RET proto-oncogene mutations in thyroid carcinomas: clinical relevance

Systemic therapies for medullary thyroid carcinoma: state of the art

Medullary thyroid carcinoma (MTC) is a rare neuroendocrine tumor accounting for less than 5% of all thyroid cancers. An estimated 25% of cases are familial secondary to a germline mutation on the rearranged during transfection proto-oncogene (RET); this gene can be present as a somatic mutation in approximately 40%-60% of sporadic MTC tumors. There is an existing genotype-phenotype correlation in the clinical behavior of MTC, with the RET M918T variant associated with aggressive disease. The current systemic treatment profile for progressive metastatic MTC involves antiangiogenics multikinase inhibitors (MKI), specifically cabozantinib and vandetanib, and high-specific RET inhibitor therapy. Decisions on the timing of systemic therapy initiation in this population should involve multidisciplinary care and individualization on a case-by-case scenario; a comprehensive evaluation of performance status, tumor burden, progression rate, medical comorbidities, possible medication interactions, and goals of care must be considered in a patient-centered approach. This review summarizes the evidence on the safety, efficacy, and limitations of systemic therapies for MTC; the aim is to empower clinicians with the knowledge to optimally manage patients with advanced, progressive, or metastatic MTC.

The Difference in Clinical Behavior of Gene Fusions Involving RET/PTC Fusions and THADA/IGF2BP3 Fusions in Thyroid Nodules

BACKGROUND

Molecular testing has been used as an adjunct to morphological evaluation in the workup of thyroid nodules. This study investigated the impact of two gene fusions, RET/PTC and THADA/IGF2BP3, that have been described as oncogenic events in thyroid neoplasms.

METHODS

We performed a retrospective, single-centered study at a McGill University teaching hospital in Montreal, Canada, from January 2016 to August 2021. We included patients who underwent surgery for thyroid nodules that pre-operatively underwent molecular testing showing either RET/PTC or THADA/IGF2BP3 gene fusion.

RESULTS

This study included 697 consecutive operated thyroid nodules assessed using molecular testing, of which five had the RET/PTC fusion and seven had the THADA/IGF2BP3 fusion. Of the five nodules in the RET/PTC group, 100% were malignant and presented as Bethesda V/VI. Eighty percent (4/5) were found to have lymph node metastasis. Twenty percent (1/5) had extrathyroidal extensions. Sixty percent (3/5) were a diffuse sclerosing variant of papillary thyroid carcinoma, and the rest were the classical variant. Of the seven THADA/IGF2BP3 nodules, all presented as Bethesda III/IV and 71.4% (5/7) were malignant based on the final pathology analysis, and 28.6% (2/7) were NIFTP. All the THADA/IGF2BP3 fusion malignancies were a follicular variant of papillary thyroid carcinoma. None had lymph node metastasis or displayed extrathyroidal extensions.

CONCLUSIONS

RET/PTC nodules presented as Bethesda V/VI and potentially had more aggressive features, whereas THADA/IGF2BP3 nodules presented as Bethesda III/IV and had more indolent behavior. This understanding may allow clinicians to develop more targeted treatment plans, such as the extent of surgery and adjuvant radioactive iodine treatment.

Preclinical Evaluation of Novel Tyrosine-Kinase Inhibitors in Medullary Thyroid Cancer

Simple Summary

Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor arising from parafollicular calcitonin-secreting C cells of the thyroid. Most of the patients affected by MTC, especially the familial form, harbor a mutation of the RET proto-oncogene. In patients with advanced disease, medical therapy is represented by two tyrosine-kinase inhibitors: cabozantinib and vandetanib. However, their usage is limited by several adverse events and drug-resistance onset. The aim of this preclinical study was to evaluate the antitumor activity of novel molecules for the therapy of MTC: SU5402, an inhibitor of the fibroblast growth factor receptor type 1 (FGFR-1) and vascular endothelial growth factor receptor (VEGFR)-2; sulfatinib, a multi-target kinase inhibitor selective for FGFR-1 and the VEGFR-1, -2, and -3; SPP86, a RET-specific inhibitor. Our results suggest a potential role in targeting the FGFR and VEGFR signaling pathways as an alternative strategy for resistant tumors and a significative antitumor activity of this new RET-specific inhibitor.

Abstract

Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor arising from parafollicular C cells of the thyroid gland. In this preclinical study, we tested three tyrosine-kinase inhibitors (TKIs): SU5402, a selective inhibitor of fibroblast growth factor receptor (FGFR)-1 and vascular endothelial growth factor receptor (VEGFR)-2; sulfatinib, an inhibitor of FGFR-1 and VEGFR-1, -2, -3; and SPP86, a RET-specific inhibitor. The effects of these compounds were evaluated in vitro in two human MTC cell lines (TT and MZ-CRC-1), and in vivo using xenografts of MTC cells in zebrafish embryos. SU5402, sulfatinib and SPP86 decreased cell viability. Sulfatinib and SPP86 significantly induced apoptosis in both cell lines. Sulfatinib and SPP86 inhibited the migration of TT and MZCRC-1 cells, while SU5402 was able to inhibit migration only in TT cells. In vivo we observed a significant reduction in TT cell-induced angiogenesis in zebrafish embryos after incubation with sulfatinib and SPP86. In conclusion, sulfatinib and SPP86 displayed a relevant antitumor activity both in vitro and in vivo. Moreover, this work suggests the potential utility of targeting FGFR and VEGFR signaling pathways as an alternative therapy for MTC.

Papillary Thyroid Carcinoma: Current Position in Epidemiology, Genomics, and Classification

Papillary thyroid carcinoma is the most common type of thyroid malignancy both in adults and pediatric population. Since the 1980s, there are changes in criteria in labelling thyroid lesions as "papillary thyroid carcinomas." Radiation exposure is a well-established risk factor for papillary thyroid carcinoma. Other environmental risk factors include dietary iodine, obesity, hormones, and environmental pollutants. Papillary thyroid carcinomas could occur in familial settings, and 5% of these familial cases have well-studied driver germline mutations. In sporadic papillary thyroid carcinoma, BRAF mutation is common and is associated with clinicopathologic and prognostic markers. The mutation could aid in the clinical diagnosis of papillary thyroid carcinoma. Globally, thyroid cancer is among the top ten commonest cancer in females. In both adult and pediatric populations, there are variations of prevalence of thyroid cancer and rising incidence rates of thyroid cancer worldwide. The increase of thyroid cancer incidence was almost entirely due to the increase of papillary thyroid carcinoma. The reasons behind the increase are complex, multifactorial, and incompletely understood. The most obvious reasons are increased use of diagnostic entities, change in classification of thyroid neoplasms, as well as factors such as obesity, environmental risk factors, and radiation. The prognosis of the patients with papillary thyroid carcinoma is generally good after treatment. Nevertheless, cancer recurrence and comorbidity of second primary cancer may occur, and it is important to have awareness of the clinical, pathological, and molecular parameters of papillary thyroid carcinoma.

Long-term follow-up of differentiated thyroid carcinoma in children and adolescents

Objectives The aims were to analyze the clinical features, response to treatment, prognostic factors and long-term follow-up of children and adolescents with differentiated thyroid carcinoma (DTC). Methods Eighty patients with DTC were studied retrospectively. All underwent total or near-total thyroidectomy, and in 75 cases, ablative iodine therapy was recommended. Patients were assessed periodically by tests for serum thyroglobulin levels and whole-body iodine scans. Age, gender, initial clinical presentation, histology, tumor stage, postoperative complications, radioiodine treatment protocol, treatment response, thyroglobulin (Tg), recurrence and long-term disease progression were evaluated. Results Seventy patients completed >2 years of follow-up (23 males, 47 females; median age: 14 years; range: 3-18 years). Sixty-two patients showed papillary DTC and eight, follicular DTC. Sixty-five percent presented nodal metastasis and 16%, pulmonary metastasis at diagnosis. Six months after first radioiodine treatment, 36.2% of patients were free of disease. Seven recurrences were documented. At the end of follow-up, overall survival was 100%, and 87.2% of patients were in complete remission. Nine patients had persistent disease. We found a significant association between stage 4 and persistent disease. Hundred percent of patients with negative Tg values at 6 months posttreatment were documented free of disease at the end of the follow-up. The analysis of disease-free survival based on radioiodine treatment protocols used showed no statistically significant differences. Conclusions DTC in children and adolescents is frequently associated with presence of advanced disease at diagnosis. Despite this, complete remission was documented after treatment in most cases, with a good prognosis in the long-term follow-up. Negative posttreatment thyroglobulin and stage 4 at diagnosis were significant prognostic variables.

Classical point mutations of RET, BRAF and RAS oncogenes are not shared in papillary and medullary thyroid cancer occurring simultaneously in the same gland

BACKGROUND

Papillary (PTC) and medullary (MTC) thyroid carcinomas represent two distinct entities, but quite frequently, they may occur simultaneously.

AIM

To provide genetic analysis of PTC and MTC occurring in the same patient (PTC/MTC) to elucidate their origin.

METHODS

Sequencing analysis of RAS, BRAF and RET oncogenes hot spots mutations in tumoral and normal tissues of 24 PTC/MTC patients.

RESULTS

Two of 24 patients (8.3 %) were affected by familial MTC (FMTC) harboring RET germline mutations in all tissues. Eight of 22 (36.4 %) sporadic cases did not show any somatic mutation in the three tissue components. Considering the MTC component, 10/22 (45.4 %) patients did not show any somatic mutation, 7 of 22 (31.8 %) harbored the M918T RET somatic mutation and 4/22 (18.2 %) presented mutations in the H-RAS gene. In an additional case (1/22, 4.6 %), H-RAS and RET mutations were simultaneously present. Considering the PTC component, 1 of 24 (4.2 %) patients harbored the V600E BRAF mutation, 1 of 24 (4.2 %) the T58A H-RAS mutation and 1 of 24 (4.2 %) the M1T K-RAS mutation, while the remaining PTC cases did not show any somatic mutation. In one case, the MTC harbored a RET mutation and the PTC a BRAF mutation. None of the mutations found were present in both tumors.

CONCLUSIONS

To our knowledge, this is the first study analyzing a possible involvement of RET, BRAF and RAS oncogene mutations in PTC/MTC. These data clearly suggest that the classical activating mutations of the oncogenes commonly involved in the pathogenesis of PTC and MTC may not be responsible for their simultaneous occurrence.

Oncocytic Variant of Medullary Thyroid Carcinoma: A Rare Case of Sporadic Multifocal and Bilateral RET Wild-Type Neoplasm with Revision of the Literature

Oncocytic variant of medullary thyroid carcinoma (OV-MTC) is a very unusual entity, up to date only 17 cases have been reported in the literature. MTC is a neuro-endocrine malignancy arising from the para-follicular C cells of the thyroid gland. It generally has a slight female predominance and appears as a single lesion. However in the Multiple Endocrine Neoplasia Syndrome 2, linked to the point mutation of RET oncogene, multifocal MTCs may also occur. Herein, we report the case of a 75 years old man with a rare form of sporadic multifocal and bilateral OV-MTC expressing wild-type RET gene. The histological and molecular features of this rare entity are presented and discussed with revision of the pertinent literature.

Management of Differentiated Thyroid Cancer in Children: Focus on the American Thyroid Association Pediatric Guidelines

First introduced in 1946, radioactive iodine (I-131) produces short-range beta radiation with a half-life of 8 days. The physical properties of I-131 combined with the high degree of uptake in the differentiated thyroid cancers (DTCs) led to the use of I-131 as a therapeutic agent for DTC in adults. There are two indications for the potential use of I-131 therapy in pediatric thyroid disorders: nonsurgical treatment of hyperthyroidism owing to Graves' disease and the treatment of children with intermediate- and high-risk DTC. However, children are not just miniature adults. Not only are children and the pediatric thyroid gland more sensitive to radiation than adults but also the biologic behavior of DTC differs between children and adults as well. As opposed to adults, children with DTC typically present with advanced disease at diagnosis; yet, they respond rapidly to therapy and have an excellent prognosis that is significantly better than that in adult counterparts with advanced disease. Unfortunately, there are also higher rates of local and distant disease recurrence in children with DTC compared with adults, mandating lifelong surveillance. Further, children have a longer life expectancy during which the adverse effects of I-131 therapy may become manifest. Recognizing the differences between adults and children with DTC, the American Thyroid Association commissioned a task force of experts who developed and recently published a guideline to address the unique issues related to the management of thyroid nodules and DTC in children. This article reviews the epidemiology, diagnosis, staging, treatment, therapy-related effects, and suggestions for surveillance in children with DTC, focusing not only on the differences between adults and children with this disease but also on the latest recommendations from the inaugural pediatric management guidelines of the American Thyroid Association.

The influence of gender, age, and RET polymorphisms on C-cell hyperplasia and medullary thyroid carcinoma

BACKGROUND

RET germline mutations predispose to the development of hereditary medullary thyroid carcinoma (hMTC). Several single nucleotide polymorphisms (SNPs) are described associated with sporadic MTC (sMTC). However, the findings regarding their influence on the clinical course and biological behavior of this disorder are discordant. To clarify the contradictory findings, we studied the association of certain SNPs considering age, gender, and histopathology in a large Austrian cohort with C-cell hyperplasia (CCH) and MTC.

METHODS

Genotyping of SNPs located in RET codons 691, 769, 836, and 904 from 199 patients with MTC and CCH (basal calcitonin > 10 pg/mL, pentagastrin stimulated > 100 pg/mL) was performed, and the results were analyzed considering gender, age at diagnosis, and histopathology.

RESULTS

No significant difference of SNP frequencies was found in the study patients versus normal controls. In sMTC and sporadic CCH (sCCH) no significant association of SNP frequency with the age at diagnosis was found. In patients with sporadic C-cell disease (sCCH and sMTC), 3.7 times more males than females suffered synchronously from papillary or follicular thyroid cancer (20/97 [20.6%] males; 3/54 [5.6%] females; p = 0.02). sCCH was revealed more frequently in males (89/97, 91.7%) than in females (27/54, 50%; p = 10(-8)). In contrast to males, the ratio of CCH to total C-cell disease was significantly higher in females with hereditary (26/32, 81%) compared to those with sporadic disease (27/54, 50%; p = 0.006).

CONCLUSIONS

In this study RET SNPs had no clinical impact on the development of sporadic C-cell disease when the age of diagnosis or gender is considered. C-cell disease seems to predispose males to the development of papillary and follicular thyroid cancer. In addition, at least in females with CCH RET germline mutation, screening is recommended even if the family history is negative for MTC.

Differentiated Pediatric Thyroid Cancer: Correlates With Adult Disease, Controversies in Treatment

The biologic behavior of differentiated thyroid cancer can differ between adults and children, especially in those children younger than 10 years of age. Unlike adults, young children typically present with advanced disease at diagnosis. Despite this, children respond rapidly to therapy and have an excellent prognosis that is significantly better than that of their adult counterparts with advanced disease. In contradistinction to adults, children with thyroid cancer also have higher local and distant disease recurrences with progression-free survival of only 70% at 5 years, mandating life-long surveillance. Although thyroid cancer is the most common carcinoma in children, overall incidence is low, a factor that has prevented performance of a controlled, randomized, prospective study to determine the most efficacious treatment regimen in this age group. So, although extensively investigated, treatment of pediatric patients with differentiated thyroid cancer remains controversial. This article reviews the current controversies in the treatment of pediatric differentiated thyroid cancer, focusing on issues of optimal initial and subsequent therapy as well as that of long-term follow-up. Our approach to treatment is presented. In so doing, similarities and differences between adults and children with differentiated thyroid cancer as regards unique considerations in epidemiology, diagnosis, staging, treatment, therapy-related late effects, and disease surveillance are presented. The expanding use of and appropriate roles for thyrogen and fluorine-18-fluorodeoxyglucose positron emission tomography in disease evaluation and surveillance will be addressed.

Carcinoma de tireóide na infância e adolescência

Aproximadamente 10% das neoplasias de tireóide aparecem abaixo dos 21 anos e representam 3% das neoplasias da infância, com predomínio em meninas (2F:1M). São papilíferos em 90% casos e mais freqüentemente bilaterais, multifocais e de maior dimensão. Invasão de cápsula e metástases ganglionar ou pulmonar são mais freqüentes que no adulto. O efeito carcinogênico da radiação é especialmente importante na criança pré-púbere. Em 5% dos casos de PTC existe história familial. Genes como o RET/PTC, RAS e BRAF estão habitualmente envolvidos na gênese do processo. A apresentação clínica pode ser nódulo cervical (90% casos) sem que represente um fator de pior prognóstico. O US e a PAAF são procedimentos diagnósticos valiosos. O tratamento deve ser cirúrgico (tireoidectomia total com esvaziamento ganglionar) seguido de PCI e radioterapia ablativa. A substituição com L-tiroxina deve objetivar a supressão crônica do TSH. O prognóstico ao longo prazo é melhor que no adulto. A quantificação da Tg plasmática também é útil na detecção da doença residual.

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.

Chronic expression of RET/PTC 3 enhances basal and insulin-stimulated PI3 kinase/AKT signaling and increases IRS-2 expression in FRTL-5 thyroid cells

The RET/PTC3 oncogene is a genetically rearranged and constitutively activated tyrosine kinase receptor that is common in papillary thyroid cancer. Because RET/PTC3 is chronically overexpressed in these thyroid cancer cells, and RET/PTC3-expressing tumors are associated with overactivity of tyrosine kinase signaling pathways and a more aggressive clinical course, we questioned whether chronic RET/PTC3 expression enhances cellular responses to thyroid mitogens in vitro. We stably transfected FRTL-5 cells with the RET/PTC3 gene; transfected and control cell lines were cultured without insulin, TSH, or serum. Thymidine incorporation into DNA was enhanced in the RET/PTC3 cells, but transformation was not observed. RET/PTC3 cells demonstrated higher basal and insulin-stimulated levels of activated Akt, both of which were reduced by LY294002, a PI3 kinase inhibitor, but not PD98059, a MEK inhibitor. By contrast, mitogen activated protein kinase (MAP kinase) was only minimally activated in RET/PTC3 cells before and after stimulation. Consistent with preferential activation of PI3 kinase, increased levels of total and phosphorylated IRS2 protein, relative activation of PDK-1, and enhanced IRS2-p85 interactions were identified in RET/PTC3-expressing cells. RET/PTC3 cells were also sensitized to insulin-induced thymidine incorporation; this effect was blocked by PI3 kinase (LY294002) rather than MEK 1/2 (PD98059) inhibitors. In summary, we have demonstrated that RET/PTC3 expression enhances basal and insulin-stimulated DNA synthesis through PI3 kinase, cooperatively activates Akt with insulin via PI3 kinase, and preferentially activates the Akt rather than MAP kinase pathway in FRTL-5 cells.

Prevalence of thyroid cancer in Graves' disease: a retrospective study of a cohort of 103 patients treated surgically

BACKGROUND: Thyroid nodules in patients with Graves' disease (GD) are common, and the incidence of coexisting thyroid carcinoma is a much debated subject, which is addressed in this study. METHODS: In order to determine the incidence rate of coexisting malignancy, a retrospective study was conducted on 103 patients who underwent surgery for GD between 1990 and 2000 at the Cliniques Universitaires Saint-Luc in Brussels, Belgium. The patients were classified into groups. Those in group I had a solitary palpable nodule (4.9%), those in group II multiple palpable nodules (12.6%), group IIIa had nodule(s) revealed by imaging techniques (incidentalomas: 17.5%), and group IIIb had diffuse non-nodular goiter (65%). RESULTS: Patients with nodules (groups I, II, and IIIa) were found to have significantly more thyroid carcinomas than those with diffuse non-nodular goiters (P=0.02), and the rate of malignancy was significantly increased when the nodules were palpable (groups I and II; P=0.03). Eight patients (7.8%) were diagnosed as having coexisting carcinomas, all but one being microcarcinomas. CONCLUSIONS: Well-differentiated papillary carcinomas are found to coexist with GD surgically treated (7.8%) and occur most frequently in GD with palpable nodular lesions (35%). Even though the majority (88%) of coexisting carcinomas are microcarcinomas, the presence of palpable nodules justifies further evaluation and follow-up.

Novel sequence variants of the genes associated with the multiple endocrine neoplasia syndromes 1 and 2. analysis by an "in silico approach."

MEN syndromes (1 and 2) are hereditary tumor syndromes inherited as autosomal dominant traits. The genes that harbor the mutations responsible for the development of these syndromes have been cloned in recent years. In the present study we applied an "in silico" approach to find previously undescribed sequence variants of the RET protooncogene and the MEN1 gene. Sequence comparisons were performed at the National Center for Biotechnology Information Database by the search tool blastn. We found several sequence alterations in both coding and non-coding sequences. The majority of polymorphisms described to date were found by our approach, in addition we observed novel sequence variants of both genes as well. These sequence variants may have both diagnostic and theoretical relevance. In silico strategies may represent new, and potentially effective ways for finding novel sequence variants.

Clinical characteristics and genetic screening of an extended family with MEN2A

MEN-2A is characterized by medullary thyroid carcinoma (MTC) with pheochromocytoma and sometimes parathyroid adenoma. In affected members of the family, the risk of MTC is about 100%. Biochemical screening allows tumors to be detected early but even at this stage treatment is not always curative. Missense mutations in exon 10 and 11 of the RET proto-oncogene are associated with MEN-2A. Early detection of this mutation by DNA analysis allows the identification of the carriers of the gene. We performed genetic screening in 88 members of an extended family with MEN-2A and found 18 members positive for RET mutation (Cys634Gly). Only three of these 18 RET positive cases had a previous diagnosis of medullary cancer and/or pheochromocytoma. Up to now, 12 of the RET positive cases have undergone thyroidectomy. There was extended disease with cervical lymph node metastasis in 6 of them, bilateral medullary microcancer in 3 and c-cell hyperplasia in the remaining 3. Three of the 18 RET positive patients had also pheochromocytoma. Primary hyperparathyroidism was present in only one patient. The mean age of diagnosis of medullary cancer was between 25-50 yr and mean age of death was between 35-95 yr in affected members of the family. The family had many other affected members in other cities in Turkey and in other countries throughout the world from Australia to the Netherlands. So this family is perhaps one of the most extended families with MEN-2A.

Gene expression in papillary thyroid carcinoma reveals highly consistent profiles

Papillary thyroid carcinoma (PTC) is clinically heterogeneous. Apart from an association with ionizing radiation, the etiology and molecular biology of PTC is poorly understood. We used oligo-based DNA arrays to study the expression profiles of eight matched pairs of normal thyroid and PTC tissues. Additional PTC tumors and other tissues were studied by reverse transcriptase-PCR and immunohistochemistry. The PTCs showed concordant expression of many genes and distinct clustered profiles. Genes with increased expression in PTC included many encoding adhesion and extracellular matrix proteins. Expression was increased in 8/8 tumors for 24 genes and in 7/8 tumors for 22 genes. Among these genes were several previously known to be overexpressed in PTC, such as MET, LGALS3, KRT19, DPP4, MDK, TIMP1, and FN1. The numerous additional genes include CITED1, CHI3L1, ODZ1, N33, SFTPB, and SCEL. Reverse transcriptase-PCR showed high expression of CITED1, CHI3L1, ODZ1, and SCEL in 6/6 additional PTCs. Immunohistochemical analysis detected CITED1 and SFTPB in 49/52 and 39/52 PTCs, respectively, but not in follicular thyroid carcinoma and normal thyroid tissue. Genes underexpressed in PTC included tumor suppressors, thyroid function-related proteins, and fatty acid binding proteins. Expression was decreased in 7/8 tumors for eight genes and decreased in 6/8 tumors for 19 genes. We conclude that, despite its clinical heterogeneity, PTC is characterized by consistent and specific molecular changes. These findings reveal clues to the molecular pathways involved in PTC and may provide biomarkers for clinical use.

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.

Genetic markers in thyroid neoplasia

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

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.