BRAF mutations in anaplastic thyroid carcinoma: implications for tumor origin, diagnosis and treatment

Essential genes in thyroid cancers: focus on fascin

Although thyroid cancers are not among common malignancies, they rank as the first prevalent endocrine cancers in human. According to the results of published studies it has been shown the gradual progress from normal to the neoplastic cell in the process of tumor formation is the result of sequential genetic events. Among them we may point the mutations and rearrangements occurred in a group of proto-oncogenes, transcription factors and metastasis elements such as P53, RAS,RET,BRAF, PPARγ and Fascin. In the present article,we reviewed the most important essential genes in thyroid cancers, the role of epithelial mesenchymal transition and Fascin has been highlighted in this paper.

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.

Mutação BRAF em pacientes idosos submetidos à tireoidectomia

OBJETIVO: Avaliar a frequência da mutação V600E do gene BRAF em pacientes com mais de 65 anos de idade submetidos à tireoidectomia, correlacionando sua presença ou ausência com as diferentes lesões histológicas, com as variantes e com fatores prognósticos do carcinoma papilífero. MÉTODOS: Foram avaliados 85 pacientes com mais de 65 anos de idade submetidos à tireoidectomia, analisando a mutação BRAF V600E através de reação de PCR-RT realizada após a extração do DNA dos blocos de parafina. RESULTADOS: Detectou-se ausência ou presença da mutação BRAF V600E em 47 pacientes (55,3%). Entre os 17 carcinomas papilíferos estudados, sete apresentavam a mutação (41,2%). Demonstrou-se associação estatística entre a presença desta mutação e a variante clássica do carcinoma papilífero, além de tendência de associação com o extravasamento tireoideano. CONCLUSÃO: A mutação BRAF nos pacientes idosos também é exclusiva do carcinoma papilífero e tem frequência expressiva. Além disso, está relacionada à variante clássica e, possivelmente, ao extravasamento tireoideano.

Stem cells and cancer stem-like cells in endocrine tissues

Cancer stem-like cells are a subpopulation of self-renewing cells that are more resistant to chemotherapy and radiation therapy than the other surrounding cancer cells. The cancer stem cell model predicts that only a subset of cancer cells possess the ability to self-renew and produce progenitor cells that can reconstitute and sustain tumor growth. Evidence supporting the existence of cancer stem-like cells in the thyroid, pituitary, and in other endocrine tissues is rapidly accumulating. These cells have been studied using specific biomarkers including: CD133, CD44, Nestin, Nanog, and aldehyde dehydrogenase enzyme. Putative cancer stem-like cells can be studied in vitro using serum-free media supplemented with basic fibroblast growth factor and epidermal growth factor grown in low attachment plates or in extracellular matrix leading to sphere formation in vitro. Cancer stem-like cells can also be separated by fluorescent cell sorting and used for in vitro or in vivo studies. Injection of enriched populations of cancer stem-like cells (also referred to as tumor initiating cells) into immunodeficient mice results in growth of xenografts which express cancer stem-like biomarkers. Human cancer stem-like cells have been identified in thyroid cancer cell lines, in primary thyroid cancers, in normal pituitary, and in pituitary tumors. Other recent studies suggest the existence of stem cells and cancer stem-like cells in endocrine tumors of the gastrointestinal tract, pancreas, lungs, adrenal, parathyroid, and skin. New discoveries in this field may lead to more effective therapies for highly aggressive and lethal endocrine cancers.

Differential proteomic and phenotypic behaviour of papillary and anaplastic thyroid cell lines

Thyroid carcinomas account for a minority of all malignant tumours but, after those of the gonads, they represent the most common forms of endocrine cancers. They include several types, among which the papillary thyroid cancer (PTC) and the anaplastic thyroid cancer (ATC) are the best known. The two hystotypes display significant biological and clinical differences: PTC is a well differentiated form of tumour with a high incidence and a good prognosis, while the ATC is less frequent but represents one of the most aggressive endocrine tumours with morphological features of an undifferentiated type. To date, as far as we know, no conclusive studies, useful to design arrays of molecular markers, have been published illustrating the phenotypic and proteomic differences between these two tumours. The aim of this work was to perform a comparative analysis of two thyroid cancer cell lines, derived respectively from papillary (BCPAP) and anaplastic (8505C) thyroid carcinomas. The comparative analysis included cell behaviour assays and proteomic analysis by 2D-PAGE and mass spectrometry. The results have highlighted a new proteomic signature for the anaplastic carcinoma-derived cells, consistent with their high proliferation rate, motility propensity and metabolic shift, in relation to the well-differentiated PTC cells.

Signaling pathways in follicular cell-derived thyroid carcinomas (review)

Thyroid carcinoma is the most common malignant endocrine neoplasia. Differentiated thyroid carcinomas (DTCs) represent more than 90% of all thyroid carcinomas and comprise the papillary and follicular thyroid carcinoma subtypes. Anaplastic thyroid carcinomas correspond to less than 1% of all thyroid tumors and can arise de novo or by dedifferentiation of a differentiated tumor. The etiology of DTCs is not fully understood. Several genetic events have been implicated in thyroid tumorigenesis. Point mutations in the BRAF or RAS genes or rearranged in transformation (RET)/papillary thyroid carcinoma (PTC) gene rearrangements are observed in approximately 70% of papillary cancer cases. Follicular carcinomas commonly harbor RAS mutations and paired box gene 8 (PAX8)-peroxisome proliferator-activated receptor γ (PPARγ) rearrangements. Anaplastic carcinomas may have a wide set of genetic alterations, that include gene effectors in the mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K) and/or β-catenin signaling pathways. These distinct genetic alterations constitutively activate the MAPK, PI3K and β-catenin signaling pathways, which have been implicated in thyroid cancer development and progression. In this context, the evaluation of specific genes, as well as the knowledge of their effects on thyroid carcinogenesis may provide important information on disease presentation, prognosis and therapy, through the development of specific tyrosine kinase targets. In this review, we aimed to present an updated and comprehensive review of the recent advances in the understanding of the genetic basis of follicular cell-derived thyroid carcinomas, as well as the molecular mechanisms involved in tumor development and progression.

BRAF mutations in papillary thyroid carcinoma and emerging targeted therapies (review)

Papillary thyroid carcinoma (PTC) is the most common histotype among the thyroid cancer types. Although PTC is a curable malignancy, many patients relapse after treatment. Thus, there is a need to identify novel factors involved in the pathogenesis of PTC that may be used as targets for new therapies. The MAPK pathway has been implicated in the pathogenesis of PTC. Therefore, in this review, we summarize the role of the BRAF V600E mutation in the development and progression of thyroid cancer. The cinical implication of this molecular abnormality is also discussed. It is evident that the detection of the BRAF V600E mutation is crucial in order to identify novel avenues for thyroid cancer treatment.

Thyroid fine needle aspirate: a post-Bethesda update

The Bethesda system for reporting thyroid cytopathology formulated in 2007 has standardized reporting of thyroid cytology specimens and streamlined management algorithms. Although 3 of the categories (benign, malignant, and nondiagnostic) are standardized and improved, the remaining 3 (follicular lesion of undetermined significance, follicular neoplasm, and suspicious for malignancy) remain fraught with interobserver variability and uncertainty regarding management algorithms. Recent and ongoing morphologic and molecular studies that aim to resolve these issues are summarized.

Anaplastic thyroid carcinoma

Thyroid cancers represent about 1% of all human cancers. Differentiate thyroid carcinomas (DTCs), papillary and follicular cancers, are the most frequent forms, instead Anaplastic Thyroid Carcinoma (ATC) is estimated to comprise 1-2% of thyroid malignancies and it accounts for 14-39% of thyroid cancer deaths. The annual incidence of ATC is about one to two cases/million, with the overall incidence being higher in Europe (and area of endemic goiter) than in USA. ATC has a more complex genotype than DTCs, with chromosomal aberrations present in 85-100% of cases. A small number of gene mutations have been identified, and there appears to be a progression in mutations acquired during dedifferentiation. The mean survival time is around 6 months from diagnosis an outcome that is frequently not altered by treatment. ATC presents with a rapidly growing fixed and hard neck mass, often metastatic local lymph nodes appreciable on examination and/or vocal paralysis. Symptoms may reflect rapid growth of tumor with local invasion and/or compression. The majority of patients with ATC die from aggressive local regional disease, primarily from upper airway respiratory failure. For this reason, aggressive local therapy is indicated in all patients who can tolerate it. Although rarely possible, complete surgical resection gives the best chance of long-term control and improved survival. Therapy options include surgery, external beam radiation therapy, tracheostomy, chemotherapy, and investigational clinical trials. Multimodal or combination therapy should be useful. In fact, surgical debulking of local tumor, combined with external beam radiation therapy and chemotherapy as neoadjuvant (before surgery) or adjuvant (after surgery) therapy, may prevent death from local airway obstruction and as best may slight prolong survival. Investigational clinical trials in phase I or in phase II are actually in running and they include anti-angiogenetic drugs, multi-kinase inhibitor drugs.

Thyroid cancer: pathogenesis and targeted therapy

Therapeutic options for advanced, unresectable radioiodine-resistant thyroid cancers have historically been limited. Recent progress in understanding the pathogenesis of the various subtypes of thyroid cancer has led to increased interest in the development of targeted therapies, with potential strategies including angiogenesis inhibition, inhibition of aberrant intracellular signaling in the MAPK and PI3K/AKT/mTOR pathways, radioimmunotherapy, and redifferentiation agents. On the basis of a recent positive phase III clinical trial, the RET, vascular endothelial growth factor receptor (VEGFR), and epidermal growth factor receptor (EGFR) inhibitor vandetanib has received FDA approval as of April 2011 for use in the treatment of advanced medullary thyroid cancer. Several other recent phase II clinical trials in advanced thyroid cancer have demonstrated significant activity, and multiple other promising therapeutic strategies are in earlier phases of clinical development. The recent progress in targeted therapy is already revolutionizing management paradigms for advanced thyroid cancer, and will likely continue to dramatically expand treatment options in the coming years.

Role of BRAF in thyroid oncogenesis

BRAF, a cytoplasmic serine-threonine protein kinase, plays a critical role in cell signaling as an activator within the mitogen-activated protein kinase (MAPK) pathway. The most common BRAF mutation is the V600E transversion, which causes constitutive kinase activity. This mutation has been found in a multitude of human cancers, including both papillary thyroid cancer (PTC) and papillary-derived anaplastic thyroid cancer (ATC), in which it initiates follicular cell transformation. With such a high frequency of BRAF mutations in PTC (44%) and PTC-derived ATC (24%), research in BRAF(V600E) detection for diagnostic purposes has shown high sensitivity and specificity for tumor cell presence. BRAF(V600E) in PTC has also provided valuable prognostic information, as its presence has been correlated with more aggressive and iodine-resistant phenotypes. Such findings have initiated research in targeting oncogenic BRAF in cancer therapeutics. Although multiple phase II clinical trials in patients with iodine-refractory metastatic PTC have shown significant efficacy for sorafenib, a first-generation BRAF inhibitor, the mechanism by which it mediates its effect remains unclear because of multiple additional kinase targets of sorafenib. Additionally, preclinical and clinical studies investigating combination therapy with agents such as selective (PLX 4032) and potent (BAY 73-4506 and ARQ 736) small-molecule BRAF inhibitors and MAP/extracellular signal-regulated kinase (ERK) kinase inhibitors (AZD6244) hold great promise in the treatment of BRAF(V600E) cancers and may eventually play a powerful role in changing the clinical course of PTC and ATC.

Molecular analysis of thyroid tumors

Thyroid cancer is the most common endocrine malignancy, and its incidence is rising in the USA and other countries. Papillary and follicular thyroid carcinomas are the two most common types of thyroid cancer. Non-overlapping genetic alterations, including BRAF and RAS point mutations, and RET/PTC and PAX8/PPARγ rearrangements, are found in more than 70% of papillary and follicular thyroid carcinomas. These represent the most common genetic alterations in thyroid cancer, as well as molecular markers of diagnostic and prognostic significance. The use of these and other emerging molecular markers will likely improve the diagnosis of malignancy in thyroid nodules as well as facilitate more individualized operative and postoperative management. Herein, we provide a brief overview of the common genetic alterations in papillary and follicular thyroid carcinoma and discuss the diagnostic and prognostic significance thereof.

Molecular genetics and diagnosis of thyroid cancer

Thyroid cancer is a common type of endocrine malignancy, and its incidence has been steadily increasing in many regions of the world. Initiation and progression of thyroid cancer involves multiple genetic and epigenetic alterations, of which mutations leading to the activation of the MAPK and PI3K-AKT signaling pathways are crucial. Common mutations found in thyroid cancer are point mutation of the BRAF and RAS genes as well as RET/PTC and PAX8/PPARγ chromosomal rearrangements. The mutational mechanisms seem to be linked to specific etiologic factors. Chromosomal rearrangements have a strong association with exposure to ionizing radiation and possibly with DNA fragility, whereas point mutations probably arise as a result of chemical mutagenesis. A potential role of dietary iodine excess in the generation of BRAF point mutations has also been proposed. Somatic mutations and other molecular alterations have been recognized as helpful diagnostic and prognostic markers for thyroid cancer and are beginning to be introduced into clinical practice, to offer a valuable tool for the management of patients with thyroid nodules.

Molecular diagnostics of thyroid tumors

CONTEXT

Thyroid cancer is the most common type of endocrine malignancy and its incidence is steadily increasing. Papillary carcinoma and follicular carcinoma are the most common types of thyroid cancer and represent those tumor types for which use of molecular markers for diagnosis and prognostication is of high clinical significance.

OBJECTIVE

To review the most common molecular alterations in thyroid cancer and their diagnostic and prognostic utility.

DATA SOURCES

PubMed (US National Library of Medicine)-available review articles, peer-reviewed original articles, and experience of the author.

CONCLUSIONS

The most common molecular alterations in thyroid cancer include BRAF and RAS point mutations and RET/PTC and PAX8/PPAR γ rearrangements. These nonoverlapping genetic alterations are found in more than 70% of papillary and follicular thyroid carcinomas. These molecular alterations can be detected in surgically resected samples and fine-needle aspiration samples from thyroid nodules and can be of significant diagnostic use. The diagnostic role of BRAF mutations has been studied most extensively, and recent studies also demonstrated a significant diagnostic utility of RAS, RET/PTC, and PAX8/PPAR γ mutations, particularly in thyroid fine-needle aspiration samples with indeterminate cytology. In addition to the diagnostic use, BRAF V600E mutation can also be used for tumor prognostication, as this mutation is associated with higher rate of tumor recurrence and tumor-related mortality. The use of these and other emerging molecular markers is expected to improve significantly the accuracy of cancer diagnosis in thyroid nodules and allow more individualized surgical and postsurgical management of patients with thyroid cancer.

PAX8 immunostaining of anaplastic thyroid carcinoma: a reliable means of discerning thyroid origin for undifferentiated tumors of the head and neck

Anaplastic thyroid carcinoma can be difficult to diagnose because it does not show thyroid differentiation morphologically or immunohistochemically. Depending on the histologic variant, anaplastic thyroid carcinoma may be confused with sarcoma or squamous cell carcinoma of the head and neck. PAX8 is a transcription factor expressed in normal and neoplastic thyroid follicular epithelium and only a few other tissues. This restricted expression suggests that PAX8 staining could be useful when dealing with spindled or squamoid tumors of the neck. The purposes of this study were to determine the frequency of PAX8 staining in anaplastic thyroid carcinoma and to evaluate PAX8 immunohistochemistry as a means of distinguishing its squamoid variant from head and neck squamous cell carcinoma. PAX8 immunohistochemical staining was performed on 34 anaplastic thyroid carcinomas and 118 head and neck squamous cell carcinomas. PAX8 staining was present in 26 (76%) anaplastic thyroid carcinomas including 16 (100%) of 16 squamoid variants, 7 (58%) of 12 giant cell/pleomorphic variants, and 3 (50%) of 6 spindled variants. All head and neck squamous cell carcinomas were negative for PAX8. PAX8 expression is often retained in anaplastic thyroid carcinomas including the squamoid variant, but it is not expressed in head and neck squamous cancers. PAX8 staining is an excellent marker for carcinomas of follicular epithelial origin, including those carcinomas that are undifferentiated in other respects. The tissue specificity of PAX8 expression may be useful in resolving the differential diagnosis of anaplastic thyroid carcinoma such as the distinction between its squamoid variant and squamous cell carcinoma of the head and neck.

Clinicopathological and molecular characterization of nine cases of columnar cell variant of papillary thyroid carcinoma

The majority of papillary thyroid carcinoma is indolent and associated with long-term survival. The columnar cell variant, however, is a rare subtype that is variable in biological behavior; some are clinically aggressive, whereas others are more clinically indolent. Tumor size, tumor circumscription, and encapsulation may influence the behavior of columnar cell carcinomas. Other variables including genetic changes and putative biomarkers associated with malignant growth have not been thoroughly examined in these neoplasms. In this study, nine cases of columnar cell variant of papillary thyroid carcinoma from three institutions were classified as clinically indolent or aggressive based on pathological features, clinical history, and outcome. Indolent tumors were typically small, circumscribed or encapsulated, and from younger female patients, whereas aggressive tumors were large, locally aggressive, associated with regional and distant metastasis, and from older male patients. The missense mutation, V600E in the BRAF oncogene (BRAF(V600E)), was detected in three of nine of cases, of which two were clinically aggressive. Immunohistochemical evaluation of neoplasia-associated markers showed increased nuclear cyclin D1 expression, elevated Ki-67 proliferation indices, and predominantly weak nuclear p53 staining in both indolent and aggressive tumors. Expression of β-catenin was largely restricted to a membranous pattern in both tumor types. Cytoplasmic expression of bcl-2 was overall mildly reduced in indolent neoplasms. Nuclear expression of estrogen and progesterone receptors was increased in both indolent and aggressive neoplasms, but was without sex- or age-related differences; however, whereas progesterone receptor expression was diffuse and strong in clinically indolent carcinomas, its expression was diminished in aggressive neoplasms. Recognition of the clinicopathological characteristics and the molecular and immunophenotypic features of the columnar cell variant of papillary thyroid carcinoma may aid in characterizing neoplasms that behave indolently or aggressively.

Molecular analysis of thyroid tumors

In the recent years, a large number of molecular alterations in thyroid cancer has been discovered and characterized. Some of these markers may have significant diagnostic utility, can be used for tumor prognostication, and serve as potential therapeutic targets. The diagnostic utility of these markers is of particular importance in thyroid fine-needle aspiration samples. Some molecular markers, such as BRAF, offer help in risk stratification and can be potentially used to optimize surgical and postsurgical management of patients with thyroid cancer. This review discusses major molecular alterations known to occur in thyroid cancer, focusing on those markers that have been extensively characterized, carry clinical significance, and are being introduced into pathology practice.

Targeting BRAFV600E with PLX4720 displays potent antimigratory and anti-invasive activity in preclinical models of human thyroid cancer

PURPOSE

B-Raf(V600E) may play a role in the progression from papillary thyroid cancer to anaplastic thyroid cancer (ATC). We tested the effects of a highly selective B-Raf(V600E) inhibitor, PLX4720, on proliferation, migration, and invasion both in human thyroid cancer cell lines (8505c(B-RafV600E) and TPC-1(RET/PTC-1 and wild-type B-Raf)) and in primary human normal thyroid (NT) follicular cells engineered with or without B-Raf(V600E).

EXPERIMENTAL DESIGN

Large-scale genotyping analysis by mass spectrometry was performed in order to analyze >900 gene mutations. Cell proliferation and migration/invasion were performed upon PLX4720 treatment in 8505c, TPC-1, and NT cells. Orthotopic implantation of either 8505c or TPC-1 cells into the thyroid of severe combined immunodeficient mice was performed. Gene validations were performed by quantitative polymerase chain reaction and immunohistochemistry.

RESULTS

We found that PLX4720 reduced in vitro cell proliferation and migration and invasion of 8505c cells, causing early downregulation of genes involved in tumor progression. PLX4720-treated NT cells overexpressing B-Raf(V600E) (heterozygous wild-type B-Raf/B-Raf(V600E)) showed significantly lower cell proliferation, migration, and invasion. PLX4720 treatment did not block cell invasion in TPC-1 cells with wild-type B-Raf, which showed very low and delayed in vivo tumor growth. In vivo, PLX4720 treatment of 8505c orthotopic thyroid tumors inhibited tumor aggressiveness and significantly upregulated the thyroid differentiation markers thyroid transcription factor 1 and paired box gene 8.

CONCLUSIONS

Here, we have shown that PLX4720 preferentially inhibits migration and invasion of B-Raf(V600E) thyroid cancer cells and tumor aggressiveness. Normal thyroid cells were generated to be heterozygous for wild-type B-Raf/B-Raf(V600E), mimicking the condition found in most human thyroid cancers. PLX4720 was effective in reducing cell proliferation, migration, and invasion in this heterozygous model. PLX4720 therapy should be tested and considered for a phase I study for the treatment of patients with B-Raf(V600E) ATC.

Well differentiated follicular thyroid neoplasia: impact of molecular and technological advances on detection, monitoring and treatment

Our understanding of the molecular mechanisms responsible for follicular thyroid cell oncogenesis has been advanced significantly in recent years. Specific genetic alterations and the molecular pathways they affect have been associated with particular histologic subtypes of well-differentiated thyroid cancer and are now being evaluated for their utility as clinical tools with diagnostic, prognostic and even therapeutic relevance. This paper focuses on the most common and clinically relevant genetic alterations shown to be consistently associated with well-differentiated thyroid carcinoma. We review the impact of recent molecular and technological advances on thyroid cancer standard of care and the practice of clinical medicine.

RET rearrangements and BRAF mutation in undifferentiated thyroid carcinomas having papillary carcinoma components

AIMS

To elucidate the genetic background of anaplastic transformation, RET rearrangements and BRAF mutation were studied in composite undifferentiated carcinomas (UCs) of the thyroid, which are UCs having papillary carcinoma (PC) components.

METHODS AND RESULTS

Reverse transcription-polymerase chain reaction (RT-PCR) was performed for RET rearrangements and PCR for BRAF mutation in UC and PC components that were microdissected separately from seven composite UCs. Forty-two thyroid cancers with single component histology (14 UCs and 28 PCs) were also studied in the same manner. RET/PTC1 was undetectable in both components from all seven composite UCs, and RET/PTC3 was identified in both components of one composite UC. BRAF mutation was identified in both components from three composite UCs and only in the PC components from two composite UCs. In contrast, in thyroid carcinomas with single component histology, RET/PTC1 was detected in 11% of PCs and in none of the UCs, and RET/PTC3 was not found in any of the tumours studied. BRAF mutation was identified in 82% of PCs and in 21% of UCs.

CONCLUSIONS

The high frequency of BRAF mutation and the absence of RET rearrangements in UC components from composite UCs supports the hypothesis that UCs may actually represent progressive malignant degeneration of a BRAF-mutated, well-differentiated thyroid carcinoma.

Thyroidectomy with neoadjuvant PLX4720 extends survival and decreases tumor burden in an orthotopic mouse model of anaplastic thyroid cancer

BACKGROUND

B-Raf(V600E) is a frequent mutation in anaplastic thyroid cancers and is a novel therapeutic target. We hypothesized that PLX4720 (an inhibitor of B-Raf(V600E)) and thyroidectomy would extend survival and would decrease tumor burden in a mouse model.

METHODS

Orthotopic anaplastic thyroid tumors were induced in severe combined immunodeficient mice. Mice were treated with PLX4720 or vehicle after 7 days of tumor growth, and thyroidectomy or sham surgery was performed at day 14. The neck space was re-explored, and tumor volume was measured at day 35. Mice were sacrificed when they lost >25% of their initial weight.

RESULTS

All 5 mice that received the vehicle developed cachexia, had invasive tumors (average 61 mm(3))and were sacrificed by day 35. All 6 mice receiving PLX4720 + sham had small tumors (average 1.3 mm(3)) and maintained their weight. Three out of 6 mice receiving PLX4720+thyroidectomy had no evidence of tumor at 35 days; the other 3 mice had small tumors (average 1.4 mm(3)) and showed no signs of metastatic disease. All mice treated with PLX4720 were alive and well-appearing at 50 days.

CONCLUSION

Thyroidectomy with neoadjuvant PLX4720 could be an effective therapeutic strategy for early anaplastic thyroid cancers that harbor the B-Raf(V600E) mutation and are refractory to conventional therapeutic modalities.

Molecular and other novel advances in treatment of metastatic epithelial and medullary thyroid cancers

An understanding of the mutations of the proto-oncogenes and tumor suppressor genes that occur in thyroid cancers should eventually explain the diverse clinical characteristics of these tumors and also direct therapy. Some insights have already emerged in the last decade; some abnormalities in tumor genes are consistently associated with specific clinical and pathologic findings. These genetic abnormalities usually represent somatic mutations in tumors of follicular epithelial origin, as opposed to inherited mutations in medullary thyroid cancers of parafollicular C cells origin because most thyroid tumors are sporadic and not familial. This is different from the multiple endocrine neoplasia syndromes in which the primary tumorigenic gene mutations are inherited. This improved understanding of the molecular basis of these diseases has led to the development of novel targeted therapeutic approaches which will be discussed in this paper.

Surgical implications of B-RafV600E mutation in fine-needle aspiration of thyroid nodules

BACKGROUND

Management of patients with thyroid nodules is based on establishing an accurate diagnosis; however, differentiating benign from malignant lesions preoperatively is not always possible using current cytological techniques. Novel molecular testing on cytological material could lead to clearer treatment algorithms. B-Raf(V600E) mutation is the most common genetic alteration in thyroid cancer, specifically found in papillary thyroid cancer (PTC), and usually reported to be associated with aggressive disease.

DATA SOURCE

A literature search using PubMed identified all the pertinent literature on the identification and utilization of the B-Raf(V600E) mutation in thyroid cancer.

CONCLUSIONS

The utility of using B-Raf mutation testing for nodules with indeterminate cytology is limited since many of those nodules (benign and malignant) do not harbor B-Raf mutations. However, when the pathologist sees cytological features suspicious for PTC, B-Raf(V600E) mutation analysis may enhance the assessment of preoperative risks for PTC, directing a more aggressive initial surgical management when appropriate.

Thyroid cancer and inflammation

Some cancer types are strongly associated with chronic inflammatory or infectious diseases whereas others are not, but an inflammatory component is present in most human neoplastic lesions. This review focuses on various aspects of thyroid cancer and inflammation. The incidence of thyroid cancer, in particular of well-differentiated papillary thyroid carcinomas (PTCs), is increased in autoimmune thyroid diseases such as Hashimoto's thyroiditis. Thyroid cancer often has an inflammatory cell infiltrate, which includes lymphocytes, macrophages, dendritic cells and mast cells, whose role in thyroid cancer is still not completely understood. However, most experimental evidence suggests these cells exert a protumorigenic function. Moreover, oncoproteins typically expressed in human PTCs, such as RET/PTC, RAS, and BRAF, trigger a proinflammatory programme in thyreocytes. These data suggest that inflammatory molecules are promising targets for thyroid cancer therapy.

Thyroid cancer: current molecular perspectives

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

Detectable BRAF mutation in serum DNA samples from patients with papillary thyroid carcinomas

BACKGROUND.: An activating point mutation of the BRAF oncogene results in a V600E amino acid missense mutation found in a majority of papillary thyroid carcinomas (PTC). METHODS.: In this study, 28 matched tumor and serum samples obtained from patients with both benign and malignant thyroid disorders were analyzed for BRAF mutation using a gap-ligase chain reaction technique. RESULTS.: The BRAF mutation was absent in tumor DNA samples obtained from patients with benign adenomas, follicular neoplasms or carcinoma, and thyroid lymphoma. In contrast, 5 of 14 PTC tumors were positive for the BRAF mutation. Moreover, 3 of 14 patients with PTC were positive for BRAF mutation in serum and tumor. Of these 3 patients, 2 had lymph node metastasis and 2 had PTC in background of the Hashimoto's thyroiditis. CONCLUSIONS.: The detection of free circulating mutant BRAF in patients with PTC is possible and future studies are warranted to determine its clinical significance.

Molecular pathogenesis of follicular cell derived thyroid cancers

Thyroid cancers are the most common endocrine malignancy. Radiation exposure, family history of thyroid cancer and some inherited conditions are the most important predisposing factors for the development of thyroid cancer. Three mitogenic signalling pathways have been described in the thyroid cell, which are influenced by various stimulatory and inhibitory hormones, growth factors and neurotransmitters. Various proto-oncogenes and oncogenes like ras, braf, trk, met and RET also play a role in the signal transduction systems. Two theories have been described in thyroid cancer pathogenesis, the foetal cell carcinogenesis theory and the more common, multistep carcinogenesis theory. The multistep carcinogenesis theory is now the accepted model in many human cancers, including thyroid cancer. The early events of tumour formation are the consequence of activation of either various growth factors or the proto-oncogenes like ras, met or ret. This results in the formation of differentiated thyroid cancers like the papillary, follicular or Hurthle cell cancers. The later stages of tumour formation involve further activation of proto-oncogenes and loss or inactivation of tumour suppressor genes like p53. Based on this theory, follicular carcinomas are generated from follicular adenomas and papillary carcinomas from precursor cells generated from thyrocytes. Anaplastic carcinoma may develop from papillary or follicular carcinoma by dedifferentiation. In this review article, we highlight the molecular pathogenesis of thyroid tumours.

Molecular diagnostics and predictors in thyroid cancer

BACKGROUND

The accuracy of cancer detection in thyroid nodules by fine-needle aspiration (FNA) cytology and prognostication of thyroid cancer needs further improvement and can benefit from testing for molecular alterations known to occur in thyroid tumors.

SUMMARY

Recent studies have demonstrated the feasibility of mutation detection in clinical FNA samples from thyroid nodules and their contribution to improving the diagnostic accuracy of FNA cytology. It appears that molecular testing is most beneficial for thyroid FNA samples with indeterminate cytology, where it can resolve the diagnosis in a significant number of cases. In addition to BRAF mutation, which has been studied most extensively, detection of RAS, RET/PTC, and PAX8/PPARgamma mutations also contribute substantially to cancer diagnosis. Some of these molecular markers, particularly BRAF, can also be used for tumor prognostication. In clinical setting, molecular testing of thyroid FNA samples and surgically removed tumors should utilize a restricted number of techniques that provide high accuracy and specificity of mutation detection.

CONCLUSION

Testing for cancer-specific mutations in thyroid FNA samples and surgically removed tumor tissues increases diagnostic accuracy of FNA cytology and offers better prognostication of thyroid cancer.

A novel orthotopic mouse model of human anaplastic thyroid carcinoma

BACKGROUND

Orthotopic mouse models of human cancer represent an important in vivo tool for drug testing and validation. Most of the human thyroid carcinoma cell lines used in orthotopic or subcutaneous models are likely of melanoma and colon cancer. Here, we report and characterize a novel orthotopic model of human thyroid carcinoma using a unique thyroid cancer cell line.

METHODS

We used the cell line 8505c, originated from a thyroid tumor histologically characterized by anaplastic carcinoma cell features. We injected 8505c cells engineered using a green fluorescent protein-positive lentiviral vector orthotopically into the thyroid of severe combined immunodeficient mice.

RESULTS

Orthotopic implantation with the 8505c cells produced thyroid tumors after 5 weeks, showing large neck masses, with histopathologic features of a high-grade neoplasm (anaplasia, necrosis, high mitotic and proliferative indexes, p53 positivity, extrathyroidal invasion, lymph node and distant metastases) and immunoprofile of follicular thyroid cell origin with positivity for thyroid transcription factor-1 and PAX8, and for cytokeratins.

CONCLUSIONS

Here we describe a novel orthotopic thyroid carcinoma model using 8505c cells. This model can prove to be a reliable and useful tool to investigate in vivo biological mechanisms determining thyroid cancer aggressiveness, and to test novel therapeutics for the treatment of refractory or advanced thyroid cancers.

Thiazolidinediones and antiblastics in primary human anaplastic thyroid cancer cells

OBJECTIVE

No study has evaluated the antiproliferative effects of thiazolidinediones and antiblastics in 'primary cultured human anaplastic thyroid cancer cells'.

DESIGN

Primary anaplastic cells proliferation was evaluated after incubation with increasing concentrations of rosiglitazone or pioglitazone or antiblastics (bleomycin, cisplatin, gemcitabine) by a proliferation assay (WST-1-tetrazolium reaction) and cell counting.

MEASUREMENTS AND RESULTS

A reduction of proliferation by thiazolidinediones at 1 h (from the start of tetrazolium reaction) [of 11% and 25%, with rosiglitazone, 10 or 20 (P = 0.0001) microM, respectively; of 7% and 17%, with pioglitazone, 10 or 20 (P = 0.0125) microM, respectively], and at 2 h [of 14% and 24%, with rosiglitazone, 10 (P = 0.0043) or 20 (P < 0.0001) microM, respectively; of 9% and 21%, with pioglitazone, 10 (P = 0.0397) or 20 (P = 0.0001) microM, respectively] was shown. No significant thiazolidinediones effect was observed in normal thyroid follicular cells. Bleomycin, cisplatin and gemcitabine significantly (P < 0.0001) inhibited (> 50%) anaplastic cells proliferation. Cell counting confirmed the above mentioned results. Inhibition of proliferation was similar in tumours with or without (V600E)BRAF mutation, both for thiazolidinediones and antiblastics.

CONCLUSIONS

Thiazolidinediones exert an antiproliferative effect in primary cultured human anaplastic carcinoma cells in vitro, such as antiblastics.

Anaplastic thyroid cancer: molecular pathogenesis and emerging therapies

Anaplastic thyroid cancer (ATC) is a rare malignancy. While external beam radiation therapy has improved locoregional control, the median survival of approximately 4 months has not changed in more than half a century due to uncontrolled systemic metastases. The objective of this study was to review the literature in order to identify potential new strategies for treating this highly lethal cancer. PubMed searches were the principal source of articles reviewed. The molecular pathogenesis of ATC includes mutations in BRAF, RAS, catenin (cadherin-associated protein), beta 1, PIK3CA, TP53, AXIN1, PTEN, and APC genes, and chromosomal abnormalities are common. Several microarray studies have identified genes and pathways preferentially affected, and dysregulated microRNA profiles differ from differentiated thyroid cancers. Numerous proteins involving transcription factors, signaling pathways, mitosis, proliferation, cell cycle, apoptosis, adhesion, migration, epigenetics, and protein degradation are affected. A variety of agents have been successful in controlling ATC cell growth both in vitro and in nude mice xenografts. While many of these new compounds are in cancer clinical trials, there are few studies being conducted in ATC. With the recent increased knowledge of the many critical genes and proteins affected in ATC, and the extensive array of targeted therapies being developed for cancer patients, there are new opportunities to design clinical trials based upon tumor molecular profiling and preclinical studies of potentially synergistic combinatorial novel therapies.

Role of B-Raf(V600E) in differentiated thyroid cancer and preclinical validation of compounds against B-Raf(V600E)

B-Raf(V600E), an oncogenic protein kinase, is the most frequent genetic alteration in papillary thyroid carcinomas (PTC). PTC represents 80-90% of all thyroid cancers and over the past five years, more than 200 manuscripts have been published about the relationship between "B-Raf(V600E) and thyroid cancer". B-Raf(V600E) genetically arises from a transversion point mutation (valine-to-glutamate substitution at amino acid residue-600, V600E) and leads to over activation of the mitogen-activated protein kinases (MAPK) signaling pathway. The MAPK pathway is essential for transmitting proliferation signals generated by cell surface receptors and cytoplasmic signaling elements to the nucleus. In many cancers, including thyroid cancer, B-Raf(V600E) appears to play a crucial role in cell proliferation, survival and de-differentiation. In thyroid cancer, the V600E mutation occurs with greater frequently in aggressive subtypes of PTC, and in individuals that present at advanced stages of disease with extra-thyroidal extension and/or lymph node metastases. B-Raf(V600E) is considered a marker of aggressive disease in both PTC (>1 cm) and micro-PTC (</=1 cm), and interestingly, is associated with both loss of I-131 avidity and PTC recurrence. Though treatment of patients with thyroid cancer is usually successful and most patients are rendered disease-free, to date there are no effective therapies for patients with invasive, non-radioiodine sensitive tumors or metastatic disease. In this article we will review the relation between B-Raf(V600E) and PTC, as well as both non-selective and selective pharmacological agents currently under investigation for treatment of B-Raf(V600E) positive PTC.

Geographical mapping of a multifocal thyroid tumour using genetic alteration analysis & miRNA profiling

Background

Papillary thyroid carcinoma (PTC) frequently presents as multiple tumour-foci within a single thyroid gland or pluriform, with synchronous tumours comprising different histological variants, raising questions regarding its clonality. Among the genetic aberrations described in PTC, the BRAF V600E mutation and ret/PTC activation occur most commonly. Several studies have investigated the genetic alteration status of multifocal thyroid tumours, with discordant results.

To address the question of clonality this study examined disparate geographical and morphological areas from a single PTC (classic PTC, insular and anaplastic foci, and tumour cells adjacent to vascular invasion and lymphocytic infiltrate) for the presence of ret/PTC 1 or BRAF mutations. Moreover, we wanted to investigate the consistency of miRNA signatures within disparate areas of a tumour, and geographical data was further correlated with expression profiles of 330 different miRNAs. Putative miRNA gene targets were predicted for differentially regulated miRNAs and immunohistochemistry was performed on tissue sections in an effort to investigate phenotypic variations in microvascular density (MVD), and cytokeratin and p53 protein expression levels.

Results

All of the morphological areas proved negative for ret/PTC 1 rearrangement. Two distinct foci with classic morphology harboured the BRAF mutation. All other regions, including the insular and anaplastic areas were negative for the mutation.

MiRNA profiles were found to distinguish tumours containing the BRAF mutation from the other tumour types, and to differentiate between the more aggressive insular & anaplastic tumours, and the classic variant. Our data corroborated miRNAs previously discovered in this carcinoma, and additional miRNAs linked to various processes involved in tumour growth and proliferation.

Conclusion

The initial genetic alteration analysis indicated that pluriform PTC did not necessarily evolve from classic PTC progenitor foci. Analysis of miRNA profiles however provided an interesting variation on the clonality question. While hierarchical clustering analysis of miRNA expression supported the hypothesis that discrete areas did not evolve from clonal expansion of tumour cells, it did not exclude the possibility of independent mutational events suggesting both phenomena might occur simultaneously within a tumour to enhance cancer progression in geographical micro-environments within a tumour.

Thyroid carcinoma: molecular pathways and therapeutic targets

Thyroid cancer is the most common malignant tumor of the endocrine system. The most frequent type of thyroid malignancy is papillary carcinoma. These tumors frequently have genetic alterations leading to the activation of the mitogen-activated protein kinase (MAPK) signaling pathway. Most common mutations in papillary carcinomas are point mutations of the BRAF and RAS genes and RET/PTC rearrangement. These genetic alterations are found in >70% of papillary carcinomas and they rarely overlap in the same tumor. Most frequent alterations in follicular carcinomas, the second most common type of thyroid malignancy, include RAS mutations and PAX8-PPARgamma rearrangement. RET point mutations are crucial for the development of medullary thyroid carcinomas. Many of these mutations, particularly those leading to the activation of the MAPK pathway, are being actively explored as therapeutic targets for thyroid cancer. A number of compounds have been studied and showed antitumor effects in preclinical studies and are being tested in ongoing clinical trials.

What is New on Thyroid Cancer Biomarkers

Thyroid cancer harbours in about 5% of thyroid nodules. The majority of them are well-differentiated cancers originating from the follicular epithelium, and are subdivided into papillary and follicular carcinomas. Undifferentiated carcinomas and medullary thyroid carcinomas arising from C cells are less common.

Although most thyroid nodules are benign, distinguishing thyroid cancer from benign lesions is crucial for an appropriate treatment and follow-up. The fine needle aspiration cytology (FNAC) allows the diagnosis of nature of thyroid nodules in the majority of cases. However, FNAC has some limitations, particularly in the presence of follicular lesions which can appear dubious in rare instances even at histology.

In an effort to improve diagnostic accuracy and offer new prognostic criteria, several immunohistochemical and molecular markers have been proposed. However, most of them have to be validated on large series before being used in routine practice.

Molecular biology of thyroid cancer initiation

Thyroid cancers stand out among solid tumours because many of the tumour-initiating genetic events have been identified. Mutations leading to constitutive activation of MAP kinase effectors -the tyrosine receptor kinase RET and the intracellular signalling effectors RAS and BRAF- are essential for the pathogenesis of papillary thyroid carcinoma (PTC). Similarly, there is increasing evidence demonstrating that mutations leading to activation of the phosphatidylinositol 3- kinase (PI3K)/AKT effectors -PTEN and PI3KCa- are essential for the pathogenesis of follicular thyroid carcinoma (FTC). Besides this strong relationship between the histological phenotype and the pathway predominantly activated, the nature of the genetic event seems to determine the biological behaviour of the tumour and the ultimate clinical outcome of the patient. In this review we will summarise and discuss the main genetic events related to thyroid cancer initiation, the contribution of genomics and the convenience of using a new molecular classification of thyroid cancer, complementary to the clinicopathological classification. This may help us to predict more faithfully the clinical outcome of patients with thyroid cancer and to select more appropriately candidates for targeted therapies.

Molecular genetics of thyroid cancer: implications for diagnosis, treatment and prognosis

Thyroid cancer is the most common malignant tumor of the endocrine system and accounts for approximately 1% of all newly diagnosed cancer cases. The most frequent type of thyroid malignancy is papillary carcinoma, which constitutes approximately 80% of all cases. Papillary carcinomas frequently have genetic alterations leading to the activation of the MAPK signal pathway. Those include RET/PTC rearrangement and point mutations of the BRAF and RAS genes. Mutations in these genes are found in over 70% of papillary carcinomas and they rarely overlap in the same tumor. Frequent genetic alterations in follicular carcinomas, the second most common type of thyroid malignancy, include RAS mutations and PAX8-PPAR gamma rearrangement. RET point mutations are crucial for the development of medullary thyroid carcinomas. Many of these mutations, particularly those leading to the activation of the MAPK pathway, are being actively explored as therapeutic targets for thyroid cancer. Detection of these genetic alterations using molecular techniques is important for preoperative fine-needle aspiration diagnosis, prognosis and treatment of thyroid cancer.

BRAF mutation in papillary thyroid cancer: pathogenic role, molecular bases, and clinical implications

In recent years, the T1799A B-type Raf kinase (BRAF) mutation in thyroid cancer has received enthusiastic investigation, and significant progress has been made toward understanding its tumorigenic role and clinical significance. Among various thyroid tumors, this mutation occurs uniquely in papillary thyroid cancer (PTC), the most common endocrine malignancy, and some apparently PTC-derived anaplastic thyroid cancers. Many studies have found this mutation to be associated with those clinicopathological characteristics of PTC that are conventionally known to predict tumor progression and recurrence, including, for example, old patient age, extrathyroidal invasion, lymph node metastasis, and advanced tumor stages. Direct association of BRAF mutation with the clinical progression, recurrence, and treatment failure of PTC has also been demonstrated. The BRAF mutation has even been correlated with PTC recurrence in patients with conventionally low-risk clinicopathological factors. Some molecular mechanisms determining BRAF mutation-promoted progression and the aggressiveness of PTC have recently been uncovered. These include the down-regulation of major tumor suppressor genes and thyroid iodide-metabolizing genes and the up-regulation of cancer-promoting molecules, such as vascular endothelial growth factor, matrix metalloproteinases, nuclear transcription factor kappaB, and c-Met. Thus, BRAF mutation represents a novel indicator of the progression and aggressiveness of PTC. Significant advances have also occurred in the preclinical testing of new therapeutic strategies targeting the MAPK pathway aberrantly activated by BRAF mutation and other related mutations. New mitogen extracellular kinase (MEK) inhibitors developed recently are particularly promising therapeutic agents for thyroid cancer. With these advances, it has become clearer that BRAF mutation will likely have significant impact on the clinical management of PTC.

The prevalence and prognostic value of BRAF mutation in thyroid cancer

OBJECTIVE

To examine the prevalence of BRAF mutation among thyroid cancer histologic subtypes and determine the association of BRAF mutation with indicators of poor prognosis for papillary thyroid cancer and patient outcome.

SUMMARY BACKGROUND DATA

The appropriate extent of surgical treatment, adjuvant therapy and follow-up monitoring for thyroid cancer remains controversial. Advances in the molecular biology of thyroid cancer have helped to identify candidate markers of disease aggressiveness. A commonly found genetic alternation is a point mutation in the BRAF oncogene (BRAF V600E), which is primarily found in papillary thyroid cancer and is associated with more aggressive disease.

METHODS

BRAF V600E mutation status was determined in 347 tumor samples from 314 patients with thyroid cancer (245 with conventional papillary thyroid cancer, 73 with follicular thyroid cancer, and 29 with the follicular variant of papillary thyroid cancer). Univariate and multivariate analyses were performed to determine the association of BRAF V600E with clinicopathologic factors and patient outcome.

RESULTS

: The prevalence of BRAF V600E mutation was higher in conventional papillary thyroid cancer (51.0%) than in follicular variant of papillary thyroid cancer (24.1%) and follicular thyroid cancer (1.4%) (P < 0.0001). In patients with conventional papillary thyroid cancer, BRAF V600E mutation was associated with older age (P = 0.0381), lymph node metastasis (P = 0.0323), distant metastasis (P = 0.045), higher TNM stage (I and II vs. III and IV, P = 0.0389), and recurrent and persistent disease (P = 0.009) with a median follow-up time of 6.0 years. Multivariate analysis showed that BRAF V600E mutation [OR (95% CI) = 4.2 (1.2-14.6)] and lymph node metastasis [OR (95% CI) = 7.75 (2.1-28.5)] were independently associated with recurrent and persistent disease in patients with conventional papillary thyroid cancer.

CONCLUSIONS

BRAF V600E mutation is primarily present in conventional papillary thyroid cancer. It is associated with an aggressive tumor phenotype and higher risk of recurrent and persistent disease in patients with conventional papillary thyroid cancer. Testing for this mutation may be useful for selecting initial therapy and for follow-up monitoring.

Anaplastic carcinoma of the thyroid arising more often from follicular carcinoma than papillary carcinoma

BACKGROUND

Anaplastic thyroid carcinoma (ATC), a rare and highly malignant tumor, has long been thought to arise from well-differentiated carcinoma (WDC) such as follicular thyroid carcinoma (FTC) and papillary thyroid carcinoma (PTC). The purpose of this study was to test this notion by examining whether and, if so, how often ATC harbors the oncogenes that are commonly associated with WDC, such as RAS in FTC and BRAF in PTC.

METHODS

We analyzed the mutation hotspots of BRAF (codon 600) and N-, K-, and H-RAS (codons 12, 13, and 61) in 16 ATCs. We also examined two genes, PIK3CA (exons 9 and 20) and TP53 (exons 5-9), both of which have been reported in ATCs.

RESULTS

The results showed that approximately 31% (5 of 16) of ATCs harbored N-RAS mutation, 6% (1 of 16) had mutated BRAF, and approximately 56% (9 of 16) had mutated TP53. As to the three ATCs that had coexisted PTCs, mutated BRAF was detected in all PTC components but only in one ATC, while mutated PIK3CA was found in only one PTC component but not in the ATC.

CONCLUSION

A number of ATCs arise from WDCs, more often from RAS-mutant tumors than from BRAF-mutant tumors, implying that particular attention should be paid to the WDC harboring RAS mutation.

Diffuse sclerosing variant of papillary thyroid carcinoma: lack of BRAF mutation but occurrence of RET/PTC rearrangements

Diffuse sclerosing variant of papillary thyroid carcinoma (PTC) is a rare tumour with a characteristic morphology as well as a strong preponderance for younger female patients. The T1799A missense mutation in exon 15 of the BRAF gene and RET/PTC rearrangement have been identified as the dominant genetic tumour initiation events in the pathogenesis of PTC leading to a constitutive activation of the RAS-RAF-MAPK pathway. In order to elucidate the pathogenesis of diffuse sclerosing variant of PTC, the prevalence of BRAF mutation and RET/PTC were determined by RT-polymerase chain reaction and DNA-sequence analysis in tumour samples of seven patients with this variant (all female, age range 15-61 years, mean 33.3 years) without prior radiation exposure. None of these cases showed a BRAF mutation. RET/PTC1 (two out of seven) and RET/PTC3 (one out of seven), which have been shown in large PTC series to comprise together more than 90% of RET/PTC types, were found in <50% of the cases investigated. All seven samples expressed the RET tyrosine kinase domain but lacked its extracellular domain potentially suggesting the existence of rare types of RET/PTC rearrangement in the four remained cases of diffuse sclerosing variant of PTC. Regarding this subtype, our study confirmed the paradigm of a mutual exclusivity between RET/PTC and BRAF in PTC. Additionally, this rare variant of papillary thyroid carcinoma may represent a tumour type susceptible to RET-targeted therapies.

Clinical prognosis in BRAF-mutated PTC

BRAF mutation has recently emerged as a potential prognostic marker for papillary thyroid carcinoma (PTC) due to several studies suggesting that it may condition the development of tumors with aggressive behavior. A study of the phenotypes of thyroid follicular cell lines and transgenic mice characterized by targeted expression of BRAF mutation indicates that, at variance with RET/PTC rearrangement, it induces or facilitates genomic instability and higher invasiveness and eventually deeper tumor de-differentiation and more significant suppression of apoptosis. An analysis of differential gene expression of PTCs harboring BRAF mutation versus PTCs characterized by other genetic alterations shows an important impairment of the expression of genes related to intra-thyroidal iodine metabolism machinery, up-regulation of Glut-1 mRNA, methylation-induced gene silencing of tumor suppressor genes and up-regulation of pro-angiogenetic proteins such as VEGF. Correlation of BRAF mutation with PTC clinico-pathological features yields controversial results, with several studies showing the association with unfavourable clinico-pathological qualities, while others do not confirm the findings. This review will summarize the studies in favor of or in contrast with a role of BRAF mutation as a prognostic marker in PTC. We will also indicate what information we still need in order to routinely introduce this indicator in clinical practice.

BRAF V600E mutation in anaplastic thyroid carcinomas and their accompanying differentiated carcinomas

Frequency of a BRAF^V600E mutation in anaplastic thyroid carcinoma, which is thought to be derived mainly from papillary carcinoma by multi-step carcinogenesis, is much lower than that in papillary carcinomas. To clarify this phenomenon, we analysed BRAF^V600E mutation in 20 cases of anaplastic carcinoma and 13 accompanying differentiated carcinomas. Among twenty cases of anaplastic carcinomas, nine and four accompanied papillary and follicular carcinomas, respectively. BRAF^V600E mutation was found in four (20%) cases. BRAF^V600E mutation was found in three of nine (33.3%), none of four and one of seven (14.3%) anaplastic carcinomas with papillary carcinoma, follicular carcinoma and without differentiated components, respectively. All three papillary carcinomas accompanied by anaplastic carcinoma with a BRAF^V600E mutation were also shown to have a BRAF^V600E mutation. In summary, BRAF^V600E mutation was occasionally observed in anaplastic carcinomas with papillary carcinoma, and the low frequency of BRAF^V600E mutation in anaplastic carcinoma was thought to be due to the low frequency of anaplastic carcinomas with papillary carcinoma. These findings raise a question about the classical model of anaplastic transformation and suggest some roles of thyroid cancer stem cells in the generation of anaplastic carcinoma.

Targeting BRAFV600E in thyroid carcinoma: therapeutic implications

B-Raf is an important mediator of cell proliferation and survival signals transduced via the Ras-Raf-MEK-ERK cascade. BRAF mutations have been detected in several tumors, including papillary thyroid carcinoma, but the precise role of B-Raf as a therapeutic target for thyroid carcinoma is still under investigation. We analyzed a panel of 93 specimens and 14 thyroid carcinoma cell lines for the presence of BRAF mutations and activation of the mitogen-activated protein/ERK kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway. We also compared the effect of a B-Raf small inhibitory RNA construct and the B-Raf kinase inhibitor AAL881 on both B-Raf wild-type and mutant thyroid carcinoma cell lines. We found a high prevalence of the T1799A (V600E) mutation in papillary and anaplastic carcinoma specimens and cell lines. There was no difference in patient age, B-Raf expression, Ki67 immunostaining, or clinical stage at presentation between wild-type and BRAF(V600E) specimens. Immunodetection of phosphorylated and total forms of MEK and ERK revealed no difference in their phosphorylation between wild-type and BRAF(V600E) patient specimens or cell lines. Furthermore, a small inhibitory RNA construct targeting the expression of both wild-type B-Raf and B-Raf(V600E) induced a comparable reduction of viability in both wild-type and BRAF(V600E) mutant cancer cells. Interestingly, AAL881 inhibited MEK and ERK phosphorylation and induced apoptosis preferentially in BRAF(V600E)-harboring cells than wild-type ones, possibly because of better inhibitory activity against B-Raf(V600E). We conclude that B-Raf is important for the pathophysiology of thyroid carcinomas irrespective of mutational status. Small molecule inhibitors that selectively target B-Raf(V600E) may provide clinical benefit for patients with thyroid cancer.

RET/PTC rearrangements and BRAF mutations in thyroid tumorigenesis

Thyroid papillary carcinoma is the most common type of endocrine cancer. It is frequently associated with genetic alterations leading to activation of the MAPK signaling pathway. The two most frequently affected genes, BRAF and RET, are activated by either point mutation or as a result of chromosomal rearrangement. These mutations are tumorigenic in thyroid follicular cells and correlate with specific phonotypical features and biological properties of papillary carcinomas, including tumor aggressiveness and response to radioiodine therapy. Molecular inhibitors that block RET/PTC or BRAF kinase activity have shown substantial therapeutic effects in the experimental systems and are currently being tested in clinical trials.