Follicular-patterned afflictions of the thyroid gland: reappraisal of the most discussed entity in endocrine pathology

The diagnostic value of add-on thyroid cell block in the evaluation of thyroid lesions

Objectives

Fine-needle aspiration (FNA) cytology plays a pivotal role in diagnosing thyroid nodules. Imaging assessment, followed by thyroid lesion sampling, is a widely applied clinical practice. Tissue fragments remnants are retrieved in cell-block providing an adjunct diagnostic tool for histopathology visualization and use of ancillary testing. This study aimed to evaluate whether the auxiliary application of cell-block adds to the diagnostic accuracy of the thyroid FNA.

Material and Methods

A total of 252 thyroid FNA cases between (2020 and 2021) were reviewed from patients aged 18-76. Of those, 150 cell-blocks were recovered and examined to assess their utility. Following categories were plotted during cell-blocks revision: (A) Inadequate material retrieved; (B) cell-block shows similar features along with their accompanying smears; and (C) value added to cytology diagnosis when using cell-block.

Results

The distribution of cell-blocks according to the aforementioned classification are as follows: A - non-diagnostic 63%, B - similar observation seen in both preparations 35%, and C - value added to the rendered diagnosis 2%. Hence, the use of cell-block improved cytology diagnosis in only 2% of total cases. Mostly were of immunostains application for diagnosis confirmation.

Conclusion

The non-diagnostic and atypical cytology cases have not been upgraded to a more meaningful category by the incorporation of cell-block performed with the routine non-enhancement random method. On the other hand, cell-blocks contributed generously toward immunostaining application in malignant scenarios.

Digital Versus Optical Diagnosis of Follicular Patterned Thyroid Lesions

OBJECTIVES

To study the concordance between pathologists in the diagnosis of follicular patterned thyroid lesions using both digital and conventional optical settings.

MATERIAL AND METHODS

Five pathologists reviewed 50 hematoxylin and eosin-stained slides of follicular patterned thyroid lesions using both digital (the D-Sight 2.0 scanner and navigator viewer) and conventional optical instruments with washout interval time.

RESULTS

The mean concordance rate with the ground truth (GT) was similar between conventional optical and digital observation (83.2 and 85.2%, respectively). The most frequent reason for diagnostic discordance with GT on both systems was the evaluation of nuclear features (69.1% for conventional optical observation and 59.4% for digital observation). The intraobserver diagnostic concordance mean was 86.8%. Time for digital observation (mean time per case = 2.9 ± 0.8 min) was higher than that for conventional optical observation (mean time per case = 2.0 ± 0.7 min). Interobserver correlation of measurements was higher in the digital observation than the conventional optical observation.

CONCLUSION

Conventional optical and digital observation settings showed a comparable accuracy for the diagnosis of follicular patterned thyroid nodules, as well as substantial intraobserver agreement and a significant improvement in the reproducibility of the measurements that support the use of digital diagnosis in thyroid pathology. The origins underlying the variability of the diagnosis were the same in both conventional optical microscopy and digital pathology systems.

Follicular Thyroid Neoplasms: Comparison of Clinicopathologic and Molecular Features of Atypical Adenomas and Follicular Thyroid Carcinomas

In follicular thyroid neoplasms without invasion, a diagnosis of atypical adenoma (AA) (follicular tumor of uncertain malignant potential) may be rendered if atypical features (indefinite capsular/vascular invasion, necrosis, solid growth, increased mitoses) are present. This study compares clinical, histologic, and molecular features of patients with AAs (n=31), nonmetastatic follicular thyroid carcinoma (nmFTC) (n=18), and metastatic follicular thyroid carcinoma (mFTC) (n=38). Patients with mFTC were older. Mitotic activity in areas of solid growth was greatest in mFTC (P=0.05). Oncocytic tumors tended to show solid growth (P=0.04). The presence or frequency of capsular and/or vascular invasion was not different between nmFTC and mFTC. TERT promoter mutations were higher in patients with mFTC (50%) than nmFTC (25%) and AA (10%) (P=0.02). TERT promoter mutation was associated with necrosis (P=0.01) and solid growth plus increased mitoses (P=0.03). Necrosis and TERT promoter mutations were identified in all groups, most frequently in mFTC. The combination of solid growth with increased mitoses, necrosis, and TERT promoter mutation was only seen in follicular carcinomas. Poorly differentiated features, vascular invasion, and TERT promoter mutation correlated with metastasis in FTC. Given the low frequency of necrosis and TERT promoter mutation in AAs, close clinical follow-up is recommended in patients with these findings, especially if additional atypical features (such as solid growth plus mitoses) are present.

Pitfalls in Thyroid Cytopathology

Fine-needle aspiration (FNA) is among the first diagnostic tools used in the evaluation of thyroid nodules. It has the ability to triage patients with benign and malignant lesions, thus defining the optimum clinical and/or surgical management. The Bethesda System for Reporting Thyroid Cytopathology has found worldwide acceptance. Thyroid FNA offers high positive predictive value (97%-99%), with sensitivities and specificities of 65% to 99% and 72% to 100%, respectively. Nonetheless, many potential diagnostic pitfalls exist that can lead to false-positive and/or false-negative results. This article discusses several of the potential pitfalls in the cytologic evaluation of thyroid lesions.

Macrofollicular Variant of Follicular Thyroid Carcinoma: A Rare Underappreciated Pitfall in the Diagnosis of Thyroid Carcinoma

Background: Follicular-patterned thyroid nodules predominantly composed of macrofollicular structures without nuclear atypia are generally regarded as benign (i.e., hyperplastic nodules or follicular adenomas). In line with this concept, fine-needle aspiration cytology (FNAC) also assigns a benign connotation to the presence of macrofollicular structures, unless thyrocytes present papillary thyroid carcinoma (PTC)-related nuclear features that raise the possibility of a macrofollicular variant of PTC. However, cases showing macrofollicular architecture, capsular invasion, and no PTC features can also be observed. Methods: We describe the clinical, cytological, histological, and molecular genetic features of four cases of encapsulated follicular neoplasms that presented histologically with a predominant (>70%) macrofollicular architecture, but which also showed clear signs of capsular invasion, and thus were classified as macrofollicular variant of follicular thyroid carcinoma (MV-FTC). Results: Cytologically, macrofollicular structures were identified in all cases, leading to a benign FNAC diagnosis in three of the four cases. Due to increasing nodule size, thyroidectomy was performed in all cases. Histology showed focal and limited capsular invasion, without vascular invasion. Next-generation sequencing (custom 394 gene panel) of each tumor compared with matched normal DNA revealed a total of 7 somatic variants, including dual (likely biallelic) mutations in the DICER1 gene in 2 patients. The clinical outcome was excellent in all cases. Conclusions: Similar to the classical minimally invasive follicular thyroid carcinoma, MV-FTC appears to behave indolently. MV-FTC has a high rate of false-negative FNAC results, but MV-FTC is very rare (<0.05% of all thyroidectomies) and apparently has an indolent behavior. Further studies comprising larger series are necessary to better clarify the biology of this diagnostically challenging rare tumor.

An Evaluation of CD61 Immunohistochemistry in Identification of Vascular Invasion in Follicular Thyroid Neoplasms

The identification of vascular invasion in follicular thyroid neoplasms is essential for categorizing lesions as benign (follicular adenomas) or malignant (follicular thyroid carcinomas). Among the histologic criteria diagnostic of true vascular invasion is tumor-cell associated thrombosis, including fibrin deposition and platelet clumping. This study aims to evaluate whether an immunohistochemical stain for the platelet-associated protein CD61 could assist in identifying tumor-associated thromboses and thereby confirm vascular invasion in follicular thyroid neoplasms. Histologic review and CD61 immunostaining of 19 atypical follicular adenomas, 13 non-metastatic follicular thyroid carcinomas, and 11 metastatic follicular thyroid carcinomas was performed. Linear arrays or clustered groups of CD61-expressing intravascular platelets were present in 51% of cases overall, including 54% of follicular thyroid carcinomas and 47% of follicular adenomas, mostly within intracapsular or peritumoral vessels. In three follicular thyroid carcinomas (all with distant metastases), CD61-expressing platelets were present in association with intravascular tumor cells. This finding was not present in adenomas. CD61 staining alone did not distinguish between atypical follicular adenomas, non-metastatic carcinomas, and metastatic carcinomas. When present in association with intravascular tumor cells, however, CD61-expressing platelets may serve as a marker for vascular invasion and aid in the diagnosis of follicular thyroid carcinoma.

Modified Transverse-Vertical Gross Examination: a Better Method for the Detection of Definite Capsular Invasion in Encapsulated Follicular-Patterned Thyroid Neoplasms

The diagnosis of encapsulated follicular-patterned thyroid carcinoma (EFPTC) is challenging, and the detection of capsular invasion and/or vascular invasion is essential in distinguishing benign lesions from malignant lesions. In this study, we present a modified transverse-vertical gross examination method with additional vertical cuts at the upper and lower ends of thyroid nodules. In addition, we compared the clinicopathological characteristics of patients with EFPTC between conventional and modified methods. The diagnostic rate of follicular thyroid carcinoma and invasive encapsulated follicular variant of papillary thyroid carcinoma was higher with the modified method (p = 0.003 and p = 0.028, respectively). Furthermore, the paraffin block number and the number of capsular invasion per centimeter were significantly higher with the modified method (p < 0.001 and p = 0.007, respectively). However, vascular invasion was not significantly different between the two methods (p = 0.771). The possibility of identifying capsular invasion was around two times higher with the modified method (odds ratio = 1.91, 95% confidence interval = 1.20-3.07, p = 0.007). A total of 38 samples (23%) in the modified transverse-vertical group had capsular and/or vascular invasion in the additional vertical cuts of the upper/lower ends of the tumor. Our modified transverse-vertical gross examination method was more effective than the conventional transverse examination method for the detection of capsular invasion in EFPTC. This modified gross examination method might allow a better differential diagnosis among various encapsulated micro-follicular proliferative lesions.

Thyroid FNAC: Causes of false-positive results

In this paper, we aim to focus on false positive results in the evaluation of thyroid aspirations, covering cystic, inflammatory, follicular and oncocytic lesions, papillary carcinoma, and medullary carcinoma of thyroid. The recently described entity noninvasive follicular thyroid neoplasm with papillary-like nuclear features is also discussed detailing the impact of its introduction on the sensitivity and specificity of thyroid FNA, as well as the use of molecular tests for diagnostics. Medicolegal issues in relation to current practice in English law are also described.

Is TSH necessary for initial assessment of thyroid nodules?

OBJECTIVE

The use of thyrotropin (TSH) in the initial assessment of thyroid nodules is inefficient and leads to unnecessary assessment costs. We compared the total costs of thyroid nodule assessment with or without the use of TSH in the initial assessment.

METHODS

A total of 1808 patients with thyroid nodules received TSH, fine-needle aspiration (FNA) and thyroid scintigraphy (TS) assessment, including 83 autonomously functioning thyroid nodule (AFTN) cases and 1725 non-AFTN cases. The total costs of the TSH strategy and non-TSH strategies were compared. The ratio of single-use costs of FNA to TS (C_FNA/TS ) was used as the main outcome measure.

RESULTS

Only when 6·03 ≤ C_FNA/TS ≤ 27·17, the lowest total costs were associated with using the conventional TSH strategy. When C_FNA/TS <6·03 or C_FNA/TS >27·17, the lowest costs were found with FNA and TS, respectively.

CONCLUSION

From the perspective of cost economics, in iodine-sufficient areas, we recommend that the decision on the use of TSH for the initial assessment of thyroid nodules should be based on the testing costs of FNA and TS in that medical unit.

New Concept of the Encapsulated Follicular Variant of Papillary Thyroid Carcinoma and Its Impact on the Bethesda System for Reporting Thyroid Cytopathology: A Single-Institute Experience

BACKGROUND

The encapsulated follicular variant (EFV) of papillary thyroid carcinoma (PTC) is the most discussed entity in thyroid pathology. Recently, the question of whether or not EFV-PTC is a malignant entity has been the subject of renewed discussion in the light of recent molecular and clinical studies. The aim of this study was to analyze the malignancy ratios of each category of the Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) if EFV-PTC is no longer considered as a malignant entity.

MATERIALS AND METHODS

Data on thyroid fine-needle aspirations (n = 1,886) with surgical follow-up between 1999 and 2014 were studied. EFV-PTC cases constituted 27% (94/343) of the malignant cases.

RESULTS

Malignancy ratios were determined as nondiagnostic, benign, atypia/follicular lesion of undetermined significance, suspicious for follicular neoplasm/follicular neoplasm, suspicious for malignancy, and malignant categories of the TBSRTC in 13, 7, 45, 30, 72 and 98%, respectively. If EFV-PTC was not regarded as malignant, malignancy ratios would decrease to 6.5, 6, 30, 10, 48, and 87% for each category in the same order.

CONCLUSIONS

The current study showed that the most significant decrease in relative malignancy ratios was seen in the suspicious for follicular neoplasm/follicular neoplasm category (66% relative decrease), but all categories represented a considerable decrease.

Minimally invasive follicular carcinoma: predictors of vascular invasion and impact on patterns of care

Some studies have reported that minimally invasive follicular carcinoma (MIFC) with vascular invasion is associated with compromised prognosis, leading to an ongoing debate regarding extent of surgery for MIFC. Our goal was to identify predictors of vascular invasion and determine its impact on patterns of care. Adult patients with MIFC were culled from the National Cancer Database, 2010-2011, and segregated according to the presence/absence of capsular or vascular invasion. Variables of interest were examined using Chi-square and student's t tests. Multivariate analysis was performed with logistic regression. A total of 617 patients with MIFC were identified: 54% with capsular invasion only and 46% with vascular invasion. Demographic characteristics were similarly distributed between the two groups. Tumor size was larger in patients with vascular invasion (mean = 35.7 vs. 29.2 mm capsular invasion only, p < 0.001); a 2% increase in risk of vascular invasion was observed with each 1 mm increase in size. The rate of total thyroidectomy was similar for MIFCs with vascular invasion compared to capsular invasion only (72.9 vs. 75.1%, p = 0.537). The RAI administration rate was higher in patients with vascular invasion (62.1 vs. 52.6% capsular invasion only, p = 0.017). In multivariate analysis, the presence of vascular invasion was independently associated with increased likelihood of receiving RAI (OR 1.641, p = 0.007). MIFC remains aggressively treated despite current guidelines favoring a more conservative approach. Building consensus around MIFC management is important for standardization of practice patterns and improvement in quality of care.

Cytopathology of Follicular Cell Nodules

This article corresponds to a lecture delivered during the Endocrine Pathology Society symposium held in Boston on 21 March 2015 (104th USCAP meeting, March 21-27). It focuses on the importance of cytopathology in endocrine thyroid pathology and the limits and pitfalls of diagnosis in follicular cell lesions. Lights and shadows are present in each diagnostic technique: Fine needle aspiration has imposed itself as a gold standard in thyroid nodules thanks to its easiness of execution and high cost-effectiveness ratio. A milestone in this field is represented by the National Cancer Institute (NCI) Thyroid Fine Needle Aspiration (FNA) State of the State of the Science Conference hosted in October 22-23, 2007 by the NCI, followed by a series of documents published in Diagnostic Cytopathology and Cytojournal (2008) as well as in an atlas entitled: The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC): terminology and criteria (2010, Springer). "Gray" zones still remain, causing difficulties and anxiety to the cytopathologist when facing challenging cases. Each diagnostic category of TBSRTC is analyzed and discussed in a concise fashion with special emphasis on challenging cases such as atypia of undetermined significance (AUS), suspicion for follicular neoplasms (SFNs), diagnoses of papillary thyroid carcinoma (PTC) in Hashimoto thyroiditis and follicular variant of papillary carcinoma (FVPTC). Our aim was to better define and clarify the spectrum of follicular cell lesions in thyroid nodule samplings and to underline the diagnostic limits in order to avoid pitfalls. New emerging molecular biology techniques may represent useful tools in selected morphological challenging cases and lead to new therapeutic approaches in line with drug-tailored therapy and personalized medicine.

Immunohistochemical Subcellular Localization of Protein Biomarkers Distinguishes Benign from Malignant Thyroid Nodules: Potential for Fine-Needle Aspiration Biopsy Clinical Application

BACKGROUND

It is of critical clinical importance to select accurately for surgery thyroid nodules at risk for malignancy and avoid surgery on those that are benign. Using alterations in subcellular localization for seven putative biomarker proteins (identified by proteomics), this study aimed to define a specific combination of proteins in surgical tissues that could distinguish benign from malignant nodules to assist in future surgical selection by fine-needle aspiration biopsy (FNAB).

METHODS

Immunohistochemical subcellular localization (IHC) analyses of seven proteins were retrospectively performed on surgical tissues (115 benign nodules and 114 papillary-based thyroid carcinomas [TC]), and a risk model biomarker panel was developed and validated. The biomarker panel efficacy was verified in 50 FNAB formalin-fixed and paraffin-embedded cell blocks, and 26 cytosmears were prepared from fresh surgically resected thyroid nodules.

RESULTS

Selection modeling using these proteins resulted in nuclear phosphoglycerate kinase 1 (PGK1) loss and nuclear Galectin-3 overexpression as the best combination for distinguishing TC from benign nodules (area under the curve [AUC] 0.96 and 0.95 in test and validation sets, respectively). A computed malignancy score also accurately identified TC in benign and indeterminate nodules (test and validation sets: AUC 0.94, 0.90; specificity 98%, 99%). Its efficacy was confirmed in surgical FNAB cell blocks and cytosmears.

CONCLUSION

Using surgical tissues, it was observed that a combination of PGK1 and Galectin-3 had high efficiency for distinguishing benign from malignant thyroid nodules and could improve surgical selection for TC among indeterminate nodules. Further validation in prospective preoperative FNAB will be required to confirm such a clinical application.