Age-related activation of the tyrosine kinase receptor protooncogenes RET and NTRK1 in papillary thyroid carcinoma

Differentiated thyroid carcinoma in children: A retrospective analysis of 125 pediatric cases from a single institution in India

BACKGROUND

Thyroid carcinoma (TC) is extremely rare in children. We assessed the clinicopathological features, outcomes, recurrence pattern, and associated risk factors of differentiated thyroid carcinoma (DTC).

METHODS

Children aged ≤14 years, pathologically diagnosed as DTC at a tertiary cancer institute between January 1998 and December 2015 were retrospectively analyzed. Survival outcomes were estimated using the Kaplan-Meier method.

RESULTS

During 18 years, 125 children with DTC were treated with a male:female ratio of 1:2.3. The median age was 12 years (2-14 years). Anterior neck swelling was the commonest presentation (72.8%). Histopathology revealed papillary thyroid carcinoma (PTC) in 123 children (98.4%). Extrathyroidal extension was seen in 32 children (25.6%). Sixty-eight children (54.4%) had nodal metastases and seven had distant metastasis. Relapse developed in 12 children. All were salvaged with subsequent surgery and radioiodine therapy. Eight children had persistent disease and one had a second malignant neoplasm. The median follow-up period was 9 years 1 month (1-20 years). Five-year recurrence-free survival (RFS) was 94.8% and 5-year overall survival was 100%. Larger tumors (p-value = .001), extrathyroidal extension (p-value = .001), and nodal metastasis (p-value = .022) were significant predictors for RFS in univariate analysis.

CONCLUSIONS

Pediatric DTC showed aggressive behavior characterized by a high rate of extrathyroidal extension and nodal and pulmonary metastasis. Persistent disease should be distinguished from recurrent disease as DTCs with metastatic disease remain stable for long time and usually respond well to radioiodine therapy. Our study reaffirmed favorable prognosis despite aggressive presentation and even after relapse.

Management of pediatric differentiated thyroid cancer: An overview for the pediatric oncologist

Differentiated thyroid cancer (DTC) is the most common childhood thyroid malignancy. The standard of care for pediatric DTC is total thyroidectomy followed by radioactive iodine (RAI) treatment when indicated. Molecular changes and potential therapeutic targets have been recently described in pediatric thyroid cancer. Pediatric oncologists are increasingly involved in the evaluation of thyroid nodules in childhood cancer survivors and in the management of advanced thyroid cancer. In 2015, the American Thyroid Association published management guidelines for children with DTC. We provide an overview of the current standard of care and highlight available targeted therapies for progressive or RAI refractory DTC.

Novel TG-FGFR1 and TRIM33-NTRK1 transcript fusions in papillary thyroid carcinoma

Papillary thyroid carcinoma (PTC) is most common among all thyroid cancers. Multiple genomic alterations occur in PTC, and gene rearrangements are one of them. Here we screened 14 tumors for novel fusion transcripts by RNA‐Seq. Two samples harboring RET/PTC1 and RET/PTC3 rearrangements were positive controls whereas the remaining ones were negative regarding the common PTC alterations. We used Sanger sequencing to validate potential fusions. We detected 2 novel potentially oncogenic transcript fusions: TG‐FGFR1 and TRIM33‐NTRK1. We detected 4 novel fusion transcripts of unknown significance accompanying the TRIM33‐NTRK1 fusion: ZSWIM5‐TP53BP2, TAF4B‐WDR1, ABI2‐MTA3, and ARID1B‐PSMA1. Apart from confirming the presence of RET/PTC1 and RET/PTC3 in positive control samples, we also detected known oncogenic fusion transcripts in remaining samples: TFG‐NTRK1, ETV6‐NTRK3, MKRN1‐BRAF, EML4‐ALK, and novel isoform of CCDC6‐RET.

Fusion Oncogenes Are the Main Genetic Events Found in Sporadic Papillary Thyroid Carcinomas from Children

BACKGROUND

Previous studies reported significant differences in the clinical presentation and outcomes of papillary thyroid carcinoma (PTC) in pediatric patients compared with adults. Previous studies have suggested that the clinicopathological differences observed between pediatric and adult PTCs may be due the existence of distinct genetic alterations. However, the knowledge of genetic events in pediatric PTCs is based primarily on studies in radiation-exposed PTCs or in the few studies that enrolled predominantly adolescent patients. The aim of this study was to characterize the known oncogenic alterations of the MAPK pathway found in adult and radiation-exposed PTCs in a cohort of predominantly sporadic pediatric PTC patients.

METHODS

Thirty-five pediatric PTCs were screened for the most prevalent fusions (RET/PTC1, RET/PTC2, RET/PTC3, ETV6-NTRK3, and AGK-BRAF) and point mutations (BRAFV600E and NRASQ61) described in sporadic pediatric PTCs. The mutational status was correlated with clinicopathological data.

RESULTS

Mutations were found in 20 out of 35 (57%) PTC cases. Fusion oncogenes were the main genetic alterations found. RET/PTC1-3 rearrangements were found in 13 (37%), ETV6-NTRK3 in 3 (9%), AGK-BRAF in 4 (11%), and BRAFV600E in 3 (9%). No mutation was found in NRASQ61. BRAFV600E was associated with older age and larger tumor size (p < 0.05), and RET/PTC3 was associated with a larger tumor size and multifocality (p < 0.05).

CONCLUSIONS

The genetic signature in this cohort was remarkably different than that observed in adults. Although observed at a lower prevalence, the spectrum of mutations was quite similar to that described in radiation-exposed pediatric PTCs. As mutations were unidentifiable in over 40% of the PTC cases, more comprehensive studies conducted in these patients will help to decipher the genetic landscape of sporadic pediatric PTCs.

Mutational Analysis in Pediatric Thyroid Cancer and Correlations with Age, Ethnicity, and Clinical Presentation

BACKGROUND

Well-differentiated thyroid cancer (WDTC) incidence in pediatrics is rising, most being papillary thyroid carcinoma (PTC). The objective of the study was to assess the prevalence of different mutations in pediatric WDTC and correlate the genotype with the clinical phenotype.

METHODS

This is a single-center retrospective study. Thyroid tissue blocks from 42 consecutive pediatric WDTC patients who underwent thyroidectomy between 2001 and 2013 were analyzed at Quest Diagnostics for BRAF(V600E), RAS mutations (N,K,H), and RET/PTC and PAX8/PPARγ rearrangements, using validated molecular methods. Thyroid carcinomas included PTC, follicular thyroid carcinoma (FTC), and follicular variant of PTC (FVPTC).

RESULTS

Thirty-nine samples (29 females) were genotyped. The mean age at diagnosis was 14.7 years (range 7.9-18.4 years), and most were Hispanic (56.4%) or Caucasian (35.9%). The mean follow-up period was 2.9 years. Mutations were noted in 21/39 (53.8%), with both BRAF(V600E) (n = 9), and RET/PTC (n = 6) detected only in PTC. Mutations were detected in 2/5 FTC (PAX8/PPARγ and NRAS) and 3/6 FVPTC cases (PAX8/PPARγ). Of 28 PTC patients, 57.1% had mutations: 32.1% with BRAF(V600E), 21.4% with RET/PTC, and 3.6% with NRAS. Of patients with BRAF(V600E), 77.8% were Hispanic and 88.9% were >15 years, while all RET/PTC-positive patients were ≤15 years (p = 0.003). Tumor size, lymph node involvement, and distant metastasis at diagnosis (or soon after (131)I ablation) did not vary significantly based on the mutation.

CONCLUSIONS

BRAF(V600E) was the most common mutation, especially in older and Hispanic adolescents. A larger, ethnically diverse pediatric cohort followed long term will enable the genotypic variability, clinical presentation, and response to therapy to be better assessed.

Are we really at the dawn of understanding sporadic pediatric thyroid carcinoma?

Data from the National Cancer Institute and from the literature have disclosed an increasing incidence of thyroid cancer in children, adolescents and adults. Although children and adolescents with thyroid cancer tend to present with more advanced disease than adults, their overall survival rate is excellent; however, there is no clear explanation for the differences observed in the clinicopathological outcomes in these age groups. There has been an ongoing debate regarding whether the clinicopathological differences may be due to the existence of distinct genetic alterations. Efforts have been made to identify these acquired genetic abnormalities that will determine the tumor's biological behavior and ultimately allow molecular prognostication. However, most of the studies have been performed in radiation-exposed pediatric thyroid carcinoma. Therefore, our understanding of the role of these driver mutations in sporadic pediatric differentiated thyroid cancer development is far from complete, and additionally, there is a strong need for studies in both children and adolescents. The aim of this review is to present an extensive literature review with emphasis on the molecular differences between pediatric sporadic and radiation-exposed differentiated thyroid carcinomas and adult population.

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.

Immune response in thyroid cancer: widening the boundaries

The association between thyroid cancer and thyroid inflammation has been repeatedly reported and highly debated in the literature. In fact, both molecular and epidemiological data suggest that these diseases are closely related and this association reinforces that the immune system is important for thyroid cancer progression. Innate immunity is the first line of defensive response. Unlike innate immune responses, adaptive responses are highly specific to the particular antigen that induced them. Both branches of the immune system may interact in antitumor immune response. Major effector cells of the immune system that directly target thyroid cancer cells include dendritic cells, macrophages, polymorphonuclear leukocytes, mast cells, and lymphocytes. A mixture of immune cells may infiltrate thyroid cancer microenvironment and the balance of protumor and antitumor activity of these cells may be associated with prognosis. Herein, we describe some evidences that immune response may be important for thyroid cancer progression and may help us identify more aggressive tumors, sparing the vast majority of patients from costly unnecessary invasive procedures. The future trend in thyroid cancer is an individualized therapy.

Oncogenic rearrangements driving ionizing radiation-associated human cancer

The Chernobyl nuclear disaster has caused a remarkable increase in radiation-induced papillary thyroid carcinoma in children and young adults. In this issue of the JCI, Ricarte-Filho and colleagues demonstrate that chromosomal rearrangements are the oncogenic "drivers" in most post-Chernobyl carcinomas and that they often lead to unscheduled activation of the MAPK signaling pathway. These findings represent a major step forward in our understanding of radiation-induced carcinogenesis and suggest various hypotheses about the mechanisms underlying the formation and selection of gene rearrangements during cancer cell evolution.

Preoperative cytology with molecular analysis to help guide surgery for pediatric thyroid nodules

OBJECTIVES

To discuss the use of molecular mutation analysis in the surgical management of pediatric thyroid nodules.

METHODS

This study is a case series with retrospective chart review performed at a tertiary children's hospital. Pediatric patients who presented to the Children's Hospital of Pittsburgh of UPMC with a thyroid nodule and had subsequent fine needle aspiration with positive molecular mutation between November 2009 and February 2012 were identified and charts were reviewed. Patient demographics, presenting signs, lab results, pathologic findings, and surgical outcomes were collected.

RESULTS

5 pediatric patients with positive molecular mutation studies on preoperative FNA were identified. FNA results were categorized as follows: suspicious for follicular neoplasm (n = 2), suspicious for malignant cells (n = 1), and positive for malignant cells (n = 2). The following molecular mutations were identified: BRAF (V600E) (n = 2), PAX8/PPARγ (n = 1), HRAS (n = 1), and RET/PTC (n = 1). A total thyroidectomy was performed on each patient. In all cases the final pathology was positive for malignancy (papillary thyroid carcinoma (PTC), n = 3; follicular variant of PTC, n = 2). Three of five patients had transient postsurgical hypocalcemia. There were no other postoperative complications.

CONCLUSIONS

This series provides evidence that preoperative FNA with reflex molecular testing in pediatric thyroid nodules can help guide surgical decision making, reduce the need for repeat surgeries, and diminish the risk of complications from a staged procedure.

Genetic mutations, molecular markers and future directions in research

Recent molecular studies have described a number of abnormalities associated with the pathogenesis of thyroid carcinoma. These distinct molecular events are often associated with specific stages of tumor development and may serve as prognostic factors and therapeutic targets. A better understanding of the mechanisms involved in thyroid cancer pathogenesis, will hopefully help translate these discoveries to improved patient care.

Papillary thyroid cancer and inflammatory bowel disease: Is there a relationship?

AIM: To formally study age of diagnosis of papillary thyroid cancer (PTC) in inflammatory bowel disease (IBD) patients and evaluate the prevalence of PTC in IBD patients compared to a control population.

METHODS: We were interested in testing the hypothesis that patients with IBD are more likely to be diagnosed with PTC than a control population. A retrospective cohort analysis was performed using the University of Pennsylvania Health System’s electronic database. Outpatients from 1998-2009 were included in the search, and patients in the cohort were selected based on ICD-9 codes. Inclusion criteria included the diagnosis of Crohn’s disease (CD) or ulcerative colitis (UC) and the concurrent diagnosis of thyroid cancer in comparison to a control population. Using these methods 912 patients with CD and 1774 with UC were compared to 1638 diverticulitis and 19 447 asthma controls. Statistics were performed using corrected chi-square analysis. The primary outcome for this study was the diagnosis of PTC. Approval to conduct this study was obtained by the Institutional Review Board at the University of Pennsylvania.

RESULTS: The mean age was 47.5 years (range: 18-102 years) and 66% patients were female. An analysis of variance model was used to compare the age of PTC diagnosis between the CD, UC, asthma and diverticulitis groups, and a statistically significant difference in age at PTC diagnosis was noted across all groups (F = 6.35, df = 3, P = 0.0006). The age of PTC diagnosis in CD patients was statistically significantly lower than UC, asthma, and diverticulitis patients (average PTC diagnosis age for CD 25, UC 49, asthma 45, diverticulitis 63). After covarying for sex and age in 2009, the difference in age at PTC diagnosis remained statistically significant (F = 4.13, df = 3, P = 0.0089). A total of 86 patients were diagnosed with PTC. Nine patients (0.5%) with UC were diagnosed with PTC. Patients with UC were not shown to be more likely to develop PTC [odds ratio (OR): 1.544, 95%CI 0.767-3.108] compared to asthma controls. Four patients (0.4%) with CD were diagnosed with PTC. Patients with CD were not shown to be more likely to develop PTC (OR: 1.334, 95%CI 0.485-3.672) compared to a control population with asthma. Nine patients (0.5%) with a history of diverticulitis were diagnosed with PTC. Patients with diverticulitis were not shown to be more likely to develop PTC (OR: 1.673, 95%CI 0.831-3.368) compared to asthma controls. Patients with CD or UC were not less likely to develop PTC compared to those with diverticulitis (CD OR: 0.80, 95%CI 0.25-2.60; UC OR: 0.92, 95%CI 0.37-2.33). None of the patients used immunosuppressant medications prior to the diagnosis of PTC (azathioprine, 6-mercaptopurine, and methotrexate).

CONCLUSION: There is a significant difference in age of diagnosis of PTC in patients with CD compared to patients with UC and the control populations studied.

Cytomorphological and molecular genetic findings in pediatric thyroid fine-needle aspiration

BACKGROUND

The Bethesda System for Reporting Thyroid Cytopathology is largely based on data from adult studies. Although thyroid nodules in children are rare, the rate of malignancy is high. The authors' aim was to analyze the cytomorphology and mutational profiles in pediatric thyroid fine-needle aspirations (FNAs).

METHODS

Thyroid FNAs from patients 21 years old or younger were identified from the authors' pathology archive, categorized using the Bethesda System for Reporting Thyroid Cytopathology, and correlated with histological and molecular follow-up.

RESULTS

A total of 179 samples from 142 patients were identified, including 96 cases (54%) with histological follow-up and 66 cases (37%) with molecular data. The diagnoses included 21 (12%) unsatisfactory, 82 (46%) negative, 43 (24%) atypia or follicular lesion of undetermined significance, 19 (11%) suspicious for follicular neoplasm, 6 (3%) suspicious for malignancy, and 8 (4%) positive for malignancy. The rate of malignancy in each category was 0%, 7%, 28%, 58%, 100%, and 100%, respectively. Of the 66 FNAs with molecular data, there were 11 (17%) positive for mutations. All mutation-positive FNAs were papillary thyroid carcinomas (PTCs) on resection. The overall sensitivity and specificity in this population were 80% and 100%, respectively.

CONCLUSIONS

This study demonstrates that thyroid FNA in children is a sensitive and highly specific tool. There was a 17% positivity rate for a genetic mutation, which correlated with malignancy in all cases. In comparison to adults, there was a higher prevalence of RET/PTC mutations and lower prevalence of BRAF mutations, which may in part explain the less aggressive nature of PTCs reported in children.

Oncogenic alterations in papillary thyroid cancers of young patients

BACKGROUND

Papillary thyroid carcinoma (PTC) in young people usually has an aggressive initial presentation, though a good general prognosis despite recurrences in 10%-20% of patients. A number of genetic alterations that activate the mitogen-activated protein kinase (MAPK) pathway have been found in PTC. Some of these alterations have been identified as prognostic factors of PTC in adults. The objective of the current study was to comprehensively characterize all known oncogenic alterations of the MAPK pathway in young people.

METHODS

One hundred three PTCs removed from 9 children, 19 adolescents, and 75 young adults were submitted to molecular analyses.

RESULTS

Altogether, 57 alterations were found in 56 PTCs (55%) corresponding to V600E BRAF in 20.3%, RAS mutations in 12.6%, RET/PTC 1 in 11.6%, RET/PTC 3 in 8.7%, and rearrangement of NTRK in 1.9%. The prevalence of all alterations increased with age (22.2% in children; 52.6% in adolescents, 51.4% in adults 20-25 years, and 55.1% in adults 25-35 years). Prevalence increased from 39.2% earlier to 61.3% after 20 years mainly due to BRAF mutations. Classic-type PTC was associated with a larger prevalence of alterations, predominantly BRAF and RET/PTC, whereas the follicular variant was chiefly associated with RAS. RET/PTC (1 and 3) was significantly associated with extrathyroid extension (ET) and lymph node metastasis (es) (LNM). This association was found in the adult group. There were no associations of BRAF or RAS mutations with ET or LNM. A 3-year median follow up was available for 90 patients. RET/PTC 1 and 3 was associated with short-term disease dissemination (cervical lymph node recurrences and distant metastases) in young adults (p=0.001). Persistent illness was more prevalent in patients with (15%) than in patients without (7%) genetic alterations.

CONCLUSION

PTCs in young patients display a low prevalence of the already identified oncogenic alterations. The increasing prevalence with age is mainly due to V600E BRAF mutation. There is no relation between tumor aggressiveness and BRAF mutation. There is a relation between the presence of RET/PTC (1 and 3) and the histological and clinical short-term aggressiveness of PTC in the population of young adults. Such a relation is not found in children and adolescents.

Thyroid carcinoma in children and adolescents-systematic review of the literature

Thyroid cancer in children and adolescents is usually a major concern for physicians, patients, and parents. Controversies regarding the aggressiveness of the clinical presentation and the ideal therapeutic approach remain among the scientific community. The current recommendations and staging systems are based on data generated by studies in adults, and this might lead to overtreating in some cases as well as undertreating in others. Understanding the differences in the biology, clinical course, and outcomes in this population is crucial for therapeutic decisions. This paper evaluates the biology, clinical presentation, recurrences, and overall survival as well as the staging systems in children and adolescents with differentiated thyroid cancer.

Signal transduction in the human thyrocyte and its perversion in thyroid tumors

The study of normal signal transduction pathways regulating the proliferation and differentiation of a cell type allows to predict and to understand the perversions of these pathways which lead to tumorigenesis. In the case of the human thyroid cell, three cascades are mostly involved in tumorigenesis: The pathways and genetic events affecting them are described. Caveats in the use of models and the interpretation of results are formulated and the still pending questions are outlined.

Chromosomal aberrations in thyroid follicular-cell neoplasia: in the search of novel oncogenes and tumour suppressor genes

Thyroid cancer derived from the follicular cell is characterised by specific gene alterations that are closely linked to the various pathological types comprising papillary, follicular and anaplastic thyroid cancer. However, the correlation between molecular biology and pathology is not absolute, since about 30% of cases do not harbour the typical gene alterations. This situation, coupled with the demonstration of genetic heterogeneity in thyroid cancer, is a strong motivation for the search of novel gene alterations. Chromosomal aberrations are a good starting point to initiate this search and therefore the current knowledge on chromosomal alterations in thyroid follicular-cell neoplasia is reviewed in this article. An overview on molecular cytogenetic approaches for this strategy is also provided. The identification of novel genetic markers in thyroid cancer will be further improved by integrative approaches combining data from genomic and expression analyses with clinical data. This approach is powerful to identify genetic markers as well as new therapeutic targets in follicular-cell thyroid cancer.

Mechanisms of chromosomal rearrangements in solid tumors: the model of papillary thyroid carcinoma

Thyroid cancer, and its most common type, papillary carcinoma, frequently have chromosomal rearrangements and therefore represent a good model for the understanding of mechanisms of chromosomal rearrangements in solid tumors. Several types of rearrangement known to occur in thyroid cancer, including RET/PTC, NTRK1 and BRAF/AKAP9, are more common in radiation-associated thyroid tumors and RET/PTC can be induced experimentally by exposing human thyroid cells to ionizing radiation. In this review, the molecular mechanisms of generation of RET/PTC and other chromosomal rearrangements are discussed, with the emphasis on the role of nuclear architecture and interphase gene proximity in the generation of intrachromosomal rearrangements in thyroid cells.

Molecular rearrangements in papillary thyroid carcinomas

Papillary thyroid cancer is unusual among epithelial malignancies in that it is associated with a number of chromosomal rearrangements. The most common of these is the Ret oncogene, normally silent in the follicular cell, but which has been shown to be rearranged to the promoter region of a variety of different genes, all of which are constituently expressed in the thyroid follicular cell. It has been suggested that chromosomes in the thyroid cell are arranged within the nucleus in such a way as to predispose the cell to inappropriate fusion in the advent of DNA double-strand breakage. The presence of tumour specific fusion genes, and their transcribed proteins, presents a possible therapeutic target for thyroid cancer, but the relative contribution of the gene rearrangement in the growth and development of the tumour will need careful evaluation before clinical studies could take place.

Oncoprotein signaling mediates tumor-specific inflammation and enhances tumor progression

The RET/PTC3 (RP3) fusion protein is an oncogene expressed during the development of thyroid cancer and in thyroid epithelial cells of patients with Hashimoto's thyroiditis. RP3 has two immunological properties: 1) it encodes a chimeric protein including peptides that may be targets of antitumor immune responses and 2) it is a tyrosine kinase that can activate NF-kappaB transcriptional programs, induce secretion of proinflammatory mediators, and stimulate innate immunity. To distinguish the antigenic properties of the RP3 oncoprotein from its signaling function, a transplantable tumor system was developed. Tumors expressing the functional, but not mutant, form of RP3 show enhanced infiltration of CD8(+) lymphocytes, myeloid-derived CD11b(+)Gr1(+) cells, and enhanced growth in immunocompetent mice. In contrast, RP3 signaling mutant-expressing tumors maintained enhanced infiltration of CD8(+) lymphocytes did not enhance recruitment of CD11b(+)Gr1(+) cells and showed a decreased tumor incidence. These results implicate a role for RP3 function in enhancing a tumor-suppressive innate inflammatory response. These experiments support a mechanism whereby oncogenes can directly recruit and activate innate and adaptive immune cells, resulting in enhanced tumor progression.

Creation and characterization of a doxycycline-inducible mouse model of thyroid-targeted RET/PTC1 oncogene and luciferase reporter gene coexpression

BACKGROUND

RET/PTC1 chromosomal rearrangement is associated with papillary thyroid carcinoma formation in children exposed to ionizing radiation. We previously created a transgenic mouse model with thyroid-targeted constitutive RET/PTC1 expression and demonstrated papillary thyroid carcinoma formation.

OBJECTIVE

In this study, we aimed to create a doxycycline-inducible mouse model of thyroid RET/PTC1 and luciferase reporter gene coexpression to allow for noninvasive monitoring of transgene expression in mice of various ages and timepoints after induction.

DESIGN

Transgenic mice carrying the rtTA gene driven by the thyroglobulin promoter were generated, and crossed with responder mice carrying RET/PTC1 and firefly luciferase genes under control of a bidirectional tetracycline response element.

MAIN OUTCOMES

Most bitransgenic mice had thyroid-targeted, doxycycline-independent transgene expression. Only one line had thyroid-targeted, doxycycline-regulated RET/PTC1 and luciferase coexpression, in which doxycycline induction of RET/PTC1 led to Erk phosphorylation and reduced expression of the sodium/iodide symporter (NIS). However, thyroid lesions were not found in any bitransgenic mice examined.

CONCLUSIONS

We found that acute RET/PTC1 expression can activate the MEK/Erk pathway and downregulate NIS expression in the mouse thyroid gland. However, a higher level of RET/PTC1 is likely necessary for tumor formation. Thyroid luciferase induction was detectable noninvasively using IVIS in vivo imaging.

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.

Conditional BRAFV600E expression induces DNA synthesis, apoptosis, dedifferentiation, and chromosomal instability in thyroid PCCL3 cells

The activating mutation BRAF(T1796A) is the most prevalent genetic alteration in papillary thyroid carcinomas (PTC). It is associated with advanced PTCs, suggesting that this oncoprotein confers thyroid cancers with more aggressive properties. BRAF(T1796A) is also observed in thyroid micropapillary carcinomas and may thus be an early event in tumor development. To explore its biological consequences, we established doxycycline-inducible BRAF(V600E)-expressing clonal lines derived from well-differentiated rat thyroid PCCL3 cells. Expression of BRAF(V600E) did not induce growth in the absence of thyrotropin despite increasing DNA synthesis, which is likely explained because of a concomitant increase in apoptosis. Thyrotropin-dependent cell growth and DNA synthesis were reduced by BRAF(V600E) because of decreased thyrotropin responsiveness associated with inhibition of thyrotropin receptor gene expression. These results are similar to those obtained following conditional expression of RET/PTC. However, in contrast to RET/PTC, BRAF activation did not impair key activation steps distal to the thyrotropin receptor, such as forskolin-induced adenylyl cyclase activity or cyclic AMP-induced DNA synthesis. We reported previously that acute RET/PTC expression in PCCL3 cells did not induce genomic instability. By contrast, induction of BRAF(V600E) expression increased the frequency of micronuclei by both clastogenic and aneugenic events. These data indicate that BRAF(V600E) expression confers thyroid cells with little growth advantage because of concomitant activation of DNA synthesis and apoptosis. However, in contrast to RET/PTC, BRAF(V600E) may facilitate the acquisition of secondary genetic events through induction of genomic instability, which may account for its aggressive properties.

BRAF mutations are uncommon in papillary thyroid cancer of young patients

Mortality is low for young patients (younger than 21 years) with papillary thyroid cancer (PTC), and different mutations might contribute to this. Previous studies detected ret/PTC rearrangements more frequently in PTC from children than adults, and recent reports describe a high incidence of BRAF T1796A transversion in adult PTC. However, BRAF mutations have not been adequately studied in PTC from young patients. We amplified and sequenced segments of the BRAF gene spanning the T1796A transversion site in 14 PTC from patients 10-21 years of age (mean, 17.5 +/- 3.5 years). The PTC (7 = class 1; 5 = class 2; 1 = class 3) ranged from 0.7-2.9 cm in diameter (mean, 1.4 +/- 0.75 cm). None of them (0/14) contained BRAF T1796A and none recurred (mean follow-up, 66 +/- 40 months). This incidence of BRAF T1796A is significantly less than that reported for adult PTC (270/699, 38.6%, p = 0.0015) in several series. None of our PTC (0/10) contained ras mutations, but 7/12 (58%) contained ret/PTC rearrangements. We conclude that BRAF mutations are less common in PTC from young patients, and ret/PTC rearrangements were the most common mutation found in these childhood PTC.

Molecular events in follicular thyroid tumors

Knowledge of the molecular events that govern human thyroid tumorigenesis has grown considerably in the past ten years. Key genetic alterations and new oncogenic pathways have been identified. Molecular genetic aberrations in thyroid carcinomas bear noteworthy resemblance to those in acute myelogenous leukemias. Thyroid carcinomas and myeloid leukemias both possess transcription factor gene rearrangements-PPARgamma-related translocations in thyroid carcinoma and RARalpha-related and CBF-related translocations (amongst others) in myeloid leukemia. PPARgamma and RARalpha are closely related members ofthe same nuclear receptor subfamily, and the PML-RARalpha and PAX8-PPARgamma fusion proteins both function as dominant negative inhibitors of their wild-type parent proteins. Thyroid carcinomas and myeloid leukemias also both harbor NRAS mutations (15-25% of both cancers) and receptor tyrosine kinase mutations--RET mutations in thyroid carcinomas and FLT3 mutations in myeloid leukemias. The NRAS and tyrosine receptor kinase mutations are not observed in the same thyroid carcinoma or leukemia patients, suggesting that multiple initiating pathways exist in both. Lastly, thyroid carcinomas and myeloid leukemias possess p53 mutations at relatively low frequency (10-15%) in patients who tend to be older and have more aggressive, therapy resistant disease. Such parallels are unlikely to occur by chance alone and argue that common mechanisms underlie these diverse epithelial and hematologic cancers. The comparison of thyroid carcinomas and myeloid leukemias may highlight areas of thyroid cancer investigation worthy of further focus. For example, few collaborating mutations have been defined in thyroid carcinomas even though they play a clear role in myeloid leukemias, as exemplified by RARalpha rearrangements and FLT3 mutations that together dictate the promyleocytic leukemia phenotype. Functional interactions between collaborating mutations are possible at multiple levels, and it is tempting to speculate that some thyroid carcinomas might develop through an unique combination or co-activation of RET and RAS and/or RET and PPARgamma (and/or other) signaling systems. In fact, the ELE1-RET (PTC3) fusion protein contains the ELE1 nuclear receptor co-activator domain and it appears to physically associate with and inhibit wild-type PPARgamma in some papillary carcinomas. The similarities of the fusion proteins in thyroid carcinoma and myeloid leukemia suggest that a more directed search for fusion genes in non-thyroid carcinomas is warranted. In fact, novel fusion genes have been identified recently in aggressive midline, secretory breast, and renal cell carcinomas, although the epithelial nature of the latter is not well-documented. Interestingly, these cancers all tend to present more frequently in adolescence and young adulthood in a manner similar to thyroid and myeloid malignancies that have fusion genes. The analyses of cancers that present earlier in life may enhance fusion gene recognition in other carcinoma types. Definition and biologic characterization of the precursor cells that give rise to thyroid carcinoma will also be important. Myeloid leukemias are thought to arise from stem/progenitor cells that acquire disturbed self-renewal and differentiation capacities but retain characteristics of the myeloid lineages. Although the presence of comparable stem/progenitor cells in the thyroid are not defined, distinct thyroid cancer lineages and patterns of differentiation exist and candidate stem/progenitor cells such as the p63-immunoreactive solid cell nests are apparent. A last important area is development of molecular-based therapies for thyroid carcinoma patients resistant to standard radio-iodine treatment. Treatments for such cancers are limited and pathways defined by thyroid cancer mutations are prime targets for pharmacologic interventions with molecular inhibitors. Tyrosine kinase inhibitors and nuclear receptor ligands have proven dramatically effective in some myeloid leukemia patients. Various molecular inhibitors are being investigated now in thyroid cancer models. Such developments predict that the thyroid cancer model will continue to provide biologic insights into human carcinoma biology and that improved pathologic diagnosis and treatment for thyroid cancer patients sit on the not too distant horizon.

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.

Prognosis after lymph node recurrence in papillary thyroid carcinoma depends on age

Papillary thyroid carcinoma (PTC) is a malignancy that has good prognosis especially among patients up to 45 years of age; about half of the patients are female and of childbearing age. Lymph node recurrence (LNR) occurs in 10%-14% of patients but is considered to be associated with relatively good prognosis. The purpose of this study was to estimate the association between patient age at primary operation, and the behavior of the disease after LNR. Between 1967 and 1994, 495 patients underwent surgery for primary PTC at the Department of Surgery, Helsinki University Central Hospital. There were 391 (79.0%) women and 104 (21.0%) men with a mean age of 44.5 years (range, 10.8-85.4 years). Fifty-eight patients in whom LNR was the first clinical sign of persistent disease after complete clinical response to primary treatment were included in this series. At the time of primary operation, 37 (64.3%) of the 58 patients who developed LNR were younger than 45 years of age and 21 patients were older. The mean times to LNR in these groups were 42.0 months (range, 3.0-194.5 months) and 49.0 months (range, 3.6-209.0 months) respectively. Carcinoma-specific 5-year survival after LNR was 100% (95% confidence interval [CI] 88.8%-100.0%) in patients ages up to 45 years and 61.1% (40.5%-82.8%) in older patients; 10-year survival rates were 100%, and 41.3% (p < 0.0001), respectively. Relative survival at 10 years was 98.6% for patients ages up to 45 years and 42.6% for older patients (p = 0.0014). Using the Cox model it was shown that development of LNR after primary treatment has an independent highly significant negative effect on survival (p < 0.001) in patients over 45 years of age. Prognosis of PTC even after LNR on patients ages up to 45 years at the time of the primary operation is almost parallel to the normal reference population, but in patients over 45 years of age the prognosis is relatively poor.

Prognostic significance of RET and NTRK1 rearrangements in sporadic papillary thyroid carcinoma

BACKGROUND

The expression of RET/PTC chimeras was demonstrated in 10% to 20% of sporadic papillary thyroid carcinomas (PTCs), whereas rearrangements of NTRK1 were detected less frequently. Some investigators have hypothesized that RET/PTC activation is preferentially associated with slow-growing tumors of low malignancy in elderly patients; other studies support the contrary.

METHODS

Expression analysis of RET and NTRK1 was performed by duplex reverse transcription-polymerase chain reaction in tumor tissues from 119 patients with PTC. Samples with suspected rearrangements were further analyzed for the expression of the hybrid messenger RNAs RET/PTC 1 to RET/PTC 7 and for known NTRK1 chimeras, respectively.

RESULTS

Seventeen of 119 tumors (14.3%) revealed somatic rearrangements of RET; NTRK1-derived hybrids were demonstrated in 15 cases (12.6%). In patients with RET/PTC chimeras, a statistically not significant tendency towards younger age, lower recurrence rate, and improved survival was observed, despite increased incidence of lymph node metastasis. Cumulative survival analysis of NTRK1 rearrangement-positive individuals demonstrated a worse outcome when compared with patients with expression of RET hybrids (P =.055).

CONCLUSIONS

The high incidence of yet uncharacterized NTRK1 hybrid mRNAs in our patient cohort leads to the speculation that activating chromosomal rearrangements of several tyrosine kinase receptors may be a common feature of PTCs and that the expression of distinct chimeras may potentially be of prognostic significance.

Differentiated thyroid cancer: clinical characteristics, treatment, and outcome in patients under 21 years of age who present with distant metastases. A report from the Surgical Discipline Committee of the Children's Cancer Group

BACKGROUND/PURPOSE

Young patients with differentiated thyroid cancer typically present with regional lymph node involvement (60% to 80%), and 10% to 20% have distant metastases. This study characterizes the clinical presentation, treatment, and outcome in patients with differentiated thyroid cancer who were less than 21 years of age at diagnosis and who presented with distant parenchymal metastases.

METHODS

A retrospective, multi-institutional data base that included 327 patients in this age group with differentiated thyroid carcinoma was searched for patients who presented with distant metastases, and 83 cases (25%) were found. The median time to first disease progression was 2.4 years (range, 0.1 to 12.4 years) and the overall median follow-up was 10.9 years (range, 1.0 to 42.1 years).

RESULTS

The median age at diagnosis was 14.6 years (range, 6.6 to 20.8 years); 69% were girls and 92% were white. In 12%, there was a history of prior head and neck irradiation, and 10% of these patients had a family history of carcinoma. Preoperative needle biopsies were performed in 25%. Regional lymph nodes were positive in 90%, and extrathyroidal extension occurred in 48%. The site of distant metastases included the lungs in all patients. Total thyroidectomy, subtotal thyroidectomy, lobectomy, and nodule excision was done in 66%, 24%, 3%, and 8% of patients, respectively. There was no residual cervical disease after surgery in 75%, whereas 14% had microscopic and 11% had gross residual. Histopathologic subtypes included papillary-follicular (48%), papillary (42%), and follicular (10%). The median tumor size was 3.0 cm (range, 0.4 to 11.0 cm). In this group, 100% of patients received adjuvant iodine 131I therapy, and the overall survival rate at 10 years was 100%. The progression-free survival rate was 76% at 5 years and 66% at 10 years from diagnosis.

CONCLUSIONS

A significant number of young patients with thyroid cancer present with distant metastases and will require radioiodine therapy. This should be considered when planning the surgical approach because total or subtotal thyroidectomy facilitates 131I imaging and treatment. Although about one third of these patients will experience relapse or disease progression, the overall mortality rate is low.

Molecular basis of epithelial thyroid tumorigenesis

The results of experiments carried out in different laboratories (including ours) during the last 10 years have enabled us to propose the hypothesis that there are different initiators able to start the epithelial thyroid tumorigenic process via different pathways:--gsp and TSHR genes: at the origin of hyperfunctioning tumors (toxic nodules and adenomas);--ras and probably gsp genes (in a minority of samples): via a vesicular adenoma progressing eventually to a vesicular carcinoma. This could be also the case for ret but only in radiation-associated tumours;--ras, ret, trk and probably gsp and met: starting from small papillary lesions ('spontaneous' or radiation-induced) and progressing to a clinically evident papillary carcinoma;--the p53 gene playing a role only in the final dedifferentiation process. Simultaneous alteration in the same sample of combinations of ras, gsp, ret, trk and TSHR was found in only a minority of the approximately 150 tumours studied. These data suggest an interchangeable role for these genes in the initiation of 'spontaneous' or radiation-associated epithelial thyroid tumorigenesis. The requirement of one of the genes cited above to interact with other genes must not be neglected. Ras is the most frequently altered gene in 'spontaneous' thyroid tumours and ret in radiation-associated thyroid tumours.

Search for NTRK1 proto-oncogene rearrangements in human thyroid tumours originated after therapeutic radiation

Rearrangements of NTRK1 proto-oncogene were detected in 'spontaneous' papillary thyroid carcinomas with a frequency varying from 5 to 25% in different studies. These rearrangements result in the formation of chimaeric genes composed of the tyrosine kinase domain of NTRK1 fused to 5' sequences of different genes. To investigate if the NTRK1 gene plays a role in radiation-induced thyroid carcinogenesis, we looked for the presence of NTRK1-activating rearrangements in 32 human thyroid tumours (16 follicular adenomas, 14 papillary carcinomas and two lymph-node metastases of papillary thyroid carcinomas) from patients who had received external radiation, using the reverse transcription polymerase chain reaction, Southern blot and direct sequencing techniques. These data were compared with those obtained in a series of 28 'spontaneous' benign and malignant thyroid tumours, collected from patients without a history of radiation exposure and four in vitro culture cell lines derived from 'spontaneous' thyroid cancers. Our results concerning the radiation-associated tumours showed that only rearrangements between NTRK1 and TPM3 genes (TRK oncogene) were detected in 2/14 papillary carcinomas and in one lymph-node metastasis of one of these papillary thyroid carcinomas. All the radiation-associated adenomas were negative. In the 'spontaneous' tumours, only one of the 14 papillary carcinomas and one of the four in vitro culture cell lines, derived from a papillary carcinoma, presented a NTRK1 rearrangement also with the TPM3 gene. Twenty-five of this series of radiation-associated tumours were previously studied for the ras and RET/PTC oncogenes. In conclusion, our data: (a) show that the overall frequency of NTRK1 rearrangements is similar between radiation-associated (2/31: 6%) and 'spontaneous' epithelial thyroid tumours (2/32: 6%). The frequency, if we consider exclusively the papillary carcinomas, is in both cases 12%; (b) show that the TRK oncogene plays a role in the development of a minority of radiation-associated papillary thyroid carcinomas but not in adenomas; and (c) confirm that RET/PTC rearrangements are the major genetic alteration associated with ionizing radiation-induced thyroid tumorigenesis.

Thyroid consequences of the Chernobyl nuclear accident

It is well recognized that the use of external irradiation of the head and neck to treat patients with various non-thyroid disorders increases their risk of developing papillary thyroid carcinoma years after radiation exposure. An increased risk of thyroid cancer has also been reported in survivors of the atomic bombs in Japan, as well as in Marshall Island residents exposed to radiation during the testing of hydrogen bombs. More recently, exposure to radioactive fallout as a result of the Chernobyl nuclear reactor accident has clearly caused an enormous increase in the incidence of childhood thyroid carcinoma in Belarus, Ukraine, and, to a lesser extent, in the Russian Federation, starting in 1990. When clinical and epidemiological features of thyroid carcinomas diagnosed in Belarus after the Chernobyl accident are compared with those of naturally occurring thyroid carcinomas in patients of the same age group in Italy and France, it becomes apparent that the post-Chernobyl thyroid carcinomas were much less influenced by gender, virtually always papillary (solid and follicular variants), more aggressive at presentation and more frequently associated with thyroid autoimmunity. Gene mutations involving the RET proto-oncogene, and less frequently TRK, have been shown to be causative events specific for papillary cancer. RET activation was found in nearly 70% of the patients who developed papillary thyroid carcinomas following the Chernobyl accident. In addition to thyroid cancer, radiation-induced thyroid diseases include benign thyroid nodules, hypothyroidism and autoimmune thyroiditis, with or without thyroid insufficiency, as observed in populations after environmental exposure to radioisotopes of iodine and in the survivors of atomic bomb explosions. On this basis, the authors evaluated thyroid autoimmune phenomena in normal children exposed to radiation after the Chernobyl accident. The results demonstrated an increased prevalence of circulating thyroid antibodies not associated with significant thyroid dysfunction. This finding is consistent with the short period of follow-up, but it is highly likely that these children will develop clinical thyroid autoimmune diseases in the future. Therefore, screening programmes for this at-risk population should focus, not only on the detection of thyroid nodules and cancer, but also on the development of thyroid autoimmune diseases.

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.

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.

Rearrangements of RET and NTRK1 tyrosine kinase receptors in papillary thyroid carcinomas

A combined cytogenetic and molecular analysis of thyroid tumours has indicated that these neoplasms might represent a significant model for analysing human epithelial cell multi-step cancerogenesis. Thyroid tumours comprise a broad spectrum of lesions with different phenotypes and variable biological and clinical behaviour. Molecular analysis has detected specific genetic alterations in these different tumour types. In particular, the well-differentiated carcinomas of the papillary type are characterised by the activation of the tyrosine kinase receptors (TKRs) RET and NTRK1 proto-oncogenes. Cytogenetic analysis of these tumours has contributed to defining the chromosomal mechanisms leading to the TKRs' oncogenic activation. The results have shown that, in the majority of the cases, intra-chromosomal inversions of chromosome 10 and of chromosome 1 lead to the formation of RET-derived and NTRK1-derived oncogenes, respectively. Exposure to ionizing radiation is associated with papillary carcinomas, and RET activation has been suggested to be related to this event. All these findings are contributing to the definition of genetic and environmental factors relevant to the pathogenesis of thyroid tumours. Moreover, the molecular characterisation of specific genetic lesions could provide significant information about the association between ionising radiation and RET oncogene activation.

Irradiation and second cancers. The thyroid as a case in point

The thyroid gland is highly sensitive to radiation during childhood: the risk of thyroid tumours is increased for mean doses as low as 100 mGy and for higher doses, the risk increases linearly with the dose. Excess relative risk is important, being 7.7 for 1 Gy delivered to the thyroid gland during childhood. The risk of thyroid tumours is modified by several factors: a) age at exposure: in childhood, the risk decreases with increasing age at exposure and is not significant after 20 years; b) gender: females are two times more likely than males to develop thyroid tumours; c) genetic predisposition due to a defect in DNA repair mechanisms, and dietary and hormonal factors may modify the risk; d) the influence of fractionation and dose rate is not well established. Radioiodine 131 (1311) used for medical purposes has almost no tumourigenic effect on the adult thyroid gland. The consequences of the Chernobyl accident have clearly shown that the risk of thyroid cancer after exposure to 1311 in childhood is important, and that such exposure should be prevented by potassium iodine prophylaxis. RET/PTC rearrangements are found in 60-80% of papillary carcinomas and in 45% of adenomas occurring after radiation exposure. They are found in 5-15% of papillary carcinoma and in no follicular adenomas that occurred in the absence of radiation exposure.

ret rearrangements in Japanese pediatric and adult papillary thyroid cancers

Oncogenic rearrangements of the ret proto-oncogene (ret/PTC) are found uniquely in papillary thyroid carcinomas. The prevalence of ret/PTC in these tumors varies widely, from 0% to 87%, among patient series from different geographical regions. The differences in the prevalence of ret rearrangement have been ascribed to age, genetic, and/or environmental factors. The very high prevalence of ret/PTC in tumors arising in children after the Chernobyl nuclear accident has generated speculation that this oncogene may be an indicator of overt or inadvertent radiation exposure. In Japan, the prevalence of ret activation is reportedly quite low (0% to 9%). Here we examined the frequency of ret rearrangements in papillary carcinomas from Japanese adults and children by means of reverse transcription polymerase chain reaction (RT-PCR) followed by Southern hybridization. Ret rearrangements were detected in 4 of 11 (36%) tumors from the adult population, and in 3 of 10 (30%) pediatric tumors. One child with a solid variant papillary carcinoma had a ret-PTC3 rearrangement, further supporting the association between the solid variant histotype and this particular rearrangement of ret. The present data do not support a major geographic difference in the prevalence of ret/PTC rearrangements in papillary carcinomas between Japan, the United States, and Italy.

Ret oncogene activation in papillary thyroid carcinoma: prevalence and implication on the histological parameters

The Ret proto-oncogene is known to be rearranged in papillary carcinoma of the thyroid. The aim of this study was to investigate the in situ expression of Ret mRNA in thyroid tumors. Formalin-fixed, paraffin-embedded tissue specimens from 45 thyroid lesions were examined by in situ hybridization using manual capillary action technology (MicroProbe Staining System) and a 52-base synthetic biotinylated oligonucleotide probe complementary to the tyrosine-kinase domain of Ret proto-oncogene. The clinicopathological features of these patients with thyroid lesions also were noted. Ret was noted in 17 (43%) of 40 papillary carcinomas. In contrast, none of the three follicular carcinomas, follicular adenoma, nodular hyperplasia, and normal thyroids, showed evidence of Ret mRNA. Our results showed that, in papillary thyroid carcinoma, there is an important role of Ret activation. The Ret staining could be a useful marker for papillary carcinoma.

Differentiated thyroid cancer: determinants of disease progression in patients <21 years of age at diagnosis: a report from the Surgical Discipline Committee of the Children's Cancer Group

OBJECTIVE

This study was done to define the extent of disease and evaluate the effect of staging and treatment variables on progression-free survival in patients with differentiated thyroid carcinoma who were less than 21 years of age at diagnosis.

SUMMARY BACKGROUND DATA

Differentiated thyroid cancer in young patients is associated with early regional lymph node involvement and distant parenchymal metastases. Despite this, the overall long-term survival rate is greater than 90%, which suggests that biologic rather than treatment factors have a greater effect on outcome.

METHODS

Variables analyzed for their impact on progression-free survival in a multi-institutional cohort of 329 patients included age, antecedent thyroid irradiation, extrathyroidal tumor extension, size, nodal involvement, distant metastases, technique of thyroid surgery and lymphatic dissection, initial treatment with 131Iodine, residual cervical disease, and histopathologic subtype. Surgical complications were correlated with the specific procedures completed on the thyroid gland or cervical lymphatics.

RESULTS

The overall progression-free survival rate was 67% (95%, CI: 61%-73%) at 10 years with 2 disease-related deaths. Regional lymph node and distant metastases were present in 74% and 25% of patients, respectively. Progression-free survival was less in younger patients (p = 0.009) and those with residual cervical disease after thyroid surgery (p = 0.001). Permanent hypocalcemia was more frequent after total or subtotal thyroidectomy (p = 0.001) while wound complications increased after radical neck dissections (p < 0.00001).

CONCLUSIONS

The progression-free survival rate was better after a complete resection and in older patients. Progression-free survival rate was the same after lobectomy or more extensive thyroid procedures, but comparison was confounded by the increased use of total or subtotal thyroidectomy in patients with advanced disease. The risk of permanent hypocalcemia increased when total or subtotal thyroidectomy was done. Thyroid lobectomy alone may be appropriate for patients with small localized lesions while total or subtotal thyroidectomy should be considered for more extensive tumors.

Radioiodine-induced thyroid cancer: Studies in the aftermath of the accident at Chernobyl

While a great deal is known about the relationship between external radiation exposure and thyroid cancer, much less is known about the oncogenic effects of internal radiation exposure from isotopes of iodine. The accident at the Chernobyl nuclear power plant released massive quantities of radioiodine isotopes into the atmosphere. The large number of ensuing thyroid cancers in exposed children leaves little doubt that these malignancies have occurred as a result of the accident. However, carefully planned epidemiological studies are needed to confirm that these are due predominantly to I-131 exposure, to determine the dose-response relationship, to monitor for continuing effects and to evaluate other contributing factors. Preliminary evidence indicates that there is a distinct pattern of somatic genetic changes in the thyroid cancers from the Chernobyl area.

The molecular genetics of endocrine tumours

The molecular genetics of endocrine tumours is an area of great interest, due to the heterogeneity of endocrine tumour types, the association of hormone over-production in some cases, and the wide variation in tumour behaviour. Genes implicated fall into functional categories such as oncogenes, in which mutations tend to cause activation, and tumour suppressor genes, in which mutations lead to loss of function. Oncogenes include the receptor tyrosine kinases such as RET, signal transduction proteins and other molecules such as cell cycle regulators and nuclear proteins. Tumour suppressor genes include cell cycle regulators such as p53 and other molecules such as the MEN 1 gene. Loss of heterozygosity studies help in the initial localisation of the latter. Endocrine tumours, as with other tumours, develop as a result of a combination of genetic events, and in the paediatric age group they often occur in the setting of familial cancer syndromes. In this review we analyse the main genetic lesions which have been described in endocrine tumours. There has been an explosion of knowledge in the last 5 years including the identification of the causative genes for MEN 2 and most recently for MEN 1. Characterisation of such genes also aids in the study of somatic mutations in sporadic versions of the same tumour types as occur in the familial syndromes. Identification of a genetic predisposition to a certain tumour has management implications that are still to be clarified in most cases, although in the case of MEN 2 the guidelines for prophylactic thyroidectomy are generally well accepted.