Thyroid tumours of uncertain malignant potential: frequency and diagnostic reproducibility

Investigation of pre-operative demographic, biochemical, sonographic and cytopathological findings in low-risk thyroid neoplasms

OBJECTIVE

The present article analyses pre-operative demographic, biochemical, sonographic and histopathological characteristics of low-risk thyroid neoplasms (LRTNs), with a focus on four subgroups, "well-differentiated carcinoma-not otherwise specified" (WDC-NOS), "non-invasive follicular thyroid neoplasm with papillary like nuclear features" (NIFTP), "well-differentiated tumours of uncertain malignant potential" (WDT-UMP) and "follicular tumour of uncertain malignant potential" (FT-UMP).

METHODS

The study retrospectively analyzed the histopathology of 2453 malignant thyroids and the final analyses included 99 cases diagnosed with LRTNs. The demographic and clinical features, pre-operative thyroid function, ultrasonography results, cytopathology results, histopathology results and prognostic classifications were assessed.

RESULTS

The groups were similar demographic characteristics and the majority of clinical data, including comorbidities, thyroid function tests, thyroid cancer/neck radiotherapy history. NIFTPs represented 69.7% of all LRTNs. All (100%) WDT-UMPs had solitary nodules. Index nodule volume differed among the groups (p = .036), it was the lowest in WDC-NOS [0.68 (0.63-0.72 cc)] and highest in FT-UMP [12.6 (0.5-64 cc)]. Echogenicity findings were similar. Index nodule TIRADS demonstrated a significant difference (p = .021) but index nodule halo sign and BETHESDA scores were similar in all groups. The diameter, localisation and multicentric structure of LRTNs were again similar for all groups. Finally, prognostic scores suggested similar outcomes in all groups.

CONCLUSION

The majority of LRTNs were NIFTPs in our population and all WDT-UMPs were solitary lesions. Index nodule volume was the most essential discriminating sonographic finding but further research must be performed before discriminatory potential can be described.

Challenges in Encapsulated Follicular-Patterned Tumors: How Much Is Enough? Evaluation of Nuclear Atypia, Architecture, and Invasion

Thyroid pathology is notoriously fraught with high interobserver variability, and follicular-patterned tumors are among some of the most challenging to assess accurately and reproducibly. Given that encapsulated or well-circumscribed follicular-patterned tumors often have similar molecular profiles, that is, frequent RAS or RAS-like alterations, the diagnosis usually relies on histopathologic examination alone. Unfortunately, many of the features that are used for diagnosis and prognosis of these tumors have long been controversial and frequently debated topics, both due to their subjectivity and their evolving (or not yet resolved) definitions. In more recent years, the introduction of noninvasive follicular thyroid neoplasm with papillary-like nuclear features has added further complexity to this discussion. In particular, the criteria and significance of nuclear features of papillary thyroid carcinoma, architectural patterns, and invasive growth still pose significant diagnostic challenges and confusion. This review explores some of the challenges in evaluating encapsulated follicular-patterned tumors, focusing on those histologic elements.

Overview of the 2022 WHO Classification of Thyroid Neoplasms

This review summarizes the changes in the 5th edition of the WHO Classification of Endocrine and Neuroendocrine Tumors that relate to the thyroid gland. The new classification has divided thyroid tumors into several new categories that allow for a clearer understanding of the cell of origin, pathologic features (cytopathology and histopathology), molecular classification, and biological behavior. Follicular cell-derived tumors constitute the majority of thyroid neoplasms. In this new classification, they are divided into benign, low-risk, and malignant neoplasms. Benign tumors include not only follicular adenoma but also variants of adenoma that are of diagnostic and clinical significance, including the ones with papillary architecture, which are often hyperfunctional and oncocytic adenomas. For the first time, there is a detailed account of the multifocal hyperplastic/neoplastic lesions that commonly occur in the clinical setting of multinodular goiter; the term thyroid follicular nodular disease (FND) achieved consensus as the best to describe this enigmatic entity. Low-risk follicular cell-derived neoplasms include non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP), thyroid tumors of uncertain malignant potential, and hyalinizing trabecular tumor. Malignant follicular cell-derived neoplasms are stratified based on molecular profiles and aggressiveness. Papillary thyroid carcinomas (PTCs), with many morphological subtypes, represent the BRAF-like malignancies, whereas invasive encapsulated follicular variant PTC and follicular thyroid carcinoma represent the RAS-like malignancies. This new classification requires detailed subtyping of papillary microcarcinomas similar to their counterparts that exceed 1.0 cm and recommends not designating them as a subtype of PTC. The criteria of the tall cell subtype of PTC have been revisited. Cribriform-morular thyroid carcinoma is no longer classified as a subtype of PTC. The term "Hürthle cell" is discouraged, since it is a misnomer. Oncocytic carcinoma is discussed as a distinct entity with the clear recognition that it refers to oncocytic follicular cell-derived neoplasms (composed of > 75% oncocytic cells) that lack characteristic nuclear features of PTC (those would be oncocytic PTCs) and high-grade features (necrosis and ≥ 5 mitoses per 2 mm²). High-grade follicular cell-derived malignancies now include both the traditional poorly differentiated carcinoma as well as high-grade differentiated thyroid carcinomas, since both are characterized by increased mitotic activity and tumor necrosis without anaplastic histology and clinically behave in a similar manner. Anaplastic thyroid carcinoma remains the most undifferentiated form; squamous cell carcinoma of the thyroid is now considered as a subtype of anaplastic carcinoma. Medullary thyroid carcinomas derived from thyroid C cells retain their distinct section, and there is a separate section for mixed tumors composed of both C cells and any follicular cell-derived malignancy. A grading system for medullary thyroid carcinomas is also introduced based on mitotic count, tumor necrosis, and Ki67 labeling index. A number of unusual neoplasms that occur in the thyroid have been placed into new sections based on their cytogenesis. Mucoepidermoid carcinoma and secretory carcinoma of the salivary gland type are now included in one section classified as "salivary gland-type carcinomas of the thyroid." Thymomas, thymic carcinomas and spindle epithelial tumor with thymus-like elements are classified as "thymic tumors within the thyroid." There remain several tumors whose cell lineage is unclear, and they are listed as such; these include sclerosing mucoepidermoid carcinoma with eosinophilia and cribriform-morular thyroid carcinoma. Another important addition is thyroblastoma, an unusual embryonal tumor associated with DICER1 mutations. As in all the WHO books in the 5th edition, mesenchymal and stromal tumors, hematolymphoid neoplasms, germ cell tumors, and metastatic malignancies are discussed separately. The current classification also emphasizes the value of biomarkers that may aid diagnosis and provide prognostic information.

Mutation profiles of follicular thyroid tumors by targeted sequencing

Background

One of the major challenges remaining in the classification of thyroid tumor is the determination of whether a nodule is benign or malignant. We aimed to characterize the mutational profiles of follicular thyroid tumor and to identify markers with potential diagnostic and prognostic implications.

Methods

Targeted sequencing with a panel of 18 thyroid cancer-related genes was performed on 48 tissue samples from follicular thyroid adenoma (FTA), 32 follicular tumors of uncertain malignant potential (FT-UMP), 17 well-differentiated tumors of uncertain malignant potential (WDT-UMP) and 53 samples from follicular thyroid carcinoma (FTC). The correlation of mutation profiles and clinicopathological features and prognosis were also analyzed.

Results

We identified 95 nonsilent mutations spanning 14 genes. Specifically, TERT promoter (TERTp) mutations were exclusively detected in FTC. A total of 80% EIF1AX exon 2 mutations (4/5) and 75% TSHR mutations (3/4) occurred in FTA, whereas the rest of them occurred in FT-UMP. KRAS mutations and TP53 mutations were only presented in borderline or malignant tumors. H/N-RAS mutations were detected in all four subtypes, but were most commonly found in WDT-UMP (p = 0.031). All N-RAS mutations were located at codon 61. BRAF V600E and RET fusion were absent in the entire cohort. In FTC cases, EIF1AX mutations were all located at intron 5/exon 6 and correlated with advanced disease (p = 0.032). Both EIF1AX and TERTp mutations predicted shorter disease-free survival (p = 0.007, p = 0.024, respectively). Further analysis revealed that TERTp mutations were correlated with shorter disease-free survival in patients with minimally invasive /encapsulated angioinvasive FTC (p = 0.017), but not in those with widely invasive FTC (p = 0.297).

Conclusion

TERTp, EIF1AX, TSHR, H/N/K-RAS and TP53 mutations may have diagnostic or prognostic potential in follicular thyroid tumors. TERTp mutations may predict a poor outcome in patients with minimally invasive/encapsulated angioinvasive FTC.

Extremely Well-Differentiated Papillary Thyroid Carcinoma Resembling Adenomatous Hyperplasia Can Metastasize to the Skull: A Case Report

We describe herein histologic, immunohistochemical, and molecular findings and clinical manifestations of a rare case of an extremely well differentiated papillary thyroid carcinoma (EWD-PTC). Similarly, it is also difficult to diagnose follicular variant papillary thyroid carcinoma (FVPTC), whose diagnosis is still met with controversy. A recently reported entity of well-differentiated tumor of uncertain malignant potential (WDT-UMP) is added to the diagnostic spectrum harboring EWD-PTC and FVPTC. We report this case, because EWD-PTC is different from FVPTC in its papillary architecture, and also from WDT-UMP in its recurrence and metastatic pattern. These morphologically deceptive entities harbored diagnostic difficulties in the past because the diagnosis depended solely on histology. However, they are now diagnosed with more certainty by virtue of immunohistochemical and molecular studies. We experienced a case of EWD-PTC, which had been diagnosed as adenomatous hyperplasia 20 years ago and manifested recurrence with lymph node (LN) metastasis 7 years later. After another 7 years of follow-up, a new thyroid lesion had developed, diagnosed as FVPTC, with LN metastasis of EWD-PTC. One year later, the patient developed metastatic FVPTC in the skull. Immunohistochemically, the EWD-PTC was focally positive for CK19, negative for galectin-3, and focally negative for CD56. Molecular studies revealed BRAF-positivity and K-RAS negativity. The FVPTC in the left thyroid showed both BRAF and K-RAS negativity. In conclusion, EWD-PTC and FVPTC share similar histologic features, but they are different tumors with different molecular biologic and clinical manifestations. A large cohort of EWD-PTC should be included in further study.

Breast lesions of uncertain malignant nature and limited metastatic potential: proposals to improve their recognition and clinical management

Breast lesions comprise a family of heterogeneous entities with variable patterns of presentation, morphology and clinical behaviour. The majority of breast lesions are classified traditionally into benign and malignant conditions and their behaviour can, in the vast majority of cases, be predicted with a reasonable degree of accuracy. However, there remain lesions which show borderline features and lie in a grey zone between benign and malignant, as their behaviour cannot be predicted reliably. Defined pathological categorization of such lesions is challenging, and for some entities is recognized to be subjective and include a range of diagnoses, and forms of terminology, which may trigger over- or undertreatment. The rarity of these lesions makes the acquisition of clinical evidence problematic and limits the development of a sufficient evidence base to support informed decision-making by clinicians and patients. Emerging molecular evidence is providing a greater understanding of the biology of these lesions, but this may or may not be reflected in their clinical behaviour. Herein we discuss some breast lesions that are associated with uncertainty regarding classification and behaviour, and hence management. These include biologically invasive malignant lesions associated with uncertain metastatic potential, such as low-grade adenosquamous carcinoma, low-grade fibromatosis-like spindle cell carcinoma and encapsulated papillary carcinoma. Other lesions of uncertain malignant nature remain, such as mammary cylindroma, atypical microglandular adenosis, mammary pleomorphic adenoma and infiltrating epitheliosis. The concept of categories of (1) breast lesions of uncertain malignant nature and (2) breast lesions of limited metastatic potential are proposed with details of which histological entities could be included in each category, and their management implications are discussed.

Comparing Clinicopathologic and Radiographic Findings Between TT-UMP, Classical, and Non-Encapsulated Follicular Variants of Papillary Thyroid Carcinomas

Thyroid tumors of uncertain malignant potential (TT-UMP) comprise an accepted subgroup of follicular-patterned thyroid tumors for which benignancy or malignancy cannot be precisely assessed. We aimed to evaluate the demographic characteristics, ultrasound (US) findings, and cytological results of patients with TT-UMP and compare these findings to a classical variant of papillary thyroid carcinoma (CV-PTC) and non-encapsulated follicular variant of PTC (NEFV-PTC) patients; we also evaluated the immunohistochemical characteristics of patients with TT-UMP. Twenty-four patients with TT-UMP, 672 with CV-PTC, and 132 with NEFV-PTC were included in the study. Mean longitudinal nodule size and median nodule volume were higher in the TT-UMP group than in the CV-PTC and NEFV-PTC groups (p < 0.001 and p < 0.001 for CV-PTC; p < 0.001 and p = 0.008 for NEFV-PTC). The presence of halo and peripheral vascularization was observed more frequently in the TT-UMP group than in the CV-PTC group (p = 0.002 and p = 0.024). Benign and follicular neoplasm/suspicious for follicular neoplasm cytological results were higher in the TT-UMP group than in the CV-PTC group (p = 0.030 and p = 0.001). US findings were similar between TT-UMP and NEFV-PTC groups (all, p > 0.05). However, none of the patients with TT-UMP were called malignant; 105 patients (31.2 %) of CV-PTC and 11 patients (9.5 %) of NEFV-PTC (infiltrative FV) were classified as malignant cytologically. Tumor size was higher in the TT-UMP group than in the CV-PTC and NEFV-PTC groups (p < 0.001 and p = 0.006). In the TT-UMP group, positive expression of HBME-1, CK-19, and Gal-3 was found in 50, 33.3, and 25 % of patients, respectively. This study demonstrated that none of the TT-UMP patients were evaluated as malignant in preoperative cytology. However, patients with TT-UMP had higher nodule and tumor sizes than CV-PTC and NEFV-PTC patients; US features were similar between NEFV-PTC and TT-UMP patients.

Diagnostic criteria of well differentiated thyroid tumor of uncertain malignant potential; a histomorphological and immunohistochemical appraisal

BACKGROUND

Well differentiated thyroid tumor of uncertain malignant potential (WDT-UMP) represents a true "gray zone" of "follicular patterned" thyroid lesions, that needs to be characterized in order to outright the diagnosis of carcinoma and avoid unnecessary aggressive treatment.

AIM

To emphasize on the histomorphological criteria for more accurate diagnosis of WDT-UMP. Also to compare the immunohistochemical expression of CK19 of WDT-UMP versus adenoma and papillary thyroid carcinoma (PTC).

MATERIALS AND METHODS

The study included 60 thyroid specimens; 18 WDT-UMPs, 24 PTC (18 classic variant and 6 follicular variants) and 18 benign thyroid lesions (8 adenoma, 6 Hashimoto's thyroiditis and 4 hyperplastic nodules). H&E stained sections were assessed according to the published major and minor criteria of malignancy in the thyroid. CK 19 immunostaining was examined and evaluated according to the proportion and intensity scores.

RESULTS

We could detect the absence of nuclear inclusions, presence of characteristic nuclear groove, nuclear clearing, ovoid nuclei, nuclear crowdness, nuclear enlargement and pleomorphism as important reliable features for diagnosis of WDT-UMP with p value (<0.0001 for each). WDT-UMP showed moderate to strong CK 19 immunostaining with proportion scores 3 and 4; an intermediate expression profile; higher than adenoma and less than papillary carcinoma (p<0.0001).

CONCLUSION

The constellations of both major and minor criteria of malignancy are important clues for WDT-UMP diagnosis which could be ascertained by CK 19 immunostaining.

The Bethesda system for reporting thyroid cytopathology: an institutional experience of the outcome of indeterminate categories

OBJECTIVE

In this study, we investigated the efficacy of the Bethesda system (TBS) for reporting thyroid cytopathology in determining the risk of malignancy for indeterminate cases. These cases comprised atypia or follicular lesion of undetermined significance (AUS/FLUS), follicular neoplasia or suspicious for follicular neoplasia (FN/SFN) and suspicious for malignancy (SM) categories. AUS/FLUS cases were further subcategorized according to their patterns, and the malignancy rate for each subcategory was calculated.

METHODS

A total of 6310 thyroid fine needle aspiration (FNA) cases were analysed and 655 indeterminate cases were enrolled in the study. AUS/FLUS cases were further subcategorized into four patterns as follows: papillary thyroid carcinoma (PTC) pattern, microfollicle pattern, atypical cell pattern and Hürthle cell pattern.

RESULTS

Malignancy rates for AUS/FLUS, FN/SFN and SM were 18.9%, 45.7% and 71%, respectively. Malignancy rates for AUS/FLUS subcategories were as follows: PTC pattern, 28%; microfollicle pattern, 6.9%; atypical cell pattern, 22.2%; and Hürthle cell pattern, 0%.

CONCLUSION

The Bethesda system categorizes thyroid FNAs with increasing risk of malignancy as advocated. However, our findings suggest that the risk of malignancy for AUS/FLUS might be higher than estimated. Particularly, AUS/FLUS cases with focal features suggestive of PTC seem to be associated with a much higher risk of malignancy than other patterns.

'Indeterminate for malignancy' (Tir3/Thy3 in the Italian and British systems for classification) thyroid fine needle aspiration (FNA) cytology reporting: morphological criteria and clinical impact

BACKGROUND

The British system (Thy1-5), the Bethesda system for reporting thyroid cytopathology (BSRTC) and the Italian Society of Anatomic Pathology and Cytology (SIAPEC) classification represent the most important international classifications for thyroid cytopathology. Irrespective of the system used, the 'indeterminate' categories are still debated among cytopathologists, particularly with regard to diagnostic criteria, clinical impact of subclassification and role of molecular techniques.

AIM

We aimed to find answers to the following questions: Are there shared criteria in cytological preparations that allow the division of indeterminate follicular lesions into subcategories? What is the true clinical impact of this possible subclassification?

METHODS

Among 1150 consecutive thyroid fine needle aspiration (FNA) specimens, 80 patients had nodules with a final cytological report of Tir3 (SIAPEC)/Thy3. These 80 cases were re-evaluated and subclassified according to morphological criteria into three groups: pure follicular proliferations, Hürthle cell follicular lesions and atypical proliferations.

RESULTS

Sixteen (20%) cases were categorized as pure follicular proliferations, 40 (50%) as Hürthle cell follicular lesions and 24 (30%) as atypical proliferations. Surgery was performed in 57 cases (71%). Cyto-histological correlation showed that follicular adenoma was the most frequent final diagnosis in the cases treated by surgery (24/57, 42%). The overall malignancy rate in the Tir3 category was 28% (16/57). Atypical proliferations were more often malignant than either of the follicular groups (53% versus 19%, P = 0.019).

CONCLUSIONS

A five-tiered classification, subdividing the 'indeterminate for malignancy' class into 'follicular proliferations' and 'atypical lesions' could be adopted. As a result of their higher risk of malignancy, surgical management of the atypical lesions would be justified. In future, the introduction of a genetic panel might contribute to their stratification, to the determination of a more accurate risk of malignancy of the atypical lesions and to the verification of follicular proliferations that are benign.

Cytopathological review of patients that underwent thyroidectomies based on the diagnosis of papillary thyroid carcinoma by fine needle aspiration cytology but were later found to have benign tumors by histopathology

PURPOSE

The aim of this study is to evaluate the specificity of diagnosing PTC by fine needle aspiration (FNA) cytology.

METHODS

This study retrospectively reviewed the cytopathological reports of 1066 patients that underwent thyroidectomy based on a diagnosis of PTC by FNA between January 1993 and December 2008. This study re-evaluated the cytology and histopathology of the patients that received false positive diagnoses of PTC by FNA.

RESULTS

Ten patients (0.9 %) received false positive diagnoses of PTC by FNA. Three patients were overdiagnosed as having PTC by FNA cytology. In contrast, the nuclear features of PTC in the other seven cases were confirmed by the retrospective reviews of the patients' FNA cytology. Three of the seven patients showed follicular structures in their resection specimens, thus resulting in a diagnosis of either adenomatous goiter or follicular adenoma. However, PTC could not be diagnosed by histopathology in the remaining four patients, even though the histopathology showed the nuclear features of PTC.

CONCLUSIONS

Most cases of PTC can be easily diagnosed by cytological and morphological atypia with certain limitations. The difficulty in diagnosing PTC by cytology is because the pathological features of PTC also occur in some benign thyroid tumors. Therefore, immunohistochemical or molecular biological approaches must be combined with current cytological diagnostic techniques for the diagnosis of PTC.

Encapsulated papillary thyroid carcinoma, follicular variant: a misnomer

Papillary thyroid carcinoma (PTC) has long been diagnosed based on its unique nuclear features (PTC-N); however, significant observer discrepancies have been reported in the diagnosis of encapsulated follicular patterned lesions (EnFPLs), because the threshold of PTC-N is subjective. An equivocal PTC-N may often occur in non-invasive EnFPLs and benign/malignant disagreements often create serious problems for patients' treatment. This review collects recent publications focusing on the so-called encapsulated follicular variant of papillary thyroid carcinoma (EnFVPTC) and tries to emphasize problems in the histopathological diagnosis of this spectrum of tumors, which covers encapsulated common-type PTC (EncPTC), EnFVPTC, well-differentiated tumor of uncertain malignant potential (WDT-UMP), follicular adenoma (FA) with equivocal PTC-N and minimally invasive follicular carcinoma (mFTC). We propose that EnFVPTC and other EnFPLs with equivocal PTC-N should be classified into a unified category of borderline malignancy, such as well-differentiated tumor of uncertain behavior (WDT-UB), based on their homogeneous excellent outcome. It is suggested that the unified nomenclature of these lesions may be helpful to reduce significant observer disagreements in diagnosis, because complete agreement in the diagnosis of an EncPTC, EnFVPTC or FA by all pathologists may be not possible for this problematic group of tumors. In conclusion, a malignant diagnosis of EnFVPTC should not be used to cover this spectrum of tumors until uncertainty about the nature of this lesion is settled, whether it is benign, precancerous or malignant.

Cytological features of well-differentiated tumors of uncertain malignant potential: Indeterminate cytology and WDT-UMP

The purpose of this study was to clarify the cytopathological features of well-differentiated tumors of uncertain malignant potential (WDT-UMP), a possible borderline lesion of thyroid follicular cell tumor. We analysed the cytopathological findings of fine needle aspiration (FNA) smears from 6 cases histologically diagnosed as WDT-UMP. WDT-UMP, benign and malignant lesions were compared retrospectively and morphologically. No (0%) nuclear pseudoinclusions were found in adenomatous goiter (AG), follicular adenoma (FTA) and WDT-UMP. Nuclear pseudoinclusions were increased in number in papillary thyroid carcinoma (PTC) with indeterminate cytology (0.8%) and PTC with malignant cytology (1.2%). The incidence of nuclear grooves increased gradually from AG/FTA (0%), WDT-UMP (4.5%), PTC with indeterminate cytology (6.2%) and PTC with malignant cytology (6.5%). The nuclear area of WDT-UMP, an average of 40.0 µm(2), was between that for benign AG/FTA and PTC with malignant cytology. The maximum/minimum axis of WDT-UMP (0.934) lied between that of AG/FTA and PTC. The degree of the nuclear circularity of WDT-UMP was less than that for PTC. WDT-UMP belong to indeterminate category between PTC and follicular adenoma morphologically, and this is one of the major reasons why some of PTC can be found in the indeterminate category. Questionable PTC-N including questionable nucler inclusions (artifact vacuole) may be seen in WDT-UMP, but absolute or definite nuclear inclusions with sharp border are not found in our 6 cases. Therefore this group of thyroid tumors (EnFVPTC and WDT-UMP) may be found in indeterminate category more often, because of intermediate nuclear morphology and incomplete nuclear vacuoles.

Classification of thyroid follicular cell tumors: with special reference to borderline lesions

We propose a new classification of thyroid follicular cell tumors which is correlated with patient's prognosis. It is unique as to two new categories: borderline malignancy between benign and malignant, and moderately differentiated adenocarcinoma (MDA) as a differentiation classification to stratify tumor aggressiveness. As to diagnostic criteria, we recommend invasiveness (capsular and vascular invasion) to separate benign and malignant and it should not be based on presence or absence of papillary thyroid carcinoma (PTC) type nuclear features (PTC-N). Thus borderline malignancy in our new classification includes some of the formerly malignant tumors and they are 1) papillary microcarcinoma, 2) encapsulated conventional PTC (EncPTC), 3) encapsulated follicular variant PTC (EnFVPTC), 4) well differentiated tumor of uncertain malignant potential (WDT-UMP), 5) follicular tumors of uncertain malignant potential (FT-UMP), and 6) capsular invasion only follicular thyroid carcinoma (FTC). Review of the literature revealed that those thyroid tumors have consistently excellent outcome. Well differentiated follicular cell adenocarcinoma (WDA) in our classification includes common type PTC and low-risk follicular carcinoma (FTC). They are invasive (diffuse infiltrative) common type PTC and minimally invasive type FTC with less than 4 foci of angioinvasion. Moderately differentiated follicular cell adenocarcinoma (MDA) includes FTC with angioinvasion (more than 4), aggressive variants of PTC, such as tall cell, columnar cell, solid, loss of cellular polarity/cohesiveness (hobnail) variants and encapsulated carcinoma with high grade histology. Poorly differentiated carcinoma (PDC) includes PDC of WHO definition, insular carcinoma, tumors with minor anaplastic transformation and tumors with distant metastasis at presentation.

The use of the Bethesda terminology in thyroid fine-needle aspiration results in a lower rate of surgery for nonmalignant nodules: a report from a reference center in Turkey

The Bethesda system (BS) for reporting thyroid fine-needle aspiration (FNA), which classifies nodules as nondiagnostic (ND), benign (B), atypia/follicular lesion of undetermined significance (AUS/FLUS), suspicious for follicular neoplasm (SFN/FN), suspicious for malignancy (SFM), or malignant (M), uses clinically valuable management guidelines. The authors employed a similar in-house classification system (IS) for thyroid FNAs, using the categories of ND, B, suspicious follicular cells (SFC), follicular lesion/neoplasm (FL/FN), SFM, and M. The authors compared IS and BS, and assessed the utility of BS in clinical practice. A total of 581 nodules with cytological/histological follow-up were examined and indeterminate lesions by BS were reclassified. The sensitivity and specificity for malignancy using IS were similar to that of BS (77% vs 99%). However, when SFN/FN and SFM were both considered positive, the results for IS and BS were as follows: sensitivity, 85% versus 85%; specificity, 87% versus 94%; and diagnostic accuracy, 86% versus 90%, respectively. Discrepancies between cytological and histological data were evident in 35 cases among all categories of BS except AUS/FLUS. The rate of surgery for nonmalignant nodules was lesser (20% vs 9%) by BS. Among 34 AUS/FLUS cases with follow-up data, hypocellularity was the case in 11 (46%) nonneoplastic and 10 (100%) neoplastic nodules. The use of BS results in a lower rate of surgery for nonmalignant nodules even though patients with borderline cytopathologic features are still encountered. AUS/FLUS category can be separated into subgroups according to the factors causing difficulties in the interpretation. There is a need of accumulation of AUS/FLUS cases to do further evaluations and studies.

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.

[Molecular pathology of thyroid tumors]

Molecular genetic analysis is gaining in significance for the differential diagnosis of thyroid tumours. Identifying specific mutations and/or rearrangements offers not only the possibility to distinguish benign from malignant tumours, but also to classify thyroid malignancies more precisely, which can have a substantial influence on the clinical management of patients. In recent years expression analysis of micro-RNA (miRNA) has become an additional tool to improve diagnostic accuracy in thyroid tumours. In addition to its diagnostic contribution, molecular genetic evaluation of thyroid tumours has significantly deepened our understanding of the development, progression and therapy of these tumours.

Setting up a Prospective Thyroid Biobank for Translational Research: Practical Approach of a Single Institution (2004-2009, Pasteur Hospital, Nice, France)

In the last few years, conditions for setting up a human biobank in France have been upgraded by taking into account (1) the new laws and regulations that integrate the ethical and societal dimension of biobanking and delineate the risks for patients associated with the procurement of human cells and tissues, (2) the increasing request by scientists for human samples with proven biological quality and sophisticated sets of annotations, including information produced through the evergrowing use of molecular biology in pathology, and (3) establishment of procedures concerning the safety of the personnel working with biological products. For this purpose, health authorities and national research institutes in France have provided significant support for the set up of biobanks. The present work was conducted to describe how we set up a biobank targeting diseases of a specific organ (thyroid gland), with the aim of rapidly developing translational research projects. The prospective experience of a single institution (Pasteur Hospital, Nice, France) over a 6-year period (2004-2009) is presented from the practical point of view of a surgical pathology laboratory. We describe different procedures required to obtain high-quality thyroid biological resources and clinical annotations. The procedures were established for the management of biological products obtained from 1454 patients who underwent thyroid surgery. The preanalytical steps leading to the storage of frozen specimens were carried out in parallel with diagnostic procedures. As the number of international networks for research programs using biological products is steadily increasing, it is crucial to harmonize the procedures used by biobanks. In this regard, the described thyroid biobank has been set up using criteria established by the French National Cancer Institute (Institut National du Cancer) to guarantee the quality of different collections stored in biobanks.

Encapsulated follicular thyroid tumor with equivocal nuclear changes, so-called well-differentiated tumor of uncertain malignant potential: a morphological, immunohistochemical, and molecular appraisal

There is a continuous debate regarding the classification of thyroid follicular lesions and the term "well-differentiated tumor of uncertain malignant potential (WDT-UMP)" was recently introduced to cover this problematic spectrum of tumors. The objective of this study was to reappraise WDT-UMP using morphological, immunochemical, and molecular analysis and to shed more light on encapsulated thyroid follicular-patterned tumors. A total of 30 cases of WDT-UMP with equivocal papillary thyroid carcinoma-type nuclear changes (PTC-N) or focal unequivocal PTC-N were examined. As a control, follicular adenoma (n = 29), follicular carcinoma (n = 8), hyalinizing trabecular adenoma (n = 5), and PTC (n = 48) were included. HBME-1, cytokeratin 19, and galectin-3 were positive in 12 (40.0%), 10 (33.3%) and 11 (36.7%) cases of WDT-UMP, respectively. According to the positivity of those markers, significant differences were obtained between WDT-UMP and PTC encapsulated common type (P = 0.028, 0.010, and 0.004, respectively), infiltrative follicular variant (P = 0.020, 0.026, and 0.008, respectively), and infiltrative common type (P = 0.004, 0.001, and 0.005, respectively), but not between WDT-UMP and follicular adenoma or follicular carcinoma. BRAF(V600E) mutation was absent but RET/PTC1 rearrangement was found in only two (6.7%) cases of WDT-UMP. None of the 20 patients with WDT-UMP developed recurrence, with an average follow-up of 80 months. These findings indicate that WDT-UMP has a favorable outcome and is distinct from PTC in morphological, immunohistochemical, and molecular characteristics. We propose that WDT-UMP should be classified as "well-differentiated tumor with uncertain behavior".

[Benign thyroid nodule or thyroid cancer?]

Thyroid nodular disease is highly frequent and affects 20-23% of the adult population in Germany. Differential diagnosis of thyroid nodules is directed at exclusion of thyroid autonomy and thyroid cancer. In addition, large nodules/nodular goiters may cause oesophageal and/or tracheal compression. Besides the patient's history and clinical examination, laboratory investigations (TSH-level, calcitonin screening), functional (scintiscan) and morphological imaging (ultrasound, in rare cases also CT without contrast media and MRI), as well as fine needle aspiration biopsy are useful tools in the differential diagnosis. In the past years, major advances have been made in the understanding of the molecular pathogenesis of thyroid tumors. This has led to the possibility of a molecular classification of thyroid tumors and may have prognostic as well as therapeutic impact.