Low rate of ret proto-oncogene activation (PTC/retTPC) in papillary thyroid carcinomas from Saudi Arabia

Correlation between gene mutations and clinical characteristics in papillary thyroid cancer: a retrospective analysis of BRAF mutations and RET rearrangements

INTRODUCTION

Activation of the MAPK pathway by genetic mutations (such as BRAF and RET) initiates and accelerates the growth of papillary thyroid carcinoma (PTC). However, the correlation between genetic mutations and clinical features remains to be established. Therefore, this study aimed to retrospectively analyze major genetic mutations, specifically BRAF mutations and RET rearrangements, and develop a treatment algorithm by comparing background and clinical characteristics.

METHOD

One hundred thirteen patients with primary PTC were included in this study. BRAF mutations were detected via Sanger sequencing and RET rearrangements were detected via fluorescence in situ hybridization (FISH) analysis, and reverse transcription polymerase chain reaction (RT-PCR). The patients were categorized into two groups based on the presence of BRAF mutations and RET rearrangements and their clinical characteristics (age, sex, TNM, stage, extratumoral extension, tumor size, unifocal/multifocal lesions, vascular invasion, differentiation, chronic thyroiditis, preoperative serum thyroglobulin level, and 18F-fluorodeoxyglucose (FDG) uptake) were compared subsequently.

RESULT

After excluding unanalyzable specimens, 80 PTC patients (22 males and 58 females, mean age: 57.2 years) were included in the study. RET rearrangements were positive in 8 cases (10%), and BRAF mutation was positive in 63 (78.6%). The RET rearrangement group was significantly associated with younger age (p = 0.024), multifocal lesion (p = 0.048), distant metastasis (p = 0.025) and decreased 18F-fluorodeoxyglucose uptake (p < 0.001). The BRAF mutation group was significantly associated with unifocal lesions (p = 0.02) and increased 18F-FDG uptake (p = 0.004).

CONCLUSION

In this study, an increase in M classification cases was found in the RET rearrangements group. However, genetic mutations were not associated with the clinical stage, and no factors that could be incorporated into the treatment algorithm were identified.

Strategies for Treatment of Thyroid Cancer

More people are diagnosed with thyroid cancer than any other endocrine tumor. Differentiated thyroid cancer is often treated by removing the thyroid gland (thyroidectomy), iodizing radiation, or inhibiting thyroid stimulating hormone (TSH). Advanced thyroid carcinomas are notoriously resistant to chemotherapy, thus the pursuit of alternative treatments is vital. The best methods for treating individuals with advanced nonmedullary and medullary thyroid carcinomas are discussed in this post. Numerous tyrosine kinase inhibitors and antiangiogenic inhibitors, two types of novel target therapy, have shown promise in studies for individuals with thyroid cancer. Both the positive and unfavourable outcomes of clinical studies of these drugs were addressed. The findings presented here are encouraging, but more study is required to establish whether or not this method is effective in the treatment of thyroid cancer.

Update on Fundamental Mechanisms of Thyroid Cancer

The incidence of thyroid cancer (TC) has increased worldwide over the past four decades. TC is divided into three main histological types: differentiated (papillary and follicular TC), undifferentiated (poorly differentiated and anaplastic TC), and medullary TC, arising from TC cells. This review discusses the molecular mechanisms associated to the pathogenesis of different types of TC and their clinical relevance. In the last years, progresses in the genetic characterization of TC have provided molecular markers for diagnosis, risk stratification, and treatment targets. Recently, papillary TC, the most frequent form of TC, has been reclassified into two molecular subtypes, named BRAF-like and RAS-like, associated to a different range of cancer risks. Similarly, the genetic characterization of follicular TC has been proposed to complement the new histopathological classification in order to estimate the prognosis. New analyses characterized a comprehensive molecular profile of medullary TC, raising the role of RET mutations. More recent evidences suggested that immune microenvironment associated to TC may play a critical role in tumor invasion, with potential immunotherapeutic implications in advanced and metastatic TC. Several types of ancillary approaches have been developed to improve the diagnostic value of fine needle aspiration biopsies in indeterminate thyroid nodules. Finally, liquid biopsy, as a non-invasive diagnostic tool for body fluid genotyping, brings a new prospective of disease and therapy monitoring. Despite all these novelties, much work remains to be done to fully understand the pathogenesis and biological behaviors of the different types of TC and to transfer this knowledge in clinical practice.

Absence of RET/PTC1 rearrangement in a sample of Colombian individuals with papillary thyroid carcinoma

Introduction: Papillary thyroid carcinoma is the most common endocrine neoplasm; therefore, markers with possible prognostic utility have been evaluated.Objective: To analyze the presence of RET/PTC1 rearrangement, lymphocytic thyroiditis and associated clinical features in patients with papillary thyroid cancer treated at the Hospital de San José in Bogotá, Colombia.Materials and methods: Clinical records of patients with complete thyroidectomy and diagnosis of papillary cancer were retrospectively identified. RNA was extracted from tumor tissue, and cDNA was obtained using inverse transcriptase to detect the rearrangement of the RET/PTC1 gene by means of qPCR.Results: 55 patients with papillary thyroid cancer were selected; 93% were females, and the mean age was 45.8 years. The most frequent histological variant was classic (49%). A relationship was found between lymphocytic thyroiditis and the number of positive nodes in segments other than central draining, as well as thyroiditis and antithyroid antibody value. No RET/PTC1 rearrangement expression was found.Conclusions: A relationship between lymphocytic thyroiditis and the number of positive nodes in segments other than central draining was found. Other molecular markers should be searched to differentiate the prognosis of these patients.

RET/PTC Gene Rearrangements in Thyroid Carcinogenesis: Assessment and Clinico-Pathological Correlations

Rearranged during transfection (RET) is a proto oncogene implicated in thyroid carcinogenesis of papillary type (PTC). The RET proto-oncogene in PTC is constitutively activated by fusion of its tyrosine kinase domain with the 5 ´region of another gene thereby generating chimeric products collectively named RET/PTCs. RET/PTC1 and RET/PTC3 are best characterized among all RET/PTC rearrangements. Kashmir valley has witnessed an alarming increase in thyroid cancer incidence in young women. Therefore, we investigated the occurrence of RET/PTC 1 & 3 rearrangements by semi quantitative and qPCR in thyroid cancer patients (n = 48) of Kashmiri population and interrelated results with various clinicopathological characteristics. We observed that all the RET/PTC rearrangements were confined to PTC cases (10/40). Presence of RET/PTC rearrangement significantly correlated with gender, elevated TSH levels and lymph node metastasis. Overall, our study advocates that RET/PTC3 rearrangement is a frequent event in the carcinogenesis of thyroid gland in Kashmiri population although a study with a larger sample size is needed to get a clear scenario.

Break-apart interphase fluorescence in situ hybridization assay in papillary thyroid carcinoma: on the road to optimizing the cut-off level for RET/PTC rearrangements

OBJECTIVE

Chromosomal rearrangements of the RET proto-oncogene is one of the most common molecular events in papillary thyroid carcinoma (PTC). However, their pathogenic role and clinical significance are still debated. This study aimed to investigate the prevalence of RET/PTC rearrangement in a cohort of BRAF WT PTCs by fluorescence in situ hybridization (FISH) and to search a reliable cut-off level in order to distinguish clonal or non-clonal RET changes.

DESIGN

Forty BRAF WT PTCs were analyzed by FISH for RET rearrangements. As controls, six BRAFV600E mutated PTCs, 13 follicular adenomas (FA), and ten normal thyroid parenchyma were also analyzed.

METHODS

We performed FISH analysis on formalin-fixed, paraffin-embedded tissue using a commercially available RET break-apart probe. A cut-off level equivalent to 10.2% of aberrant cells was accepted as significant. To validate FISH results, we analyzed the study cohort by qRT-PCR.

RESULTS

Split RET signals above the cut-off level were observed in 25% (10/40) of PTCs, harboring a percentage of positive cells ranging from 12 to 50%, and in one spontaneous FA (1/13, 7.7%). Overall, the data obtained by FISH matched well with qRT-PCR results. Challenging findings were observed in five cases showing a frequency of rearrangement very close to the cut-off.

CONCLUSIONS

FISH approach represents a powerful tool to estimate the ratio between broken and non-broken RET tumor cells. Establishing a precise FISH cut-off may be useful in the interpretation of the presence of RET rearrangement, primarily when this strategy is used for cytological evaluation or for targeted therapy.

Prevalence of RET/PTC1 and RET/PTC3 gene rearrangements in Chennai population and its correlation with clinical parameters

Thyroid cancer is one of the most common endocrine disorders in the world. In India, about 42 million people suffer from various thyroid disorders. However, based on population-based cancer registry (PBCR) and Chennai cancer registry, thyroid cancer is emerging as a common cancer particularly in Chennai. Papillary thyroid carcinoma is considered as the most prevalent cancer constituting about 80-85 % of thyroid malignancies. Rearranged during transfection (RET)/papillary thyroid carcinoma (PTC) gene rearrangements are one of the major genetic alterations found in papillary thyroid carcinoma. This present study aims at estimating the frequency of RET/PTC1 and RET/PTC3 gene rearrangements in Chennai population and investigating the correlation between RET/PTC gene expressions with clinical parameters. Formalin-fixed paraffin-embedded (FFPE) tumor tissues obtained from 30 patients with papillary thyroid carcinoma were analyzed. Initially, to differentiate classic and follicular variants of papillary thyroid carcinoma samples, immunohistochemistry was performed. Thereafter, total RNA was isolated, and quantitative evaluation of RET/PTC1 and RET/PTC3 gene rearrangements by real-time PCR was performed. Chi-square test was performed to understand the correlation between positive and negative mutations of RET/PTC messenger RNA (mRNA) expression with clinical parameters. RET/PTC3 gene rearrangements were identified in 26/30 (86.67 %) cases, and none of the patient in our series had RET/PTC1 gene rearrangements. There was no statistically significant difference observed between positive and negative mutations of RET/PTC3 mRNA expression with clinic pathological parameters. Our results indicate that RET/PTC3 gene rearrangements are the most prevalent form of rearrangements in PTCs of Chennai population.

Pathologic diagnosis of papillary thyroid carcinoma: today and tomorrow

Papillary thyroid carcinoma is the most common malignancy of the thyroid. It is a well-differentiated tumor and the majority behaves in an indolent fashion. The pathologic diagnosis of papillary carcinoma in both cytology and histologic specimens is based upon demonstration of typical nuclear morphology. Using these morphologic criteria, most papillary cancers can be diagnosed with ease, except cases in which there is a paucity of diagnostic nuclear features. Despite advances in the treatment of thyroid cancer, disease recurrences and metastasis can be observed in 20% of cases. Recently, many advances have been made in the pathogenesis of papillary thyroid carcinoma. The notable genetic events include Ret/PTC rearrangements, Ras and BRAF gene mutations. The identification of these has also led to their use in diagnosis and predicting prognosis of papillary thyroid carcinoma. In addition, these involved genes may also serve as targets for cancer chemotherapy in patients where standard thyroid cancer treatment is not effective.

Concurrent overexpression of RET/PTC1 and TTF1 confers tumorigenicity to thyrocytes

A variant located on 14q13.3 nearest to thyroid transcription factor-1 (TTF1) predisposes individuals to thyroid cancer, but whether this variant is related to the RET/PTC rearrangement associated with human papillary thyroid carcinomas (PTCs) is unknown. The aims of this study were to investigate the effects of RET/PTC1 on the expression of thyroid-specific genes in thyrocytes and their relationship with malignant transformation of the thyrocytes. In the absence or presence of TSH, an extracellular signal-regulated kinase was phosphorylated in FRTL5 cells that stably expressed RET/PTC1, and these cells grew independently of TSH. FRTL (RET/PTC1) cells produced 566% more thyroglobulin mRNA and 474% more Na+/I- symporter mRNA than did the control FRTL (pcDNA) cells. FRTL (RET/PTC1) cells expressed 468% more Ttf1 mRNA than did FRTL (pcDNA) cells, but these two cell types did not differ significantly with respect to Pax8 or Ttf2 mRNA levels. When FRTL (RET/PTC1) cells and FRTL (pcDNA), cells were injected into each of nine nude mice, each mouse developed a single tumor at the site of FRTL (RET/PTC1) cell injection; in contrast, tumor formation never occurred at sites of FRTL (cDNA) cells injection. Tumors resulting from FRTL (RET/PTC1) cells retained (125)I-uptake activity; moreover, the cells invaded into surrounding skeletal muscle. When overexpression of Ttf1 in FRTL (RET/PTC1) cells was silenced, the cells completely lost their tumorigenic potential. Exogenous TTF1 cDNA enhanced the tumorigenicity of BHP18-21v cells, human PTC cells that express RET/PTC1, in nude mice. These results indicated that concurrent overexpression of RET/PTC1 and TTF1 confers tumorigenicity to FRTL5 and BHP18-21v cells in nude mice.

New treatment in advanced thyroid cancer

Thyroid cancer is the most common endocrine tumor. Thyroidectomy, radioactive iodine, and TSH suppression represent the standard treatment for differentiated thyroid cancer. Since chemotherapy has been shown to be unsuccessful in case of advanced thyroid carcinomas, the research for new therapies is fundamental. In this paper, we reviewed the recent literature reports (pubmed, medline, EMBASE database, and abstracts published in meeting proceedings) on new treatments in advanced nonmedullary and medullary thyroid carcinomas. Studies of many tyrosine kinase inhibitors as well as antiangiogenic inhibitors suggest that patients with thyroid cancer could have an advantage with new target therapy. We summarized both the results obtained and the toxic effects associated with these treatments reported in clinical trials. Reported data in this paper are encouraging, but further trials are necessary to obtain a more effective result in thyroid carcinoma treatment.

RET/PTC Translocations and Clinico-Pathological Features in Human Papillary Thyroid Carcinoma

Thyroid carcinoma is the most frequent endocrine cancer accounting for 5-10% of thyroid nodules. Papillary histotype (PTC) is the most prevalent form accounting for 80% of all thyroid carcinoma. Although much is known about its epidemiology, pathogenesis, clinical, and biological behavior, the only documented risk factor for PTC is the ionizing radiation exposure. Rearrangements of the Rearranged during Transfection (RET) proto-oncogene are found in PTC and have been shown to play a pathogenic role. The first RET rearrangement, named RET/PTC, was discovered in 1987. This rearrangement constitutively activates the transcription of the RET tyrosine-kinase domain in follicular cell, thus triggering the signaling along the MAPK pathway and an uncontrolled proliferation. Up to now, 13 different types of RET/PTC rearrangements have been reported but the two most common are RET/PTC1 and RET/PTC3. Ionizing radiations are responsible for the generation of RET/PTC rearrangements, as supported by in vitro studies and by the evidence that RET/PTC, and particularly RET/PTC3, are highly prevalent in radiation induced PTC. However, many thyroid tumors without any history of radiation exposure harbor similar RET rearrangements. The overall prevalence of RET/PTC rearrangements varies from 20 to 70% of PTCs and they are more frequent in childhood than in adulthood thyroid cancer. Controversial data have been reported on the relationship between RET/PTC rearrangements and the PTC prognosis. RET/PTC3 is usually associated with a more aggressive phenotype and in particular with a greater tumor size, the solid variant, and a more advanced stage at diagnosis which are all poor prognostic factors. In contrast, RET/PTC1 rearrangement does not correlate with any clinical-pathological characteristics of PTC. Moreover, the RET protein and mRNA expression level did not show any correlation with the outcome of patients with PTC and no correlation between RET/PTC rearrangements and the expression level of the thyroid differentiation genes was observed. Recently, a diagnostic role of RET/PTC rearrangements has been proposed. It can be searched for in the mRNA extracted from cytological sample especially in case with indeterminate cytology. However, both the fact that it can be present in a not negligible percentage of benign cases and the technical challenge in extracting mRNA from cytological material makes this procedure not applicable at routine level, at least for the moment.

Intracellular signal transduction and modification of the tumor microenvironment induced by RET/PTCs in papillary thyroid carcinoma

RET gene rearrangements (RET/PTCs) represent together with BRAF point mutations the two major groups of mutations involved in papillary thyroid carcinoma (PTC) initiation and progression. In this review, we will examine the mechanisms involved in RET/PTC-induced thyroid cell transformation. In detail, we will summarize the data on the molecular mechanisms involved in RET/PTC formation and in its function as a dominant oncogene, on the activated signal transduction pathways and on the induced gene expression modifications. Moreover, we will report on the effects of RET/PTCs on the tumor microenvironment. Finally, a short review of the literature on RET/PTC prognostic significance will be presented.

RET/PTC rearrangement in benign and malignant thyroid diseases: a clinical standpoint

Cytological examination of fine needle aspiration biopsy is the primary means for distinguishing benign from malignant nodules. However, as inconclusive cytology is very frequent, the introduction of molecular markers in the preoperative diagnosis of thyroid nodules has been proposed in recent years. In this article, we review the clinical implications of preoperative detection of rearrangements of the RET gene (RET/papillary thyroid carcinoma (PTC)) in thyroid nodules. The prevalence of RET/PTC in PTC depends on the histological subtypes, geographical factors, radiation exposure, and detection method. Initially, RET/PTC was considered an exclusive PTC hallmark and later it was also found sporadically in benign thyroid lesions. More recently, the very sensitive detection methods, interphase fluorescence in situ hybridization (FISH) and Southern blot on RT-PCR amplicons, demonstrated that the oligoclonal occurrence of RET rearrangement in benign thyroid lesions is not a rare event and suggested that it could be associated with a faster enlargement in benign nodules. For this reason, RET/PTC cannot be considered as an absolute marker of PTC, and its diagnostic application must be limited to assays able to distinguish between clonal and oligoclonal expression. Detection of RET/PTC by quantitative assays will be useful for diagnostic purposes in cytology specimens when a precise cutoff will be fixed in a clinical setting. Until that time, less sensitive RET/PTC detection methods and FISH analysis remain the most appropriate means to refine inconclusive cytology. Future studies with a long follow-up will further clarify the clinical significance of low level of RET rearrangements in benign nodules.

Fine-needle aspiration of the thyroid: today and tomorrow

This review describes the morphological features of the common thyroid lesions that are sampled by fine-needle aspiration (FNA), including hyperplastic (adenomatous, adenomatoid) nodules, inflammatory and autoimmune conditions (lymphocytic thyroiditis), and benign and malignant neoplasms. For the last category of lesions, the cytological features are described and the differential diagnoses are discussed. Finally, an assessment of modern techniques such as immunohistochemistry and molecular analyses is given with emphasis on their validity for FNA samples as well as the pitfalls that are encountered in their use.

Clinical significance of RET/PTC and p53 protein expression in sporadic papillary thyroid carcinoma

AIMS

Rearranged during Transfection (RET)/papillary thyroid carcinoma (PTC) and p53 are two genes involved in the pathogenesis of PTC. It has been suggested that RET/PTC expression is associated with higher rates of local extension and lymph node involvement, whereas p53 mutations are more frequent in poorly differentiated and anaplastic carcinomas. In addition, experimental studies have shown that p53 activity can modify the behaviour of PTC carrying RET/PTC. The aim of this study was to investigate the expression of both RET/PTC and p53 in order to evaluate their usefulness as prognostic factors.

METHODS AND RESULTS

Resected specimens of 61 cases of PTC were studied immunohistochemically using a polyclonal antibody to RET and a monoclonal antibody to p53 protein. RET/PTC expression was associated with extrathyroid extension of PTC, at diagnosis (P < 0.05). In contrast, no relationship between p53 immunoreactivity and clinical status was found. In addition, p53 expression was more prevalent among RET/PTC+ patients, and significantly influenced the relationship observed between RET/PTC and extrathyroid extension of the disease.

CONCLUSION

Our results suggest that immunohistochemistry for both PTC/RET and p53 could be useful in the clinical evaluation of patients with PTC.

Follicular carcinoma presenting as autonomous functioning thyroid nodule and containing an activating mutation of the TSH receptor (T620I) and a mutation of the Ki-RAS (G12C) genes

Most autonomous functioning thyroid nodules (AFTN) are benign thyroid follicular neoplasms. There are rare reports of malignant hot nodules, in which activating mutations of the TSH receptor (TSHR) were found. We report a case of follicular carcinoma presenting as an AFTN causing subclinical hyperthyroidism in a 64-year-old woman who had a 6-cm hot nodule in the left thyroid lobe. Genomic DNA was extracted from paraffin-embedded tissues from the tumor and extratumoral thyroid tissue. Sequence analyses revealed point mutations in two different genes: the normal ACC sequence at codon 620 of the TSHR gene was replaced by ATC, changing the threonine by isoleucine (T620I); and the wild-type GGT at codon 12 of Ki-RAS mutated to TGT, replacing glycine by cysteine (G12C). In transfection experiments the T620I mutant showed constitutive activity in terms of cyclic adenosine monophosphate (cAMP) production when permanently transfected in 3T3 cells. Here, we describe for the first time an activating mutation in 3codon 620 of the TSHR. In addition, the cancerous AFTN also contained a G12C Ki-RAS mutation. We hypothesize that the combination of these two mutations might have played an important role in both the hyperfunction of the tumor and the carcinogenetic process.

Low prevalence of RET rearrangements (RET/PTC1, RET/PTC2, RET/PTC3, and ELKS-RET) in sporadic papillary thyroid carcinomas in Taiwan Chinese

Somatic rearrangement of the tyrosine kinase receptor RET is restricted to papillary thyroid carcinoma (PTC). The prevalence of RET/PTC1, RET/PTC2, and RET/PTC3 has been found to vary between 0% and 20% in most series of sporadic (nonradiation-induced) PTCs analyzed by type-specific reverse transcription-polymerase chain reaction (RT-PCR) alone. However, high prevalence reported from Taiwan (6 out of 11, 55%) indicates RET rearrangement is an important genetic lesion underlying the development of PTC in Taiwan. Because the high prevalence of RET rearrangements in Chinese patients was particularly striking, we were prompted to reexamine chimeric transcripts of RET/PTC1, RET/PTC2, and RET/PTC3 using the same experimental designs in a larger number of cases in the same population. RT-PCR was performed to amplify fusion products of RET/PTC1, RET/PTC2, RET/PTC3, and ELKS-RET from frozen tissue of 105 sporadic PTCs. RT-PCR was also performed with two different primer sets for RET/PTC1, RET/PTC2, and RET/PTC3 followed by Southern hybridization in the first 62 tumors. In our study, RET/PTC1, RET/PTC2, and RET/PTC3 oncogenes were found in only 7 of 105 (7%) sporadic PTCs. Of these tumors, 3 involved RET/PTC1 and 4 involved RET/PTC3. No RET/PTC2 rearrangements were observed. In the first 62 tumor samples, another two different primer sets for each rearrangement also gave concordant results. Furthermore, application of Southern hybridization in these 62 PTCs did not identify additional tumor harboring RET chimeric transcripts. We identified one tumor as having an ELKS-RET rearrangement (1 of 105, 1%). In conclusion, we detected RET rearrangements in 8 of 105 (8%) sporadic PTCs in Taiwan, a much lower prevalence than previously reported for this population but comparable to those reported in other nations using similar methodology. RET chimeric oncogenes only account for a small fraction of PTCs in Taiwan.

RET/PTC and CK19 expression in papillary thyroid carcinoma and its clinicopathologic correlation

Recently, the rearrangement of RET proto-oncogene has been reported to be the most common genetic change in papillary thyroid carcinoma (PTC). However, its prevalence has been reported variably and its relation to clinical outcome has been controversial. The characteristic nuclear features of PTC usually render the diagnosis, but problem arises with equivocal cytologic features that are present focally. Although there remains some controversy, CK19 has been reported to be a useful ancillary tool for diagnosis of PTC. To evaluate the expression rate of RET/PTC rearrangement and CK19 in PTCs in a Korean population, we studied 115 papillary thyroid carcinomas in 3 mm-core tissue microarray based immunohistochemical analysis. The prevalence of Ret protein expression was 62.6% and the CK19 immunoreactivity was 80.9%. There was no statistically significant association between the Ret positivity and CK19 immunoreactivity, although the percent agreement of the two was relatively high. The clinicopathological variables did not correlate with the expression of Ret. In conclusion, the prevalence of Ret protein expression and its clinicopathological implications in a Korean population are not much different from those reported in previous studies. However, its detection via immunohistochemistry can be a useful diagnostic tool for diagnosing papillary thyroid carcinoma in conjunction with CK19.

RET gene rearrangements (RET/PTC1 andRET/PTC3) in papillary thyroid carcinomas from an iodine-rich country (Japan)

BACKGROUND

The frequency of RET rearrangements (RET/PTC) in papillary thyroid carcinomas varies significantly according to geographic area, with the greatest incidence reported in the Belarus region, which is iodine-deficient and was contaminated severely after the Chernobyl reactor accident, and with the lowest incidence in iodine-rich, nonirradiated Japan. The authors investigated the prevalence of RET/PTC in a large number of thyroid tumors from Japanese patients.

METHODS

Fresh and paraffin embedded tumor tissues from 215 Japanese patients were examined for RET rearrangements (RET/PTC1 and RET/PTC3) by means of reverse transcriptase-polymerase chain reaction analysis, with primers flanking the chimeric region, followed by direct-sequence analysis.

RESULTS

RET/PTC was found only in papillary carcinomas and was not observed in other histologic types of thyroid tumors. The overall frequency of RET/PTC in papillary carcinomas was 28.4%, with a greater frequency in younger patients, including 41.9% of younger patients age < 20 years, 27.6% of patients age 20-40 years, and 24.8% of patients age > 40 years. Among the patients in these 3 age groups, the prevalence rate of RET/PTC1 was similar, but RET/PTC3 was observed most frequently among patients age < 20 years. When the tumors were grouped further according to histologic subtypes, the prevalence of RET/PTC3 was greater in solid/solid-follicular papillary carcinomas than in classic papillary carcinomas.

CONCLUSIONS

The results indicated that RET/PTC may be useful as a specific molecular marker for papillary thyroid carcinomas. Furthermore, its incidence in such tumors was not low in Japanese patients, and it seemed to be associated with patient age. Therefore, the current results raise questions regarding the belief that the frequency of RET/PTC differs geographically and is especially low in Japan.

Real-time quantitative RT-PCR identifies distinct c-RET, RET/PTC1 and RET/PTC3 expression patterns in papillary thyroid carcinoma

RET/PTC1 and RET/PTC3 are the markers for papillary thyroid carcinoma. Their reported prevalence varies broadly. Nonrearranged c-RET has also been detected in a variable proportion of papillary carcinomas. The published data suggest that a wide range in expression levels may contribute to the different frequency of c-RET and, particularly, of RET/PTC detection. However, quantitative expression analysis has never been systematically carried out. We have analyzed by real-time RT-PCR 25 papillary carcinoma and 12 normal thyroid samples for RET/PTC1, RET/PTC3 and for RET exons 10-11 and 12-13, which are adjacent to the rearrangement site. The variability in mRNA levels was marked and four carcinoma groups were identified: one lacking RET/PTC rearrangement with balanced RET exon levels similar to those of the normal samples (7/25 cases, 28%), the second (6/25 cases, 24%) with balanced RET expression and very low levels of RET/PTC1, the third with unbalanced RET exons 10-11 and 12-13 expression, high RET/PTC1 levels but no RET/PTC3 (7/25 cases, 28%), and the fourth with unbalanced RET expression, high RET/PTC1 levels and low levels of RET/PTC3 (5/25 cases, 20%). Papillary carcinomas with high RET/PTC1 expression showed an association trend for large tumor size (P=0.063). Our results indicate that the variability in c-RET and RET/PTC mRNA levels contributes to the apparent inconsistencies in their reported detection rates and should be taken into account not only for diagnostic purposes but also to better understand the role of c-RET activation in thyroid tumorigenesis.

Immunohistochemical localisation of RET and p53 mutant protein of thyroid lesions in a North-Eastern Malaysian population and its prognostic implications

AIMS

To investigate RET and p53 expression in local thyroid lesions, in order to shed light on the pathogenesis of papillary carcinoma and explain the high prevalence of this condition among the nodular hyperplasia (multi-nodular goitre) cases.

METHODS

Archival thyroid tissue was retrieved from Hospital Universiti Sains Malaysia (HUSM) Pathology Department files and studied by immunohistochemistry for RET and p53 mutant protein. Normal tissues from 74 cases served as controls.

RESULTS

Fifty follicular adenoma, 66 nodular hyperplasia and 53 papillary carcinoma cases were studied. RET was expressed in 5.4% of normal thyroid tissue, 18% of follicular adenomas, 22.7% of nodular hyperplasia cases and 71.7% of papillary carcinomas. Its expression in papillary carcinoma was not associated with the coexistence of nodular hyperplasia lesions. p53 was expressed by 17% of papillary carcinomas. No association was found between p53 expression of nodular hyperplasia with or without co-existing papillary carcinoma. p53, rather than RET, was an excellent predictor of tumour lymph node metastasis and capsular invasion. p53 was also a significant prognosticator of survival outcome.

CONCLUSIONS

RET expression is highly prevalent in local papillary carcinoma, indicating a significant role in the pathogenesis of this tumour, with no apparent role in tumour behaviour and survival outcome. p53 on the other hand appears to be a significant factor in the latter events. The two genes appear to act in two different pathways: the former being an initiator, and the later a propagator of papillary carcinoma.

Molecular pathogenesis of thyroid cancer

A number of molecular abnormalities have been described in association with the progression from normal thyroid tissue to benign adenomas to well-differentiated and finally anaplastic epithelial thyroid cancer. These include upregulation of proliferative factors, such as growth hormones and oncogenes, downregulation of apoptotic and cell-cycle inhibitory factors, such as tumor suppressors, disruption of normal cell-to-cell interactions, and cellular immortalization. The progression model for thyroid carcinoma has not been proven, but evidence suggests that an evolutionary molecular process is involved, especially in the development of follicular thyroid cancers for which there are distinct intermediate phenotypes. We present a comprehensive evaluation of factors involved in thyroid tumorigenesis and attempt to describe preliminary attributes of a progression model. The organization of this model should also provide a template for the incorporation of new information as it is derived from large-scale genomic studies.

RET expression in papillary thyroid cancer from patients irradiated in childhood for benign conditions

Both external and internal exposure to radiation have been linked to the development of papillary thyroid cancer. Rearrangement of the gene for RET tyrosine kinase and subsequent expression of this protein has also been found to occur in many papillary thyroid cancers, and with increased frequency in radiation-related cancers following the Chernobyl accident. However, little has been reported on the frequency of RET rearrangements in cancers after exposure to external radiation. We here report on RET protein immunoreactivity in paraffin-embedded thyroid samples from 30 patients with papillary thyroid cancer who received radiation treatment during childhood for benign conditions at Michael Reese Hospital in Chicago, and in 34 patients identified from the tumor registry as having papillary thyroid cancer with no history of therapeutic radiation. The subjects were characterized by sex, age at surgery, and the following attributes of tumor pathology: size, number of lobes involved, number of foci, lymph node metastases, and soft tissue invasion. Representative tissue samples were reacted with an antibody against the RET tyrosine kinase domain whose expression has been shown to correlate highly with RET/PTC rearrangements. A greater percentage of cancers positive for RET immunoreactivity was found in the radiation-exposed group (86.7% vs. 52.9%, P = 0.006). Although the mean age at surgery of the exposed group was lower than the control group, there was no correlation of positive RET immunoreactivity with the age at surgery. No characteristics of the tumors were associated with positive RET immunoreactivity. In summary, the greater incidence of RET-immunopositives in the irradiated group indicates that the expression of RET immunoreactivity is strongly associated with radiation exposure, but the prognostic significance of this is not yet clear.

RET/PTC rearrangement in thyroid tumors

Rearrangement of the RET gene, also known as RET/PTC rearrangement, is the most common genetic alteration identified to date in thyroid papillary carcinomas. The prevalence of RET/PTC in papillary carcinomas shows significant geographic variation and is approx 35% in North America. RET/PTC is more common in tumors in children and young adults, and in papillary carcinomas associated with radiation exposure. There are at least 10 different types of RET/PTC, all resulting from the fusion of the tyrosine kinase domain of RET to the 5' portion of different genes. RET/PTC1 and RET/PTC3 are the most common types, accounting for >90% of all rearrangements. There is some evidence that different types of RET/PTC may be associated with distinct biologic properties of papillary carcinomas. RET/PTC1 tends to be more common in tumors with typical papillary growth and microcarcinomas and to have a more benign clinical course, whereas RET/PTC3 in some populations shows a strong correlation with the solid variant of papillary carcinoma and more aggressive tumor behavior. RET/PTC has recently been found in hyalinizing trabecular adenomas of the thyroid gland, providing molecular evidence in favor of this tumor to be a variant of papillary carcinoma. The occurrence of RET/PTC in Hashimoto thyroiditis and thyroid follicular adenomas and hyperplastic nodules reported in several studies has not been confirmed in other observations and remains controversial.

Etiology and significance of the optically clear nucleus

Papillary thyroid carcinoma (PTC) is diagnosed in both cytology and surgical pathology specimens on the basis of distinct nuclear morphology, characterized by nuclear elongation, chromatin clearing, intranuclear grooves, and inclusions. Although these nuclear features are specific to papillary carcinoma, they can be mimicked in some benign conditions. The majority of PTC cases do not pose diagnostic problems. However, a distinct subset of cases has generated controversy among experts. These cases are follicular patterned tumors that show minimal nuclear changes in PTC. Several investigators have explored the role of immunohistochemical markers in the histologic diagnosis of PTC. Somatic rearrangements of the RET protooncogene are the most frequent genetic abnormality found in PTC. The frequency of these rearrangements has varied according to the geographic region, radiation exposure, and methodologies used and histologic variant of PTC. Recent studies have suggested that RET/PTC may be the cause of this specific nuclear change in PTC; however, the role of RET/PTC in tumor progression still needs to be defined.

The GDNF/RET signaling pathway and human diseases

Glial cell line-derived neurotrophic factor (GDNF) and related molecules, neurturin, artemin and persephin, signal through a unique multicomponent receptor system consisting of RET tyrosine kinase and glycosyl-phosphatidylinositol-anchored coreceptor (GFRalpha1-4). These neurotrophic factors promote the survival of various neurons including peripheral autonomic and sensory neurons as well as central motor and dopamine neurons, and have been expected as therapeutic agents for neurodegenerative diseases. In addition, it turned out that the GDNF/RET signaling plays a crucial role in renal development and regulation of spermatogonia differentiation. RET mutations cause several human diseases such as papillary thyroid carcinoma, multiple endocrine neoplasia types 2A and 2B, and Hirschsprung's disease. The mutations resulted in RET activation or inactivation by various mechanisms and the biological properties of mutant proteins appeared to be correlated with disease phenotypes. The signaling pathways activated by GDNF or mutant RET are being extensively investigated to understand the molecular mechanisms of disease development and the physiological roles of the GDNF family ligands.

Karyotypic characterization of papillary thyroid carcinomas

BACKGROUND

Cytogenetic studies performed in papillary thyroid carcinoma (PTC) identified chromosome 10q rearrangements with breakpoints at 10q11.2 as the most frequent aberrations in these tumors. In the current study, the authors aimed to identify other chromosomal abnormalities nonrandomly associated with papillary thyroid carcinomas.

METHODS

Cytogenetic analysis was performed on 94 papillary thyroid carcinomas after short-term culture of the tumors sterile fragments.

RESULTS

Clonal chromosomal changes were found in 37 tumors (40%). Structural cytogenetic abnormalities were observed in 18 carcinomas. Chromosomes 1, 3, 7, and 10 were the most frequently involved in rearrangements. Pooled results of the breakpoints detected in these tumors, as well as those described in the literature, allowed the authors to verify as the most common breakpoint loci 1p32-36, 1p11-13, 1q, 3p25-26, 7q34-36, and 10q11.2. The correlation between the karyotype features of the 94 PTCs and the histologic data revealed that some PTC follicular variants were characterized by chromosomal aberrations commonly found in thyroid follicular adenomas: a del(11)(q13q13), a t(2;3)(q13;p35), and gains of chromosomes 3, 5, 7, 9, 12, 14, 17, and 20. In the tall cell PTC variant group, 4 of the 7 tumors presented clonal cytogenetic changes, 3 (75%) of which were characterized by anomalies of chromosome 2 that lead to a overrepresentation of the long arm of this chromosome. Noted also in these series was an association between complex karyotypes and tumors with poorly differentiated histiotypes.

CONCLUSIONS

In this study, the authors report chromosome 1p32-36, 1p11-13, 3p25-26, and 7q32-36 as novel breakpoint cluster regions in PTC, and they suggest that there are cytogenetic changes preferentially associated with the follicular and tall cell PTC variants.

RET oncogene activation in papillary thyroid carcinoma

The RET proto-oncogene encodes a cell membrane tyrosine-kinase receptor protein whose ligands belong to the glial cell line-derived neurotrophic factor. RET functions as a multicompetent receptor complex that includes alphaGFRs and RET. Somatic rearrangements of RET designated as RET/PTC (from papillary thyroid carcinoma) were identified in papillary thyroid carcinoma before RET was recognized as the susceptibility gene for MEN2. There are now at least at least 15 types of RET/PTC rearrangements involving RET and 10 different genes. RET/PTC1 and RET/PTC3 are by far the most common rearrangements. All of the rearrangements are due to DNA damage and result in the fusion of the RET tyrosine-kinase (RET-TK) domain to the 5'-terminal region of heterologous genes. RET/PTC rearrangements are very common in radiation-induced tumors but have been detected in variable proportions of sporadic (i.e., non-radiation associated) papillary carcinomas. It is estimated that up to approximately half the papillary thyroid carcinomas in the United States and Canada harbor RET/PTC rearrangements, most commonly RET/PTC-1, followed by RET/PTC-3 and occasionally RET/PTC-2. The cause of these rearrangements in sporadic papillary carcinomas is not known, but the close association between their presence and the papillary carcinoma phenotype indicates that they play a causative role in tumor development. The proposed mechanisms of RET/PTC-induced tumorigenesis and the clinical and pathologic implications of RET/PTC activation are discussed.

RET/PTC rearrangements in thyroid nodules: studies in irradiated and not irradiated, malignant and benign thyroid lesions in children and adults

Rearrangements of the RET proto-oncogene may occur in both naturally occurring and radiation-induced papillary thyroid carcinomas. Conflicting results on the frequency and type of RET/PTC rearrangements have been reported in relation to age, radiation exposure, and histological tumor variant. We designed the present study to evaluate in a single laboratory, using the same methodologies, the pattern of RET/PTC activation in thyroid tumors from different groups of patients (exposed or not exposed to radiation, children or adults, with benign or malignant tumors) in relationship to the above mentioned variables. We studied 154 patients with benign nodules (n = 65) or papillary thyroid cancer (n = 89). In the last group, 25 were Belarus children exposed to the post-Chernobyl radioactive fallout, 17 were Italian adults exposed to external radiotherapy for benign diseases, and 47 were Italian subjects (25 children and 22 adults) with no history of radiation exposure. Among patients with benign thyroid nodules, 21 were Belarus subjects (18 children and 3 adults) exposed to the post-Chernobyl radioactive fallout, 8 were Italian adults exposed to external radiation on the head and neck, and 36 were Italian adults with naturally occurring benign nodules. The overall frequency of RET/PTC rearrangements in papillary thyroid cancer was 55%. The highest frequency was found in post-Chernobyl children and was significantly higher (P = 0.02) than that found in Italian children not exposed to radiation, but not significantly higher than that found in adults exposed to external radiation. No difference of RET/PTC rearrangements was found between samples from irradiated (external x-ray) or not irradiated adult patients, as well as between children and adults with naturally occurring, not irradiated, thyroid cancer. When analyzing the type of RET/PTC rearrangement (RET/PTC1 or RET/PTC3), no major difference was apparent. In addition, eight cases with an unknown RET/PTC rearrangement and three cases with the concomitant expression of RET/PTC1 and RET/PTC3 were found. No significant correlation was observed between the frequency and/or the type of RET/PTC rearrangement and clinical-epidemiological features of the patients such as age at diagnosis, age at exposure, histological variant, gender and tumor-node-metastasis (TNM) categories. RET/PTC rearrangements were also found in 52.4% of post-Chernobyl benign nodules, in 37.5% of benign nodules exposed to external radiation and in 13.9% of naturally occurring nodules (P = 0.005, between benign post-Chernobyl nodules and naturally occurring nodules). The relative frequency of RET/PTC1 and RET/PTC3 in rearranged benign tumors showed no major difference. In conclusion, our results indicate that the presence of RET/PTC rearrangements in thyroid tumors is not restricted to the malignant phenotype, is not higher in radiation-induced tumors compared with those naturally occurring, is not different after exposure to radioiodine or external radiation, and is not dependent from young age. Other factors, probably influenced by ethnic or genetic background, may act independently from or in cooperation with radiation, to trigger the DNA damage leading to RET proto-oncogene activation.

Pathogenesis of thyroid nodules: histological classification?

Thyroid nodule genesis may be considered as an amplification of thyroid heterogeneity due to genetic and/or epigenetic mechanisms. We classified the thyroid nodules in five types with distinct histological features: hyperplastic, neoplastic, colloid, cystic and thyroiditic nodules. Hyperplastic: Thyrocyte proliferation is under the control of TSH but several other paracrine and autocrine factors are secreted by follicular cells, the stromal apparatus and the lymphocytes, which are implicated in initiation and perpetuation of thyroid hyperplasia. Growth occurs mainly through TSHR, cAMP and PKA. Constitutive cAMP overproduction has been shown to be due to point mutation of the TSHR or Gs protein, producing overgrowth and hyperfunction. Neoplastic: Several activated oncogenes have been identified in thyroid malignancies. Oncogenes relevant to the thyroid carcinogenesis are: mutated TSHR and gsp (constitutive activation of cAMP); TRK (receptor for NGF); RET/PTC (phosphorylation of tyrosine kinase receptor)--an isoform of this oncogene is induced by radiation: ras (it encodes Gs proteins transducing mitogenic signals); and c-MET (receptor for hepatocyte growth factor). The evolution of a differentiated thyroid cancer towards an undifferentiated cancer is due to a mutation of a family of proteins (i.e., p53), which acts as a brake, preventing the genomic instability of cancer. It is suggested that a tumor initiates by RET or ras and possibly progresses--as a result of additional mutations and by p53 mutation--to anaplastic carcinoma. Colloid: Flattening of the epithelium and dilatation of follicles containing viscous material--made up by a concentrated solution of thyroglobulin (hTg)--is the characteristic of the colloid nodule. A defect of intraluminal reabsorption of hTg has been suggested but not proven. Experimentally, a load of iodine is able to change thyroid hyperplasia to a colloid feature; however, a load of iodine is rarely found in the clinical history of patients. A new clue to the pathogenesis comes from the finding that a relevant part of the colloid (10-20%) is made up of insoluble globules, where hTg is compacted in a polymeric form. It is suggested that stocking hTg into globules is defective in colloid nodules, leading to enormous enlargement of the follicle. Cystic: It is estimated that between 15 and 40% of thyroid nodules are partly or entirely cystic. The 'true cyst' is rare; most of the so-called cystic nodules are 'pseudocysts', which follow necrosis and colliquation. Necrosis issues as an imbalance between growth and the precisely regulated process of angiogenesis. More recently, the VEGF/VPF has been found to be at the origin of recent and recurrent cysts. Immunotoxic and apoptotic mechanisms have also been suggested. Chemical analysis of cystic fluid showed a 'denatured' and 'serum-like' pattern suggesting different mechanisms in the pathogenesis of the pseudocystic thyroid nodules. Thyroiditic: Nodular lymphocytic thyroiditis (NLT) includes two different entities: 1) lymphocyte thyroiditis growing as a nodule in a hyperplastic or normal gland, and 2) lymphocyte thyroiditis associated in the same nodule with other nodular diseases of the thyroid: papillary thyroid carcinoma and lymphoma have been found to be associated to chronic lymphocytic thyroiditis.

High prevalence of RET tyrosine kinase activation in Mexican patients with papillary thyroid carcinomas

RET/PTC oncogene expression is restricted to papillary thyroid carcinomas (PTC). At least three forms of this oncogene have been described. These are generated by the rearrangement of the 5'-terminal region of different expressed genes with the tyrosine-kinase (TK) domain of the ret proto-oncogene. Several studies showing the correlation between the expression of this oncogene, clinical outcome, and histological subtypes have been published. Thirty-five paraffin-embedded PTC samples from patients without a history of radiation exposure were studied. Immunohistochemistry (IHC) and in situ hybridization (ISH) were used to determine a possible correlation between RET activation, clinical outcome, and tumor subtype. Almost half of the studied cases presented with tumoral extension or metastases. Ret gene transcripts and protein were found in all PTC variants as well as in their corresponding metastases. In contrast, none of the follicular adenomas, goiters, or normal follicular cells from the thyroid gland showed evidence of ret activation. We observed a high frequency of ret expression in PTCs, suggesting that ret activation is a common event in nonradiation-related PTC from Mexican patients.

Evaluation of diagnostic efficiency of computerized image analysis based quantitative nuclear parameters in papillary and follicular thyroid tumors using paraffin-embedded tissue sections

Computerized image analysis (IA) system has emerged in recent years as a very powerful tool for objective and reproducible quantification of histological features. It has shown considerable potential for diagnostic application in diverse histological situations. The objectives of the present study were to evaluate the discriminatory diagnostic efficiency of computerized image analysis based quantitative subvisual nuclear parameters in papillary and follicular neoplasms of thyroid. A total of 60 cases were studied. Forty-four cases belonged to training set and 16 cases belonged to a test set. A minimum of 100 nuclei was analyzed in each case using uniform 5 m mm thick hematoxylin stained sections. The IA workstation comprised of an Olympus microscope, a 10 bit digital video camera, an image grabber card and a pentium 120 MHz computer. Optimas 5.2 software was utilized for data collection on 8 morphometric and 8 densitometric parameters. Multivariate stepwise discriminant statistical analysis of data was done with the help of BMDP statistical software release 7.0. Results from a training set revealed correct classification rates of 98.0%, 84.5% and 61.2% for the histological groups of hyperplastic papillae versus papillae of papillary carcinoma (group I), follicular variant of papillary carcinoma versus the broad category of follicular neoplasms consisting of both follicular adenoma and follicular carcinoma (group II) and follicular adenoma versus follicular carcinoma (group III), respectively. Results of test set revealed correct classification rates of 100%, 80% and 50% for groups I, II and III respectively. It was concluded that computerized nuclear IA parameters have potential usefulness for discriminating benign versus malignant papillary lesions of thyroid, follicular variant of papillary carcinoma versus follicular adenoma and/or follicular carcinoma but are of no value in discriminating between follicular adenoma and follicular carcinoma.

Molecular pathogenesis of thyroid nodules and cancer

Tumours derived from the thyroid follicular epithelium represent an informative model for understanding the molecular pathogenesis of multistage tumourigenesis, which is the prevailing theory on cancer development and progression nowadays. The early stages of thyroid tumour development appear to be the consequence of the activation or 'de novo' expression of several proto-oncogenes or growth factor receptors, such as ras, ret, NTRK, met, gsp and the thyrotropin (TSH) receptor. Alterations in the expression pattern of these genes are associated with the development of differentiated neoplasms, ranging from benign toxic adenomas (gsp and TSH receptor), to follicular (ras) and papillary (ret/PTC, NTRK, met) carcinomas. They may all be considered to be early events of thyroid cell transformation and, for some, experimental evidence derived from gene transfer studies supports this hypothesis. Alterations in tumour suppressor genes (p53, Rb) are associated instead with the most aggressive and poorly differentiated forms of thyroid cancer, indicating that, in the thyroid tumourigenic process, they represent late genetic events. Specific environmental factors (iodine deficiency, ionizing radiations) have been shown to play a crucial role in promoting the development of thyroid cancer, influencing both its genotypic and phenotypic features. Interestingly, a high percentage of genetic lesions causing thyroid cancer originate from gene rearrangements and chromosomal translocations (ret/PTC, NTRK, Pax-8/PPARgamma) a finding which, being a rare event in most epithelial tumours, makes the molecular pathogenesis of thyroid cancer unique. The uninterrupted flow of information on the molecular genetics of thyroid nodules and cancer will broaden the correlation between genotype and phenotype and will also provide important information for the development of more accurate preoperative diagnostic tools and more efficient treatment choices for the different forms of thyroid cancer.

RET/PTC activation in hyalinizing trabecular tumors of the thyroid

Hyalinizing trabecular tumor (HTT) of the thyroid is a neoplasm of follicular derivation with a histogenesis that is still the subject of debate. Morphologic affinities between HTT and papillary carcinoma, including nuclear pseudoinclusions and grooves, suggest that these tumors may be of similar origin. The authors investigated the relationship between these two types of tumors by assessing HTT for the presence of rearrangements of the proto-oncogene rearranged during transfection (RET) that, in thyroid tumors, are specific for papillary carcinoma. A series of 14 HTTs, including two cases associated with classic papillary carcinoma, was studied by means of immunohistochemistry and reverse transcription-polymerase chain reaction. Seven follicular adenomas with focal hyalinized trabecular areas served as control cases. Three of the 14 HTT cases under consideration displayed rearrangements of RET generating the RET/papillary thyroid carcinoma type 1 (PTC1) oncogene. In another case, RET expression was detected focally by immunohistochemistry alone. Finally, in one mixed HTT-papillary carcinoma sample, RET/PTC1 expression was detected, but only in the papillary component. None of the control follicular adenomas contained rearrangements of RET/PTC. These findings demonstrate that a comparable percentage (28.6%) of HTTs and papillary carcinomas exhibit the same RET proto-oncogene alterations. Thus, HTT may represent the "hyalinizing trabecular" variant of papillary carcinoma rather than a separate entity.

Cloning of TC-1 (C8orf4), a novel gene found to be overexpressed in thyroid cancer

A novel gene highly expressed in thyroid cancer, designated TC-1 (thyroid cancer-1), was cloned from suppression subtractive hybridization between papillary thyroid carcinoma and its surrounding normal thyroid tissue. Overexpression of TC-1 in thyroid cancer was confirmed in 15/16 paired samples by RT-PCR and Northern analysis. Ubiquitously expressed in human tissues, the TC-1 sequence showed no homology to any known gene, but matched a cluster of ESTs. After alignment of our sequence with the ESTs, the missing transcription start site was obtained by 5'-RACE and verified by primer extension analysis. The full-length mRNA sequence of 1327 bp has an open reading frame of 321 bp, which encodes a highly conserved protein. Three regulatory motifs were identified at the expected positions within 1 kb of the 5' flanking sequence obtained by genome walking. Using fluorescence in situ hybridization, TC-1 was localized to chromosome 8p11.2. The overexpression of TC-1 in papillary carcinoma suggests that it may have an important role in thyroid carcinogenesis.

Prevalence and distribution of ret/ptc 1, 2, and 3 in papillary thyroid carcinoma in New Caledonia and Australia

The world's highest incidence of thyroid cancer has been reported among females in New Caledonia, a French overseas territory in the Pacific located between Australia and Fiji. To date, no molecular genetic studies in this population are available. Over the past few years, the oncogenic rearrangement of the ret protooncogene (ret/ptc) has been studied in papillary carcinomas in different populations. In this study, we investigated the prevalence and distribution of ret/ptc1, 2, and 3 in papillary thyroid carcinoma from the New Caledonian population and compared the pattern with that of an Australian population. Fresh-frozen and paraffin-embedded papillary carcinomas from 27 New Caledonian and 20 Australian patients were examined for ret rearrangements by means of RT-PCR with primers flanking the chimeric region, followed by hybridization with radioactive probes. ret/ptc was present in 70% of the New Caledonian and in 85% of the Australian samples. Multiple rearrangements were detected and confirmed by sequencing in 19 cases, 4 of which had 3 types of rearrangements in the same tumor. This study demonstrates a high prevalence of ret/ptc in New Caledonian and Australian papillary carcinoma. The findings of multiple ret/ptc in the same tumor suggest that some thyroid neoplasms may indeed be polyclonal.

RET proto-oncogene mutations in thyroid carcinomas: clinical relevance

Different forms of RET mutations are found in papillary and medullary thyroid carcinomas. Rearrangements with other genes (RET/PTC oncogene) play a causative role in a significant proportion of papillary thyroid carcinomas. In this case, several factors influence the frequency and the type of RET/PTC, such as exposure to radiation, age and histological variant of the papillary tumor. On the other hand, the presence of the mutation does not seem to influence the biological behavior of the tumor or its response to conventional treatment modalities. In the setting of medullary thyroid cancer, germline RET point-mutations are implicated in the pathogenesis of virtually all hereditary forms and somatic point-mutations in nearly half of the sporadic forms. The clinical impact of this finding is that family members at-risk of hereditary MTC may be screened by genetic analysis, to distinguish those carrying or not-carrying the mutation. The last can be reassured on their status and relieved from further follow-up. Those with the mutation may be treated at a pre-clinical stage of the disease or even before the disease is started. The present review is focused on the clinical implication of RET gene mutations in thyroid cancer patients.

Oncogenes and thyroid cancer

Human thyroid tumors can be derived either from epithelial follicular cells or from parafollicular C-cells. Follicular cell-derived tumors represent a wide spectrum of lesions, ranging from benign adenomas through differentiated (follicular and papillary) and undifferentiated (anaplastic) carcinomas, thus providing a good model for finding a correlation between specific genetic lesions and histologic phenotype. Follicular adenomas and carcinomas show frequently the presence of mutations in one of the three ras genes. Papillary carcinomas show frequently a specific gene rearrangement which gives rise to the formation of several types of so-called RET/PTC chimeric genes. This lesions occur in almost 50% of papillary cancers and consist in the juxtaposition of the 3' or tyrosine kinase domain of the RET gene (which codes for a receptor protein not normally expressed in follicular thyroid cells) with the 5' domain of ubiquitously expressed genes, which provide the promoter and dimerization functions, necessary for the constitutive activation of RET/PTC proteins. Anaplastic carcinomas are frequently associated with mutations of the p53 tumor suppressor. Finally, point mutations of the RET gene are found in familial endocrine syndromes (FMTC; MEN2A and MEN2B), a common feature of which is the medullary thyroid carcinoma, a malignant tumor derived from parafollicular C-cells.

Detection of RET/PTC oncogene rearrangements in Korean papillary thyroid carcinomas

The prevalence of RET/PTC rearrangement in papillary thyroid carcinomas has been found to vary widely in different populations. Recent studies, however, have reported no significant geographical difference between Asian and Western countries. In addition, there are some disagreements about the correlation of RET/PTC expression with clinical aggressiveness. We have performed this study in order to examine the prevalence of RET/PTC-1, RET/PTC-2, and RET/PTC-3 rearrangements in Korean papillary thyroid carcinomas, and to ascertain its clinical relevance. Thyroid tumors from 31 patients histologically confirmed to be papillary carcinomas were included in this study. To find rearrangements, we utilized reverse transcription-polymerase chain reaction (RT-PCR) and automated direct sequencing. Initial and follow-up clinical data were obtained from the patients' medical records. We identified two tumors containing RET/PTC-1 (2/31, 6.5%) and two containing RET/PTC-2 (2/31, 6.5%). However, we could not find RET/PTC-3 rearrangement in any patients (0/31). In conclusion, we report RET/PTC rearrangements in 4 of 31, (12.9%) Korean patients with papillary thyroid carcinomas, a higher prevalence than previously reported in this population.

High prevalence of RET/PTC rearrangements in Ukrainian and Belarussian post-Chernobyl thyroid papillary carcinomas: a strong correlation between RET/PTC3 and the solid-follicular variant

A sharp increase in the incidence of pediatric thyroid papillary cancer was documented after the Chernobyl power plant explosion. An increased prevalence of rearrangements of the RET protooncogene (RET/PTC rearrangements) has been reported in Belarussian post-Chernobyl papillary carcinomas arising between 1990 and 1995. We analyzed 67 post-Chernobyl pediatric papillary carcinomas arising in 1995-1997 for RET/PTC activation: 28 were from Ukraine and 39 were from Belarus. The study, conducted by a combined immunohistochemistry and RT-PCR approach, demonstrated a high frequency (60.7% of the Ukrainian and 51.3% of the Belarussian cases) of RET/PTC activation. A strong correlation was observed between the solid-follicular subtype of papillary carcinoma and the RET/PTC3 isoform: 19 of the 24 RET/PTC-positive solid-follicular carcinomas harbored a RET/PTC3 rearrangement, whereas only 5 had a RET/PTC1 rearrangement. Taken together these results support the concept that RET/PTC activation plays a central role in the pathogenesis of thyroid papillary carcinomas in both Ukraine and Belarus after the Chernobyl accident.

Aspectos moleculares do câncer tiroideano

A proliferação da célula tiroideana normal é regulada por fatores de crescimento estimuladores e inibidores, que atuam através de seus receptores de membrana e, subseqüentemente, através de transdutores citoplasmáticos. Na glândula normal adulta, o equilíbrio de sinais é tal que a proliferação é mínima, enquanto nas neoplasias o crescimento resulta de um distúrbio irreversível desse equilíbrio. Apesar do número de moléculas envolvidas nesse processo ser grande, apenas um pequeno subgrupo parece estar envolvido na tumorigênese tiroideana. Tais proteínas são codificadas pelos genes RAS, RET, NTRK1 e TP53. O transdutor de sinais ras é ativado por mutações em ponto e constitui uma alteração genética precoce nos tumores com histologia folicular. Os genes dos receptores de crescimento RET e NTRK1 são alterados por rearranjos cromossômicos do tipo translocação ou inversão nos carcinomas papilares e por mutações em ponto nos medulares. As alterações do gene TP53, por sua vez, têm sido observadas em carcinomas tiroideanos pobremente diferenciados e na maioria dos indiferenciados, o que sugere sua participação na progressão dessas lesões. O modelo molecular da carcinogênese tiroideana, embora ainda incompleto, pode fornecer instrumentos importantes para o diagnóstico diferencial e para o desenvolvimento de novas técnicas terapêuticas nesse grupo de neoplasias.

Molecular genetics of childhood papillary thyroid carcinomas after irradiation: high prevalence of RET rearrangement

Epidemiological studies have revealed a connection between thyroid carcinogenesis and a history of radiation. The molecular mechanisms involved are not well understood. It has been claimed that RAS, p53 or GSP mutations and RET or TRK rearrangements might play a role in adult thyroid tumors. In childhood, the thyroid gland is particularly sensitive to ionizing radiation. The reactor accident in Chernobyl provided a unique chance to study molecular genetic aberrations in a cohort of children who developed papillary thyroid carcinomas after a short latency time after exposure to high doses of radioactive iodine isotopes. According to the concepts of molecular genetic epidemiology, exposure to a specific type of irradiation might result in a typical molecular lesion. Childhood papillary thyroid tumors after Chernobyl exhibit a high prevalence of RET rearrangement as almost the only molecular alteration. The majority showed RET/PTC3 (i.e., ELE/RET rearrangements), including several subtypes. Less frequently, RET/PTC1 (i.e., H4/RET rearrangements), and a novel type (RET/PTC5, i.e., RFG5/RET) were observed. Proof of reciprocal transcripts suggests that a balanced intrachromosomal inversion leads to this rearrangement. Breakpoint analyses revealed short homologous nucleotide stretches at the fusion points. In all types of rearrangement, the RET tyrosine kinase domain becomes controlled by 5' fused regulatory sequences of ubiquitously expressed genes that display coiled-coil regions with dimerization potential. Oncogenic activation of RET is apparently due to ligand-independent constitutive ectopic RET tyrosine kinase activity. The analysis of this cohort of children with radiation-induced thyroid tumors after Chernobyl provides insights into typical molecular aberrations in relation to a specific mode of environmental exposure and may serve as a paradigm for molecular genetic epidemiology.