BRAF T1796A transversion mutation in various thyroid neoplasms

BRAF: A Two-Faced Janus

Gain-of-function of V-Raf Murine Sarcoma Viral Oncogene Homolog B (BRAF) is one of the most frequent oncogenic mutations in numerous cancers, including thyroid papillary carcinoma, melanoma, colon, and lung carcinomas, and to a lesser extent, ovarian and glioblastoma multiforme. This mutation aberrantly activates the mitogen-activated protein (MAP) kinase extracellular signal-regulated kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling pathway, thereby eliciting metastatic processes. The relevance of BRAF mutations stems from its prognostic value and, equally important, from its relevant therapeutic utility as an actionable target for personalized treatment. Here, we discuss the double facets of BRAF. In particular, we argue the need to implement diagnostic molecular algorithms that are able to detect this biomarker in order to streamline and refine diagnostic and therapeutic decisions.

Utilities of RAS Mutations in Preoperative Fine Needle Biopsies for Decision Making for Thyroid Nodule Management: Results from a Single-Center Prospective Cohort

Background: It has been advocated to apply individualized strategies to evaluate thyroid nodules due to the growing awareness that the pathogenesis of thyroid cancer is not uniform. Molecular markers in fine needle biopsies (FNBs) may be helpful for the diagnosis and management decisions. Unlike the detection of BRAF mutations, the clinical utility of rat sarcoma viral oncogene homolog (RAS) mutations has not been fully elucidated. This study aimed at presenting a real-world performance of RAS mutations in identifying thyroid malignancies, at investigating the nature of thyroid tumors carrying RAS mutations, and at providing an additional reference for interpreting how to utilize the presence of RAS mutations in the decision-making process of thyroid nodule management. Methods: Between February 2015 and December 2017, 1400 sequential thyroid biopsies were performed at Boston Medical Center. Of these, 546 FNBs were evaluated for RAS mutations by using a ThyroSeq next-generation sequencing panel. Nodules carrying RAS mutations were prospectively followed, and medical records were collected. Results: ThyroSeq successfully provided molecular information in 504 nodules; 173 with molecular alteration(s); and 80 positive for mutations in the Kirsten-, Neuroblastoma-, or Harvey-RAS genes. RAS gene mutations constituted up to 46.2% of the total molecular alterations found in the study. Fifty-six of the 80 RAS-positive nodules underwent surgery, 33 (58.9%) were confirmed to be benign, 7 (12.5%) were noninvasive follicular thyroid neoplasms with papillary-like nuclear features (NIFTP), and 16 (28.6%) were thyroid carcinomas. The positive predictive value, negative predictive value, and accuracy of RAS mutations for identifying malignancies among cytologically indeterminate nodules were 25.5%, 89.7%, and 54.0% when NIFTP was not counted as cancer. A combination of RAS and other mutations increased the risk of malignancy. Twelve histopathologically proved RAS-only-positive malignant nodules all showed low-risk features and favorable prognosis. RAS isoforms added little assistance for predicting a malignancy and the response to therapy in our series. Conclusions:RAS mutations represent the most frequently detected genetic alterations in our series. RAS mutations, when occurring alone, are not helpful markers to identify malignancy among Bethesda III/IV cytologies, but may predict favorable behavior, and hence should be considered to guide initial management.

A BRAF V600E Mutation in RET-Negative Medullary Thyroid Cancer

We report the case of a woman with a sporadic medullary thyroid carcinoma. Genomic analysis found that her tumor did not contain any common RET mutations but did harbor a BRAF V600E mutation. Only one other well-confirmed example of the BRAF V600E mutation has been reported in an MTC patient. We conclude that this common BRAF mutation may independently drive neoplastic transformation of human parafollicular C cells.

Conventional Ultrasound, Immunohistochemical Factors and BRAFV600E Mutation in Predicting Central Cervical Lymph Node Metastasis of Papillary Thyroid Carcinoma

The study was aimed at evaluating the correlation between central cervical lymph node metastasis (CLNM) in papillary thyroid carcinoma (PTC) patients and ultrasound (US) features, immunohistochemical factors and BRAF^V600E mutation. A total of 225 consecutive patients (225 PTCs) who had undergone surgery were included. All PTCs were pre-operatively analysed by US with respect to size, components, echogenicity, shape, margins, microcalcification, multiple cancers or not, internal vascularity and capsule contact or involvement. The presence of four immunohistochemical factors, including cytokeratin 19, human bone marrow endothelial cell 1, galectin-3 and thyroid peroxidase, and BRAF^V600E mutation was also evaluated. Univariate and multivariate analyses were performed to identify the risk factors for central CLNM, and a risk model was established. Pathologically, 44% (99/225) of the PTCs had central CLNMs. Multivariate analysis revealed that size ≤10mm, microcalcification, internal vascularity, capsule contact or involvement and BRAF^V600E mutation were independent risk factors for central CLNM. The risk score for central CLNM was calculated as follows: risk score = 1.5 × (if lesion size ≤10 mm) + 1.9 × (if microcalcification) + 0.8 × (if internal flow) + 3.0 × (if capsule contact or involvement) + 1.5 × (if BRAF^V600E mutation). The rating result was divided into six stages, and the relevant risk rates of central CLNM were 0% (0/1), 0% (0/22), 7.4% (4/54), 48.6% (34/70), 71.2% (42/59) and 100% (19/19), respectively. In conclusion, PTC ≤10mm, microcalcification, internal vascularity, capsule contact or involvement and BRAF^V600E mutation are risk factors for central CLNM. The risk model may be useful in treatment planning and management of patients with PTCs.

Poorly Differentiated and Anaplastic Thyroid Cancer

BACKGROUND

Poorly differentiated thyroid carcinoma (PDTC) and anaplastic (undifferentiated) thyroid carcinoma (ATC) comprise a small subset of thyroid tumors that are associated with a poor prognosis and account for a significant portion of the morbidity and mortality related to thyroid cancer. Since management strategies vary between these two entities, it is important for clinicians to be able to differentiate PDTC from ATC.

METHODS

We reviewed the literature on PDTC and ATC and compared clinical and histopathologic features important in defining the disease process.

RESULTS

Both PDTC and ATC display aggressive behavior with increased locoregional and distant disease. In most cases, patients are older and have large, locally advanced tumors. PDTC may represent an intermediate entity in the progression of well-differentiated thyroid carcinoma to ATC. The use of surgical management may be curative or palliative and differs between PDTC and ATC. The roles of radiotherapy and chemotherapy have not been well described.

CONCLUSIONS

PDTC and ATC are rare diseases that carry a poor prognosis. Recognition of their different clinicopathologic features is important to the optimal management of these tumors.

Characterization of the novel tumor-suppressor gene CCDC67 in papillary thyroid carcinoma

Background

Some studies showed an association of coiled-coil domain-containing (CCDC) genes with cancers. Our previous limited data specifically suggested a possible pathogenic role of CCDC67 in papillary thyroid cancer (PTC), but this has not been firmly established. The present study was to further investigate and establish this role of CCDC67 in PTC.

Results

The expression of CCDC67, both at mRNA and protein levels, was sharply down-regulated in PTC compared with normal thyroid tissues. Lower CCDC67 expression was significantly associated with aggressive tumor behaviors, such as advanced tumor stages and lymph node metastasis, as well as BRAF mutation. Introduced expression of CCDC67 in TPC-1 cells robustly inhibited cell proliferation, colony formation and migration, induced G1 phase cell cycle arrest, and increased cell apoptosis.

Methods

Primary PTC tumors and matched normal thyroid tissues were obtained from 200 unselected patients at the initial surgery for detection of CCDC67 mRNA and protein by RT-PCR and Western blotting analyses, respectively. Genomic DNA sequencing was performed to detect BRAF mutation in PTC tumors. Clinicopathological data were retrospectively reviewed for correlation analyses. PTC cell line TPC-1 with stable transfection of CCDC67 was used to investigate the functions of CCDC67.

Conclusions

This large study demonstrates down-regulation of CCDC67 in PTC, an inverse relationship between CCDC67 expression and PTC aggressiveness and BRAF mutation, and a robust inhibitory effect of CCDC67 on PTC cellular activities. These results are consistent with CCDC67 being a novel and impaired tumor suppressor gene in PTC, providing important prognostic and therapeutic implications for this cancer.

Genomic Alterations of Anaplastic Thyroid Carcinoma Detected by Targeted Massive Parallel Sequencing in a BRAF(V600E) Mutation-Prevalent Area

BACKGROUND

Anaplastic thyroid carcinoma (ATC), the most aggressive type of thyroid cancer, has no effective therapy. Due to its dismal prognosis, it is vital to understand the genetic alterations of ATC and identify effective molecular targets. Targeted next-generation sequencing was performed to investigate the mutational profile of ATC using a massive parallel sequencing approach.

METHODS

DNA from formalin-fixed, paraffin-embedded archival samples of 11 ATCs and normal matched pairs were used. A total of 48 genetic alterations were identified by targeted exome sequencing. These alterations were validated by mass spectrometric genotyping and direct Sanger sequencing.

RESULTS

The most commonly mutated gene was BRAF, identified in 10 samples (91%), all showing the V600E point mutation. A KRAS point mutation was observed in the one sample (9%) without the BRAF(V600E) mutation. All 11 ATCs harbored BRAF or RAS mutations, reflecting the possibility that differentiated thyroid carcinomas progress to ATCs after the accumulation of mutations. A loss of function mutation of TP53 was observed in eight samples (73%), a PIK3CA mutation was observed in two samples (18%), and a frameshift mutation of PTEN was observed in one sample (9%). Twenty-eight novel mutated genes were found that had not previously been associated with ATC. Of these, loss of function mutations of NF2, KMT2D, and PKHD1 were repeatedly seen in three samples (27%), two samples (18%), and two samples (18%), respectively. Using direct Sanger sequencing, two samples (18%) were also found with a RASAL1 mutation. KMT2D and RASAL1 mutations were significantly associated with shorter ATC patient survival.

CONCLUSIONS

This comprehensive analysis of ATCs using targeted massive parallel sequencing identified several novel mutations in ATCs, such as loss of function mutations of NF2 or KMT2D. Future studies are needed to confirm the role of these novel mutations as independent drivers of ATC development.

Clinical Manifestations and Gene Expression in Patients with Conventional Papillary Thyroid Carcinoma Carrying the BRAF(V600E) Mutation and BRAF Pseudogene

BACKGROUND

The association of BRAF(V600E) with the clinical manifestations of papillary thyroid carcinoma (PTC) remains controversial. Recent studies have shown that the BRAF pseudogene can activate the MAPK pathway and induce tumorigenesis. This study investigated the association of BRAF(V600E), the BRAF pseudogene, and their mRNA levels with clinical features and thyroid-specific gene expression in conventional PTCs.

MATERIALS AND METHODS

A total of 78 specimens were collected from patients with conventional PTCs. RNA was isolated, and quantitative polymerase chain reaction was used to measure the mRNA levels of BRAF, the BRAF pseudogene, and thyroid-specific and tumor-related genes. Immunohistochemical (IHC) staining of BRAF, ERK, sodium-iodide symporter (NIS), thyrotropin receptor, glucose transporter 1, and Ki67 was also performed.

RESULTS

BRAF(V600E) and the BRAF pseudogene were detected in 73.0% (57/78) and 91.7% (44/48), respectively, of the conventional PTCs. The presence of BRAF(V600E) was not associated with the multiple clinical features assessed or the recurrence rate during 76.9 ± 47.2 months of follow-up. Neither was it associated with IHC staining or tumor-related/thyroid-specific gene expression, except for decreased NIS gene expression. The BRAF pseudogene was not associated with clinical characteristics or thyroid-specific gene expression, except for decreased decoy receptor 3 (DCR3) expression. High BRAF mRNA levels were associated with bilateral and multifocal lesions, and BRAF-pseudogene mRNA levels were positively correlated with BRAF mRNA levels (r = 0.415, p = 0.009).

CONCLUSION

These results do not support the use of the BRAF(V600E) mutation as a prognostic marker of conventional PTC. However, the association of high BRAF mRNA levels with more advanced clinical features suggests that BRAF mRNA levels might be a more useful clinical marker of PTCs, independent of the BRAF(V600E) mutation status. The correlation between BRAF-pseudogene mRNA levels and BRAF mRNA levels in PTCs is in agreement with the hypothesis that the BRAF pseudogene regulates BRAF expression during tumorigenesis by acting as competitive noncoding RNA. However, additional studies with larger sample sizes are required to confirm these findings.

RAS proto-oncogene in medullary thyroid carcinoma

Medullary thyroid carcinoma (MTC) is a rare malignancy originating from the calcitonin-secreting parafollicular thyroid C cells. Approximately 75% of cases are sporadic. Rearranged during transfection (RET) proto-oncogene plays a crucial role in MTC development. Besides RET, other oncogenes commonly involved in the pathogenesis of human cancers have also been investigated in MTC. The family of human RAS genes includes the highly homologous HRAS, KRAS, and NRAS genes that encode three distinct proteins. Activating mutations in specific hotspots of the RAS genes are found in about 30% of all human cancers. In thyroid neoplasias, RAS gene point mutations, mainly in NRAS, are detected in benign and malignant tumors arising from the follicular epithelium. However, recent reports have also described RAS mutations in MTC, namely in HRAS and KRAS. Overall, the prevalence of RAS mutations in sporadic MTC varies between 0-43.3%, occurring usually in tumors with WT RET and rarely in those harboring a RET mutation, suggesting that activation of these proto-oncogenes represents alternative genetic events in sporadic MTC tumorigenesis. Thus, the assessment of RAS mutation status can be useful to define therapeutic strategies in RET WT MTC. MTC patients with RAS mutations have an intermediate risk for aggressive cancer, between those with RET mutations in exons 15 and 16, which are associated with the worst prognosis, and cases with other RET mutations, which have the most indolent course of the disease. Recent results from exome sequencing indicate that, besides mutations in RET, HRAS, and KRAS, no other recurrent driver mutations are present in MTC.

What to do with thyroid nodules showing benign cytology and BRAF(V600E) mutation? A study based on clinical and radiologic features using a highly sensitive analytic method

BACKGROUND

BRAF(V600E) mutation analysis has been used as a complementary diagnostic tool to ultrasonography-guided, fine-needle aspiration (US-FNA) in the diagnosis of thyroid nodule with high specificity reported up to 100%. When highly sensitive analytic methods are used, however, false-positive results of BRAF(V600E) mutation analysis have been reported. In this study, we investigated the clinical, US features, and outcome of patients with thyroid nodules with benign cytology but positive BRAF(V600E) mutation using highly sensitive analytic methods from US-FNA.

METHODS

This study included 22 nodules in 22 patients (3 men, 19 women; mean age, 53 years) with benign cytology but positive BRAF(V600E) mutation from US-FNA. US features were categorized according to the internal components, echogenicity, margin, calcifications, and shape. Suspicious US features included markedly hypoechogenicity, noncircumscribed margins, micro or mixed calcifications, and nonparallel shape. Nodules were considered to have either concordant or discordant US features to benign cytology. Medical records and imaging studies were reviewed for final cytopathology results and outcomes during follow-up.

RESULTS

Among the 22 nodules, 17 nodules were reviewed. Fifteen of 17 nodules were malignant, and 2 were benign. The benign nodules were confirmed as adenomatous hyperplasia with underlying lymphocytic thyroiditis and a fibrotic nodule with dense calcification. Thirteen of the 15 malignant nodules had 2 or more suspicious US features, and all 15 nodules were considered to have discordant cytology considering suspicious US features. Five nodules had been followed with US or US-FNA without resection, and did not show change in size or US features on follow-up US examinations.

CONCLUSION

BRAF(V600E) mutation analysis is a highly sensitive diagnostic tool in the diagnosis of papillary thyroid carcinomas. In the management of thyroid nodules with benign cytology but positive BRAF(V600E) mutation, thyroidectomy should be considered in nodules which have 2 or more suspicious US features and are considered discordant on image-cytology correlation.

Quasi-digital PCR: Enrichment and quantification of rare DNA variants

Rare variant enrichment and quantification was achieved by allele-specific, competitive blocker, digital PCR for aiming to provide a noninvasive method for detecting rare DNA variants from circulating cells. The allele-specific blocking chemistry improves sensitivity and lowers assay cost over previously described digital PCR methods while the instrumentation allowed for rapid thermal cycling for faster turnaround time. Because the digital counting of the amplified variants occurs in the presence of many wild-type templates in each well, the method is called "quasi-digital PCR". A spinning disk was used to separate samples into 1000 wells, followed by rapid-cycle, allele-specific amplification in the presence of a molecular beacon that serves as both a blocker and digital indicator. Monte Carlo simulations gave similar results to Poisson distribution statistics for mean number of template molecules and provided an upper and lower bound at a specified confidence level and accounted for input DNA concentration variation. A 111 bp genomic DNA fragment including the BRAF p.V600E mutation (c.T1799A) was amplified with quasi-digital PCR using cycle times of 23 s. Dilution series confirmed that wild-type amplification was suppressed and that the sensitivity for the mutant allele was <0.01 % (43 mutant alleles amongst 500,000 wild-type alleles). The Monte Carlo method presented here is publically available on the internet and can calculate target concentration given digital data or predict digital data given target concentration.

Molecular pathogenesis and targeted therapies in well-differentiated thyroid carcinoma

Four proto-oncogenes commonly associated with well-differentiated thyroid carcinoma, rearranged during transfection (RET)/papillary thyroid cancer, BRAF, RAS, and PAX8/peroxisome proliferator activated receptor-γ, may carry diagnostic and prognostic significance. These oncogenes can be used to improve the diagnosis and management of well-differentiated thyroid carcinoma. Limited therapeutic options are available for patients with metastatic well-differentiated thyroid cancer, necessitating the development of novel therapies. Vascular endothelial growth factor (VEGF)- and RET-directed therapies such as sorafenib, motesanib, and sunitinib have been shown to be the most effective at inducing clinical responses and stabilizing the disease process. Further clinical trials of these therapeutic agents may soon change the management of thyroid cancer.

New insights into the diagnosis of nodular goiter

Preoperative diagnostic investigations of nodular goiter are based on two main examinations: ultrasonography of the thyroid gland and ultrasound-guided fine-needle aspiration biopsy. So far, FNAB has been the best method for the differentiation of nodules, but in some cases it fails to produce a conclusive diagnosis. Some of the biopsies do not provide enough material to establish the diagnosis, in some other biopsies cytological picture is inconclusive.

Determining the eligibility of thyroid focal lesions for surgery has been more and more often done with molecular methods. The most common genetic changes leading to the development of thyroid cancer include mutations, translocations and amplifications of genes, disturbances in gene methylation and dysregulation of microRNA. The mutations of Ras proto-oncogenes and BRAF gene as well as disturbances of DNA methylation in promoter regions of genes regulating cell cycle (e.g. hypermethylation of RASSF1A gene and TIMP-3 gene) play an important role in the process of neoplastic transformation of thyreocyte. The advances in molecular biology made it possible to investigate these genetic disturbances in DNA and/or RNA from peripheral blood, postoperative thyroid tissue material and cytology specimens obtained through fine-needle aspiration biopsy of focal lesions in the thyroid gland.

As it became possible to analyze the mutations and methylation of genes from cell material obtained through fine-needle aspiration biopsy, it would be beneficial to introduce the techniques of molecular biology in the pre-operative diagnosis of nodular goiter as a valuable method, complementary to ultrasonography and FNAB. The knowledge obtained from molecular studies might help to determine the frequency of follow-up investigations in patients with nodular goiter and to select patients potentially at risk of developing thyroid cancer, which would facilitate their qualification for earlier strumectomy.

Pre-operative role of BRAF in the guidance of the surgical approach and prognosis of differentiated thyroid carcinoma

OBJECTIVE

The p.V600E BRAF and RAS mutations are found in 30-80% of differentiated thyroid carcinoma (DTC). BRAF mutation has been associated with poor prognosis. This study investigated the role of molecular studies in preoperative diagnosis of DTC and the association of p.V600E mutation with prognostic factors.

DESIGN

Prospective study.

METHODS

A total of 202 patients with cytological diagnosis of Bethesda III-VI underwent preoperative molecular studies and subsequent thyroidectomy. p.V600E and RAS mutations were studied in the cytology smears, using real-time PCR genotyping technique. The BRAF mutation (BRAF(+) or BRAF(-)) was correlated with histological and clinical findings.

RESULTS

Molecular study of 172 nodules with Bethesda III-V cytology improved negative predictive value and accuracy of Bethesda III and IV diagnosis. BRAF mutation was present in 65% of 94 DTC and p.Q61R NRAS in one. Except for age, BRAF(+) and BRAF(-) did not differ in sex, tumor size, histological subtype, multifocality, vascular invasion, extrathyroidal extension, or prognostic staging. Among papillary carcinomas, lymph node (LN) metastasis was diagnosed in 23% BRAF(+) and 37% BRAF(-). Distant metastasis occurred in four BRAF(-). Recurrent or persistent disease was more frequent in BRAF(-) (26.7 vs 3.3% BRAF(+), P=0.002) along follow-up of 29.8±10 months. BRAF(+) patients without LN metastasis by pre-operative evaluation submitted to thyroidectomy with central neck dissection (CND) had more frequent LN metastasis (45 vs 5% no CND, P=0.002), but no difference in clinical outcome was observed.

CONCLUSIONS

Pre-operative identification of BRAF mutation improved cytological diagnosis of DTC, but it was not associated with poor prognostic factors. Prophylactic CND did not guarantee better outcome in BRAF(+) patients.

Unusual thyroid tumors: a review of pathologic and molecular diagnosis

The most common thyroid neoplasms are either follicular derived (papillary, follicular and Hürthle cell lesions) or C-cell derived (medullary carcinoma). The diagnosis of these tumors can usually be made at the histologic level, with immunohistochemical stains necessary in some circumstances. Specific molecular mutations have been described that can be diagnostically useful or explain, in part, their pathogenesis, including the well-known Ret/PTC and PPARgamma-PAX8 translocations, point mutations in the Ret, Ras and BRAF genes, and loss of heterozygosity of multiple different tumor suppressor genes. Some unusual tumors of the thyroid gland are more difficult to diagnose. In examining these lesions, the pathologist may use the hematoxylin and eosin-stained morphology, coupled with an analysis of the immunohistochemical staining profiles and possibly analysis of the underlying molecular mutational patterns. These less common thyroid tumors include tall cell and cribriform-morular variants of papillary carcinoma, hyalinizing trabecular tumor, mucoepidermoid and sclerosing mucoepidermoid carcinoma with eosinophilia, poorly differentiated (insular) carcinoma, and undifferentiated (anaplastic) carcinoma. The diagnostic features of these rare tumors, including the histology, immunohistochemical expression profiles and the known molecular mutational profiles of each, are reviewed.

Clinicopathologic implications of the BRAF(V600E) mutation in papillary thyroid cancer: a subgroup analysis of 3130 cases in a single center

BACKGROUND

The BRAF mutation has been shown to be associated with aggressive clinicopathologic characteristics of papillary thyroid cancer (PTC). However, several studies that analyzed hundreds of patients have not demonstrated any correlation. The objective of this study was to investigate the relationship of the BRAF mutation with clinicopathologic factors in a large group of homogenous PTC patients.

METHODS

We collected data of PTC patients who received curative resection of the thyroid gland and who had undergone BRAF mutation tests of their thyroid cancer tissue. Minor variant PTCs and mixed-type thyroid cancers were excluded in this analysis. Clinicopathologic characteristics, including age, sex, BRAF mutation, tumor histology, size, extrathyroidal extension, tumor margin, lymph node metastasis, multifocality, stage, and associated thyroid disease, were collected. The relationship of the BRAF mutation with clinicopathologic factors was analyzed in each homogenous histologic PTC.

RESULTS

There were 3130 PTC patients who met the criteria, and these patients were divided into three major histologic groups: conventional PTC (n = 2947), diffuse sclerosing variant PTC (n = 98), and follicular variant PTC (n = 85). The BRAF mutation was variably detected in 75.3%, 61%, and 40% of patients, respectively. In conventional PTC cases, the BRAF mutation was significantly associated with large tumor size, extrathyroidal extension, and lymph node metastasis. Coexistent chronic lymphocytic thyroiditis was significantly less prevalent in the BRAF mutant group. Age, sex, and tumor margin status were not significantly correlated with the BRAF status. There was no evidence that any clinicopathologic factors were linked with the BRAF mutation status in diffuse sclerosing and follicular variant PTCs.

CONCLUSIONS

The BRAF mutation was differentially detected in each histologic subtype of PTC and was strongly correlated with pathologic factors, most strongly with no coexistent chronic lymphocytic thyroiditis, in conventional PTC. The BRAF mutation is suggested to be a poor prognostic marker in conventional PTC, and the BRAF mutational analysis may lead to better management for individual PTC patients.

Genetic mutations in the treatment of anaplastic thyroid cancer: a systematic review

BACKGROUND

Anaplastic thyroid cancer (ATC) is a rare, lethal disease associated with a median survival of 6 months despite the best multidisciplinary care. Surgical resection is not curative in ATC patients, being often a palliative procedure. Multidisciplinary care may include surgery, loco-regional radiotherapy, and systemic therapy. Besides conventional chemotherapy, multi kinase-targeted inhibitors are emerging as novel therapeutic tools. The numerous molecular alteration detected in ATC are targets for these inhibitors. The aim of this review is to determine the prevalence of the major genetic alterations occurring in ATC and place the results in the context of the emerging kinase-targeted therapies.

METHODS

The study is based on published PubMed studies addressing the prevalence of BRAF, RAS, PTEN, PI3KCA and TP53 mutations and RET rearrangements in ATC.

RESULTS

21 articles dealing with 652 genetic analyses of the selected genes were used. The overall prevalence determined were the following: RET/PTC, 4%; BRAF, 23%; RAS, 60%; PTEN, 16%; PI3KCA, 24%; TP53, 48%. Genetic alterations are sometimes overlapping.

CONCLUSIONS

Mutations of BRAF, PTEN and PI3KCA genes are common in ATC, with RAS and TP53 being the most frequent. Given ATC genetic complexity, effective therapies may benefit from individualized therapeutic regimens in a multidisciplinary approach.

Somatic RAS mutations occur in a large proportion of sporadic RET-negative medullary thyroid carcinomas and extend to a previously unidentified exon

CONTEXT

Medullary thyroid carcinoma (MTC) is characterized by proto-oncogene RET mutations in almost all hereditary cases as well as in more than 40% of sporadic cases. Recently, a high prevalence of RAS mutations was reported in sporadic MTC, suggesting an alternative genetic event in sporadic MTC tumorigenesis.

OBJECTIVE

This study aimed to extend this observation by screening somatic mutational status of RET, BRAF, and the three RAS proto-oncogenes in a large series of patients with MTC.

MATERIALS AND METHODS

Direct sequencing of RET (exons 8, 10, 11, 13, 14, 15, 16), BRAF (exons 11 and 15), and KRAS, HRAS, and NRAS genes (exons 2, 3, and 4) was performed on DNA prepared from 50 MTC samples, including 30 sporadic cases.

RESULTS

Activating RET mutations were detected in the 20 hereditary cases (germline mutations) and in 14 sporadic cases (somatic mutations). Among the 16 sporadic MTC without any RET mutation, eight H-RAS mutations and five K-RAS mutations were found. Interestingly, nine RAS mutations correspond to mutation hot spots in exons 2 and 3, but the other four mutations were detected in exon 4. The RET and RAS mutations were mutually exclusive. No RAS gene mutation was found in hereditary MTC, and no BRAF or NRAS mutation was observed in any of the 50 samples.

CONCLUSIONS

Our study confirms that RAS mutations are frequent events in sporadic MTC. Moreover, we showed that RAS mutation analysis should not be limited to the classical mutational hot spots of RAS genes and should include analysis of exon 4.

Allele specific locked nucleic acid quantitative PCR (ASLNAqPCR): an accurate and cost-effective assay to diagnose and quantify KRAS and BRAF mutation

The use of tyrosine kinase inhibitors (TKIs) requires the testing for hot spot mutations of the molecular effectors downstream the membrane-bound tyrosine kinases since their wild type status is expected for response to TKI therapy. We report a novel assay that we have called Allele Specific Locked Nucleic Acid quantitative PCR (ASLNAqPCR). The assay uses LNA-modified allele specific primers and LNA-modified beacon probes to increase sensitivity, specificity and to accurately quantify mutations. We designed primers specific for codon 12/13 KRAS mutations and BRAF V600E, and validated the assay with 300 routine samples from a variety of sources, including cytology specimens. All were analyzed by ASLNAqPCR and Sanger sequencing. Discordant cases were pyrosequenced. ASLNAqPCR correctly identified BRAF and KRAS mutations in all discordant cases and all had a mutated/wild type DNA ratio below the analytical sensitivity of the Sanger method. ASLNAqPCR was 100% specific with greater accuracy, positive and negative predictive values compared with Sanger sequencing. The analytical sensitivity of ASLNAqPCR is 0.1%, allowing quantification of mutated DNA in small neoplastic cell clones. ASLNAqPCR can be performed in any laboratory with real-time PCR equipment, is very cost-effective and can easily be adapted to detect hot spot mutations in other oncogenes.

BRAF, p53 and SOX2 in anaplastic thyroid carcinoma: evidence for multistep carcinogenesis

AIMS

The aim of this study was to genotype a series of papillary thyroid carcinomas (PTCs) and anaplastic thyroid carcinomas (ATCs) for BRAF mutation, and to evaluate p53 and SOX2 expression as factors implicated in tumour progression.

METHODS

The study included 17 PTCs and 14 ATCs. Analysis of the exon 15 of BRAF was based on direct sequencing. Immunohistochemistry was used to evaluate p53 and SOX2 expression.

RESULTS

V600E (c.1799T>A) mutation was observed in 53% (9/17) of PTCs. Two cases of ATCs (2/14; 14%), both with PTC component, harboured BRAF mutation: the classical V600E mutation and an undocumented duplication of codon 599 (c.1795_1797dup; p.Thr599dup). These mutations were present in ATC as well as PTC tumour cells. Overexpression of p53 and SOX2 was depicted respectively in 64% (9/14) and 29% (4/14) of ATCs, and absent in PTCs.

CONCLUSION

We confirm that V600E mutation is a frequent and specific event in PTC. BRAF-mutated ATCs are associated with a PTC component displaying the same mutation. We describe a new mutation of BRAF, T599dup, in a case of ATC with tall cell PTC component. Moreover, progression from PTC to ATC could be favoured by further TP53 mutation and SOX2 expression.

Reflex BRAF testing in thyroid fine-needle aspiration biopsy with equivocal and positive interpretation: a prospective study

BACKGROUND

The BRAF V600E mutation has been reported in 50%-80% of papillary thyroid carcinoma (PTC) cases and is highly specific for PTC. Reflex BRAF testing may improve the diagnostic accuracy of thyroid fine-needle aspiration (FNA) tests having equivocal cytologic interpretations and provide prognostic information that helps guide management in patients with PTC.

PATIENTS AND METHODS

Cases with equivocal thyroid FNA readings (indeterminate and suspicious for PTC) or a positive diagnosis for PTC and concomitant BRAF mutation analysis were included in this prospective study. BRAF mutation analysis was performed by polymerase chain reaction combined with single-strand conformation polymorphism gel electrophoresis using lavage fluid obtained from needle rinsing. The results of histopathologic follow-up were correlated with the cytologic interpretations and BRAF status.

RESULTS

One hundred fifty-seven FNAs with equivocal or positive cytologic interpretations were eligible for the study. All but one (99.4%) FNAs were found to have sufficient DNA quality and quantity for the assay. Based on the follow-up diagnosis of nodules after surgical resection, the sensitivity for diagnosing PTC was 63.3% with cytology alone and 80.0% with the combination of cytology and BRAF testing, respectively. No false positives were noted with either cytology or BRAF mutation analysis. All PTCs with extrathyroidal extension and of tall-cell variant were postive for BRAF mutation.

CONCLUSIONS

BRAF V600E mutation analysis can be easily performed on cytologic preparation using lavage fluids obtained from needle rinsing. By combining morphologic evaluation and BRAF testing, there is a substantial improvement in the preoperative identification of PTC when compared with cytology alone. Patients with equivocal cytologic diagnosis and BRAF V600E mutation are candidates for total thyroidectomy ± central lymph node dissection.

Aberrant promoter methylation in overexpression of CITED1 in papillary thyroid cancer

BACKGROUND

More than 80% of all thyroid cancers, the most common endocrine malignancy, are papillary thyroid cancer (PTC). It is well established that CITED1 (Cbp/p300 Interacting Transactivators with glutamic acid [E] and aspartic acid [D]-rich C-terminal domain) mRNA is characteristically overexpressed in PTC. Our previous study suggested a positive association of BRAF mutation with CITED1 overexpression. However, the mechanism of CITED1 expression in PTC remains to be elucidated. In the present study, we analyzed whether aberrant methylation of CITED1 gene promotes CITED1 overexpression in PTC.

METHOD

CITED1 mRNA expression levels were analyzed by quantitative polymerase chain reaction in three PTC-derived cell lines, TPC1, K1, and KTC-1, and in surgically dissected PTC and surrounding normal tissues from 19 patients. The BRAF mutation status of the cells and clinical specimens was determined by direct sequencing. The methylation status of the deoxycitidine-phosphate-deoxyguanosine dinucleotides (CpGs) in the CITED1 promoter was analyzed by the bisulfite-sequencing method using genomic DNA. Finally, the expression of CITED1 mRNA in TPC1 cells, when subjected to pharmacological inhibition of methylation, was analyzed.

RESULTS

CITED1 mRNA was expressed at lower levels in TPC1 than in K1 and KTC-1 cells. A BRAF mutation was present in K1 and KTC-1 cells, but not in TPC1 cells. CITED1 promoter was hypomethylated in K-1 and KTC-1 cells, but not in TPC1 cells. In surgically dissected specimens, the mean expression level of CITED1 mRNA was 30-fold higher in PTC tissues than in normal tissues. CpGs in the CITED1 promoter were more heavily methylated in normal tissues than in PTC tissues. In PTC specimens without a BRAF mutation, two CpGs were more heavily methylated than in PTC specimens with the BRAF V600E mutation. Pharmacological inhibition of methylation in TPC1 cells by 5'-aza-2'-deoxycitidine resulted in increased expression of CITED1 mRNA.

CONCLUSION

Hypomethylation of the CpGs in the promoter region of CITED1 is associated with higher expression of CITED1 mRNA in PTC tissues, consistent with the hypothesis that epigenetic regulation is involved in the overexpression of CITED1. This hypothesis is supported by pharmacologic inhibition studies in TPC1 cells.

Molecular pathogenesis of nodular goiter

INTRODUCTION

Familial clustering of goiters mostly with an autosomal dominant pattern of inheritance has repeatedly been reported. Moreover, other environmental and etiologic factors are likely to be involved in the development of euthyroid goiter. Therefore, a multifactorial etiology based on complex interactions of both genetic predisposition and the individuals' environment is likely.

METHODS

The line of events from early thyroid hyperplasia to multinodular goiter argues for the predominant neoplastic (i.e., originating from a single mutated cell) character of nodular structures. Etiologically, relevant somatic mutations are known in two thirds of papillary and follicular thyroid carcinomas and hot thyroid nodules. In contrast, the somatic mutations relevant for benign cold or benign isocaptant thyroid nodules which constitute the majority of thyroid nodules are unknown.

RESULTS

The nodular process is triggered by the oxidative nature of thyroid hormone synthesis or additional oxidative stress caused by iodine deficiency or smoking. If the antioxidant defense is not effective, this oxidative stress will cause DNA damage followed by an increase of the spontaneous mutation rate which is a substrate for tumorogenesis.

CONCLUSIONS

Therefore, the hallmark of thyroid physiology--H(2)O(2) production during hormone synthesis--is very likely the ultimate cause for the frequent mutagenesis in the thyroid gland. Because iodine deficiency increases the oxidative burden, DNA damage and mutagenesis could provide the basis for the frequent nodular transformation of endemic goiters.

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.

The evolving field of tyrosine kinase inhibitors in the treatment of endocrine tumors

Activation of tyrosine kinase receptors (TKRs) and their related pathways has been associated with development of endocrine tumors. Compounds that target and inactivate the kinase function of these receptors, tyrosine kinase inhibitors (TKIs), are now being applied to the treatment of endocrine tumors. Recent clinical trials of TKIs in patients with advanced thyroid cancer, islet cell carcinoma, and carcinoid have shown promising preliminary results. Significant reductions in tumor size have been described in medullary and papillary thyroid carcinoma, although no complete responses have been reported. Case reports have described significant tumor volume reductions of malignant pheochromocytomas and paragangliomas. In addition, these compounds showed an initial tumoricidal or apoptotic response followed by long-term static effects on tumor growth. Despite the promising preliminary results, this class of therapeutic agents has a broad spectrum of adverse effects, mediated by inhibition of kinase activities in normal tissues. These adverse effects will have to be balanced with their benefit in clinical use. New strategies will have to be applied in clinical research to achieve optimal benefits. In this review, we will address the genetic alterations of TKRs, the rationale for utilizing TKIs for endocrine tumors, and current information on tumor and patient responses to specific TKIs. We will also discuss the adverse effects related to TKI treatment and the mechanisms involved. Finally, we will summarize the challenges associated with use of this class of compounds and potential solutions.

[BRAF V600E mutation in papillary thyroid carcinoma: prevalence and detection in fine needle aspiration specimens]

BRAF V600E mutation in papillary thyroid carcinoma (PTC): prevalence and detection in fine needle aspiration (FNA) specimens.

BACKGROUND AND OBJECTIVE

The activating mutation of the BRAF gene, T1799A, is the most common and specific genetic alteration in PTC. In the present study, our aims were to confirm these data and investigate the feasibility of BRAF mutation detection in FNA specimens.

METHODS

In a retrospective study, we examined paraffin-embedded surgical samples of 57 PTC and 51 non-PTC thyroid tumors for the presence of BRAF mutation by dideoxy sequencing. We analyzed thyroid aspirates (drop and washed-out solution) and smears from 31 patients who underwent thyroidectomy, before intraoperative frozen sections, and 25 archival thyroid FNA smears.

RESULTS

The BRAF mutation was present in 58 % of PTC. Among non-PTC thyroid tumors, only one medullary thyroid carcinoma contained the BRAF mutation. BRAF mutation was correctly detected from the FNA-derived materials. Considering the search of BRAF mutation in preoperative FNA smears, the diagnosis of PTC would have been affirmed in 31 % (4/13) of indeterminate and suspicious FNA.

CONCLUSION

BRAF mutation detection in FNA specimens is feasible and could be used as an adjunct tool for preoperative diagnosis of PTC classified as indeterminate and suspicious with conventional cytology (categories 3, 4 and 5 according to NCI/Bethesda 2008 terminology).

BRAFV600E mutation in the pathogenesis of a large series of papillary thyroid carcinoma in Czech Republic

BACKGROUND

Activating point mutation of the BRAF gene, the most common genetic alteration reported in papillary thyroid carcinomas (PTC), has been associated with poor prognostic characteristics.

AIM

Our objective was to determine the frequency of BRAFV600E mutation in PTC tumor tissues from the period 1960-2007 and to correlate it with clinicopathological parameters.

SUBJECTS AND METHODS

DNAs were extracted from 242 PTCs, 23 sporadic medullary carcinomas, one anaplastic carcinoma and 6 poorly differentiated carcinomas. The presence of BRAFV600E mutation was determined using single strand conformation polymorphism method and verified by direct sequencing.

RESULTS

BRAFV600E mutation was detected in 81 of 242 PTCs (33.5%), in one of 6 poorly differentiated carcinomas (16.7%) and in anaplastic carcinoma. BRAFV600E mutation was much less frequent in the follicular variant compared to classical variant and mixed follicular- classical variant of PTCs (p=0.001). BRAFV600E mutation was significantly associated with presence of nodal metastasis (p=0.029), more advanced TNM stage (p=0.014) and recurrence of disease (p=0.008). The mutation correlated with a higher age at diagnosis (p=0.049) and with a greater tumor size (p=0.041). Multivariate analysis confirmed these findings. The prevalence of BRAFV600E mutation before 1986 was significantly lower than after it (p=0.008).

CONCLUSIONS

Our data suggest that BRAFV600E mutation is associated with high-risk clinicopathological characteristics of PTC and worse prognosis of patients. The frequency of the mutation significantly varied during the observed period but rather because of the different age distribution of patients in particular periods than as a consequence of Chernobyl accident.

Mutant BRAF(T1799A) can be detected in the blood of papillary thyroid carcinoma patients and correlates with disease status

CONTEXT

The BRAF(T1799A) transversion is the most frequent morphotype-specific somatic mutation in papillary thyroid carcinoma (PTC). The ability to detect this mutation in the circulation could aid in diagnosis and follow-up of PTC patients.

OBJECTIVE

Our objective was to develop and clinically validate a sensitive and specific assay for the detection of BRAF(T1799A) in blood samples from PTC patients.

DESIGN

We developed an allele-specific real-time PCR method for the detection of BRAF(T1799A) in blood samples and studied prospectively blood samples from 193 patients with thyroid cancer (173 PTC, 20 non-PTC) attending for routine follow-up. The results of molecular testing were correlated with disease status and thyroglobulin measurements. BRAF(T1799A) status of the original tumor samples was also confirmed, where available.

RESULTS

The assay had a detection sensitivity of fewer than one heterozygote BRAF(T1799A)-carrying cell per 100,000 diploid cells, without detectable cross-reactivity between wild-type BRAF and BRAF(T1799A). Circulating BRAF(T1799A) was detected in 20 of 173 PTC patients and in none of the 20 non-PTC patients. BRAF(T1799A)-positive samples contained between one in 326 and fewer than one in 100,000 copies of BRAF(T1799A). Tissue BRAF status correlated with blood BRAF status, whereas BRAF(T1799A) positivity in blood correlated with the presence of active disease at the time of the blood draw, with eight of the 38 PTC patients with persistent/recurrent disease being positive for circulating BRAF(T1799A) (relative risk vs. circulating BRAF(T1799A)-negative, 2.55; P < 0.04).

CONCLUSIONS

BRAF(T1799A) can be detected in the blood of PTC patients with residual or metastatic disease and may provide diagnostic information.

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.

The role of BRAFV600E mutation and ultrasonography for the surgical management of a thyroid nodule suspicious for papillary thyroid carcinoma on cytology

BACKGROUND

This study was designed to investigate the role of BRAFV600E mutation status in cytology specimens and ultrasonography (US) when planning surgery for thyroid nodules with cytologic results suspicious for papillary thyroid carcinoma (PTC).

METHODS

From July 2008 to November 2008, 91 consecutive patients with cytologic results of suspicious for PTC underwent thyroidectomy. Before surgery, all patients received US-guided fine needle aspiration biopsy (US-FNAB) solely for the purpose of BRAFV600E mutation analysis of thyroid nodules suspicious for PTC on cytology. BRAFV600E mutations were tested by direct sequencing. We investigated the role of BRAFV600E mutation and US in planning the thyroid surgery.

RESULTS

Of 91 nodules suspicious for PTC, 42 (46.2%) were positive for the BRAFV600E mutation and confirmed to be PTC by histopathology. The positive predictive values of BRAFV600E mutation was 100%. Of the 49 nodules without the BRAFV600E mutation, 42 (85.7%) proved to be PTC. Thirty-nine of 42 (92.9%) PTCs were suspicious for malignant features on US. Two of seven (28.6%) benign lesions showed probably benign features. The sensitivity, positive predictive value, and accuracy of US in thyroid nodules without BRAFV600E mutations was 92.9% (39/42), 88.6% (39/44), and 83.7% (41/49), respectively.

CONCLUSIONS

The BRAFV600E mutation is a useful molecular marker for preoperative diagnosis of PTC and an indicator for therapeutic thyroid surgery in the nodule with cytologic results suspicious for PTC. In thyroid nodules without the BRAFV600E mutation, suspicious malignant features on US may help in planning the extent of thyroid surgery.

How molecular pathology is changing and will change the therapeutics of patients with follicular cell-derived thyroid cancer: Table 1

Well-differentiated thyroid carcinomas comprise two well-defined histological types: papillary and follicular (PTCs and FTCs, respectively). Despite being derived from the same cell (thyroid follicular cell), these two types of tumour accumulate distinct genetic abnormalities during progression. The molecular pathology of thyroid cancer is now better understood because of our ability to identify RET/PTC rearrangements and BRAF mutations in the aetiopathogenesis of the large majority of PTCs and the high prevalence of RAS mutations and PAX8/PPARγ rearrangements in follicular patterned carcinomas (FTCs and follicular variant of PTCs). This review summarises most of the molecular alterations currently used as targets for new biological treatments and looks at some of the changes that are already occurring or may occur in the treatment of patients with thyroid cancer. For simplicity, the review is divided up according to the major genetic alterations identified in well-differentiated thyroid carcinomas (RET/PTC rearrangements, BRAF mutations, RAS mutations and mitochondrial DNA deletions and mutations) and their respective treatments.

Hypermethylation of the DNA mismatch repair gene hMLH1 and its association with lymph node metastasis and T1799A BRAF mutation in patients with papillary thyroid cancer

BACKGROUND

It remains to be investigated whether the aberrant methylation of DNA repair genes plays a pathogenic role in BRAF mutation-promoted tumorigenesis of papillary thyroid cancer (PTC).

METHODS

In the current study, the promoter methylation status of 23 DNA repair genes in relation to clinicopathologic characteristics and BRAF mutation was examined in PTC tumors using methylation-specific polymerase chain reaction.

RESULTS

Among the 38 PTC tumors examined, 3 of 23 DNA repair genes were hypermethylated, including the hMLH1 gene in 8 of 38 samples (21%), the PCNA gene in 5 of 38 samples (13%), and the OGG1 gene in 2 of 38 samples (5%). Methylation of these genes was also found in some thyroid cancer cell lines. Methylation of the hMLH1 gene in particular was found to be associated with lymph node metastasis of PTC (5 of 8 samples [63%] in the methylation group vs 3 of 30 samples [10%] in the nonmethylation group; P = .0049). Methylation of the hMLH1 gene was also found to be associated with the T1799A BRAF mutation in PTC (6 of 19 samples (32%) in the BRAF mutation-positive group vs 2 of 19 samples (11%) in the BRAF mutation-negative group; P = .042).

CONCLUSIONS

The data from the current study suggest that, as shown previously in colon cancer, aberrant methylation of the hMLH1 gene may play a role in BRAF mutation-promoted thyroid tumorigenesis.

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.

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.

BRAF mutations in melanocytic lesions and papillary thyroid carcinoma samples identified using melting curve analysis of polymerase chain reaction products

CONTEXT

Mutations of the proto-oncogene B-raf (BRAF) have been detected in melanocytic lesions and papillary carcinomas of the thyroid, and identification of these mutations could be useful in resolving some diagnostic problems.

OBJECTIVE

To develop a method to evaluate mutations of BRAF that could provide results much more rapidly than conventional polymerase chain reaction and DNA sequencing assays.

DESIGN

An assay using a LightCycler was developed to evaluate DNA sequences encoding amino acids within the activation loop of BRAF.

RESULTS

Using this real-time polymerase chain reaction method, we analyzed 55 paraffin-embedded melanoma or nevus samples. The V600E mutation was found in 0 (0%) of 13 samples diagnosed histologically as Spitz nevi, 9 (24.3%) of 37 invasive melanomas, and 5 (100%) of 5 other melanocytic nevi. Two additional mutations, V600K and VK600-1E, also were identified in cases of invasive melanoma. We analyzed 14 paraffin-embedded papillary thyroid cancer (PTC) samples, 6 of which showed the V600E mutation. We found that our test worked efficiently with fine-needle aspirate specimens, and it identified 6 V600E mutations in 10 fine-needle aspirate specimens diagnosed as PTC. We also identified 4 V600E mutations in 6 specimens of PTC metastatic to lymph node. Unlike the melanocytic lesions, the PTC specimens yielded only V600E mutations. Comparison of our real-time polymerase chain reaction results with conventional polymerase chain reaction and DNA sequencing demonstrated 100% concordance. Surprisingly, we did not identify the previously reported VK600-1E or K601E mutations in our PTC specimens.

CONCLUSIONS

Our results show that the real-time polymerase chain reaction method is a rapid and accurate method for identifying BRAF mutations, such as V600E, in both paraffin-embedded tissue and fine-needle aspirate specimens.

Identification of a novel noncoding RNA gene, NAMA, that is downregulated in papillary thyroid carcinoma with BRAF mutation and associated with growth arrest

In search of tumor suppressor genes in papillary thyroid carcinoma (PTC), we previously used gene expression profiling to identify genes underexpressed in tumor compared with paired unaffected tissue. While searching for loss of heterozygosity (LOH) in genomic regions harboring candidate tumor suppressor genes, we detected LOH in a approximately 20 kb region around marker D9S176. Several ESTs flanking D9S176 were underexpressed in PTC tumors, and for one of the ESTs, downregulation was highly associated with the activating BRAF mutation V600E, the most common genetic lesion in PTC. A novel gene, NAMA, (noncoding RNA associated with MAP kinase pathway and growth arrest) containing the affected EST was cloned and characterized. NAMA is weakly expressed in several human tissues, and the spliced forms are primarily detected in testis. Several characteristics of NAMA suggest that it is a nonprotein coding but functional RNA; it has no long open reading frames (ORFs); the exons exhibit low sequence identity in the evolutionarily conserved regions; it is inducible by knockdown of BRAF, inhibition of the MAP kinase pathway, growth arrest and DNA damage in cancer cell lines. We suggest that NAMA is a noncoding RNA associated with growth arrest.

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 maintains proliferation, transformation, and tumorigenicity of BRAF-mutant papillary thyroid cancer cells

CONTEXT

Although the BRAF V600E mutant can initiate the formation of papillary thyroid cancer (PTC), it is unclear whether it is required to maintain cell proliferation, transformation, and tumor growth of BRAF mutation-harboring PTC.

OBJECTIVE

The aim of the study was to investigate whether BRAF V600E is required for the proliferation, transformation, and tumorigenicity of BRAF mutation-harboring PTC cells.

DESIGN

We addressed this issue using BRAF small interference RNA (siRNA) to transfect stably several BRAF mutation-harboring PTC cell lines, isolated clones with stable suppression of BRAF, and assessed their ability to proliferate, transform, and grow xenograft tumors in nude mice.

RESULTS

PTC cell proliferation and transformation were suppressed in specific BRAF siRNA clones, but not in control scrambled siRNA clones. Specifically, taking the advantage of stable BRAF knockdown, we were able to show continued suppression of PTC cell proliferation and transformation, or anchorage-independent colony formation in soft agar, after long-term culture. Moreover, we also demonstrated that in vivo tumorigenicity and growth of tumors from the specific BRAF siRNA cell clones in nude mice were suppressed compared with control clones.

CONCLUSIONS

BRAF V600E is not only an initiator of PTC as demonstrated previously but is also a maintainer of proliferation, transformation, and tumorigenicity of PTC cells harboring BRAF mutation, and growth of tumors derived from such cells continues to depend on BRAF V600E. These results provide further support for potentially effective therapy targeted at BRAF for BRAF mutation-harboring PTC.

Clinical implications of pre-operative rapid BRAF analysis for papillary thyroid cancer

The activating point mutation of the BRAF gene, BRAF(T1799A), is the most common and specific genetic alteration in adult papillary thyroid carcinoma (PTC) and a possible marker of malignant potential of PTC. We have applied the PCR-RFLP method using fine-needle aspiration biopsy samples not only to our clinical practice but also to the international medical assistance effort around the Semipalatinsk Nuclear Testing Site in Kazakhstan. Seventy-seven cases (100 nodules) from Japan and 131 cases (137 nodules) from Kazakhstan were examined. There were 14 Japanese and 76 Kazakhstani cases of cytological malignant tumors from the examined samples. We detected 12 (85.7% of PTC) and 19 (25% of PTC) cases with BRAF(T1799A) among the Japanese and Kazakhstani cases, respectively. Of these cases, we found mutations in one cytologically "suspicious" case and even in two pathologically "benign" cases (after surgery in Kazakhstan). All of the BRAF mutation-positive cases, including those three, were confirmed as PTC by careful pathological examination, including immunohistochemical analysis. In summary, our PCR-RFLP method for BRAF(T1799A) detection using FNAB samples is useful not only for preoperative diagnosis of PTC but also as a complementary diagnostic tool for accurate pathological diagnosis, even after surgery.

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.

Detection of BRAF V600E activating mutation in papillary thyroid carcinoma using PCR with allele-specific fluorescent probe melting curve analysis

BACKGROUND

A single hotspot mutation at nucleotide 1799 of the BRAF gene has been identified as the most common genetic event in papillary thyroid carcinoma (PTC), with a prevalence of 29-83%.

AIMS

To use a PCR assay to molecularly characterise the BRAF activating point mutation in a series of PTC and benign thyroid cases and correlate the mutation results with histological findings.

METHODS

Formalin-fixed paraffin-embedded (FFPE) sections were evaluated for the BRAF V600E mutation using LightCycler PCR with allele-specific fluorescent probe melting curve analysis (LCPCR).

RESULTS

42 (37 PTC; 5 benign) surgical tissue samples were analysed for the BRAF V600E activating point mutation. Using LCPCR and direct DNA sequencing, the BRAF mutation was identified in 23/37 (62.2%) PTC FFPE samples. DNA sequencing results demonstrated confirmation of the mutation.

CONCLUSIONS

Detection of BRAF-activating mutations in PTC suggests new approaches to management and treatment of this disease that may prove worthwhile. Identification of the BRAF V600E activating mutation in routine FFPE pathology samples by a rapid laboratory method such as LCPCR could have significant value.