation of long-term follow-up cases may provide valuable prognostic information on this composite tumor.

High expression of neuropeptide y receptors in tumors of the human adrenal gland and extra-adrenal paraganglia

PURPOSE

Recently, a role of neuropeptide Y (NPY) in tumor biology was suggested based on the high density of NPY receptors in breast and ovarian cancers. The high frequency of NPY receptors in steroid hormone-producing ovarian sex cord-stromal tumors, together with the known influence of NPY on steroid hormone and catecholamine secretion in the rodent adrenal gland, led to the investigation of NPY receptor expression in the human adrenal gland and related tumors.

EXPERIMENTAL DESIGN

Fifteen adrenal cortical tumors, 20 paragangliomas, 23 pheochromocytomas, 20 neuroblastomas, and 8 normal adrenal glands were investigated by in vitro NPY receptor autoradiography using 125I-labeled peptide YY in competition experiments with receptor subtype selective analogs.

RESULTS

Ninety three percent of cortical tumors express Y1, 35% of pheochromocytomas and 61% of paragangliomas express Y1 and Y2, and 90% of neuroblastomas express Y2 receptors. The NPY receptors in pheochromocytomas, paragangliomas, and neuroblastomas are often expressed concomitantly with the NPY hormone detected immunohistochemically. The adrenal cortex strongly expresses Y1, whereas no NPY receptors are found in the adrenal medulla.

CONCLUSIONS

These receptor data suggest a role of NPY in adrenal cortical tumors and, together with the strong NPY innervation of the cortex, a physiologic role in the adrenal gland, mediated by Y1 receptors. These NPY receptors are a potential new molecular target for the therapy of malignant tumors.

Duodenal gangliocytic paraganglioma: a radiological-pathological correlation

Duodenal gangliocytic paraganglioma is a rare tumor that characteristically occurs in the second portion of the duodenum and typically presents with gastrointestinal bleeding. Gangliocytic paragangliomas have a characteristic triphasic microscopic appearance with epithelioid cells, spindle cells, and ganglion cells, resulting in a complex histology with features of paraganglioma, carcinoid, and ganglioneuroma. Duodenal gangliocytic paragangliomas have an excellent prognosis after surgical resection but metastatic spread to regional lymph nodes and recurrence may rarely occur. We report a case of duodenal gangliocytic paraganglioma and discuss the radiological and pathological differential diagnosis of this rare entity.

Avoiding Pitfalls in Surgery of the Neck, Parapharyngeal Space, and Infratemporal Fossa

The region of the upper neck, parapharyngeal space, and infratemporal fossa contains many vital structures in a confined area. Access is often limited, making surgical treatment challenging. Preoperative assessment is critical in determining the optimal surgical approach. In spite of improvements in preoperative evaluation and surgical techniques, sequelae from surgical therapy are sometimes unavoidable. Awareness of the potential problems is necessary to counsel patients appropriately regarding treatment options and all potential risks.

Cerebellopontine angle paraganglioma – report of a case and review of literature

Majority of the cerebellopontine angle (CPA) tumors are acoustic neuromas, while bulk of the non-acoustic tumors are formed by meningiomas and epidermoid cysts. Primary paraganglioma is a rare tumor in this location, with only two such cases having been reported in the literature, till date. Recently, a case has been described wherein a paraganglioma was apparently arising as a primary lesion in the cerebellar hemisphere. We report another case of an intracranial paraganglioma of the CPA in a 40-year-old female, which did not have any vascular attachment but had focal cerebellar extension.

Paraganglioma with ganglioneuromatous component located in the posterior mediastinum

A 4-cm paravertebral mediastinal tumor was resected in a 70-year-old male patient treated for hypertension. The tumor displayed both paraganglioma and ganglioneuroma areas that were in equal proportion and often merged one into the other. Paraganglioma areas contained synaptophysin and chromogranin-positive chief cells and PS100-positive sustentacular cells. Ganglioneuroma areas contained neurofilament-positive mature ganglion cells and PS100-positive Schwann cells. Such pheochromocytoma-ganglioneuroma has not been previously reported in the mediastinum and appears as the adrenal and aorticosympathetic counterpart of gangliocytic paraganglioma described in other anatomic sites.

Accumulation of Krebs cycle intermediates and over-expression of HIF1alpha in tumours which result from germline FH and SDH mutations

The nuclear-encoded Krebs cycle enzymes, fumarate hydratase (FH) and succinate dehydrogenase (SDHB, -C and -D), act as tumour suppressors. Germline mutations in FH predispose individuals to leiomyomas and renal cell cancer (HLRCC), whereas mutations in SDH cause paragangliomas and phaeochromocytomas (HPGL). In this study, we have shown that FH-deficient cells and tumours accumulate fumarate and, to a lesser extent, succinate. SDH-deficient tumours principally accumulate succinate. In situ analyses showed that these tumours also have over-expression of hypoxia-inducible factor 1alpha (HIF1alpha), activation of HIF1alphatargets (such as vascular endothelial growth factor) and high microvessel density. We found no evidence of increased reactive oxygen species in our cells. Our data provide in vivo evidence to support the hypothesis that increased succinate and/or fumarate causes stabilization of HIF1alpha a plausible mechanism, inhibition of HIF prolyl hydroxylases, has previously been suggested by in vitro studies. The basic mechanism of tumorigenesis in HPGL and HLRCC is likely to be pseudo-hypoxic drive, just as it is in von Hippel-Lindau syndrome.

November 2004: intradural mass of the cauda equina in a woman in her early 60s

November 2004. A 63-year-old woman presented with slowly aggravating lower back pain and recent urinary urge incontinence. MRI revealed a sharply-delineated, partly cystic intradural mass with inhomogenous contrast-enhancement and ectatic vessels at the upper pole. An ependymoma was suspected, and the tumor was resected in toto. Histologically, at first glance, the tumor strongly resembled an ependymoma, showing a monomorphic cellular pattern, perivascular pseudorosettes and ependymal canal-like structures. However, the finding of a delicate collagen capsule, compartmentation of tumor cells into zellballen and the presence of ganglionic cells were untypical. These features were indicative of a paraganglioma with a gangliocytic component. Immunoreactivity of the tumor cells for neuroendocrine antigens, the detection of GFAP-positive sustentacular cells and the ultrastructural confirmation of neurosecretory granules substantiated this diagnosis. The clinical, radiological and morphological similarity between ependymomas, which are far more common in the cauda equina region than paragangliomas, has led to substantial diagnostic confusion in the past.

The importance of the interpretation of urine catecholamines is essential for the diagnosis and management of patient with dopamine-secreting paraganglioma

Phaeochromocytoma or paraganglioma that exclusively secretes dopamine is very rare. This case illustrates its atypical presentation and the importance of interpretative reporting for urine catecholamines leading to the diagnosis and subsequent management of a patient with this condition. We report a 71-year-old Chinese woman with a large dopamine-secreting paraganglioma. She presented with low back pain for six months. On examination, a right abdominal mass was palpable incidentally. Her blood pressure was normal throughout. Serial 24-h urine collections for catecholamines showed enormous elevation of urine dopamine excretion to 80.7 micromol/day (normotensive:<2.6 m mol/day). However, the daily excretions of urine adrenaline and noradrenaline, as well as their metabolites were within their respective reference intervals. Good communication between chemical pathologists and physicians prompted the arrangement of the whole body 131I-meta-iodobenzylguanidine (MIBG) scintigraphy, which showed a large signal in the right upper quadrant of the abdomen corresponding to a large extra-adrenal tumour detected by both ultrasonography and computerized tomography (CT) of the abdomen. Histological section of the tumour tissue revealed paraganglioma, which stained positive for chromogranin and neuron-specific enolase. After four months, the patient presented with chest symptoms and CT of the thorax revealed multiple nodules. Lung metastases were suspected. However, follow-up urine catechola- mine and dopamine excretions were again within their respective normotensive reference intervals. A second MIBG scintigraphy was performed, but no specific uptake at either the thorax or the abdomen could be demonstrated. Fine-needle aspiration cytology using the thoracoscopic technique was performed and immunochemical staining of the biopsy specimen showed the presence of non- small-cell carcinoma of the lung.

New insights in the genetics of adrenocortical tumors, pheochromocytomas and paragangliomas

Recent advances in the molecular genetic of adrenal tumors give new insights in the pathophysiology of these neoplasms in both hereditary and sporadic cases. The practice of genetic counselling in patients with adrenal tumors have been recently changed by the identification and the understanding of new specific hereditary cancer susceptibility syndromes. In the case of sporadic adrenocortical tumors these progress also offer new prognosis predictors. The genetic predisposition to adrenocortical cancer in children has been well established in the Li-Fraumeni and Beckewith-Wiedeman syndromes due to germline p53 mutation located at 17p13 and dysregulation of the imprinted IGF-2 locus at 11p15, respectively. Adrenocortical tumors are also observed in Multiple Endocrine Neoplasia type I syndrome. Cushing's syndrome due to primary pigmented nodular adrenocortical disease have been observed in patients with germline PRKAR1A inactivating mutations. Interestingly allelic loss at 17p13 and 11p15 have been observed in sporadic adrenocortical cancer and somatic PRKAR1A mutations in secreting adrenocortical adenomas. The potential interest of these finding for the diagnosis of these tumors will be discussed. In the case of pheochromocytoma and paraganglioma, the demonstration that three genes encoding three succinate dehydrogenase subunits (SDHD, SDHB, SDHC), belonging to the complex II of the respiratory chain in the mitochondria, are involved in the genetics of familial and especially in apparently sporadic phaeochromocytomas have dramatically modified our practice. Up to date, four diagnosis of familal disease (multiple endocrine neoplasia type II, von Hippel Lindau disease, neurofibromatosis type 1 and hereditary paraganglioma) should be discussed and causative mutations in six different phaechomocytoma susceptibility genes (RET, VHL, NF1, SDHB, SDHD, SDHC) could be identified. In this review, we will perform an update compiling these new clinical, genetic and functional data recently published. We will suggest guidelines for the practice of the phaeochomocytoma genetic testing in the patients and their families, and for an early detection of tumors in the patients or in individuals determined to be at-risk of disease by the presymptomatic genetic testing.

Genetic aberrance of sporadic MEN 2A component tumours: analysis of RET

AIM

The molecular pathogenesis of familial multiple endocrine neoplasia (MEN) type 2 (parathyroid adenoma with medullary thyroid carcinoma and adrenal pheochromocytoma) is associated with a germ-line mutation in the RET proto-oncogene. We undertook this study to clarify the relationship between the tumorigenesis of apparently sporadic MEN type 2 component endocrine tumours and RET mutations.

METHODS

Direct sequencing for RET exon 10, 11, 12, 13, 14, 15 and 16 and immunohistochemistry for RET monoclonal antibody were performed on the archival tissues of 84 cases of sporadic endocrine tumours, including 22 medullary thyroid carcinomas (MTCs), 35 adrenal pheochromocytomas (APCs), 18 paragangliomas (PGs), and nine parathyroid adenomas (PTAs).

RESULTS

PCR-based direct sequencing revealed somatic point missense mutation within 22.7% of exon 13 of the RET proto-oncogene (four cases of E768D, one case of S7781) in MTCs. No RET genotype and morphological association was observed in MTCs or APCs. APCs revealed significantly lower levels of immunoexpression of RET, even versus PGs.

CONCLUSIONS

The genetic mutation in RET is relatively low in incidence, and likely to play an insignificant role in the molecular pathogenesis of sporadic MTC. The molecular bases of PG and APC seem to be different despite their embryological and histological similarities.