Follicular variant of papillary thyroid carcinoma: genome-wide appraisal of a controversial entity

Molecular testing in fine-needle aspiration of thyroid nodules

BACKGROUND

Thyroid nodules are commonly faced by clinicians as palpable nodules or incidentally identified on imaging. Nodules that are found to be suspicious by imaging can be biopsied by fine needle aspiration, which can yield material for molecular testing to refine the diagnosis.

METHODS

The current literature concerning molecular testing in thyroid nodules including available commercial assays was reviewed and summarized.

RESULTS/CONCLUSIONS

Commonly encountered alterations include mutations in RAS, BRAF, TERT promoter, PTEN, and DICER1 as well as fusions of RET, ALK, PAX8-PPARγ, and NTRK. This article provides a summary of these molecular alterations, commercially available molecular assays, and general considerations for thyroid epithelial malignancies and benign thyroid nodules.

Copy number variations identified in thyroid FNA specimens are associated with Hürthle cell cytomorphology

BACKGROUND

The fine-needle aspiration (FNA) diagnosis of thyroid Hürthle cell neoplasms (HCNs) remains challenging. This study explored a possible association of copy number variations (CNVs) with Hürthle cell lesions of the thyroid.

METHODS

Thyroid FNA cases that were diagnosed as follicular lesion of undetermined significance (FLUS) or follicular neoplasm (FN)/HCN for which the ThyroSeq version 3 genomic classifier test was performed were retrieved.

RESULTS

A total of 324 thyroid FNA cases (228 FLUS cases, 46 HCN cases, and 50 FN cases) were included in the study. FLUS cases were further classified as Hürthle cell type (follicular lesion of undetermined significance-Hürthle cell type [FLUS-HCT]; 20 cases) or non-Hürthle cell type (follicular lesion of undetermined significance-non-Hürthle cell type [FLUS-NHCT]; 208 cases). HCN and FLUS-HCT cases showed a higher prevalence of CNVs (23 of 66 [35%]) in comparison with those classified as FN or FLUS-NHCT (14 of 258 [5%]; P < .001). A total of 105 patients had histopathologic follow-up. Cases with CNVs were more likely to be neoplastic (18 of 26 [69%]) and associated with Hürthle cell changes (14 of 26 [54%]) in comparison with cases without any molecular alterations (neoplastic, 8 of 24 [33%]; Hürthle cell changes, 2 of 24 [8%]; P < .05). In HCN/FLUS-HCT cases with CNVs (n = 14), Hürthle cell changes (13 of 14 [93%]) and neoplasms (9 of 14 [64%]) were more likely to be seen on surgical follow-up in comparison with the 17 cases without CNVs (Hürthle cell changes, 6 of 17 [35%]; neoplastic, 3 of 17 [18%]; P < .05).

CONCLUSIONS

CNVs identified in thyroid FNA cases are associated with Hürthle cell morphology and are suggestive of a neoplasm with Hürthle cell features in thyroid FNAs classified as FLUS-HCT/HCN. This finding may be helpful in triaging patients who would benefit from surgical management.

Relationship of PPARG overexpression with prognostic parameters in papillary thyroid carcinoma

Objectives

PAX8/PPARG chromosomal rearrangement is frequently seen in thyroid cancer, and PPARG overexpression has been shown in the follicular variant of papillary thyroid carcinoma, but not in papillary thyroid carcinoma other than the follicular variant. The main aim of this study was to investigate the frequency of PPARG overexpression among papillary thyroid carcinoma and if there were any variants of papillary thyroid carcinoma with PPARG overexpression other than the follicular variant.

Methods

Immunohistochemical analysis of PPARG overexpression was performed using a PPARG monoclonal antibody in a series of 111 paraffin-embedded blocks of thyroid tumours. Of the patients in our study, 100 were diagnosed with papillary thyroid carcinoma, 9 with follicular adenoma and 2 with follicular carcinoma.

Results

PPARG staining was detected in 19 of the 111 cases. Sixteen patients with PPARG overexpression had papillary thyroid carcinoma and 3 had follicular adenoma.

Conclusion

PPARG overexpression was detected mainly in follicular-variant papillary thyroid carcinoma. Vascular invasion, lymphatic invasion, thyroid capsule invasion and lymph node positivity were lower in patients with PPARG overexpression.

Non-invasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features (NIFTP) lowers the risk of malignancy in the bethesda system for reporting thyroid cytopathology diagnostic categories

Background:

The introduction of non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) has been shown to decrease the risk of malignancy (ROM) in The Bethesda System for Reporting Thyroid Cytopathology. This knowledge may alter the management of patients with thyroid nodules.

Objectives:

To correlate cytological diagnosis with histological diagnosis for establishing the ROM of all Bethesda system categories after the introduction of NIFTP.

Methods:

This was a retrospective cohort study. All consecutive fine-needle aspiration cytology (FNAC) specimens collected from January 1, 2013, to December 31, 2017, at King Abdullah Medical City, Jeddah, Saudi Arabia, were assessed, and patients who underwent surgical excision of thyroid nodules were further analyzed. The ROM and overall ROM for each Bethesda category were calculated with and without considering NIFTP as a malignant tumor.

Results:

Overall, 1066 FNAC specimens were collected, of which 281 had a surgical correlation. Our cases included 18 (6.4%) non-diagnostic (ND), 109 (38.8%) benign, 28 (9.9%) atypia/follicular lesion of undetermined significance (AUS/FLUS), 39 (13.8%) follicular neoplasm or suspicion for follicular neoplasm (FN/SFN), 20 (7.1%) suspicion for malignancy (SM), and 67 (23.8%) malignant (POM) cases. After considering NIFTP diagnosis on resection specimens, the ROM decreased as follows: ND, 38.8% to 27.7% (P = 0.2388); benign, 21.1% to 11.9% (P = 0.0343); AUS/FLUS, 50% to 39.2% (P = 0.2089); FN/SFN, 53.8% to 33.3% (P = 0.0336); SM, 85% to 75% (P = 0.2147); POM, 95.5% to 88% (P = 0.0582).

Conclusion:

The introduction of NIFTP would significantly decrease the ROM of thyroid FNAC in both benign and FN/SFN categories of the Bethesda system.

Characterization of TERT and BRAF copy number variation in papillary thyroid carcinoma: An analysis of the cancer genome atlas study

Alterations in the genome, including mutations and copy number variation (CNV), can drive cancer progression. The Cancer Genome Atlas (TCGA) project studying papillary thyroid cancer (PTC) identified a number of recurrent arm-level copy number amplifications, some spanning genes that are also commonly mutated in thyroid cancer. Herein, we focus on the role of TERT and BRAF CNV in PTC, including its relation to mutation status, gene expression, and clinicopathological characteristics. Utilizing TCGA CNV data, we identified focal amplifications and deletions involving the TERT and BRAF loci. TERT amplifications are more frequent in later stage thyroid tumors; in contrast, BRAF amplifications are not associated with stage. Furthermore, TERT amplifications are more frequently found in tumors also harboring TERT mutations, the combination further increasing TERT expression. Conversely, BRAF amplifications are more frequently found in BRAF wildtype tumors, and are more common in the follicular subtype of PTC as well as classic PTCs associated with a high follicular component and a RAS-like expression profile (assessed by the BRAF/RAS score). This is the first study to examine the TCGA thyroid dataset for gene-level CNV of TERT and BRAF, and their relationship with mutation status, tumor type and tumor stage. Assessing the differences in patterns of TERT and BRAF amplifications in the context of the mutation status of these genes may provide insight into the differing roles CNV can play depending on tumor type, and may lead to a better understanding of cancer drivers in thyroid cancer.

Deep learning prediction of BRAF-RAS gene expression signature identifies noninvasive follicular thyroid neoplasms with papillary-like nuclear features

Noninvasive follicular thyroid neoplasms with papillary-like nuclear features (NIFTP) are follicular-patterned thyroid neoplasms defined by nuclear atypia and indolent behavior. They harbor RAS mutations, rather than BRAFV600E mutations as is observed in papillary thyroid carcinomas with extensive follicular growth. Reliably identifying NIFTPs aids in safe therapy de-escalation, but has proven to be challenging due to interobserver variability and morphologic heterogeneity. The genomic scoring system BRS (BRAF-RAS score) was developed to quantify the extent to which a tumor's expression profile resembles a BRAFV600E or RAS-mutant neoplasm. We proposed that deep learning prediction of BRS could differentiate NIFTP from other follicular-patterned neoplasms. A deep learning model was trained on slides from a dataset of 115 thyroid neoplasms to predict tumor subtype (NIFTP, PTC-EFG, or classic PTC), and was used to generate predictions for 497 thyroid neoplasms within The Cancer Genome Atlas (TCGA). Within follicular-patterned neoplasms, tumors with positive BRS (RAS-like) were 8.5 times as likely to carry an NIFTP prediction than tumors with negative BRS (89.7% vs 10.5%, P < 0.0001). To test the hypothesis that BRS may serve as a surrogate for biological processes that determine tumor subtype, a separate model was trained on TCGA slides to predict BRS as a linear outcome. This model performed well in cross-validation on the training set (R2 = 0.67, dichotomized AUC = 0.94). In our internal cohort, NIFTPs were near universally predicted to have RAS-like BRS; as a sole discriminator of NIFTP status, predicted BRS performed with an AUC of 0.99 globally and 0.97 when restricted to follicular-patterned neoplasms. BRAFV600E-mutant PTC-EFG had BRAFV600E-like predicted BRS (mean -0.49), nonmutant PTC-EFG had more intermediate predicted BRS (mean -0.17), and NIFTP had RAS-like BRS (mean 0.35; P < 0.0001). In summary, histologic features associated with the BRAF-RAS gene expression spectrum are detectable by deep learning and can aid in distinguishing indolent NIFTP from PTCs.

Molecular trait of follicular-patterned thyroid neoplasms defined by MALDI-imaging

In the field of thyroid neoplasms, the most interesting recent change regards the introduction of a new terminology for follicular-patterned thyroid tumors, named Noninvasive Thyroid Neoplasm with Papillary-like Nuclear Features (NIFTP). This pre-malignant tumor is considered to be the putative precursor of invasive carcinoma. However, given that several issues are still unresolved, the application of ancillary tools, based on omics-techniques, may improve the clinical management of these challenging cases. The present paper highlights the proteomic profiles of a series of NIFTPs submitted to Fine Needle Aspirations (FNAs) and analysed by MALDI-imaging in order to confirm the heterogeneous phenotype of nodules included in the present NIFTP terminology and to underline the necessity of more accurate biomarkers that can be used for their characterization. Ethical and economic implications in terms of healthcare costs, operative risks, morbidity, as well as the potential need for lifelong hormone replacement therapy, seem to be significant reasons to approach the characterization of NIFTPs using alternative tools such as MALDI-MSI.

Loss of Integrase Interactor 1 (INI1) Expression in a Subset of Differentiated Thyroid Cancer

Alterations in the switching defective/sucrose non-fermenting (SWI/SNF) chromatin-remodeling complex are enriched in advanced thyroid cancer. Integrase interactor 1 (INI1), encoded by the SMARCB1 gene on the long arm of chromosome 22, is one of the core subunits of the SWI/SNF complex. INI1 immunohistochemistry is frequently used for the diagnosis of malignant rhabdoid neoplasms. In the present study, we found normal and benign thyroid tissues generally had diffusely intense nuclear immunostaining. Loss of INI1 immunohistochemical expression was observed in 8% of papillary thyroid cancer and 30% of follicular thyroid cancer. Furthermore, loss of INI1 expression was associated with extrathyroidal extension (p < 0.001) and lymph node metastasis (p = 0.038). Analysis of The Cancer Genome Atlas database revealed that SMARCB1 underexpression was associated with the follicular variant subtype and aneuploidy in papillary thyroid cancer. We speculate that SMARCB1 is an important effector in addition to NF2 and CHEK2 inactivation among thyroid cancers with chromosome 22q loss.

Noninvasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features (NIFTP): An Update

Based on evidence accumulated over the past three decades showing that noninvasive encapsulated follicular variant of papillary thyroid carcinoma has an indolent clinical behavior and a RAS-like molecular profile similar to follicular adenoma, the Endocrine Pathology Society working group in 2016 proposed to rename this entity as "noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP)" in order to eliminate the term "carcinoma" from the diagnosis. It is a major evidence-based attempt initiated by an international group of endocrine pathologists to tackle the epidemic of thyroid cancer overdiagnosis and overtreatment. However, its creation and continuous existence are not without controversies. NIFTP has sparked a wave of follow up studies aiming to decipher the exact nature of this new entity. In this review, we summarize the rationale, diagnostic criteria, controversies and subsequent changes to the NIFTP concept, and their impact on patient care and pathology practice.

Genomic Characterization of Differentiated Thyroid Carcinoma

Since the release of The Cancer Genome Atlas study of papillary thyroid carcinoma (PTC) in 2014, additional genomic studies of differentiated thyroid carcinoma (DTC) using massively-parallel sequencing (MPS) have been published. Recent advances in MPS technology have started to provide important insights into the molecular pathogenesis of DTC. In the genomic landscape, the most recurrently altered genes in DTC, which has a low mutational burden relative to other cancers, are BRAF, RAS, and fusion genes. Some novel driver candidates also have been identified. The frequency of these genomic alterations varies across the subtypes of DTC (classical PTC, follicular variant of PTC, and follicular thyroid carcinoma). Telomerase reverse transcriptase (TERT) promoter mutations are the alteration that makes the most important contribution to the progression of DTC. In the transcriptomic landscape, DTC can be classified according to its gene expression profile, and each subtype has a distinct mutational profile, intracellular signaling output, and clinicopathological characteristics. Herein, we review the results of genomic studies using MPS technology, and describe the types and frequencies of genomic alterations according to histological classifications of DTC and the characteristics and significance of the gene expression signatures of DTC.

A user's guide to non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP)

The term non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) was recently introduced to replace a subset of follicular variant of papillary thyroid carcinoma (FVPTC). The goal of this change was to promote more conservative management of these tumours and spare patients the psychological burden of a cancer diagnosis. The histological diagnosis of NIFTP is stringent: the tumour needs to demonstrate encapsulation or circumscription, a purely follicular architecture and the presence of nuclear features of papillary thyroid carcinoma, while lacking capsular and vascular invasion, a significant component of solid growth and high-grade features (increased mitotic activity and necrosis). In order to ensure that these inclusion and exclusion criteria are met, the tumour must be sampled extensively, with the entire capsule/periphery submitted in all cases. When sampled by fine-needle aspiration, NIFTP is usually classified within the indeterminate categories of the Bethesda System for Reporting Thyroid Cytopathology. NIFTP is characterized genetically by frequent RAS mutations, although rarely other alterations, such as the BRAF K601E mutation and gene rearrangements in PPARG or THADA, may occur. In this review, we will examine the history of FVPTC and the findings and factors that culminated in the introduction of the NIFTP terminology. A discussion will follow with the histological, cytological and molecular characteristics of NIFTP. We will conclude by considering the potential impact of the introduction of the NIFTP terminology.

Noninvasive Follicular Thyroid Neoplasms With Papillary-like Nuclear Features Are Genetically and Biologically Similar to Adenomatous Nodules and Distinct From Papillary Thyroid Carcinomas With Extensive Follicular Growth

CONTEXT

- Proposed noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTPs), formerly noninvasive encapsulated papillary carcinoma, follicular variant (PTC-FV), is an indolent tumor with follicular growth and frequent RAS mutations.

OBJECTIVE

- To detect histologic and molecular differences separating NIFTP from follicular adenomas (FAs) and invasive carcinomas, particularly papillary carcinomas with extensive follicular growth (PTC-EFGs) and invasive encapsulated PTC-FV (IE-PTC-FV).

DESIGN

- Sixty-one tumors were reviewed histologically and reclassified into 32 NIFTPs (52%), 4 IE-PTC-FVs (7%), 14 PTC-EFGs (23%), and 11 FAs (18%). Next-generation sequencing for mutations in 50 genes was performed. Clinical outcomes were recorded.

RESULTS

- The NIFTPs and FAs were well circumscribed and unencapsulated. The FAs had bland nuclei, whereas the NIFTPs showed at least 2 of 3 (67%; sufficient) nuclear features (enlargement, irregular contours, chromatin clearing). The IE-PTC-FVs had follicular growth, sufficient nuclear features, and extensive capsular invasion. The PTC-EFGs had a median of 5% papillae with intrathyroidal invasion (broad-based, sclerotic, or small follicle growth patterns); intranuclear pseudoinclusions were present only in PTC-EFGs (9 of 14; 64%). Mutations included RAS in 20 of the 32 NIFTPs (62%), 4 of the 11 FAs (36%), and 3 of the 4 IE-PTC-FVs (75%); BRAF K601E in 1 NIFTP (3%); BRAF V600E in 5 PTC-EFGs (36%). No NIFTPs or FAs recurred or metastasized. All 4 IE-PTC-FVs (100%) had hematogenous metastasis. Two PTC-EFGs (14%) had lymphatic metastasis.

CONCLUSIONS

- The morphologic similarity and RAS mutations in FAs, NIFTPs, and IE-PTC-FVs supports the genetic similarity of those follicular neoplasms in contrast to the unique presence of BRAF V600E mutations in PTC-EFGs. Using strict diagnostic criteria supported by molecular testing, tumors with extensive follicular growth can be classified into follicular type or RAS-like (FA, NIFTP, IE-PTC-FV) versus papillary type or BRAF V600E-like (PTC-EFG).

The contribution of molecular pathology to the classification of thyroid tumors

Significant molecular advances have been undertaken for the past two decades in the field of thyroid follicular neoplasms, including a detailed genomic profile of papillary thyroid carcinoma (PTC) by The Cancer Genome Atlas (TCGA) project. These molecular discoveries led to a better understanding of the pathogenesis of thyroid neoplasms and resulted in reclassification of certain types of thyroid tumors. This review discusses how, 1) the molecular profiles of follicular-patterned lesions led to the reclassification of the follicular variant of PTC into non-invasive follicular thyroid neoplasm with papillary like nuclei, 2) the genotyping of Hürthle cell neoplasm provided the rationale to classify these tumors independently from follicular adenomas and carcinomas, and 3) BRAF and RAS molecular signatures have the potential of subclassifying PTC and poorly differentiated thyroid carcinoma into clinically relevant molecular subtypes.

A novel integrative risk index of papillary thyroid cancer progression combining genomic alterations and clinical factors

Although the majority of papillary thyroid cancer (PTC) is indolent, a subset of PTC behaves aggressively despite the best available treatment. A major clinical challenge is to reliably distinguish early on between those patients who need aggressive treatment from those who do not. Using a large cohort of PTC samples obtained from The Cancer Genome Atlas (TCGA), we analyzed the association between disease progression and multiple forms of genomic data, such as transcriptome, somatic mutations, and somatic copy number alterations, and found that genes related to FOXM1 signaling pathway were significantly associated with PTC progression. Integrative genomic modeling was performed, controlling for demographic and clinical characteristics, which included patient age, gender, TNM stages, histological subtypes, and history of other malignancy, using a leave-one-out elastic net model and 10-fold cross validation. For each subject, the model from the remaining subjects was used to determine the risk index, defined as a linear combination of the clinical and genomic variables from the elastic net model, and the stability of the risk index distribution was assessed through 2,000 bootstrap resampling. We developed a novel approach to combine genomic alterations and patient-related clinical factors that delineates the subset of patients who have more aggressive disease from those whose tumors are indolent and likely will require less aggressive treatment and surveillance (p = 4.62 × 10-10, log-rank test). Our results suggest that risk index modeling that combines genomic alterations with current staging systems provides an opportunity for more effective anticipation of disease prognosis and therefore enhanced precision management of PTC.

Noninvasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features: Historical Context, Diagnosis, and Future Challenges

The encapsulated/well-demarcated non-invasive form of follicular variant of papillary thyroid carcinoma (FVPTC) that occurs annually in 45,000 patients worldwide was thought for 30 years to be a carcinoma. Many studies have now shown almost no recurrence in these non-invasive tumors, even in patients treated by surgery without radioactive iodine therapy. The categorization of the tumor as cancer has led to aggressive forms of treatment, with their side effects, financial costs, and the psychological and social impact of a cancer diagnosis. Recently, the encapsulated/well-demarcated non-invasive, FVPTC was renamed as noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) by an international group of experts. The new terminology lacks the carcinoma label enabling clinicians to avoid aggressive therapy. By taking the reader through the history of FVPTC, this article explains how diagnostic criteria for thyroid carcinoma of follicular cells have evolved over the last 60 years. It discusses the steps that led to the labeling of FVPTC as cancer and highlights the various studies that helped reclassify and rename this tumor. It also sheds light on the impact of this reclassification on cytologic diagnosis and focuses on the studies needed to refine and expand the histologic criteria of NIFTP. By understanding the history of this change in nomenclature, future classification of tumors will be greatly improved.

Evolution of the histologic classification of thyroid neoplasms and its impact on clinical management

The vast majority of low grade follicular cell derived thyroid carcinomas follows an indolent clinical course and is associated with very low mortality. Risk stratification using multiple clinical and pathologic characteristics has become the standard of care to guide appropriate management and avoid overtreatment. Over the past few decades, the field of thyroid pathology has witnessed several major changes that significantly impacted upon patients' care. These are: 1) The reclassification of non-invasive encapsulated follicular variant of papillary thyroid carcinoma as noninvasive follicular thyroid neoplasm with papillary-like nuclear features; 2) the diagnosis of Hurthle cell carcinoma based on the presence of capsular and vascular invasion; 3) a detailed definition of poorly differentiated thyroid carcinoma, taking into consideration mitosis and necrosis; and 4) the emphasis on a detailed pathologic analysis such as the extent of vascular invasion and extrathyroidal extension. This review describes these histological concepts and details the history, rationale, and clinical impacts of such changes. These shifts in the classification and characterization of thyroid carcinoma provided a platform supporting therapy de-escalation. In addition several lessons were learned from these changes especially from the misclassification of the non-invasive encapsulated follicular variant of papillary thyroid carcinoma. We hope that the lessons learned will help better classify tumors in the future whether arising in the thyroid or other organs.

The History of the Follicular Variant of Papillary Thyroid Carcinoma

CONTEXT

This review provides historical context to recent developments in the classification of the follicular variant of papillary thyroid carcinoma (FVPTC). The evolution of the diagnostic criteria for papillary thyroid carcinoma is described, clarifying the role of molecular analysis and the impact on patient management.

METHODS

A PubMed search using the terms "follicular variant" and "papillary thyroid carcinoma" covering the years 1960 to 2016 was performed. Additional references were identified through review of the citations of the retrieved articles.

RESULTS

The encapsulated/well-demarcated, noninvasive form of FVPTC that occurs annually in 45,000 patients worldwide was thought for 30 years to be a carcinoma. Many studies have shown almost no recurrence in these noninvasive tumors, even in patients treated by surgery alone without radioactive iodine therapy. The categorization of the tumor as outright cancer has led to aggressive forms of treatment, with their side effects, financial costs, and the psychological and social impacts of a cancer diagnosis. Recently, the encapsulated/well-demarcated, noninvasive FVPTC was renamed as noninvasive follicular thyroid neoplasm with papillary-like nuclear features. The new terminology lacks the carcinoma label, enabling clinicians to avoid aggressive therapy.

CONCLUSIONS

By understanding the history of FVPTC, future classification of tumors will be greatly improved.

Predicting histological subtypes of follicular variant of papillary thyroid carcinoma based on cytomorphology. Can cytomorphology optimize use of molecular testing?

INTRODUCTION

Follicular variant papillary thyroid carcinoma (FVPTC) can be further subclassified into one of 3 subtypes: non-invasive encapsulated FVPTC, invasive encapsulated FVPTC, and infiltrative FVPTC. Longitudinal and molecular studies have demonstrated that, in terms of both molecular profiles and prognosis, encapsulated FVPTC is comparable to follicular adenoma, invasive FVPTC to follicular carcinoma, and infiltrative FVPTC to classic PTC. To improve triaging and prevent overtreatment of patients with FVPTC, we sought to determine cytologic features likely to occur within each subtype.

METHODS

A laboratory database search from 2010-2015 was conducted to identify patients with biopsy-proven FVPTC and prior fine-needle aspiration. Surgical specimens were reviewed to determine the appropriate subcategorization. Accompanying cytology reports were reviewed for features common in classic PTC and follicular neoplasms.

RESULTS

Encapsulated variants were more likely to be graded as Bethesda category 4 compared with invasive or infiltrative variants. In contrast, infiltrative variants were more likely to be graded as Bethesda categories 5 and 6 compared with invasive or encapsulated variants. Compared with the encapsulated variant, infiltrative FVPTC was more likely to have nuclear pseudo-inclusions (31.82% versus 8.11%, P = 0.0468) and less likely to have microfollicular architecture (22.73% versus 54.05%, P = 0.0374).

CONCLUSION

This study identified cytomorphologic differences between encapsulated and infiltrative FVPTC. With a higher threshold of suspicion for FVPTC, improved awareness of the differences between these subtypes and incorporation of molecular testing, it is likely that the Bethesda category can be revised and patient triaging can be significantly improved.

Comprehensive Analysis of the Transcriptional and Mutational Landscape of Follicular and Papillary Thyroid Cancers

Follicular thyroid carcinoma (FTC) and benign follicular adenoma (FA) are indistinguishable by preoperative diagnosis due to their similar histological features. Here we report the first RNA sequencing study of these tumors, with data for 30 minimally invasive FTCs (miFTCs) and 25 FAs. We also compared 77 classical papillary thyroid carcinomas (cPTCs) and 48 follicular variant of PTCs (FVPTCs) to observe the differences in their molecular properties. Mutations in H/K/NRAS, DICER1, EIF1AX, IDH1, PTEN, SOS1, and SPOP were identified in miFTC or FA. We identified a low frequency of fusion genes in miFTC (only one, PAX8–PPARG), but a high frequency of that in PTC (17.60%). The frequencies of BRAF^V600E and H/K/NRAS mutations were substantially different in miFTC and cPTC, and those of FVPTC were intermediate between miFTC and cPTC. Gene expression analysis demonstrated three molecular subtypes regardless of their histological features, including Non–BRAF–Non–RAS (NBNR), as well as BRAF–like and RAS–like. The novel molecular subtype, NBNR, was associated with DICER1, EIF1AX, IDH1, PTEN, SOS1, SPOP, and PAX8–PPARG. The transcriptome of miFTC or encapsulated FVPTC was indistinguishable from that of FA, providing a molecular explanation for the similarly indolent behavior of these tumors. We identified upregulation of genes that are related to mitochondrial biogenesis including ESRRA and PPARGC1A in oncocytic follicular thyroid neoplasm. Arm-level copy number variations were correlated to histological and molecular characteristics. These results expanded the current molecular understanding of thyroid cancer and may lead to new diagnostic and therapeutic approaches to the disease.

Recently, The Cancer Genome Atlas proposed an improved classification of the subtypes of papillary thyroid carcinoma (PTC) based on gene expression profiles, which better represents cell signaling and differentiation. However, a molecular characterization of follicular thyroid carcinoma (FTC), which has a greater tendency for hematogenous spread to lung and bone is not yet fully elucidated. In this study, we describe the first RNA sequencing data of minimally invasive FTC (miFTC) and benign follicular adenoma (FA), which cause diagnostic difficulties due to their similar histological features. Additionally, classical PTC and follicular variant of PTC (FVPTC) were sequenced to compare their transcriptional and mutational landscape. BRAF, H/K/NRAS, fusion genes, and copy number variations were associated with tumor histology. Based on gene expression profiles, thyroid tumors were classified as three molecular subtypes regardless of histological subtypes, BRAF–like, RAS–like, and Non–BRAF–Non–RAS. In particular, we found identical gene expression profiles between miFTC, FA, and encapsulated FVPTC. Oncocytic follicular thyroid tumors have gene expression signatures related to mitochondrial biogenesis including ESRRA and PPARGC1A. These results expanded the current molecular understanding of thyroid cancer to its follicular types.

A Subset of the Follicular Variant of Papillary Thyroid Carcinoma Harbors the PAX8-PPARγ Translocation

The occurrence of the PAX8-PPARγ fusion gene is thought to be restricted to follicular tumors (adenomas and carcinomas) of the thyroid (FTA and FTC). Using interphase fluorescent in situ hybridization (FISH), together with recombinant tissue-type polymerase chain reaction (RT-PCR) and immunohistochemistry, we detected the PAX8-PPARγ translocation in 4 of 8 cases of the follicular variant of papillary thyroid carcinoma (FVPTC) exclusively or almost exclusively (>95%) composed of follicles. The 4 tumors with the translocation were larger and apparently more invasive than the remaining tumors, but the series is too small to allow a statistically meaningful comparison of the data. Our findings show that follicular thyroid carcinoma (PTC) may also harbor the PAX8-PPARγ fusion gene and indicate that a subset of FVPTC shares some molecular features of FTA and FTC.

Serum Immunoproteomics Combined With Pathological Reassessment of Surgical Specimens Identifies TCP-1ζ Autoantibody as a Potential Biomarker in Thyroid Neoplasia

CONTEXT

Current methods of preoperative diagnostics frequently fail to discriminate between benign and malignant thyroid neoplasms. In encapsulated follicular-patterned tumors (EnFPT), this discrimination is challenging even using histopathological analysis. Autoantibody response against tumor-associated antigens is a well-documented phenomenon with prominent diagnostic potential; however, autoantigenicity of thyroid tumors remains poorly explored.

OBJECTIVES

Objectives were exploration of tumor-associated antigen repertoire of thyroid tumors and identification of candidate autoantibody biomarkers capable of discrimination between benign and malignant thyroid neoplasms.

DESIGN, SETTING, AND PATIENTS

Proteins isolated from FTC-133 cells were subjected to two-dimensional Western blotting using pooled serum samples of patients originally diagnosed with either papillary thyroid carcinoma (PTC) or EnFPT represented by apparently benign follicular thyroid adenomas, as well as healthy individuals. Immunoreactive proteins were identified using liquid chromatography-tandem mass-spectrometry. Pathological reassessment of EnFPT was performed applying nonconservative criteria for capsular invasion and significance of focal PTC nuclear changes (PTC-NCs). Recombinant T-complex protein 1 subunitζ (TCP-1ζ) was used to examine an expanded serum sample set of patients with various thyroid neoplasms (n = 89) for TCP-1ζ autoantibodies. All patients were included in tertiary referral centers.

RESULTS

A protein demonstrating a distinct pattern of EnFPT-specific seroreactivity was identified as TCP-1ζ protein. A subsequent search for clinicopathological correlates of TCP-1ζ seroreactivity revealed nonclassical capsular invasion or focal PTC-NC in all TCP-1ζ antibody-positive cases. Further studies in an expanded sample set confirmed the specificity of TCP-1ζ autoantibodies to malignant EnFPT.

CONCLUSIONS

We identified TCP-1ζ autoantibodies as a potential biomarker for presurgical discrimination between benign and malignant encapsulated follicular-patterned thyroid tumors. Our results suggest the use of nonconservative morphological criteria for diagnosis of malignant EnFPT in biomarker identification studies and provide a peculiar example of uncovering the diagnostic potential of a candidate biomarker using incorporation of pathological reassessment in the pipeline of immunoproteomic research.

Encapsulated Thyroid Carcinoma of Follicular Cell Origin

Encapsulated carcinomas of follicular cell origin are subject to considerable controversies. This group includes an encapsulated/well-circumscribed (E/WC) follicular variant of papillary carcinoma (FVPTC) and encapsulated follicular and Hurthle cell carcinoma (EFC, EHC respectively). FVPTC usually presents as an E/WC tumor and less commonly as an infiltrative neoplasm. E/WC FVPTC rarely metastasizes to lymph nodes, whereas infiltrative tumors often present with cervical nodal metastases. Many studies revealed FVPTC in general to be genetically close to the follicular adenomas (FA)/EFC group of tumors. This is particularly true for the E/WC FVPTC which has a high rate of RAS and lack BRAFV600E mutations. Infiltrative FVPTC has an opposite molecular profile closer to classical papillary carcinoma than to FA/EFC (BRAFV600E > RAS mutations). Noninvasive E/WC FVPTCs are extremely indolent even if treated with lobectomy alone. While EFC and EHC with capsular invasion only have an excellent outcome, those with extensive (≥4 foci) lymphovascular invasion (LVI) have a significant rate of distant recurrence. The prognosis of those with focal LVI seems good, but more studies are needed to confirm their behavior. In EHC, those with extensive/significant LVI have a different RNA expression profile than those with less LVI. EHC appear to recur earlier, are less RAI avid, and have a different mutation profile than EFC. Noninvasive E/WC FVPTC should be treated conservatively. There is therefore a need to reclassify the E/WC FVPTC in order to prevent overtreatment. In view of their molecular and behavioral differences, EHC should not be considered a subset of EFC.

Comparison of the clinicopathological behavior of the follicular variant of papillary thyroid carcinoma and classical papillary thyroid carcinoma: A systematic review and meta-analysis

The follicular variant of papillary thyroid carcinoma (FV-PTC) is the second most common type of papillary thyroid carcinoma (PTC), and it has been increasingly diagnosed in recent years. However, whether FV-PTC behaves differently from classical PTC (C-PTC) remains controversial. To address this controversy, a meta-analysis was performed to determine the potential differences between FV-PTC and C-PTC in their clinicopathological behavior. The relevant published studies between January 1, 2003 and August 31, 2014 were reviewed according to the defined selection criteria using the PubMed database. Review Manager was used to calculate the pooled odds ratio (OR) or the mean difference (MD) with a 95% confidence interval (CI), using a random- or fixed-effect model for all analyses. In total, 112 studies were identified and examined; finally, only 36 studies met the inclusion criteria. In the 36 studies, compared to the clinicopathological behavior of patients with C-PTC, patients with FV-PTC had the following parameters: Similar mean age and similar prevalence of gender, tumor size ≥10 mm, multifocality, capsular invasion, vascular invasion, lymphocytic and/or Hashimoto's thyroiditis, and clinical stage; a larger mean tumor size and higher prevalence of age ≥45 years; and lower prevalence of extrathyroidal extensions, lymph node metastases, BRAF mutation and recurrence. The meta-analysis suggested that patients with FV-PTC have a more favorable clinicopathological behavior and improved prognosis compared to patients with C-PTC. Thus, patients with FV-PTC and C-PTC may be managed differently, and the two types of PTC should be clearly distinguished in future retrospective or prospective studies.

Integrated genomic characterization of papillary thyroid carcinoma

Papillary thyroid carcinoma (PTC) is the most common type of thyroid cancer. Here, we describe the genomic landscape of 496 PTCs. We observed a low frequency of somatic alterations (relative to other carcinomas) and extended the set of known PTC driver alterations to include EIF1AX, PPM1D, and CHEK2 and diverse gene fusions. These discoveries reduced the fraction of PTC cases with unknown oncogenic driver from 25% to 3.5%. Combined analyses of genomic variants, gene expression, and methylation demonstrated that different driver groups lead to different pathologies with distinct signaling and differentiation characteristics. Similarly, we identified distinct molecular subgroups of BRAF-mutant tumors, and multidimensional analyses highlighted a potential involvement of oncomiRs in less-differentiated subgroups. Our results propose a reclassification of thyroid cancers into molecular subtypes that better reflect their underlying signaling and differentiation properties, which has the potential to improve their pathological classification and better inform the management of the disease.

Invasion rather than nuclear features correlates with outcome in encapsulated follicular tumors: further evidence for the reclassification of the encapsulated papillary thyroid carcinoma follicular variant

The prognosis of the encapsulated follicular variant of papillary thyroid carcinoma (EFVPTC) and its relationship to encapsulated follicular carcinoma (EFC) and follicular adenoma (FA) is subject to controversy. All EFVPTCs, EFCs, and FAs identified at a single institution between 1981 and 2003 were analyzed microscopically. A cohort of FAs from a different hospital was also examined. EFVPTCs were subdivided into noninvasive EFVPTC (NIEFVPTC) and invasive EFVPTC (IEFVPTC) displaying capsular/vascular invasion. There were 83 EFVPTCs (57 noninvasive, 26 invasive), 14 EFCs, and 52 FAs. Similar to FA, over a median follow-up of 9.5 years, none of the NIEFVPTCs manifested lymph node metastasis (LNM) or recurred. Furthermore, with a median follow-up of 10.5 years, none of 39 NIEFVPTCs without radioactive iodine therapy recurred. Four (15%) of 26 IEFVPTCs and none of 14 EFCs harbored distant metastasis (P = .29). There was no difference in LNM rate and degree of vascular or capsular invasion between IEFVPTC and EFC (P > .1). All 4 IEFVPTCs with adverse behavior presented with distant metastasis and no LNM. Sixteen percent of IEFVPTCs had poor outcome, whereas there was none in the NIEFVPTCs (P = .007). In conclusion, NIEFVPTC seems to behave similarly to FA, whereas IEFVPTC can metastasize and spread like EFC. Thus, invasion rather than nuclear features drives outcome in encapsulated follicular tumors. Non-IEFVPTC could be treated in a conservative manner sparing patients unnecessary total thyroidectomy and radioactive iodine therapy. The position of the EFVPTC in the classification of thyroid neoplasia should be reconsidered.

Heterochromatin protein 1 expression is reduced in human thyroid malignancy

Owing to the loss of heterochromatin integrity that occurs during thyroid tumorigenesis, the expression of Heterochromatin Protein 1 isoforms HP1α and HP1β was assessed by immunohistochemistry in 189 thyroid tumors and non-neoplastic tissues. Expression of HP1β was significantly decreased in all thyroid lesions, except in follicular adenomas, when compared with matched adjacent normal tissue. This loss of HP1β expression may in part be caused by microRNA dysregulation. An example is miR-205, a microRNA that is abundantly upregulated in thyroid carcinomas and shown to reduce the expression of HP1β. In contrast to HP1β, HP1α expression was only reduced in metastatic carcinomas and poorly differentiated lesions. These results suggest the reduction of HP1β followed by a decrease in HP1α contributes to the pathogenesis of thyroid carcinomas, and their loss is a potential marker of thyroid malignancy and metastatic potential, respectively.

Molecular alterations in partially-encapsulated or well-circumscribed follicular variant of papillary thyroid carcinoma

BACKGROUND

Studies have described an encapsulated and an infiltrative form of the follicular variant of papillary thyroid carcinoma (FVPTC). Encapsulated FVPTCs have been reported to have virtually no recurrence risk or metastatic potential and to harbor RAS mutations but not BRAF mutations. In contrast, infiltrative tumors have significant metastatic potential, a risk of recurrence, and a BRAF mutation frequency of approximately 25%. In our experience, a substantial number of FVPTCs are neither fully encapsulated nor infiltrative, but instead are partially encapsulated (PE) or well circumscribed (WC). We have previously reported that PE/WC FVPTCs behave in an indolent fashion similar to encapsulated tumors. The purpose of the current study was to evaluate the molecular alterations in PE/WC FVPTC.

METHODS

We identified 28 PE/WC FVPTCs resected consecutively at our institution. Targeted mutation analysis of 41 genes including members of the RAS and RAF families was performed on DNA extracted from formalin-fixed, paraffin-embedded blocks using single-base extension chemistry and mass spectrometry.

RESULTS

Lymph node metastases were absent in all cases with sampled lymph nodes, and no patients developed tumor recurrences (median follow-up time, 72.8 months). Overall, 13 cases (46%) harbored RAS mutations, including seven (25%) with NRAS mutations (p.Gln61Arg) and six (21%) with HRAS mutations (five had p.Gln61Arg and one had a p.Gln61Lys substitution). No PE/WC FVPTCs had BRAF mutations.

CONCLUSIONS

The results of this study confirm our previous finding that PE/WC FVPTCs pursue an indolent clinical course. Additionally, we found that PE/WC tumors have a similar molecular profile to that of encapsulated FVPTCs with frequent RAS mutations (46%) and no BRAF mutations. These molecular results provide further evidence that PE/WC and encapsulated FVPTCs are biologically similar and should be distinguished from more aggressive infiltrative FVPTCs.

A Case of Multifocal Papillary Thyroid Carcinoma Consisting of One Encapsulated Follicular Variant with BRAF K601E Mutation and Three Conventional Types with BRAF V600E Mutation

Multifocal papillary thyroid carcinoma (mPTC) comprises about 20-30% of PTC. In mPTC, individual tumor foci can be identical or frequently composed of different histological types including follicular, solid, tall-cell or conventional patterns. We report a case of mPTC consisting of one encapsulated follicular variant of papillary thyroid carcinoma (FVPTC) and three conventional PTCs in a 44-year-old woman. This case genetically demonstrates unique features including the simultaneous presence of the BRAF V600E (T1799A) mutation and the BRAF K601E (A1801G) mutation in conventional PTC and FVPTC, respectively.

Risk stratification of follicular variant of papillary thyroid carcinoma

BACKGROUND

Recent studies have described an encapsulated and an infiltrative form of follicular variant of papillary thyroid carcinoma (FVPTC). While encapsulated tumors have been reported to have virtually no metastatic potential or recurrence risk if angioinvasion and capsular penetration are absent, infiltrative tumors have been found to have a significant metastatic potential and a risk of recurrence. In our experience, a substantial number of FVPTCs are neither fully encapsulated nor infiltrative, but instead are partially-encapsulated (PE) or well-circumscribed (WC). Thus, the aim of this study was to investigate the metastatic potential and recurrence risk of PE/WC FVPTCs in comparison with that of encapsulated and infiltrative tumors.

METHODS

We studied 77 FVPTCs resected between 2000 and 2002 and characterized the tumors as encapsulated, PE/WC, or infiltrative. Histologic assessment was then correlated with lymph node status and clinical outcome.

RESULTS

In our cohort, 27 (35%) tumors were encapsulated, 35 (45%) were PE/WC, and 15 (19%) were infiltrative. Lymph node status was similar between PE/WC and encapsulated tumors, but was significantly different between encapsulated and infiltrative groups (p<0.001), and PE/WC and infiltrative groups (p<0.001). Lymph node metastases were absent in all 15 cases of encapsulated tumors and all 9 cases of PE/WC tumors with sampled lymph nodes, but were present in 7 of 9 (78%) cases of infiltrative tumors with sampled lymph nodes. For patients with available clinical follow-up (66 cases, 86%), the median follow-up time was 111 months. No patients with encapsulated tumors recurred, one (3%) patient with a PE/WC tumor had recurrent/residual disease, and two (15%) patients with infiltrative tumors had recurrent/residual disease. The one patient with a PE/WC tumor who had recurrent/residual disease had a tumor bed recurrence 7 years after initial resection. Significantly, this was the only patient in the PE/WC group that had a positive resection margin.

CONCLUSIONS

Our results demonstrate that PE/WC FVPTCs have a very low metastatic potential/recurrence risk, indicating that they should be distinguished from more aggressive infiltrative FVPTCs.

DNA copy number variations characterize benign and malignant thyroid tumors

CONTEXT

Fine-needle aspiration (FNA) is the best diagnostic tool for preoperative evaluation of thyroid nodules but is often inconclusive as a guide for surgical management.

OBJECTIVE

Our hypothesis was that thyroid tumor subtypes may show characteristic DNA copy number variation (CNV) patterns, which may further improve the preoperative classification.

DESIGN

Our study cohorts included benign follicular adenomas (FAs), classic papillary thyroid carcinomas (PTCs), and follicular variant PTCs (FVPTCs), the three subtypes most commonly associated with inconclusive preoperative cytopathology.

SETTING

Tissue and FNA samples were obtained at an academic tertiary referral center.

PATIENTS

Cases were identified that underwent partial or complete thyroidectomy for malignant or indeterminate thyroid lesions between 2000 and 2008 and had adequate snap-frozen tissue.

INTERVENTIONS

Pairs of tumor tissue and matching normal thyroid tissue-derived DNA were compared using 550K single-nucleotide polymorphism arrays.

MAIN OUTCOME MEASURE

Statistically significant differences in CNV patterns between tumor subtypes were identified.

RESULTS

Segmental amplifications in chromosomes (Ch) 7 and 12 were more common in FAs than in PTCs or FVPTCs. Additionally, a subset of FAs and FVPTCs showed deletions in Ch22. We identified the 5 CNV-associated genes best at discriminating between FAs and PTCs/FVPTCs, which correctly classified 90% of cases. These 5 Ch12 genes were validated by quantitative genomic PCR and gene expression array analyses on the same patient cohort. The 5-gene signature was then successfully validated against an independent test cohort of benign and malignant tumor samples. Finally, we performed a feasibility study on matched FA-derived intraoperative FNA samples and were able to correctly identify FAs harboring the Ch12 amplification signature, whereas FAs without amplification showed a normal Ch12 signature.

CONCLUSIONS

Thyroid tumor subtypes possess characteristic genomic profiles that may further our understanding of structural genetic changes in thyroid tumor subtypes and may lead to the development of new diagnostic biomarkers in FNA samples.

Copy number alteration and uniparental disomy analysis categorizes Japanese papillary thyroid carcinomas into distinct groups

The aim of the present study was to investigate chromosomal aberrations in sporadic Japanese papillary thyroid carcinomas (PTCs), concomitant with the analysis of oncogene mutational status. Twenty-five PTCs (11 with BRAF(V600E), 4 with RET/PTC1, and 10 without mutation in HRAS, KRAS, NRAS, BRAF, RET/PTC1, or RET/PTC3) were analyzed using Genome-Wide Human SNP Array 6.0 which allows us to detect copy number alteration (CNA) and uniparental disomy (UPD), also referred to as copy neutral loss of heterozygosity, in a single experiment. The Japanese PTCs showed relatively stable karyotypes. Seven cases (28%) showed CNA(s), and 6 (24%) showed UPD(s). Interestingly, CNA and UPD were rarely overlapped in the same tumor; the only one advanced case showed both CNA and UPD with a highly complex karyotype. Thirteen (52%) showed neither CNA nor UPD. Regarding CNA, deletions tended to be more frequent than amplifications. The most frequent and recurrent region was the deletion in chromosome 22; however, it was found in only 4 cases (16%). The degree of genomic instability did not depend on the oncogene status. However, in oncogene-positive cases (BRAF(V600E) and RET/PTC1), tumors with CNA/UPD were less frequent (5/15, 33%), whereas tumors with CNA/UPD were more frequent in oncogene-negative cases (7/10, 70%), suggesting that chromosomal aberrations may play a role in the development of PTC, especially in oncogene-negative tumors. These data suggest that Japanese PTCs may be classified into three distinct groups: CNA(+), UPD(+), and no chromosomal aberrations. BRAF(V600E) mutational status did not correlate with any parameters of chromosomal defects.

Follicular thyroid carcinoma

Follicular thyroid carcinoma is being diagnosed less and less frequently despite the increasing incidence of well-differentiated thyroid carcinomas everywhere. This review will discuss the reasons underlying such an observation focusing on the evolution of the morphological and immunohistochemical diagnostic criteria of follicular thyroid tumors. It will address the differential diagnosis between follicular carcinoma and three tumor types--follicular adenoma, follicular variant of papillary carcinoma and poorly differentiated carcinoma--as well as the problems raised by the newly described categories of follicular tumors: follicular tumor of uncertain malignant potential, well-differentiated tumor of uncertain malignant potential and well-differentiated carcinoma, not otherwise specified. Finally, the prognostic and therapeutic significance of some promising molecular biomarkers will be discussed within the frame of the aforementioned histopathological classification.

Distinct genetic changes characterise multifocality and diverse histological subtypes in papillary thyroid carcinoma

AIMS

This study was undertaken to investigate the genetic factors underlying the development of multifocality and phenotypic diversity in multifocal papillary thyroid carcinoma (mPTC).

METHODS

Loss of heterozygosity (LOH) and BRAF(V600E) mutation status were analysed in a total of 55 individual tumour foci from 18 cases of mPTC. The genetic findings and morphology of tumour foci were then compared.

RESULTS

Multifocal PTC LOH rates were higher than observed previously in solitary PTC. Different patterns of LOH and BRAF(V600E) positivity separated follicular variant tumours and tumour foci from other PTC histological subtypes. In five cases, genetic alterations were detected in morphologically normal thyroid epithelium.

CONCLUSIONS

These findings support the concept that multifocal PTCs develop through clonal selection from a field of pre-neoplastic cells, with morphotype differentiation correlating with specific tumour-genetic alterations. The relatively high genetic disarray in multifocal PTC may underlie their ability to spread throughout the thyroid gland.

Encapsulated malignant follicular cell-derived thyroid tumors

Encapsulated malignant follicular cell-derived thyroid tumors are subject to considerable controversies. This group includes encapsulated follicular variant of papillary carcinoma (FVPTC) and encapsulated (so-called minimally invasive) follicular carcinoma (EFC). FVPTC usually presents as an encapsulated tumor and less commonly as a partially/nonencapsulated infiltrative neoplasm. The encapsulated form rarely metastasizes to lymph node, whereas infiltrative tumors often harbor nodal metastases. Encapsulated FVPTC have a molecular profile very close to follicular adenomas/carcinomas (high rate of RAS and absence of BRAF mutations). Infiltrative follicular variant has an opposite molecular profile closer to classical papillary thyroid carcinoma than to follicular adenoma/carcinoma (BRAF > RAS mutations). Noninvasive encapsulated FVPTC are extremely indolent even if treated with lobectomy without radioactive iodine therapy. Although most EFC are thought to have an excellent outcome, there are cases of EFC that recur and metastasize. EFC with angioinvasion, especially if extensive, have a significant rate of distant recurrence. Encapsulated FVPTC have a molecular profile and a clinical behavior very similar to the follicular adenoma/carcinoma class of tumor. If noninvasive, encapsulated FVPTC should be treated in a very conservative fashion. EFC with angioinvasion, especially if extensive, should not be termed minimally invasive in order to prevent undertreatment of the patient.

Cytogenetic and molecular events in adenoma and well-differentiated thyroid follicular-cell neoplasia

In spite of its simple organization, the thyroid gland can give rise to a wide spectrum of neoplasms, ranging from innocuous to highly malignant lesions. Approximately 94% of the malignancies is represented by well-differentiated thyroid carcinoma originating from follicular cells. These neoplasms are divided into two main categories, papillary thyroid carcinoma and follicular thyroid carcinoma. Despite their origin from the same type of cells, the two neoplasias show different biological behavior and a different set of genetic features, including specific cytogenetic patterns. Thyroid adenoma is the benign counterpart of follicular carcinoma. No benign counterpart of papillary carcinoma has yet been identified. The chromosomes of thyroid nodules have been investigated since 1965, and different cytogenetic subgroups have been recognized, some of which show structural chromosomal rearrangements. These structural changes lead to the formation of fusion genes RET-PTC, TRK(-T), and BRAF-AKAP9, which originate as a result of intrachromosomal or interchromosomal rearrangements and are found in papillary thyroid carcinoma. Fusion genes involving PPARγ are caused mainly by translocations and are characteristic of follicular neoplastic tissue. Radiation exposure and the particular architectural arrangement of chromatin regions in which the affected genes lie during interphase are thought to favor the formation of fusion genes in papillary thyroid carcinoma and possibly also in follicular thyroid carcinoma.

Clinical implications of molecular markers in follicular cell-derived thyroid cancer

The increasing use/applications of molecular biology techniques have provided new insights on the genetic changes that underlie carcinogenesis and tumor progression in thyroid cancer. Molecular analysis may improve the histopathologic evaluation of follicular cell-derived thyroid carcinoma, not only elucidating some unresolved problems related to the diagnosis and disease prognosis, but also by improving patient management. Besides increasing our comprehension of cancer biology, either genetic alterations or gene expression profiles implicated in thyroid carcinogenesis shed new light on innovative diagnostic procedures as well as on targeted therapies.

Gene expression profiling associated with the progression to poorly differentiated thyroid carcinomas

BACKGROUND

Poorly differentiated thyroid carcinomas (PDTC) represent a heterogeneous, aggressive entity, presenting features that suggest a progression from well-differentiated carcinomas. To elucidate the mechanisms underlying such progression and identify novel therapeutic targets, we assessed the genome-wide expression in normal and tumour thyroid tissues.

METHODS

Microarray analyses of 24 thyroid carcinomas - 7 classic papillary, 8 follicular variants of papillary (fvPTC), 4 follicular (FTC) and 5 PDTC - were performed and correlated with RAS, BRAF, RET/PTC and PAX8-PPARG alterations. Selected genes were validated by quantitative RT-PCR in an independent set of 28 thyroid tumours.

RESULTS

Unsupervised analyses showed that gene expression similarity was higher between PDTC and fvPTC, particularly for tumours harbouring RAS mutations. Poorly differentiated thyroid carcinomas presented molecular signatures related to cell proliferation, poor prognosis, spindle assembly checkpoint and cell adhesion. Compared with normal tissues, PTC had 307 out of 494 (60%) genes over-expressed, FTC had 137 out of 171 (80%) genes under-expressed, whereas PDTC had 92 out of 107 (86%) genes under-expressed, suggesting that gene downregulation is involved in tumour dedifferentiation. Significant UHRF1 and ITIH5 deregulated gene expression in PDTC, relatively to normal tissues, was confirmed by quantitative RT-PCR.

CONCLUSION

Our findings suggest that fvPTC are possible precursors of PDTC. Furthermore, UHRF1 and ITIH5 have a potential therapeutic/prognostic value for aggressive thyroid tumours.

Problems and controversies in the histopathology of thyroid carcinomas of follicular cell origin

CONTEXT

Despite past and recent efforts, many problems and controversies remain in the classification of thyroid carcinomas of follicular cell origin. These controversies have an impact on the prognosis and therapy of patients with thyroid carcinoma as well as on the development of robust cutting-edge research aimed at better outcome and quality of life.

OBJECTIVE

To focus on 3 contentious areas with significant clinical value: the follicular variant of papillary thyroid carcinoma, the extent of invasion in follicular carcinoma, and the poorly differentiated thyroid carcinomas.

DATA SOURCES

The published English language literature was reviewed.

CONCLUSIONS

Recent data show that prognosis and therapy for many disease entities can be better delineated if a meticulous microscopic examination is performed. An accurate assessment of the extent of invasion (especially vascular) is crucial. Proliferative grading (ie, mitosis and necrosis) is of high prognostic value and should be looked for in every specimen. In addition, molecular data gathered to date can help reassess these tumors at the histologic level. Classification proposals based on personal experience rather than adequate and careful clinical follow-up should be discouraged.

Expression of iodine metabolism genes in human thyroid tissues: evidence for age and BRAFV600E mutation dependency

CONTEXT

Children present a higher susceptibility to developing thyroid cancer after radioiodine exposure and also a higher frequency of functional metastases than adults.

OBJECTIVE

To assess the mRNA expression of the sodium/iodide (Na(+)/I(-)) symporter (NIS), the Pendred syndrome gene (PDS), thyroperoxidase (TPO), thyroglobulin (Tg) and TSH receptor (TSH-R) in normal thyroid tissues (NTTs) and papillary thyroid carcinomas (PTCs) among different age groups.

METHODS

Analysis included 59 samples: 21 NTTs and 38 PTCs, of which 21 were the classic type (CPTC) and 17 the follicular variant (FVPTC). Patients were divided into three age groups: I (n = 16) 5-21 years, II (n = 13) 22-59 years, and III (n = 10) 60-91 years. The relative mRNA expression of the five target genes was determinate by quantitative reverse transcription polymerase chain reaction (QRT-PCR).

RESULTS

Expression of all genes was significantly higher in NTTs than in PTCs, and it was not age dependent in the NTT group. Among PTCs, the mean expression of PDS, TPO and TSH-R was significantly lower in group II than in group I. PDS, TPO and Tg expression was significantly lower in classic PTCs than in FVPTCs. The difference was related to a higher frequency of the BRAF(V600E) mutation in the former group.

CONCLUSIONS

The finding of higher PDS, TPO and TSH-R mRNA expression in paediatric vs. adult primary tumour tissues supports the hypothesis that this might contribute to the increased functional activity of metastases in the paediatric group. The finding that mRNA expression of the target genes in NTT was not age dependent does not provide an explanation for the higher susceptibility in the paediatric group.

Encapsulated papillary thyroid carcinoma: a clinico-pathologic study of 106 cases with emphasis on its morphologic subtypes (histologic growth pattern)

BACKGROUND

Encapsulated papillary thyroid carcinoma (EPTC) can have a histologic growth pattern similar to the one seen in classical papillary thyroid carcinoma (PTC) or akin to the follicular variant of PTC (FVPTC). This study aims to assess the behavior of EPTC according to its growth pattern.

METHODS

All cases of thyroid carcinomas treated at our institution between 1980 and 2000 were reviewed and reclassified according to current histopathologic criteria.

RESULTS

After review by two pathologists, 106 cases were included. Forty-three (41%) of the cases were identified as encapsulated classical PTC (E-CPTC) and 63 (59%) as encapsulated FVPTC (E-FVPTC). E-FVPTC had a higher rate of vascular invasion (16/63; 25%) than E-CPTC (2/43; 5%) (p = 0.007). In contrast, E-CPTC had a higher frequency of capsular invasion (28/43; 65%) than E-FVPTC (24/63, 38%) (p = 0.01). The lymph node metastatic rate was significantly higher in E-CPTC (11/43, 26%) compared to E-FVPTC (2/63, 3%) (p = 0.0014). All 34 noninvasive E-FVPTC lacked evidence of nodal metastases while 4 of 15 (27%) noninvasive E-CPTC presented with nodal disease (p = 0.006). Distant metastasis occurred only in four cases of E-FVPTC at presentation. These four FVPTC had extensive capsular and/or vascular invasion and no nodal disease. None of noninvasive EPTC recurred, including 30 patients treated by lobectomy without radioactive iodine (RAI) therapy (median follow-up: 8.9 years).

CONCLUSION

E-CPTC resembles classical PTC in its propensity to metastasize to lymph nodes and its vascular/capsular invasive pattern while E-FVPTC behaves more like follicular carcinoma/adenoma group of tumors. Meticulous search for capsular and vascular invasion can reliably predict the metastatic potential of E-FVPTC but not of E-CPTC. The latter can therefore be treated like unencapsulated classical PTC. Noninvasive E-FVPTC could be managed like minimally invasive follicular carcinoma by lobectomy without RAI therapy. Invasive E-FVPTC seem quite indolent if no distant metastases are found at presentation.

The Role of the PAX8/PPARgamma Fusion Oncogene in Thyroid Cancer

Thyroid cancer is uncommon and exhibits relatively low mortality rates. However, a subset of patients experience inexorable growth, metastatic spread, and mortality. Unfortunately, for these patients, there have been few significant advances in treatment during the last 50 years. While substantial advances have been made in recent years about the molecular genetic events underlying papillary thyroid cancer, the more aggressive follicular thyroid cancer remains poorly understood. The recent discovery of the PAX8/PPARγ translocation in follicular thyroid carcinoma has promoted progress in the role of PPARγ as a tumor suppressor and potential therapeutic target. The PAX8/PPARγ fusion gene appears to be an oncogene. It is most often expressed in follicular carcinomas and exerts a dominant-negative effect on wild-type PPARγ, and stimulates transcription of PAX8-responsive promoters. PPARγ agonists have shown promising results in vitro, although very few studies have been conducted to assess the clinical impact of these agents.

Sonographic features of the follicular variant of papillary thyroid carcinoma

OBJECTIVE

The purpose of this study was to evaluate the sonographic findings of the follicular variant of papillary thyroid carcinoma (FVPTC) and to assess the role of preoperative fine-needle aspiration biopsy (FNAB).

METHODS

The sonographic findings of 27 thyroid nodules in 26 patients (2 male and 24 female; mean age, 45 years) with surgically proven FVPTC were reviewed retrospectively. Findings were categorized according to the echogenicity, margin, shape, and presence of microcalcifications. Malignant findings included marked hypoechogenicity, irregular or microlobulated margins, a taller-than-wide shape, and microcalcifications. Thyroid nodules with a single malignant finding as described above were classified as malignant. All patients underwent sonographically guided FNAB, and the sensitivity of the cytologic results was calculated.

RESULTS

Lesion sizes varied from 3 to 34 mm (mean, 15.2 mm), and lesions were most commonly solid (23 [85.2%]), hypoechoic (14 [51.9%]), and oval (17 [63%]) with well-defined margins (14 [51.9%]) and no microcalcifications (23 [85.2%]). Eighteen lesions (66.7%) were correctly classified as malignant, whereas 9 (33.3%) were classified as benign on the basis of sonographic criteria. Twenty-four samples were adequate for cytologic examination, and 3 were inadequate. Twenty-one of 24 diagnostic cytologic results (87.5%) were suspicious for papillary carcinoma (5 of 21 [20.8%]) or malignant (16 of 21 [66.7%]), whereas 3 lesions (12.5%) had benign results. The sensitivity of FNAB was 77.8% (21 of 27).

CONCLUSIONS

The follicular variant of papillary thyroid carcinoma tends to have relatively benign sonographic features, such as hypoechogenicity, well-defined margins, an oval shape, and no microcalcifications, but most lesions were correctly classified as malignant by both sonography and FNAB. The possibility of FVPTC should be considered when thyroid nodules with a relatively benign sonographic appearance have suspicious or malignant FNAB results.