Novel germline RET proto-oncogene mutations associated with medullary thyroid carcinoma (MTC): mutation analysis in Japanese patients with MTC

Unleashing a Lazarus Effect With Selpercatinib in a Never-Smoker Patient With Stage IV, Chemo-Immunotherapy Refractory, RET C630Y-Mutant, Small-Cell Lung Cancer: A First Case Report

The discovery of a RET gene mutation opens the door to targeted therapy in SCLC. #LCSM

Discrepancies of RET gene and risk of differentiated thyroid carcinoma

BACKGROUND

Somatic variations in rearranged during transfection (RET) proto-oncogene acts to influence Thyroid cancer (TC) in a low penetrance manner, but their effects tend to vary between different populations.

OBJECTIVE

This case-control study was aimed to evaluate effect of RET G691S, S904S and L769L single nucleotide polymorphisms (SNPs) on the risk for differentiated thyroid carcinoma (DTC).

METHODS

A total of 180 patients and 220 controls were genotyped by Polymerase chain reaction - restriction fragment length polymorphism (PCR-RFLP). Di-Deoxy Sanger sequencing was performed on 100 samples with variations and 20 wild samples for each amplified exon. In addition, In Silico tools were used to evaluate structural and functional impact of individual SNPs in disease progression.

RESULTS

In RET G691S/L769L/S904S SNPs, frequency of variant genotypes in DTC cases was 61.1%, 54.4% and 76.6% as compared to 45.9%, 43.6% and 89.09% in controls respectively (P⩽ 0.05). In Silico analysis revealed that different protein formed due to G691S substitution decreases the stability of 3D structure of protein. The RET G691S and L769L SNP followed "Dominant" but RET S904S SNP confirmed an "Additive" mode of inheritance.

CONCLUSION

RET G691S/L769L/S904S SNPs are significantly associated with DTC with G691S SNP declining the stability of final protein product.

Multiple endocrine neoplasia type 2: A reveiw

Multiple endocrine neoplasias are rare hereditary syndromes some of them with malignant potential. Multiple endocrine neoplasia type 2 (MEN 2) is an autosomal dominant hereditary cancer syndrome due to germline variants in the REarranged during Transfection (RET) proto-oncogene. There are two distinct clinical entities: MEN 2A and MEN 2B. MEN 2A is associated with medullary thyroid carcinoma (MTC), phaeochromocytoma, primary hyperparathyroidism, cutaneous lichen amyloidosis and Hirschprung's disease and MEN 2B with MTC, phaeochromocytoma, ganglioneuromatosis of the aerodigestive tract, musculoskeletal and ophthalmologic abnormalities. Germline RET variants causing MEN 2 result in gain-of-function; since the discovery of the genetic variants a thorough search for genotype-phenotype associations began in order to understand the high variability both between families and within family members. These studies have successfully led to improved risk classification of prognosis in relation to the genotype, thus improving the management of the patients by thorough genetic counseling. The present review summarizes the recent developments in the knowledge of these hereditary syndromes as well as the impact on clinical management, including genetic counseling, of both individual patients and families. It furthermore points to future directions of research for better clarification of timing of treatments of the various manifestations of the syndromes in order to improve survival and morbidity in these patients.

Features of Multiple Endocrine Neoplasia Type 1 and 2A in a Patient with Both RET and MEN1 Germline Mutations

The coexistence of multiple endocrine neoplasia type 1 (MEN1) and type 2A (MEN2A) is a rare occurrence and has been reported only twice in the literature. We present a patient with primary hyperparathyroidism and medullary thyroid cancer with strong family history of both MEN1- and MEN2A-associated conditions. Genetic testing showed the patient had a novel MEN1 loss-of-function mutation, c0.525_526insTT (p.Ala176Leufs*10), and an uncommon Cys630Tyr RET mutation. This case highlights the importance of obtaining a detailed family history when heritable endocrine disorders are suspected.

RET Proto-oncogene Gene Mutation Is Related to Cervical Lymph Node Metastasis in Medullary Thyroid Carcinoma

RET proto-oncogene (RET) mutations were proved to be related to the development of medullary thyroid carcinoma (MTC). We aimed to analyze the role of RET mutations in cervical lymph node metastasis in patients with MTC. Forty-nine patients with preoperatively diagnosed MTC by fine-needle aspiration cytology (FNAC) who underwent bilateral total thyroidectomy with cervical lymphadenectomy were included. Postoperative RET gene test and pathological analysis were performed with the surgical specimens; serum calcitonin (Ctn) and carcinoembryonic antigen (CEA) levels were tested pre- and postoperatively, to evaluate the association between RET mutations and cervical lymph node metastasis in MTC. In these 49 patients, the RET mutation rates of Exon 11, Exon 10, Exon 11&13, Exon 13, and Exon 16 were 20.4%, 4.1%, 38.8%, 22.4%, and 0%, respectively. The lymph node metastasis rates of patients with RET mutation in the central and lateral compartments were 71.4% and 64.3%, respectively, versus 28.6% and 14.3% of patients without RET mutation. The preoperative basal serum levels of Ctn (234.8 ± 188.4 vs. 44.4 ± 27.5, p < 0.01) and postoperative Ctn (49.8 ± 86.4 vs. 3.7 ± 2.2, p = 0.001) in MTC patients with RET mutations were significantly higher than those in MTC patients without RET mutation. In addition, the preoperative (50.2 ± 76.7 vs. 7.4 ± 6.8, p = 0.001) and postoperative serum levels of CEA (13.2 ± 19.5 vs. 1.3 ± 1.6, p < 0.01) in MTC patients with RET mutations were significantly higher than those in MTC patients without RET mutation (p < 0.05). RET mutation was related to cervical lymph node metastasis in patients with MTC, especially the mutation in Exon 11&13. Patients with RET mutation in Exon 11&13 might be regarded as the predictor for prophylactic ipsilateral total cervical lymphadenectomy even without clear evidence of lateral cervical lymph node metastasis.

Plasma Calcitonin Levels and miRNA323 Expression in Medullary Thyroid Carcinoma Patients with or without RET Mutation

Background: Medullary thyroid cancer (MTC) is an endocrine tumor featuring parafollicular or C-cell differentiation, with calcitonin as a specific biomarker in MTC diagnosis. Germline mutations in the RET proto-oncogene are considered responsible for its familial occurrence and somatic mutations can cause sporadic lesions. MicroRNAs can act as oncogenes or tumor suppressors by inhibiting the expression of target genes.. The aim of this study was to investigate relationships between plasma levels of calcitonin and miRNA323 expression in MTC patients with or without RET mutation. Methods: In this cross-sectional study, MTC lesions (based on pathological confirmation) were investigated. Genomic DNA was extracted and Exons 10 and 11 of RET were genotyped using PCR-sequencing. Division was into two groups of 43 cases each with or without mutation. Plasma levels of calcitonin were determined in both. Results: miRNA323 was measured using real-time-PCR. After performing normality tests, independent T-tests and Mann Whitney tests were used for the statistical comparison of parametric and nonparametric data, respectively. Plasma levels of calcitonin were significantly higher in MTC cases without a RET mutation compared to those with a mutation. Conclusion: There was no significant difference between the two groups regarding the expression of miRNA323 so that this parameter could not be used as a bio-index germ line mutations in MTCs. However, determination of calcitonin levels in plasma might be helpful in this regard.

The genetics of endocrine neoplasia

The hereditary endocrine neoplasias are characterized by the development of benign or malignant tumors in more than one endocrine tissue. These tumors typically occur at a younger age than sporadic endocrine tumors and follow an autosomal dominant pattern of inheritance. Because of the age-related penetrance and extreme phenotypic variability both within and between families, clinicians cannot always rely on the family history to make the diagnosis. Recognition of the features of a hereditary endocrine syndrome can allow for appropriate and timely risk assessment, genetic counseling and genetic testing, and identification of at-risk family members who may benefit from early and regular screening.

Molecular diagnosis of multiple endocrine neoplasia Type 2

Multiple endocrine neoplasia Type 2 is a rare familial cancer syndrome transmitted in an autosomal dominant manner. It is characterized by the association of medullary thyroid carcinoma with pheochromocytoma and hyperparathyroidism. Medullary thyroid carcinoma, present in virtually all patients, is the principal cause of death. In 1993, germline mutations in the RET proto-oncogene were identified as the underlying cause of the syndrome. Genetic screening of at-risk family members can now be performed with high specificity and sensitivity. The ability to determine gene carrier status at a preclinical stage is of great value as it allows early prophylactic thyroidectomy. The specific RET codon mutation correlates with clinical variants of the syndrome, age at onset and aggressiveness of medullary thyroid carcinoma. This review will focus on mutational spectrum, genotype-phenotype correlations and clinical decisions based on genetic information.

Thyroid cancer: current molecular perspectives

The thyroid cancer is a rare oncological entity, representing no more than 1% of all human malignant neoplasms. Recently, it has been demonstrated a sharp increase in incidence of differentiated thyroid carcinoma, equally occurring in both sexes. So far, multiple genetic alterations have been identified in differentiated thyroid carcinoma, leading to investigate the clinical utility of genetic studies. In particular, molecular genetic approaches searching for gene mutations in the material collected by fine needle ago-biopsy may have a particular utility in small nodules and in those specimens with an indeterminate cytology. The expansion of knowledge about genetic mutations occurring in different thyroid tumors has characterized recent years, allowing the identification of a correlation between specific mutations and phenotypic characteristics of thyroid cancers, essential for their prognosis. This review will briefly report on the histological features and the new entity represented by thyroid microcarcinoma and will focus on both environmental and genetic aspects associated with the occurrence of thyroid cancer.

Multiple endocrine neoplasia type 2 RET protooncogene database: repository of MEN2-associated RET sequence variation and reference for genotype/phenotype correlations

Multiple endocrine neoplasia type 2 (MEN2) is an inherited, autosomal-dominant disorder caused by deleterious mutations within the RET protooncogene. MEN2 RET mutations are mainly heterozygous, missense sequence changes found in RET exons 10, 11, and 13-16. Our group has developed the publicly available, searchable MEN2 RET database to aid in genotype/phenotype correlations, using Human Genome Variation Society recommendations for sequence variation nomenclature and database content. The MEN2 RET database catalogs all RET sequence variation relevant to the MEN2 syndromes, with associated clinical information. Each database entry lists a RET sequence variation's location within the RET gene, genotype, pathogenicity classification, MEN2 phenotype, first literature reference, and comments (which may contain information on other clinical features, complex genotypes, and additional literature references). The MEN2 phenotype definitions were derived from the International RET Mutation Consortium guidelines for classification of MEN2 disease phenotypes. Although nearly all of the 132 RET sequence variation entries initially cataloged in the database were from literature reports, novel sequence variation and updated phenotypic information for any existing database entry can be submitted electronically on the database website. The database website also contains links to selected MEN2 literature reviews, gene and protein information, and RET reference sequences. The MEN2 RET database (www.arup.utah.edu/database/MEN2/MEN2_welcome.php) will serve as a repository for MEN2-associated RET sequence variation and reference for RET genotype/MEN2 phenotype correlations.

DNA-based test: when and why to apply it to primary hyperparathyroidism clinical phenotypes

Several cancer-related genes have been discovered and molecular test for the cancer genetic risk assessment has been widely increasing. Disorders such as Multiple Endocrine Neoplasia syndromes have received benefits from the identification of the responsible genes whose mutations account for the genetic susceptibility to develop endocrine tumours. Primary hyperparathyroidism (PHPT)is a clinical phenotype frequently associated to Multiple Endocrine Neoplasia syndromes, but it can also represent the unique endocrinopathy recurring as a familial cluster. In recent years, care options have been made available to patients and families with hereditary PHPT, and the process of systematically assessing the genetic risk has been becoming increasingly important. This review aims to help health providers not frequently dealing with genetic testing use and it will introduce some general concepts concerning genetic diagnosis issues. As an example the role and the practical usefulness of DNA-based diagnosis in patients affected by different forms of congenital PHPT is described, with a close look on why, when and how genetic testing should be performed in these subjects and their relatives. Some practical recommendations and suggestions concerning on how to deal when a suspect or known case of familial PHPT has to be faced conclude this manuscript.

Medullary thyroid cancer: management guidelines of the American Thyroid Association

BACKGROUND

Inherited and sporadic medullary thyroid cancer (MTC) is an uncommon and challenging malignancy. The American Thyroid association (ATA) chose to create specific MTC Clinical Guidelines that would bring together and update the diverse MTC literature and combine it with evidence-based medicine and the knowledge and experience of a panel of expert clinicians.

METHODS

Relevant articles were identified using a systematic PubMed search and supplemented with additional published materials. Evidence-based recommendations were created and then categorized using criteria adapted from the United States Preventive Services Task Force, Agency for Healthcare Research and Quality.

RESULTS

Clinical topics addressed in this scholarly dialog included: initial diagnosis and therapy of preclinical disease (including RET oncogene testing and the timing of prophylactic thyroidectomy), initial diagnosis and therapy of clinically apparent disease (including preoperative testing and imaging, extent of surgery, and handling of devascularized parathyroid glands), initial evaluation and treatment of postoperative patients (including the role of completion thyroidectomy), management of persistent or recurrent MTC (including the role of tumor marker doubling times, and treatment of patients with distant metastases and hormonally active metastases), long-term follow-up and management (including the frequency of follow-up and imaging), and directions for future research.

CONCLUSIONS

One hundred twenty-two evidence-based recommendations were created to assist in the clinical care of MTC patients and to share what we believe is current, rational, and optimal medical practice.

Histopathologic and Clinical Features of Medullary Microcarcinoma and C-Cell Hyperplasia in Prophylactic Thyroidectomies for Medullary Carcinoma: A Study of 42 Cases

Context.—Prophylactic thyroidectomies are increasingly performed on patients at risk for developing medullary thyroid carcinoma (MTC); consequently, pathologists are more commonly encountering these specimens in routine practice.

Objective.—To describe the detailed clinicopathologic features of prophylactic thyroidectomies for medullary carcinoma.

Design.—We present a retrospective series of 42 prophylactic thyroidectomies for MTC performed for one or more of the following: family history of multiple endocrine neoplasia (MEN) or MTC, elevated serum calcitonin level, or detection of a RET proto-oncogene mutation.

Results.—Patients included 22 men and 20 women (mean age, 26.2 years). Among those with known RET proto-oncogene mutations, affected sites included exons 10, 11, 14, and 16. In 93% (n = 39) of cases, either C-cell hyperplasia (n = 36), medullary microcarcinoma (MMC; n = 29), or medullary macrocarcinoma (n = 1) was found. C-cell hyperplasia was often multifocal (n = 30) and bilateral (n = 23) and included both nonnodular and nodular patterns. A total of 94% of C-cell hyperplasia cases and all MMC cases were microscopically detectable using hematoxylin-eosin stains. The MMCs were characterized by a complex microarchitectural pattern with a desmoplastic stromal response (n = 29) and focal amyloid deposition (n = 12). Most MMCs exhibited a solid pattern (n = 24) of round, polygonal, spindled, or plasmacytoid-shaped cells. Only 1 case of MMC showed evidence of metastatic disease to a pretracheal lymph node.

Conclusions.—Based upon our clinicopathologic findings and review of the literature, we conclude that thyroidectomies in at-risk patients are very frequently associated with C-cell hyperplasia and/or MMC; however, the clinical prognosis for these patients is very good.

A family of multiple endocrine neoplasia type 2A (MEN 2A) with Cys630Tyr RET germline mutation: report of a case

Since the majority of multiple endocrine neoplasia type 2A (MEN 2A) patients have missense mutations at codon 634 and those with the Cys630 RET genotype mutations are extremely rare, limited clinical information is available about this rare type. We report here three members of one Japanese MEN 2A family with the Cys630Tyr genotype. A 67-year-old woman presented a firm thyroid nodule, and preoperative examination revealed medullary thyroid carcinoma with primary hyperparthyoidism and no pheochromocytoma. At surgery, bilateral medullary thyroid carcinomas and parathyroid adenoma were found. No lymph node metastasis was identified. Computed tomography scans and laboratory examination of blood have shown no evidence of tumor recurrence and no abnormality of parathyroid function during the 4 years after surgery. A 40-year-old man, the proband's son, was shown to have the same RET mutation, underwent total thyroidectomy prophylactically, and only microscopic foci of medullary thyroid carcinoma were found. A 10-year-old boy, the proband's grandson also having the same RET mutation, showed normal basal serum calcitonin level and has been followed up conservatively. To our knowledge, 18 patients of 6 families with the Cys630 mutations have been reported so far. This is only the second reported case with primary hyperparathyroidism. RET 630 mutations might be associated with lower penetrance of primary hyperparthyoidism and pheochromocytoma.

Nine novel germline gene variants in the RET proto-oncogene identified in twelve unrelated cases

We report nine novel DNA alterations in the RET proto-oncogene in 12 unrelated cases identified by DNA sequencing of exons 10 and 11 of the gene. The novel variants K666E, IVS9-11G-->A, D631V in cis with H665Q, D631E (with C634Y), E623K (in trans with C618S), 616delGAG (in trans with C609Y), Y606C, C630R, and R635-T636insELCR;T636P were detected in patients with various clinical presentations ranging from thyroid goiter, medullary thyroid carcinoma, and pheochromocytoma to classic multiple endocrine neoplasia type 2A. When novel DNA alterations are found, extended family studies can be helpful in determining the clinical significance of such findings. Segregation within families suggests that K666E and T636insELCR;T636P are likely to be disease-causing mutations. However, the mechanism by which they affect the normal activity of the RET receptor is unclear. Absence of segregation with disease was observed for E623K and 616delGAG. For the remainder of the DNA alterations, family studies were not possible, and the clinical significance of these novel variants needs further assessment. Additional case reports, animal models, and/or functional studies are needed to determine the clinical significance of these newly identified variants.

Penetrance and clinical manifestations of non-hotspot germline RET mutation, C630R, in a family with medullary thyroid carcinoma

Germline mutations in specific hot spot-codons of the RET proto-oncogene are associated with multiple endocrine neoplasia type 2 (MEN 2). Clinical RET gene testing has been routine for the last 10 years in some countries. In Argentina, RET testing excluding MEN 2B was always reported with a mutation at codon 634, with one exception: we described a novel mutation T > C transition at codon 630 (C630R), the family to which we extend the study in the present report. This family comprised 29 members in four generations including 6 individuals affected with medullary thyroid cancer (MTC), positive for the C630R mutation and normal adrenaline/ noradrenaline and ionized calcium/parathyroid hormone levels. Two asymptomatic mutation carriers aged 5 and 11 years underwent total thyroidectomy. The histopathologic examination showed C-cell hyperplasia and microcarcinoma foci, while preoperative basal calcitonins were normal for both. Our report emphasizes the importance of testing for non-hot spot RET mutations in apparently mutation negative MEN 2 families. Furthermore, it would appear that C630R mirrors C634R in penetrance (100% in this family) and in early age of onset of MTC, although paradoxically, no pheochromocytomas and hyperparathyroidism have developed. In addition to recommending RET testing before 5 years of age; we also can postulate that codon 630 may be the key point along the extracellular domain, important in the tissue-specific penetrance.

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.

Genetic cancer risk assessment and counseling: recommendations of the national society of genetic counselors

These cancer genetic counseling recommendations describe the medical, psychosocial, and ethical ramifications of identifying at-risk individuals through cancer risk assessment with or without genetic testing. They were developed by members of the Practice Issues Subcommittee of the National Society of Genetic Counselors Cancer Genetic Counseling Special Interest Group. The information contained in this document is derived from extensive review of the current literature on cancer genetic risk assessment and counseling as well as the personal expertise of genetic counselors specializing in cancer genetics. The recommendations are intended to provide information about the process of genetic counseling and risk assessment for hereditary cancer disorders rather than specific information about individual syndromes. Key components include the intake (medical and family histories), psychosocial assessment (assessment of risk perception), cancer risk assessment (determination and communication of risk), molecular testing for hereditary cancer syndromes (regulations, informed consent, and counseling process), and follow-up considerations. These recommendations should not be construed as dictating an exclusive course of management, nor does use of such recommendations guarantee a particular outcome. These recommendations do not displace a health care provider's professional judgment based on the clinical circumstances of a client.

Emergence of medullary thyroid carcinoma in a family with the Cys630Arg RET germline mutation

BACKGROUND

Individual germline mutations in the RET (REarranged during Transfection) proto-oncogene may set the time window for malignant progression from C-cell hyperplasia to familial medullary thyroid carcinoma. Owing to the close genotype-phenotype correlation, genetic information may lend to individual timing of prophylactic thyroidectomy according to RET genotype. Limited information exists on the Cys630 RET genotype. Most of the few published carriers of this genotype who developed medullary thyroid carcinomas (MTCs) were in their mid-30s.

METHODS

This case series of a German RET family with the Cys630Arg genotype was assembled to study malignant progression of MTC in this rare RET genotype.

RESULTS

There was considerable variability of malignant progression from C-cell hyperplasia to MTC in carriers of the Cys630Arg genotype. In these persons, MTCs had developed by the age of 32 years (index patient, pT2bN0M0), and 15 years and 1 year (non-index patients; pT1apN1bM0 and pT1bpN0M0, respectively). The Cys630Arg genotype always segregated with the familial medullary thyroid carcinoma phenotype.

CONCLUSIONS

The Cys630 RET genotype may have a more vigorous transforming activity than currently thought and can cause MTC in RET gene carriers within the first year of life. Starting in early infancy, identified RET gene carriers should be scrutinized until stimulated serum calcitonin levels become positive or, when these remain normal, should undergo prophylactic thyroidectomy before they reach 5 years of age.

Identification of critical residues required for the mutation avoidance function of human MutY (hMYH) and implications in colorectal cancer

Mutations found in human tumors often include transversions of GC to TA that may result from the mis-pairing of 8-oxoG with adenine during DNA replication. The human MutY (hMYH) enzyme, an adenine-specific DNA glycosylase, initiates repair at this mismatch. It has recently been demonstrated that inherited variants of hMYH may predispose individuals to multiple colorectal adenomas and carcinoma [Nat. Genet. 30 (2002) 227]. In this study, we demonstrate that two of these cancer-associated hMYH mutants, Y165C and G382D, are devoid of glycosylase activity directed towards 8-oxoG:A mispairs. These findings implicate a total loss of hMYH function associated with colorectal cancers.

Early malignant progression of hereditary medullary thyroid cancer

BACKGROUND

An age-related progression from C-cell hyperplasia to medullary thyroid carcinoma is associated with various germ-line mutations in the rearranged during transfection (RET) proto-oncogene that could be used to identify the optimal time for prophylactic surgery.

METHODS

In this European multicenter study conducted from July 1993 to February 2001, we enrolled patients who had a RET point mutation in the germ line, were 20 years of age or younger, were asymptomatic, and had undergone total thyroidectomy after confirmation of the RET mutation. Exclusion criteria were medullary thyroid carcinomas of more than 10 mm in greatest dimension and distant metastasis.

RESULTS

Altogether, 207 patients from 145 families were identified. There was a significant age-related progression from C-cell hyperplasia to medullary thyroid carcinoma and, ultimately, nodal metastasis in patients whose RET mutations were grouped according to the extracellular- and intracellular-domain codons affected and in those with the codon 634 genotype. No lymph-node metastases were noted in patients younger than 14 years of age. The age-related penetrance was unaffected by the type of amino acid substitution encoded by the various codon 634 mutations. The codon-specific differences in the age at presentation of cancer and the familial rates of concomitant adrenal and parathyroid involvement suggest that the risk of progression was based on the transforming potential of the individual RET mutation.

CONCLUSIONS

These data provide initial guidelines for the timing of prophylactic thyroidectomy in asymptomatic carriers of RET gene mutations.

Malignant progression from C-cell hyperplasia to medullary thyroid carcinoma in 167 carriers of RET germline mutations

BACKGROUND

Hereditary medullary thyroid carcinoma (MTC) is the most common and potentially life-shortening phenotypic manifestation of RET (rearranged during transfection) germline mutations. If a distinct time lag between the successive stages of malignant progression were identifiable, the information could be used to individualize prophylactic surgery. The study objective was to investigate the impact of RET genotype on disease progression from C-cell hyperplasia (CCH) to MTC.

METHODS

An institutional series of 167 (67 index, 100 nonindex) consecutive carriers of RET gene point mutations in exons 10, 11, 13, 14, or 16 who underwent total thyroidectomy between November 1994 and November 2002.

RESULTS

Regarding codons 618, 620, 634, 768, 790, and 804, patient age at diagnosis differed significantly depending on the type of pathology encountered (CCH, MTC without and with nodal metastasis). The variability in age, which may reflect the number of necessary somatic mutations, explained the pathological strata in 38% (codon 634) to 77% (codon 768) of patients. Conversely, 62% (codon 634) to 23% (codon 768) of variability in age at different pathological strata may have been determined by the RET genotype.

CONCLUSIONS

The pace of malignant progression of the RET genotype should be taken into account when considering prophylactic thyroidectomy in RET gene carriers.

Genetic analysis of RET, GFR alpha 1 and GDNF genes in Spanish families with multiple endocrine neoplasia type 2A

Multiple endocrine neoplasia type 2A (MEN 2A) is associated with specific germline missense mutations in the RET proto-oncogene. This locus encodes a receptor tyrosine kinase whose activation requires the formation of a multimeric receptor complex including GDNF as a ligand and GFR alpha 1 as a coreceptor. In order to explore the role of RET, GFR alpha 1 and GDNF genes in the variation of phenotypes observed in MEN2A families, we analysed germline mutations of these genes in 4 unrelated Spanish MEN2A families (23 cases studied). We found 2 novel variants corresponding to a single change in position + 47 (intron 12) of RET and position +22 (intron 7) of GFR alpha 1. Furthermore, we observed strong co-segregation between 2 polymorphisms of RET [G691S (exon 11) and S904S (TCC-TCG, exon 15) (100%, Fisher's exact test, p< 0.001)]. More interestingly, we found that these polymorphisms occurred at a significantly high frequency in patients with age at onset < 20 years old (Kruskal-Wallis's and Fisher's exact test, p = 0.007). These findings suggest that the G691S and S904S variants of RET may somehow play a role on the age of onset of MEN 2A.

Genetic markers in thyroid neoplasia

Cancer is a disease of genes. Detection of genetic abnormalities associated with cancers of various cell types can now be used for genetic counseling, diagnosis or treatment selection. In the case of thyroid cancer, genetic testing for mutations of the RET oncogene has had a profound effect on the management of medullary thyroid carcinomas. There is also considerable information on the genetic changes associated with development and progression of cancers of thyroid follicular cells, although these have not yet proven to be of practical value for clinical diagnosis or to guide prognosis and therapy.

Estimation of risk of inherited medullary thyroid carcinoma in apparent sporadic patients

PURPOSE

The study was undertaken to evaluate the frequency of inherited medullary thyroid carcinoma (MTC) among patients with apparent sporadic disease. A stepwise algorithm was used depending on clinical indices and the age of patient at MTC diagnosis.

PATIENTS AND METHODS

One hundred sixteen patients with MTC verified by postoperative pathologic examination were subjected to genetic analysis of RET exons 10, 11, 13, 14, and 16 by means of polymerase chain reaction, restriction endonuclease digestion, and DNA sequencing.

RESULTS

Among 116 apparent sporadic MTC patients, we identified eleven (9.5%) RET germline mutation carriers. Seven of these (6.0%) were found by routine analysis (exons 10 and 11). The frequency of inherited disease among patients younger than 45 years at diagnosis was 10.2% by analysis of typical mutations in exons 10 and 11. Extended genetic analysis (sequencing of exons 11, 13, 14, and 16) yielded 6.1% additional diagnoses, giving a risk of 16.3% in this age group. One previously unreported mutation in exon 11 affected codon 649 (TCG>TTG, Ser>Leu). In the true sporadic MTC patients younger than 30 years at diagnosis, frequencies of 36% and 4.5% in polymorphic variants L769L and S836S, respectively, were observed. The frequency for L769L was higher than in older patients (P <.05).

CONCLUSION

The frequency of inherited disease among apparent sporadic medullary thyroid carcinoma patients is close to 10% in the Polish population of MTC patients. The extended analysis of all known RET proto-oncogene mutation sites is obligatory in patients younger than 45 years at diagnosis, but we also see the need to analyze the impact of rarer mutations in older patients.

Multiple endocrine neoplasias

The multiple endocrine neoplasia syndromes form a distinct group of genetic tumor syndromes. They include multiple endocrine neoplasia types 1 and 2, von Hippel Lindau syndrome, neurofibromatosis, and Carney complex. Research over the past decade has identified a molecular basis for each of these syndromes. This knowledge has revolutionized not only the clinical management but also has illuminated the field of human cancer research by the identification of new and important genes critical for regulation of cell growth, differentiation, and death. This review focuses on the structure, physiologic function, and molecular abnormalities of the genes involved in these syndromes.

Initiation of base excision repair: glycosylase mechanisms and structures

The base excision repair pathway is an organism's primary defense against mutations induced by oxidative, alkylating, and other DNA-damaging agents. This pathway is initiated by DNA glycosylases that excise the damaged base by cleavage of the glycosidic bond between the base and the DNA sugar-phosphate backbone. A subset of glycosylases has an associated apurinic/apyrimidinic (AP) lyase activity that further processes the AP site to generate cleavage of the DNA phosphate backbone. Chemical mechanisms that are supported by biochemical and structural data have been proposed for several glycosylases and glycosylase/AP lyases. This review focuses on the chemical mechanisms of catalysis in the context of recent structural information, with emphasis on the catalytic residues and the active site conformations of several cocrystal structures of glycosylases with their substrate DNAs. Common structural motifs for DNA binding and damage specificity as well as conservation of acidic residues and amino groups for catalysis are discussed.

Somatic mutations in RET exons 12 and 15 in sporadic medullary thyroid carcinomas: different spectrum of mutations in sporadic type from hereditary type

Germline mutations in the RET proto-oncogene are responsible for multiple endocrine neoplasia type 2 (MEN 2A and 2B) and familial medullary thyroid carcinoma (FMTC). Point mutations or in-frame deletions of exons 10, 11, 13, 14 and 16 are associated with sporadic medullary thyroid carcinoma (MTC). To understand further the role of the RET gene in sporadic MTC, we examined mutations in exons 12 and 15 of RET in patients with sporadic MTC. DNAs were extracted from 39 formalin-fixed tumor tissues and corresponding normal thyroid tissues or peripheral blood leukocytes. DNA sequencing was used to identify mutations in exons 12 and 15 of RET. In this study, one novel somatic mutation was found in exon 12 and five novel mutations or deletions were found in exon 15. Of the patients with mutations, one had an in-frame 12-bp deletion (nt. 2625-2636), one had point mutations in both codons 884 and 908, and the remaining three had point mutations in codons 748, 876 and 901, respectively. Together with our previous identification of somatic mutations in exons 10, 11, 13, 14 and 16, somatic alterations were found in 10 out of 39 (25.6%) sporadic MTCs. There was no association of RET gene mutations with tumor recurrence or prognosis. These results suggest that mutations occur frequently in the RET coding region in addition to the previously reported mutation hot spots, and there is a different spectrum of mutations between sporadic and hereditary MTC.

The presence of two distinct 8-oxoguanine repair enzymes in human cells: their potential complementary roles in preventing mutation

8-Oxoguanine (8-oxoG), induced by reactive oxygen species (ROS) and ionizing radiation, is arguably the most important mutagenic lesion in DNA. This oxidized base, because of its mispairing with A, induces GC-->TA transversion mutations often observed spontaneously in tumor cells. The human cDNA encoding the repair enzyme 8-oxoG-DNA glycosylase (OGG-1) has recently been cloned, however, its activity was never detected in cells. Here we show that the apparent lack of this activity could be due to the presence of an 8-oxoG-specific DNA binding protein. Moreover, we demonstrate the presence of two antigenically distinct OGG activities with an identical reaction mechanism in human cell (HeLa) extracts. The 38 kDa OGG-1, identical to the cloned enzyme, cleaves 8-oxoG when paired with cytosine, thymine and guanine but not adenine in DNA. In contrast, the newly discovered 36 kDa OGG-2 prefers 8-oxoG paired with G and A. We propose that OGG-1 and OGG-2 have distinct antimutagenic functions in vivo . OGG-1 prevents mutation by removing 8-oxoG formed in DNA in situ and paired with C, while OGG-2 removes 8-oxoG that is incorporated opposite A in DNA from ROS-induced 8-oxodGTP. We predict that OGG-2 specifically removes such 8-oxoG residues only from the nascent strand, possibly by utilizing the same mechanism as the DNA mismatch repair pathway.

Novel point mutations and allele loss at the RET locus in sporadic medullary thyroid carcinomas

Germline mutations in the RET proto-oncogene have been shown to be the underlying cause of multiple endocrine neoplasia type 2 (MEN 2A and 2B) and familial medullary thyroid carcinoma (FMTC). Some cases of sporadic medullary thyroid carcinoma (sporadic MTC) are reported to have specific codon 918, 883 and 768 mutations of the RET gene in tumor tissues. We examined RET gene mutations in 40 Japanese cases who had previously undergone surgery for sporadic MTC. DNA extracted from formalin-fixed tumor tissues and corresponding normal thyroid tissues or peripheral blood leukocytes was analyzed for mutations of exon 10, 11, 13, 14 and 16 of the RET gene by DNA sequencing and by mutation-specific restriction enzyme analysis. Germline RET point mutations were found in six of 40 cases (15%), cysteine residues at codon 618 in two, codon 634 in three and valine residue at codon 804 in one, and were newly identified as heritable MTC. Of the remaining 34 sporadic MTC cases, four (12%) had tumor-specific RET point mutations. Two were found in exon 16; one case showed an ATG to ACG (Met to Thr) mutation at codon 918, and the other showed two point mutations, ATG to ACG (Met to Thr) at codon 918 and GCA to GTA (Ala to Val) at codon 919 with loss of the wild-type allele, suggesting that both alleles at the RET locus were altered. The other two were found in exon 13; one case showed a CCG to TCG (Pro to Ser) mutation at codon 766 and the other showed a silent mutation, GTC to GTT (Val) at codon 778 with loss of the wild-type allele. There was no association of sporadic mutations with recurrence or prognosis in patients with sporadic MTC. The low rate of somatic RET mutation at codon 918 in our sporadic MTC suggests that as yet unknown factors may be involved. Genetic alterations in both alleles may have an important role in small fraction of sporadic MTCs.