Hyalinizing Trabecular Tumor of the Thyroid: An Update

Hyalinizing trabecular tumor (HTT) is a rare thyroid tumor of follicular cell origin with a trabecular pattern of growth and marked intratrabecular hyalinization. This tumor is known to share morphological and architectural similarities with paraganglioma and medullary thyroid carcinoma, as well as the nuclear features and RET/PTC1 translocations of papillary thyroid carcinoma. These tumors are not associated with RAS or BRAF mutations. Whether the presence of RET alterations in HTT are sufficient molecular proof of its relationship with papillary thyroid carcinoma (PTC) is still to be defined. Of great interest is the characteristic strong peripheral cytoplasmic and membranous staining of the tumor cells with MIB1 immunostain, not seen in any other thyroid neoplasm. Although cases of malignant HTT have been recorded, HTT should be considered a benign neoplasm or, at most, a neoplasm of extremely low malignant potential.     

Der hyalinisierende trabekul?re Tumor der Schilddrüse

Hyalinizing trabecular tumours of the thyroid represent a rare entity of follicular cell derived tumours and are characterized by a marked intratrabecular hyalinisation. These tumours share architectural similarities with medullary thyroid carcinomas and exhibit nuclear features such as nuclear pseudoinclusions resembling papillary thyroid carcinoma. However, the clinical behaviour remains unclear. On the basis of their inconspicuous appearance and absence of invasion or recurrence during follow-up, the tumour was initially classified as an adenoma. Subsequently, molecular findings such as the detection of RET?/?PTC rearrangements in some hyalinizing trabecular tumours favoured the designation as a variant of papillary thyroid carcinoma. However, miRNA profiling of hyalinizing trabecular tumours compared with benign thyroid lesions and papillary thyroid carcinoma failed to demonstrate the characteristic up-regulation found in papillary thyroid carcinoma. This article summarizes conventional diagnostic criteria with supplementary information regarding molecular pathogenesis of hyalinizing trabecular tumours of the thyroid.     

Overexpression of wild-type c-RET and zero prevalence of RET/PTC rearrangements are associated with papillary thyroid cancer (PTC) in Kuwait

Background

Papillary thyroid carcinoma (PTC) is common in Kuwait. The activation of the RET oncogene by DNA rearrangement (RET/PTC) is known to have an important role in PTC carcinogenesis. However, the real frequency of the RET/PTC expression in PTC is variable between different studies. This study seeks to determine the prevalence of RET/PTC and to analyze the RET oncogene expression associated with PTC in Kuwait.

Methods

RET expression and DNA rearrangements (RET/PTC 1, RET/PTC 2 and RET/PTC 3) were studied by RT–PCR in different thyroid diseases. Results were confirmed by the Southern blot and by immunohistochemistry. Quantitative real-time PCR was used to determine the level of RET mRNA expression in PTCs.

Results

Wild-type (nonrearranged) c-RET oncogene was overexpressed in 60% of PTC cases and absent in follicular thyroid carcinoma (FTC), anaplastic thyroid carcinoma (ATC), follicular adenomas (FA) or normal thyroid. No RET/PTC rearrangement was detected in any sample. The c-RET expression in Hashimoto's thyroiditis and multinodular goiter was limited to follicular cells with PTC-like nuclear changes.

Conclusions

The overexpression of wild-type c-RET is a characteristic molecular event of PTCs in Kuwait. The prevalence of RET/PTC is zero and among the lowest recorded in the world.     

Aberrant BRAF splicing as an alternative mechanism for oncogenic B‐Raf activation in thyroid carcinoma

Activating BRAF mutations have recently been reported in 28–83% of papillary thyroid carcinomas (PTCs). However, it is not known whether aberrant BRAF splicing occurs in thyroid carcinoma. To investigate aberrant BRAF splicing and its association with BRAF mutation in thyroid tumours, we studied aberrant BRAF splicing and BRAF mutation from 68 thyroid tumours. BRAF^V600E mutation was detected in 20 of 43 PTCs and all three anaplastic thyroid carcinomas (ATCs). There is a higher frequency of BRAF mutation in PTC patients with stage III and IV tumours compared with stage I and II. Novel BRAF splicing variants were detected in 12 PTCs, three follicular variants of PTC (FVPTCs), and one ATC, as well as in two thyroid carcinoma cell lines, ARO and NPA. These variants did not have the N‐terminal auto‐inhibitory domain of wild‐type B‐Raf, resulting in an in‐frame truncated protein that contained only the C‐terminal kinase domain and caused constitutive activation of B‐Raf. These variants were significantly associated with advanced disease stage and BRAF^V600E mutation (p < 0.001, Fisher exact test). Furthermore, expression of these variants in NIH3T3 and CHO cells could activate the MAP kinase signalling pathway, transform them in vitro, and induce tumours in nude mice. These data suggest that BRAF splicing variants may function as an alternative mechanism for oncogenic B‐Raf activation. Combination of the BRAF^V600E mutation and its splicing variants may contribute towards disease progression to poorly differentiated thyroid carcinoma. Copyright © 2008 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

<Emphasis Type="Italic">BRAF</Emphasis> mutations typical of papillary thyroid carcinoma are more frequently detected in undifferentiated than in insular and insular-like poorly differentiated carcinomas

Somatic mutations of the BRAF gene (BRAF^V599E and BRAF^K600E) were found to be closely associated with different histotypes of papillary thyroid carcinoma (PTC). The V599E mutation is highly prevalent in PTC with a papillary or mixed papillary follicular growth pattern, and the K600E mutation is apparently restricted to the follicular variant of PTC. It is usually accepted that thyroid malignancies may follow a progression path from well-differentiated to poorly differentiated (PDC) and undifferentiated (UC) carcinomas. One would expect that at least some of the less differentiated carcinomas would harbour the genetic alterations of pre-existing well-differentiated tumours. In order to find the prevalence of BRAF mutations in PDC and UC, we screened a series of 19 PDCs and 17 UCs, as well as 3 UC-derived cell lines, for both mutation types. The group of PDCs was restricted to the so-called insular and insular-like PDCs, thus excluding PTCs with solid, insular or trabecular foci of growth and PDCs displaying typical PTC nuclei. No BRAF mutations were detected in any of the 19 cases of PDC, whereas 6 of the UCs (35%) and one UC-derived cell line presented the BRAF^V599E mutation. The BRAF^K600E mutation was not detected in any case. We conclude that UC may progress from BRAF^V599E-mutated PTC. The absence of BRAF mutations in our series of PDC supports the assumption that pure insular and insular-like PDCs are more closely related to follicular carcinoma than to PTC.Paula Soares and Vítor Trovisco contributed equally to this work.     

RET/PTC rearrangement in thyroid tumors

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

Immunophenotypic heterogeneity of hyalinizing trabecular tumours of the thyroid

 

Aims:

We studied 12 cases of hyalinizing trabecular tumour of the thyroid gland (HTT) with the aim of reviewing the cytological, histological and immunophenotypic features and of investigating the relationships of HTT with other thyroid neoplasms.  

Methods and results:

Eleven patients were female and one male, aged 8–74 years (median 58). Ten cases had a benign behaviour, while two cases were locally aggressive. Of the latter, one developed distant metastases and the other is a recent case. All patients are alive 6–311 months after diagnosis. Cytologically, HTT was characterized by hypercellular smears with aggregates of roundish cells having features of papillary carcinoma (nuclear grooves, vacuoles) and fragments of fibrous tissue. Histologically, prominent nesting, trabecular growth patterns and a hyaline stroma (partly positive for laminin and collagen type IV) were found. One case was associated with a papillary microcarcinoma. Two additional cases had extensive areas of papillary carcinoma. In one of these, hyalinized papillary stalks were observed. All tumours contained thyroglobulin but not calcitonin. High molecular weight cytokeratin (a marker of papillary carcinoma) was focally positive in 4/12 cases only and thyroperoxidase (a marker of follicular adenomas, but not of papillary carcinoma) was found in 3/12 cases.  

Conclusions:

The immunophenotypic profile and the morphological features suggest that HTTs are an heterogeneous group of tumours, some of them probably representing variants of papillary carcinoma with hyalinized stroma.     

甲状腺乳头状癌RET、CK19、TG、Ki-67的表达

目的 研究甲状腺乳头状癌RET、CK19、TG、Ki-67蛋白表达特点及其临床意义。方法 应用免疫组织化学SP法检测RET、CK19、TG、Ki-67蛋白在30例甲状腺乳头状癌、10例结节性甲状腺肿和18例癌旁正常甲状腺中的表达。结果 RET、CK19在乳头状癌的阳性率（66．7％、83．3％）明显高于结节性甲状腺肿和正常甲状腺阳性率（7．1％、25．0％）,两者差异有显著性（P〈0．01）。乳头状癌组及良性病例组TG表达阳性率差异无显著性（P〉0．05）。96．7％的乳头状癌Ki-67阳性细胞数小于10％。结论 RET及CK19在甲状腺乳头状癌表达增加,具有一定的病理诊断价值。     

野生型RET和RET/PTC融合基因在成人散发性甲状腺乳头状癌中的表达及其意义

目的探讨野生型BET（WT-RET）及RET／PTC1、3融合基因在成人散发性甲状腺乳头状癌（PTC）中的表达及其与临床病理学指标的关系和意义。方法用逆转录-聚合酶链反应（RT-PCR）检测102例石蜡与新鲜（43例）甲状腺病变组织（PTC66例,对照组各种良恶性肿瘤及良性病变共36例）中WT-RET和RET／PTC1、3融合基因的表达并结合临床资料进行分析。结果（1）62％（41／66）PTC患者≥40岁。38％（25／66）PTC伴淋巴细胞性甲状腺炎,59％（39／66）伴淋巴结转移,5例（7.6％）有远处转移。（2）RET原癌基因的酪氨酸激酶区（BET-TK）检出率为68．1％（45／66）。BET原癌基因断裂点（BP）与TK的同时检出率在PTC中28．8％（19／66）,腺瘤中12．5％（1／8）,表明存在WT-BET转录物。（3）RET／PTC检出率21．2％（14／66）,其中5例BET／PTC1阳性（7．6％）,9例RET／PTC3阳性（13．6％）。6例（9％）PTC同时表达BET／PTC和WT-BET。36例对照组病例中未检测到RET／PTC融合基因。（4）统计学分析,PTC病例中WT-BET与RET／PTC1融合基因的表达与性别、年龄、肿瘤大小、多灶性、伴淋巴细胞浸润及淋巴结转移等临床病理学指标无关（P〉0．05）。结论RET／PTC融合基因在散发性成人PTC中表达率低,其诊断和判断预后的价值不大。WT-BET在甲状腺肿瘤的滤泡形成过程中起一定作用。     

Survey of 548 oncogenic fusion transcripts in thyroid tumors supports the importance of the already established thyroid fusions genes

Neoplasms frequently present structural chromosomal aberrations that can alter the level of expression of a protein or to the expression of an aberrant chimeric protein. In the thyroid, the PAX8‐PPARG fusion is present in the neoplastic lesions that have a follicular architecture—follicular thyroid carcinoma (FTC) and follicular variant of papillary thyroid carcinoma (FVPTC), and less frequently in follicular thyroid adenoma (FTA), while the presence of RET/PTC fusions are largely restricted to papillary thyroid carcinoma (PTC). The ability to detect fusion genes is relevant for a correct diagnosis and for therapy. We have developed a new fusion gene microarray‐based approach for simultaneous analysis of all known and predicted fusion gene variants. We did a comprehensive screen for 548 known and putative fusion genes in 27 samples of thyroid tumors and three positive controls—one thyroid cancer cell line (TPC‐1) and two PTCs with known CCDC6‐RET (alias RET/PTC1) fusion gene, using this microarray. Within the thyroid tumors tested, only well known, previously reported fusion genes in thyroid oncology were identified. Our results reinforce the pathogenic role played by RET/PTC1, RET/PTC3, and PAX8‐PPARG fusion genes in thyroid tumorigenesis. © 2012 Wiley Periodicals, Inc.     

BRAF mutations are associated with some histological types of papillary thyroid carcinoma

Mutations in the BRAF gene have recently been detected in a wide range of neoplastic lesions with a particularly high prevalence in melanoma and papillary thyroid carcinoma (PTC). The hot-spot mutation BRAF(V599E) is frequently detected in PTC (36-69%), in contrast to its absence in other benign or malignant thyroid lesions. In order to unravel whether there is any association between the occurrence of the BRAF mutation and the histological pattern of PTC, in this study a previous series of 50 PTCs was extended to 134 cases, including ten cases of PTC-related entities-hyalinizing trabecular tumour (HTT) and mucoepidermoid carcinoma (MEC). Using PCR/SSCP and sequencing, the BRAF(V599E) mutation was detected in 45 of the 124 PTCs (36%). No mutations were detected in any case of HTT and MEC. BRAF(V599E) was present in 75% of Warthin-like PTCs and 53% of conventional PTCs, whereas no BRAF(V599E) mutations were detected in any of the 32 cases of the follicular variant of PTC. BRAF(V599E) was also detected in 6 of 11 cases of the oncocytic variant of PTC that displayed a papillary or mixed follicular-papillary growth pattern and in none of the four oncocytic PTCs with a follicular growth pattern. A distinct mutation in BRAF (codon K600E) was detected in three cases of the follicular variant of PTC. This study has confirmed the high prevalence of BRAF(V599E) in PTC and has shown that the mutation is almost exclusively seen in PTC with a papillary or mixed follicular-papillary growth pattern, regardless of the cytological features of the neoplastic cells. The results support the existence of an oncocytic variant of PTC that should be separated from the oncocytic variant of follicular carcinoma and suggest that the follicular variant of PTC may be genetically different from conventional PTC.     

Hyaline matrix in hyalinizing trabecular tumor

Hyalinizing trabecular tumor (HTT) is a rare neoplasm which usually follows an indolent clinical course. The cytologic diagnosis of HTT can be challenging as these neoplasms share cytomorphological features with other thyroid neoplasms and paraganglioma. In fine‐needle aspiration (FNA) smears a diagnosis of papillary thyroid carcinoma (PTC) or suspicion of PTC is often made. Herein we report cytologic findings in two patients with HTT examined by FNA. The key to a correct diagnosis is the recognition of a hyaline and colloid/amyloid‐like material in the background of the smears. Immunocytochemical examination showing aberrant membranous and peripheral cytoplasmic staining for MIB‐1 can help in rendering a correct diagnosis. Diagn. Cytopathol. 2015;43:710–713. © 2014 Wiley Periodicals, Inc.     

<Emphasis Type="Italic">BRAF</Emphasis><Superscript>V600E</Superscript> Mutation in Papillary Thyroid Carcinoma: Significant Association with Node Metastases and Extra Thyroidal Invasion

B-Raf (BRAF) is the strongest activator in the downstream of MAP kinase signaling. The somatic point mutation of BRAF gene (V600E) is the most common and specific event in papillary thyroid carcinoma (PTC). However, its prevalence is variable among different studies and its association with clinico-pathological features is controversial. This study tests the prevalence of BRAF ^V600E mutation in thyroid cancer patients in Indian subcontinental population. We analyzed 140 thyroid tumor specimens for BRAF gene mutation at codon 600 using mutant-allele-specific amplification, single-strand conformation polymorphism, Mutector assay, and DNA sequencing of the PCR-amplified exon 15. BRAF mutation at codon 600 was detected in 46 of 86 PTC patients (53.4%) from Indian subcontinental cohort. Frequency of mutation varied across the subtypes of PTCs. BRAF ^V600E mutation was more common in the conventional PTC (38 out of 62; 61%) than in the follicular variant of PTC (2 out of 17; 11.7%). None of the 8 follicular thyroid adenomas, 14 follicular thyroid carcinomas, 16 medullary thyroid carcinomas, and 16 benign hyperplasia patients showed any exon 15 mutation. We found significant correlation between BRAF mutation status and extra-thyroidal invasion, lymph node metastasis, and tumor stage. However no correlation was observed with gender, age, and tumor size of the patients. Thus our findings suggest that BRAF ^V600E is a prevalent genetic alteration in adult sporadic PTCs in Indian cohort and it may be responsible for the progression of classic variant of PTC to metastatic and poorly differentiated subtype and likely to have significant impact on its diagnostic and prognostic management.     

Papillary thyroid carcinomas with and without BRAF V600E mutations are morphologically distinct

Finkelstein A, Levy G H, Hui P, Prasad A, Virk R, Chhieng D C, Carling T, Roman S A, Sosa J A, Udelsman R, Theoharis C G & Prasad M L
(2012) Histopathology  60, 1052–1059 Papillary thyroid carcinomas with and without BRAF V600E mutations are morphologically distinct Aims: The BRAF V600E mutation resulting in the production of an abnormal BRAF protein has emerged as the most frequent genetic alteration in papillary thyroid carcinomas (PTCs). This study was aimed at identifying distinctive features in tumours with and without the mutation. Methods and results: Thirty‐four mutation‐positive and 22 mutation‐negative tumours were identified by single‐strand conformation polymorphism of the amplified BRAF V600E region in the tumour DNA. Mutation‐positive tumours were more common in patients older than 45 years (24/33, P = 0.05), in classic (23/30, P = 0.01), tall cell (4/5) and oncocytic/Warthin‐like (2/2) variants of PTC, and in subcapsular sclerosing microcarcinomas (4/4). In contrast, all 12 follicular variants (P < 0.0001) and two diffuse sclerosing variants were negative for the mutation. Mutation‐positive tumours displayed infiltrative growth (32/34, P = 0.02), stromal fibrosis (33/34, P < 0.001), psammoma bodies (17/34, P = 0.05), plump eosinophilic tumour cells (22/34, P = 0.01), and classic fully developed nuclear features of PTC (33/34, P = 0.0001). Encapsulation was significantly associated with mutation‐negative tumours (15/22, P = 0.02). Conclusions: BRAF V600E mutation‐positive and negative PTCs are morphologically different. Recognition of their morphology may help in the selection of appropriate tumours for genetic testing.