Forms Of Medullary Thyroid Carcinoma Research Articles

Clinic Heterogeneity and Management of Pediatric Patients With Germline RET Proto-oncogene Mutation: Single-center Experience.

Inherited forms of medullary thyroid carcinoma (MTC) can cause serious problems in diagnosis and follow-up. Family screening is performed, and prophylactic thyroidectomy at an appropriate age can be life-saving. This study aimed to investigate the diagnostic, clinical, laboratory characteristics, and treatment methods of cases with rearranged during transfection ( RET) mutation in the childhood age group. Patients diagnosed with hereditary MTC and patients who were evaluated by detecting MTC and/or RET mutations in their families were included in this study. Nine cases from 6 families were included in the study. Seven patients were evaluated as a result of screening, whereas 2 patients, one of whom was MEN2B, were symptomatic. Prophylactic thyroidectomy was performed in 7 cases. Medullary microcarcinoma was found in all, and additional papillary thyroid carcinoma in one. An inoperable tumor was detected in one patient, and sorafenib treatment was applied. A very heterogeneous clinical presentation can be seen in a group of pediatric patients with RET mutation. In rare RET mutations, the genotype-phenotype relationship is still unclear, and different clinical pictures can be seen. Although prophylactic thyroidectomy is life-saving, it can cause iatrogenic hypothyroidism and hypoparathyroidism. Concomitant papillary microcarcinomas may occur in very young children with germline RET mutation.

Revisiting the Significance of Prominent C Cells in the Thyroid.

C cell hyperplasia is considered a precursor lesion for hereditary forms of medullary thyroid carcinoma. It has therefore been suggested as a morphological marker to distinguish hereditary from sporadic medullary thyroid carcinoma and to triage genetic testing in resource poor settings. However, numerous definitions for C cell hyperplasia have been suggested, and there is surprisingly little data regarding the number of C cells present in thyroid glands removed for conditions other than medullary carcinoma. We therefore sought to investigate the specificity of different criteria for C cell hyperplasia. We examined the number of C cells and solid cell nests (ultimobranchial body remnants) present in 118 completion thyroidectomy specimens from patients without medullary carcinoma and with no risk factors for MEN2. Morphological review was performed on all H&E-stained slides, and immunohistochemistry for calcitonin was performed on one block from each case. Solid cell nests were found in 4 (3.3%) of thyroids. Increased numbers of C cells sufficient to fulfil criteria for C cell hyperplasia were found in 5 (4.2%) to 36 (30.5%) cases depending on the criteria used. We conclude that large numbers of C cells are commonly found in thyroids not associated with medullary carcinoma. Therefore, regardless of which criteria are used, the presence of C cell hyperplasia is not a specific marker for hereditary medullary thyroid carcinoma.

Medullary Thyroid Carcinoma With Exon 2 p.L56M RET Variant: Clinical Particular Features in Two Patients

RET (REarranged during Transfection) proto-oncogene variants are essential for the development of familial and sporadic forms of medullary thyroid carcinoma (MTC). The most frequent variants are usually located in exons 10, 11, and 13 through 16 of the RET gene. We report two cases of apparently sporadic MTC associated with the variant in exon 2 of RET gene. Patient 1, a 62-year old man who had undergone adrenalectomy for a 5 cm pheochromocytoma, was screened for type 2 multiple endocrine neoplasia (MEN 2) which showed elevated basal and post-intravenous calcium gluconate calcitonin levels. A fine needle aspiration biopsy (FNAB) confirmed the suspicion of MTC. The patient underwent total thyroidectomy and lymphadenectomy, and the histology showed C-cell hyperplasia with medullary microcarcinoma. Patient 2, a 57 years old woman, underwent total thyroidectomy for toxic multinodular goiter. Pre-operative FNAB had shown benign features, while basal calcitonin levels were only borderline increased. Final histology revealed medullary multifocal microcarcinoma. Genetic testing for RET protoncogene on DNA extracted from peripheral blood was performed in both patients and a missense variant on exon 2 (c.166C>A, p.L56M) was identified. To our knowledge, these are the first time two cases of MTC associated to RET p.L56M variant. Interestingly, one patient had also a pheochromocytoma suggesting a possible pathogenetic role of this variant in the genesis of MEN2A. While the association of this variant with MTC or MEN2A has been never reported, it has been described in association with Hirschsprung's disease.

Analysis of Newly Identified and Rare Synonymous Genetic Variants in the RET Gene in Patients with Medullary Thyroid Carcinoma in Polish Population

Gain-of-function germline mutations of the RET proto-oncogene are responsible for initiation of carcinogenesis within the thyroid gland and development of hereditary form of medullary thyroid carcinoma and MEN2 syndrome. Genotype-phenotype correlations are established for most RET mutations, but the importance of the synonymous changes in this gene remains debatable. We aimed to analyze RET gene variants in Polish population. Genetic testing for the RET gene variants was performed with standard methods in 585 people aged 1–85, including 448 patients with medullary thyroid carcinoma and 131 of their first- and second-degree relatives, as well as six patients suspected of MTC/MEN2. Besides the most frequent synonymous changes, p.Leu769Leu, p.Ser836Ser, and p.Ser904Ser, four rare changes—c.1827C>T (p.Cys609Cys), c.2364C>T (p.Ile788Ile), c.2418C>T (p.Tyr806Tyr), and c.2673G>A (p.Ser891Ser)—were found in the RET gene, in the Polish population. Two of the rare changes, p.Cys609Cys and p.Ile788Ile, had not been previously described. The frequency of molecular synonymous variants in the general population was evaluated by testing 400 anonymous blood samples of neonates. Our findings may contribute to a better understanding of the genetic diversity of the RET gene and the involvement of synonymous variants in this diversity.

A comprehensive overview of the role of the RET proto-oncogene in thyroid carcinoma.

The rearranged during transfection (RET) proto-oncogene was identified in 1985 and, very soon thereafter, a rearrangement named RET/PTC was discovered in papillary thyroid carcinoma (PTC). After this discovery, other RET rearrangements were found in PTCs, particularly in those induced by radiation. For many years, it was thought that these genetic alterations only occurred in PTC, but, in the past couple of years, some RET/PTC rearrangements have been found in other human tumours. 5 years after the discovery of RET/PTC rearrangements in PTC, activating point mutations in the RET proto-oncogene were discovered in both hereditary and sporadic forms of medullary thyroid carcinoma (MTC). In contrast to the alterations found in PTC, the activation of RET in MTC is mainly due to activating point mutations. Interestingly, in the past year, RET rearrangements that were different to those described in PTC were observed in sporadic MTC. The identification of RET mutations is relevant to the early diagnosis of hereditary MTC and the prognosis of sporadic MTC. The diagnostic and prognostic role of the RET/PTC rearrangements in PTC is less relevant but still important in patient management, particularly for deciding if a targeted therapy should be initiated. In this Review, we discuss the pathogenic, diagnostic and prognostic roles of the RET proto-oncogene in both PTC and MTC.

Abstract 778: The identification and structure-guided optimisation of potent and selective inhibitors of oncogenes in medullary thyroid carcinoma and lung adenocarcinoma

Abstract RET (REarranged during Transfection) is a receptor tyrosine kinase (TK), which plays pivotal roles in regulating cell survival, differentiation, proliferation, migration and chemotaxis. Activating mutations in RET (C634W and M918T) have been identified in both familial and sporadic forms of medullary thyroid carcinoma (MTC) and correlate with aggressive disease progression, validating RET as a classical oncogene. Furthermore the recent identification of RET fusions (CCDC6-RET and KIF5B-RET) present in ∼1% of lung adenocarcinoma (LAD) patients has renewed interest in the identification and development of more selective RET inhibitors lacking the toxicities associated with the current treatments. At present, there are no known specific RET inhibitors in clinical development, although many potent inhibitors of RET have been identified opportunistically through selectivity profiling of compounds initially designed to target other TKs. Such “secondary RET inhibitors” include the clinical agents Vandetanib and Cabozantinib, both approved for use in MTC, but additional pharmacological activities (most notably inhibition of KDR) lead to dose-limiting toxicity. Using a robust screening cascade developed in house, we have measured RET and KDR inhibitory activity in vitro and in relevant cell line models to assess compound potency and selectivity. Anti-proliferative activity and off-target toxicity of these agents have also been measured. Although these competitor compounds displayed reasonable RET potency in cellular assays and this translated into anti-proliferative effects in our MTC and LAD disease models, as expected none met our target candidate criteria, clearly highlighting the need for therapeutic agents with improved selectivity. Guided by structure-based drug design, we have identified and optimised a novel series of potent and selective inhibitors of the RET kinase domain. These agents met our stringent criteria for enzyme and cell selectivity and, whilst potent in a RET-driven cell line, display little overt toxicity in a matched non-RET driven cell line. Herein, we describe the chemical optimisation of these agents and, using structural information, rationalise their improved selectivity. Citation Format: Roger J. Butlin, Rebecca Newton, Mandy Watson, Gemma Hopkins, Ben Acton, Kate Bowler, Samantha Fritzl, Kristin Goldberg, Niall Hamilton, Sarah Holt, Stuart Jones, Allan Jordan, Nikki March, Daniel Mould, Helen Small, Alexandra Stowell, Ian Waddell, Bohdan Waszkowycz, Donald Ogilvie. The identification and structure-guided optimisation of potent and selective inhibitors of oncogenes in medullary thyroid carcinoma and lung adenocarcinoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 778. doi:10.1158/1538-7445.AM2015-778

Abstract 3923: Molecular characterization of an animal model for neuroendocrine thyroid cancer

Abstract Neuroendocrine tumors are rare forms of cancers originating from hormone-producing cells that are scattered throughout the body. Medullary thyroid carcinoma (MTC) develops from calcitonin-secreting, C cells, in the thyroid gland. Surgical removal of the thyroid is the best treatment currently available for early stage cancer patients but advanced forms of MTC are often incurable and fatal. Thus, better therapies are needed. A lack of relevant animal models for this disease has slowed the development of new treatments. We have recently reported a novel conditional mouse model for MTC. In these mice, overexpression of the cyclin-dependent kinase 5 (Cdk 5), activator, p25 in C cells induces MTC tumors. Furthermore, interruption of p25 overexpression results in growth arrest of these tumors. Here we take advantage of our conditional mouse model to investigate the molecular pathways underlying MTC tumorigenesis. We used Illumina Mouse WG-6 v2.0 Expression BeadChip to compare the gene expression profile of proliferating versus arrested mouse MTC tumors. We found that a total of 920 genes encoding transcription factors, cell cycle proteins, motor proteins and angiogenesis factors were differentially regulated in growing versus arrested tumors. Particularly the genes encoding cell cycle proteins that are involved in the regulation of Rb pathway were significantly up-regulated in the proliferating tumors. Selected genes with higher degrees of change were evaluated by quantitative PCR and immunoblotting analyses. Taken together these findings suggests that the Rb signaling pathways is involved in MTC tumorigenesis and that Cdk5 may act as a critical regulator of the Rb signaling pathway in this cancer. Thus, targeting Cdk5 and/or the Rb pathway may be a valid strategy to stop the progression of neuroendocrine thyroid cancer. Citation Format: Karine Pozo, Antje Hillmann, Alexander Augustyn, Tanvir Singh, Florian Plattner, John Minna, Herbert Chen, Gilbert J. Cote, James A. Bibb, Fiemu E. Nwariaku. Molecular characterization of an animal model for neuroendocrine thyroid cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3923. doi:10.1158/1538-7445.AM2014-3923

Do clinical events always suggest familial form of medullary thyroid carcinoma (MTC)? - two case reports

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Genetics of thyroid lesions updated

Advances in research into molecular biology of thyroid cancers have made exciting progress in the understanding of genetic pathways of the cancers. Despite the huge amount of genetic information of thyroid cancers, only a few genetic changes are of clinical value in the current settings. The best known genetic change is the roles of RET mutation in the diagnosis of the familial form of medullary thyroid carcinoma. The other important mutation of some clinical use is the detection of BRAF mutation in papillary thyroid carcinoma. BRAF mutation is associated with aggressive pathological parameters, radioiodine-refractory and increased cancer mortality. Other than these genetic changes in thyroid cancer, familial predisposition of non-medullary thyroid carcinoma is beginning to emerge. This includes a group that is syndromic which is characterized by predominance of non-thyroidal tumours such as familial adenomatous polyposis and PTEN hamartoma syndromes. The other group non-medullary thyroid carcinoma includes familial syndromes of thyroid cancers. Greater than 85% of these are papillary thyroid carcinoma. Overall, new genetic information continues to emerge in thyroid cancers and applications of the information would be expected in the diagnosis, prognosis and molecular target therapies.

Functional characterization of the MTC-associated germline RET-K666E mutation: evidence of oncogenic potential enhanced by the G691S polymorphism

Activating mutations of RET, a gene encoding two isoforms of a tyrosine kinase receptor physiologically expressed in several neural crest-derived cell lineages, are associated with the inherited forms of medullary thyroid carcinoma (MTC). The identification and characterization of novel RET mutations involved in MTC is valuable, as RET gene testing plays a crucial role in the management of these patients. In an MTC patient, we have identified a germline c.1996A>G transition in heterozygosis leading to K666E substitution. In addition, the conservative S904S (c.2712C>G) and the non-conservative functional G691S (c.2071G>A) polymorphisms have been identified. Through functional studies, we demonstrate for the first time that K666E is a gain-of-function mutation with oncogenic potential, based on its ability to transform NIH3T3 cells. It was not possible to define whether K666E is a de novo or inherited RET variant in the patient, as the family history was negative for MTC, and the carrier status of family members could not be tested. Our results, together with a recent report of co-segregation of the mutation in three MTC families, suggest that K666E is a causative MTC mutation. As we have shown that the same patient allele carries both K666E and G691S variants, the latter known to increase downstream RET signaling, a possible role for the G691S polymorphism has also been investigated. We have demonstrated that, although RET-G691S is not oncogenic per se, it enhances the transforming activity of the RET-K666E mutant, thus suggesting a modifier role for this functional polymorphism.

Familial thyroid cancer: a review

Thyroid carcinomas can be sporadic or familial. Familial syndromes are classified into familial medullary thyroid carcinoma (FMTC), derived from calcitonin-producing C cells, and familial non-medullary thyroid carcinoma, derived from follicular cells. The familial form of medullary thyroid carcinoma (MTC) is usually a component of multiple endocrine neoplasia (MEN) IIA or IIB, or presents as pure FMTC syndrome. The histopathological features of tumors in patients with MEN syndromes are similar to those of sporadic tumors, with the exception of bilaterality and multiplicity of tumors. The genetic events in the familial C-cell-derived tumors are well known, and genotype–phenotype correlations well established. In contrast, the case for a familial predisposition of non-medullary thyroid carcinoma is only now beginning to emerge. Although, the majority of papillary and follicular thyroid carcinomas are sporadic, the familial forms are rare and can be divided into two groups. The first includes familial syndromes characterized by a predominance of non-thyroidal tumors, such as familial adenomatous polyposis and PTEN-hamartoma tumor syndrome, within others. The second group includes familial syndromes characterized by predominance of papillary thyroid carcinoma (PTC), such as pure familial PTC (fPTC), fPTC associated with papillary renal cell carcinoma, and fPTC with multinodular goiter. Some characteristic morphologic findings should alert the pathologist of a possible familial cancer syndrome, which may lead to further molecular genetics evaluation.

Early diagnosis of multiple endocrine neoplasia type 2B: a challenge for physicians

The hereditary form of medullary thyroid carcinoma may occur isolated as a familial medullary thyroid carcinoma (FMTC) or as part of Multiple Endocrine Neoplasia 2A (MEN2A) and 2B (MEN2B). MEN2B is a rare syndrome, its phenotype may usually, but not always, be noted by the physician. In the infant none of the MEN2B characteristics are present, except by early gastrointestinal dysfunction caused by intestinal neuromas. When available, genetic analysis confirms the diagnosis and guides pre-operative evaluation and extent of surgery. Here we report four cases of MEN2B in which the late diagnosis had a significant impact in clinical evolution and, potentially, in overall survival. We report four cases, 2 men and 2 women, with differences in their phenotypes and with a late diagnosis. The first case has a history of severe gastrointestinal obstruction requiring a surgery intervention two days after his birth. The second told had nodules in the oral mucosa and constipation since childhood. The third case referred a history of constipation from birth until 5 months of life. The fourth has had a history of chronic constipation since childhood. New concepts have emerged since the RET oncogene was identified in 1993 as the responsible gene for hereditary medullary thyroid carcinoma. The majority of MEN2B individuals have M918T mutation in the exon 16 of RET, with a few cases having a mutation A883F or the association of V804M with E805K, Y806C or S904C mutations. The consensus classifies the RET mutation in codon 918 as of highest risk and recommends total thyroidectomy and central lymph node dissection until 6 months after birth. A fast and precise diagnosis is essential to reach these goals. The identification of early manifestations such as intestinal ganglioneuromatosis and oral mucosal neuromas should prompt the physician to initiate an investigation for multiple endocrine neoplasia type 2B. The diagnosis of MEN2B is very important to allow appropriate investigation of associated diseases and to allow counseling and appropriate screening of relatives for a RET mutation. Even patients with MEN2B, which often have typical physical features, may not be properly recognized and be followed as a sporadic case. Based on this, all suspicious cases of multiple endocrine neoplasia should undergo a molecular genetic test.

Dendritic Cell Vaccination Induces Tumor Epitope-specific Th1 Immune Response in Medullary Thyroid Carcinoma

The existence of inherited aggressive forms of medullary thyroid carcinoma (MTC) and their resistance to classical therapies make it a prime candidate for adoptive immunotherapy. Highly potent antigen-presenting cells, namely dendritic cells (DCs), may serve as an interesting tool for anticancer vaccination. Here we report on the IN VITRO findings of a vaccination trial in five MTC patients, who were treated with a new DC generation protocol consisting of granulocyte-macrophage colony-stimulating factor and interferon-alpha (IFN-DCs). These cells were pulsed with tumor-specific calcitonin and administered twice. In two patients who responded to therapy we found a large increase (in mean 2.9+/-1.9%) of antigen-specific IFN-gamma-secreting CD4+ cells as well as an increase of granzyme B positive CD8+ cells (mean 2.2+/-0.2%) in the peripheral blood. In parallel, a decrease of CD4+/CD25+/FoxP3+ regulatory T cells was seen. Importantly, IN VITRO stimulation of PBMC with 10 different 15mer calcitonin peptides resulted in the identification of two HLA class II epitope regions within the central part of full-length calcitonin. These data were in accordance with the results drawn from the computer-based algorithm epitope prediction software SYFPEITHI. Measurement of different pro- and anti-angiogenic factors did not allow for a distinct outcome of prediction of the treated patients. In summary, we have demonstrated that immunization with IFN-DCs leads to a tumor epitope-specific immune response in MTC patients and may, therefore, represent a promising tool for future vaccination trials.

Pathology and genetics of thyroid carcinoma

Carcinomas of the thyroid comprise a heterogeneous group of neoplasms with distinctive clinical and pathological characteristics. Over the past 15 years, the application of molecular technologies to the study of these neoplasms has elucidated critical genetic pathways associated with the development of specific thyroid tumor types. In papillary thyroid carcinoma (PTC), genetic events involve RET and TRK (rearrangements) and BRAF and RAS (mutations), although RAS mutations are uncommon except in the follicular variant of PTC. These genetic alterations, which rarely overlap in the same tumor, result in signaling abnormalities in the mitogen-activated protein kinase pathway. In contrast, genetic alterations in follicular carcinomas include PAX8-PPARgamma translocations and RAS mutations while mutations of CTNNB1 and p53 have been implicated in the development and progression of poorly differentiated and undifferentiated (anaplastic) thyroid carcinomas. Germline mutations of RET are responsible for the development of heritable forms of medullary thyroid carcinoma (MTC) while somatic mutations of this oncogene are found in a significant proportion of sporadic MTCs. The results of these studies not only have provided additional approaches to thyroid tumor classification, but also have stimulated the development of novel approaches to tumor diagnosis and additional parameters for prognostic assessment and potential biologic therapeutic strategies.

A dog pedigree with familial medullary thyroid cancer

Multiple endocrine neoplasia (MEN) is defined as concurrent neoplasia or hyperplasia in more than one endocrine gland. MEN is well known in humans and has also been reported in small animals. We report on a dog family of a mixed breed with Alaskan malamute as a major influence, where three members developed thyroid carcinomas and another dog had clinical signs mimicking the other three but without a confirmed diagnosis. The age of onset of the tumour was between 96-109 months. Clinical, biochemical and immunohistochemical examinations revealed that the affected individuals typically demonstrated symptoms including calcitonin positive thyroid cancer, hypothyroidism and chronic dermatitis. In addition, elevated serum calcium and multinodular adrenocortical hyperplasia were demonstrated in a single member. The diagnosis observed is similar to the familial form of medullary thyroid carcinoma (FMTC) in human. This is the first report of FMTC in dog. Up to 95% of FMTC and MEN2 is known to be caused by activating mutations in the RET gene. The dog Ret gene was analysed as a candidate in this pedigree. The complete dog Ret genomic sequence was predicted in silico. The lack of demonstratable Ret mutation suggests the involvement of alternative predisposing mutation in this pedigree. The unique occurrence of familial MTC makes this potentially an important model in further defining the genetic basis of MTC.

Mutation analysis of the RET proto-oncogene and early thyroidectomy: results of a Portuguese cancer centre

Evidence that germline mutations in the RET proto-oncogene are the underlying cause of the familial form of medullary thyroid carcinoma (MTC) made it possible to identify gene carriers with a very high degree of accuracy. Aiming to define the mutational profile observed in our patients and to assess gene carriers' compliance with an early surgery, we reviewed results of molecular analysis of RET performed at our institution since 1994. One hundred fifty-eight individuals were screened for germline mutations of the RET proto-oncogene. Seventy-seven patients had apparently sporadic MTC; 8 patients had both MTC and pheochromocytoma or MTC and clinical features of multiple endocrine neoplasia type 2B despite a negative family history; 8 patients were known to belong to affected kindreds; and 65 individuals were at-risk individuals to develop MTC. A germline mutation in RET was identified in 4% of apparently sporadic MTC patients, in 100% of patients with MTC and pheochromocytoma or MTC and clinical features of multiple endocrine neoplasia type 2B, and in 100% of probands of clinically established kindreds. The most affected codon was 634 (58%) followed by codon 804 (16%). Among at-risk individuals, 49% were identified as gene carriers. Seven individuals were submitted to prophylactic thyroidectomy (mean age, 17.7 +/- 12.5 years; range: 3-42 years), and all but 1 had MTC. RET mutational spectrum observed in the present population disclosed a higher frequency of codon 804 mutations than expected. Compliance with an early prophylactic surgery seemed to be influenced not only by medical advice and cultural factors but also by the aggressiveness of disease in gene carriers' families.

Caractérisation de la mutation C634Y du proto-oncogène RET dans une famille marocaine de néoplasie endocrinienne multiple de type 2A

Medullary thyroid carcinoma (MTC) is a rare cancer which originates from the calcitonin producing "C" cells of thyroid gland. It presents in as isolated form or as part of the multiple endocrine neoplasia type 2 (MEN 2). The familial form of MTC which frequency remains underestimated, account for 25 to 40% of all MTC presentations. All hereditary forms are transmitted in an autosomal dominant manner and are due to proto-oncogene RET germ line mutations. Although MCT is relatively rare, preclinical or prebiological diagnosis can be achieved with genetic screening with high specificity and sensitivity. Early diagnosis is crucial for disease prevention. In this study we identified the first RET mutation underlying NEM 2A in Morocco. The C634Y mutation was present in the heterozygous state in a Moroccan family with MEN 2A. Genetic screening showed that six asymptomatic members of this family were not C364Y carriers. This report should contribute to the development of genetic screening for NEM 2 and F-MTC in Morocco.

<I>RET </I>Polymorphisms and Sporadic Medullary Thyroid Carcinoma in a Portuguese Population

The genetic basis of the sporadic form of medullary thyroid carcinoma, derived from "C" cells, is still poorly understood. Somatic mutations of RET proto-oncogene have been reported at a variable frequency ranging from 23% to 69%. The hypothesis that low penetrance factors, such as polymorphisms, might contribute to the phenotype of this neoplasm has been addressed in a few studies conducting to conflicting results. Herein, we studied 100 individuals (50 patients and 50 controls) aiming to compare the frequencies of G691S, L769L, S836S, and S904S RET polymorphisms observed in patients with respect to controls. Furthermore, meta-analysis of published studies including the present results was conducted. To test the contributory role of the above polymorphisms for the development of "C"-cell hyperplasia, we studied a group of 10 individuals selected for having a positive pentagastrin test despite the absence of a RET germline mutation. An over-representation of the G691S polymorphism, particularly in females, was observed in patients with respect to controls, although not reaching the level of significance. Allelic frequencies of the other three polymorphisms were not different in patients and controls. Results obtained in the admittedly small group of individuals with a positive pentagastrin test are unlikely to support a major influence of any polymorphism in the development of "C"-cell hyperplasia. The meta-analysis provided evidence for a significant association of the S691 allele with MTC (odds ratio 1.54, 95% confidence interval 1.12-2.12, p=0.008) and found no significant associations for the other polymorphisms.

Polymorphisms in the RET Proto-Oncogene and the Phenotypic Presentation of Familial Medullary Thyroid Carcinoma

Medullary thyroid carcinoma (MTC) occurs in a sporadic or as an autosomal dominant hereditary form. Inherited forms of MTC are related to mutations in the RET proto-oncogene. We screened genomic DNA from 11 patients with MTC for mutations in exons 10, 11, 13, 14, 15, and 16 of the RET proto-oncogene. Subsequently, we also evaluated a family of 1 patient with presumed diagnosis of sporadic MTC. Three patients with MEN2A from two unrelated families presented mutations in exon 11 (C634Y and C634R). A heterozygous mutation in exon 14 (V804M) was identified in the patient with the presumed sporadic MTC. We also observed two different polymorphisms: S904S in exon 15 (2 patients) and L769L in exon 13 (4 patients). The L769L polymorphism has been associated with earlier onset of sporadic MTC. On the other hand, mutations in exon 14 are associated with MTC of later onset and lower aggressiveness. Indeed, the carrier of the V804M mutation associated with L769L polymorphism presented MTC at 32 years of age, in contrast to her asymptomatic mother, who had only the V804M mutation and had MTC diagnosed by fine-needle aspiration biopsy at 60 years of age. In conclusion, the present study confirms the need for genetic screening to differentiate sporadic and hereditary forms of MTC. In addition, the genetic study allows the identification of asymptomatic carriers of hereditary forms of MTC. Finally, we speculated that the L769L polymorphism of the RET proto-oncogene may be related to earlier age of onset in the patient with the V804M mutation.

RET oncogene mutations in 75 cases of familial medullary thyroid carcinoma in Japan

The familial form of medullary thyroid carcinoma (MTC) is caused by mutations of the RET protooncogene. We registered 60 multiple endocrine neoplasia (MEN) 2A patients, 12 familial non-MEN medullary carcinoma (FMTC) patients, and three MEN2B patients with a confirmed RET germline mutation. All 60 MEN2A patients had RET mutations in a cysteine-rich domain. Seven of the FMTC patients had a mutation in cysteine-rich domain, and the other five had a mutation in codon 768, which encodes a tyrosine-kinase domain. Two of the MEN2B patients had a mutation in codon 918, and one patient had a double mutation, one in codon 804 and the other in codon 806, both of which are all encoded tyrosine-kinase domain. The genotype–phenotype correlations of our data will allow individualized recommendations for the optimal timing of prophylactic surgery.