Impact of non-invasive follicular thyroid neoplasms with papillary-like nuclear features (NIFTP) on risk of malignancy in patients undergoing lobectomy/thyroidectomy for suspected malignancy or malignant fine-needle aspiration cytology findings: a systematic review and meta-analysis

The International System for Reporting Serous Fluid Cytopathology: A Systematic Review and Meta-Analysis of Diagnostic Test Accuracy Studies

This is the first systematic review and meta-analysis of The International System (TIS) for reporting serous fluid cytopathology. Our aims were to present the pooled malignancy rate of each TIS reporting category and the diagnostic accuracy of cytology using this system. Database search using a predefined strategy was followed by study selection, data extraction, study quality assessment, and statistical analysis. Data derived from 16 eligible studies were pooled. The pooled rates of malignancy were as follows: 27% (95% CI; 16%-41%) for "nondiagnostic" (ND), 11% (95% CI; 7%-18%) for negative for malignancy" (NFM), 49% (95% CI; 37%-61%) for "atypia of undetermined significance" (AUS), 90% (95% CI; 81%-95%) for "suspicious for malignancy" (SFM), and 100% (95% CI; 98%-100%) for "positive for malignancy" (MAL). Studies performed exclusively in cancer hospitals showed higher pooled malignancy rates, compared with academic and community hospitals serving the general population, in the ND [40% (95% CI; 21%-62%) vs. 22% (95% CI; 11%-39%)], NFM [20% (95% CI; 13%-30%) vs. 9% (95% CI; 5%-17%)], and AUS categories [55% (95% CI; 47%-63%) vs. 46% (95% CI; 31%-62%)]. Notably, the difference was significant in the NFM category ( P =0.04). When both SFM and MAL cytology interpretations were considered as malignant outcomes, the pooled sensitivity and specificity were 68.74% (95% CI; 59.90%-76.39%) and 98.81% (95% CI; 98.18%-99.22%), respectively. In addition, the diagnostic odds ratio (DOR) was found to be 170.7 (95% CI; 96.2-303.3). Despite its strengths, our study also had some limitations. Therefore, future large-scale longitudinal studies could strengthen the findings of this review.

Thyroid Nodules: Past, Present & Future

The ability to distinguish benign from malignant thyroid nodules has been a challenge for over a century. Historically, thyroidectomy, as the only definitive method to diagnose thyroid cancer, led to a significant number of thyroid resections for benign disease considering that approximately 90-95% of thyroid nodules are benign. Diagnostic advancements including highly sensitive ultrasonography, fine needle aspiration cytology, molecular studies and future use of artificial intelligence, help distinguish benign from malignant and has significantly reduced the number of unnecessary surgeries for benign nodules. Current and likely future diagnostic improvements have led us to a new conundrum. While decreasing the number of surgeries for benign disease, we are now overdiagnosing and overtreating low-risk subclinical malignancies. Here we describe some of the changes leading to our current state.

EphB3 protein is a potential ancillary diagnostic biomarker for thyroid cancers

OBJECTIVE

To investigate the expression of ephrin type B receptor 3 (EphB3) in thyroid tumors and its usage as an ancillary diagnostic biomarker for thyroid tumors.

METHODS

Formalin-fixed and paraffin-embedded (FFPE) tissue samples (78 cases) and FNAC samples (57 cases) were assessed with the EphB3 antibody using immunohistochemistry. PTC and other thyroid follicular tumors were compared regarding their EphB3 expression. Sanger sequencing was used to assess for the presence of a BRAF V600E mutation.

RESULTS

EphB3 was positive in 81.8 % (27/33) of papillary thyroid carcinoma (PTC), 83.3 % (5/6) of medullary thyroid carcinoma (MTC), 25 % (1/4) of hyperplastic/adenomatoid nodule (HN), 14.3 % (1/7) of follicular adenoma (FA), and negative in follicular tumors of uncertain malignant potential (FT-UMP) (0/13), noninvasive follicular neoplasm with papillary-like nuclear features (NIFTP) (0/7), thyroid follicular carcinoma (TFC) (0/4), Hashimoto's thyroiditis (0/4), and normal thyroid follicular tissues (0/33). In cellular blocks, EphB3 was positive in 87.1 % (20/23) of PTC, 75 % (3/4) of MTC, 20 % (2/10) of HN, and negative in atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS) (0/20) and normal thyroid follicular cells (0/10).

CONCLUSION

EphB3 is expressed in the majority of PTC, but less so in benign follicular nodules. EphB3 expression in fine needle aspiration cytology (FNAC) specimens can be used as a diagnostic tool to differentiate thyroid cancer from other follicular lesions in its differential diagnosis, especially AUS/FLUS and PTC.

Two-tier subclassification of the Bethesda category III (atypia of undetermined significance/follicular lesion of undetermined significance) in thyroid cytology

BACKGROUND

The Bethesda category III, AUS/FLUS, comprises a heterogeneous group of thyroid lesions with variable risk of malignancy (ROM). This study evaluates ROM in two subgroups of this category based on nuclear atypia and architectural atypia.

METHODS

Cases in Bethesda category III were reported based on nuclear atypia (AUS) and architectural atypia (FLUS). ROM was calculated by comparing the cytologic diagnosis to the follow-up histologic diagnosis.

RESULTS

Among the 610 Bethesda category III cases in this study, 306 (50.2%) and 304 (49.8%) cases were reported as AUS and FLUS, respectively. One hundred and eighty six of 306 AUS (60.8%) and 193 of 304 FLUS (63.5%) cases underwent surgical intervention. ROM of the cases in Bethesda category III was 12.8% if all cases were counted and 20.6% if only surgical cases were counted. When analyzing separately, ROM of AUS cases was 17.0% and 28.0% with all cases and surgical cases only, respectively. For FLUS cases, ROM was 8.6% and 13.5% with all cases and surgical cases only, respectively.

CONCLUSION

In Bethesda category III, ROM in the cases with nuclear atypia was significantly higher than the cases with architectural atypia. Sub-classifying the Bethesda Category III cases with nuclear atypia and architectural atypia, respectively may better stratify the ROM.

Radiation Dose Does Not Affect the Predictive Value of Thyroid Biopsy for Diagnosing Papillary Thyroid Cancer in a Belarusian Cohort Exposed to Chernobyl Fallout

INTRODUCTION

The Chernobyl nuclear accident exposed residents of contaminated territories to substantial quantities of radioiodines and was followed by an increase in thyroid cancer, primarily papillary thyroid cancer (PTC), among exposed children and adolescents. Although thyroid biopsy is an essential component of screening programs following accidental exposure to radioiodines, it is unknown whether the predictive value of biopsy is affected by different levels of environmental exposure.

METHODS

A cohort of 11,732 Belarusians aged ≤18 years at the time of the Chernobyl accident with individual thyroid radiation dose estimates was screened at least once 11-22 years later. Paired cytologic conclusions and histopathologic diagnoses were possible for 258 thyroid nodules from 238 cohort members. Cytologic conclusions were divided into five reporting categories, with all follicular lesion aspirates combined into a single indeterminate category. Standard performance indicators, risk of malignancy (ROM), and odds ratios for a correct cytologic conclusion were calculated, both overall and according to quintile of thyroid radiation dose.

RESULTS

The arithmetic mean thyroid dose estimate for the study group was 1.73 Gy (range: 0.00-23.64 Gy). The final histopathologic diagnosis was cancer for 136 of 258 biopsies (52.7%; 135 papillary and 1 follicular). The overall ROM was 96.7% for cytologies definite for PTC, 83.7% for suspicious for PTC, 33.0% for indeterminate, 8.1% for benign, and 31.0% for non-diagnostic. The ROM showed little change according to level of radiation exposure. Overall, there was no association between thyroid radiation dose and the odds ratio for a correct cytologic conclusion (p = 0.24). When analyzed according to dose quintile, the odds ratio for a correct conclusion increased two-fold at 0.10-0.29 Gy compared to a dose of 0.00-0.09 Gy and decreased at doses of 0.3-24 Gy (p value for linear trend = 0.99).

CONCLUSIONS

At radiation doses received by a cohort of young Belarusians exposed to radioiodines by the Chernobyl accident, the predictive value of thyroid biopsy for diagnosing PTC was not significantly affected by level of radiation exposure.

Clinical use of Molecular Data in Thyroid Nodules and Cancer

Over the past 3 decades, advances in the molecular genetics of thyroid cancer (TC) have been translated into diagnostic tests, prognostic markers, and therapeutic agents. The main drivers in differentiated TC pathogenesis are single-point mutations and gene fusions in components of the Mitogen-activated protein kinase (MAPK) and phosphoinositide-3-kinase-protein kinase B/Akt (PI3K/Akt) pathways. Other important genetic alterations in the more advanced types of TC include TERT promoter, TP53, EIF1AX, and epigenetic alterations. Using this knowledge, several molecular tests have been developed for cytologically indeterminate thyroid nodules. Currently, 3 commercially available tests are in use including a DNA/RNA-based test (ThyroSeq v.3), an RNA-based test (Afirma Gene Sequencing Classifier), and a hybrid DNA/miRNA test, ThyGeNEXT/ThyraMIR. These tests are mostly used to rule out malignancy in Bethesda III and IV thyroid nodules because they all have high sensitivities and negative predictive values. Their common use, predominantly in the United States, has resulted in a significant reduction in unnecessary thyroid surgeries for benign nodules. Some of these tests also provide information on the underlying molecular drivers of TC; this may support decision making in initial TC management planning, although this practice has not yet been widely adopted. More importantly, molecular testing is essential in patients with advanced disease before using specific mono-kinase inhibitors (eg, selpercatinib for RET-altered TC) because these drugs are ineffective in the absence of a specific molecular target. This mini-review discusses the utilization of molecular data in the clinical management of patients with thyroid nodules and TC in these different clinical situations.

The Impact of the 2022 WHO Classification of Thyroid Neoplasms on Everyday Practice of Cytopathology

This review outlines how the alterations in the 5th edition of the WHO Classification of Endocrine and Neuroendocrine Tumors of the thyroid gland are likely to impact thyroid cytopathology. It is important to note that WHO subclassifies thyroid tumors into several new categories based on increased comprehension of the cell of origin, pathologic features (including cytopathology), molecular classification, and biological behavior. The 3rd edition of the Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) will debut in the near future and will include changes in diagnostic category designations. The changes in the 5th edition of the WHO will in some instances subtly, and in other instances significantly, impact the cytological diagnoses. Moreover, these changes will also affect other thyroid FNA classification schemes used internationally for classifying thyroid FNA specimens.

Cytological Features of "Non-Invasive Follicular Tumour with Papillary like Nuclear Features" - A Single Institutional Experience in India

Background

The term noninvasive follicular tumor with papillary-like nuclear features (NIFTP) was introduced as a surrogate for noninvasive encapsulated follicular variant of papillary thyroid carcinoma with a defined set of histopathologic criteria. There are very few studies depicting the cytological cues for the diagnosis of NIFTP. The objective of the study was to determine the spectrum of cytological features in fine needle aspiration cytology (FNAC) smears of cases histopathologically diagnosed as NIFTP.

Methods

This was a retrospective cross-sectional study conducted over a duration of four years between January 2017 and December 2020. All surgically resected cases (n-21), who met the diagnostic criteria of NIFTP on histopathology and who underwent preoperative FNAC were included and reviewed in the study.

Results

Out of a total of 21 cases, at FNAC, diagnosis of benign, suspicious for malignancy, follicular variant of papillary thyroid carcinoma, and classic papillary thyroid carcinoma (PTC) was rendered in 14 (66.6%), 2 (9.5%), 2 (9.5%), and 3 (14.28%), respectively. Scanty cellularity was noted in 12 (57.1%) cases. Papillae, sheets, and microfollicles were seen in 1 (4.7%), 10 (47.6%), and 13 (61.9%) cases, respectively. Nucleomegaly, nuclear membrane irregularities, nuclear crowding, and overlapping were seen in 7 (33.3%), 9 (42.8%), and 9 (42.8%), respectively. Nucleoli, nuclear grooving, and inclusions were seen in 3 (14.2%) 10 (47.6%), and 5 (23.8%) cases, respectively.

Conclusion

At FNAC, NIFTP can be found in every category of The Bethesda System for Reporting Thyroid cytopathology (TBSRTC). Nuclear membrane irregularities, nuclear grooving, mild nuclear crowding, and overlapping were noted in a modest number of cases. However, the absence or rare occurrence of features such as papillae, inclusions, nucleoli, and metaplastic cytoplasm may help prevent an overdiagnosis of malignancy.

SFE-AFCE-SFMN 2022 Consensus on the management of thyroid nodules : Recommendations in thyroid cytology: from technique to interpretation

The SFE-AFCE-SFMN 2022 consensus deals with the management of thyroid nodules, a condition that is a frequent reason for consultation in endocrinology. In more than 90% of cases, patients are euthyroid, with benign non-progressive nodules that do not warrant specific treatment. The clinician's objective is to detect malignant thyroid nodules at risk of recurrence and death, toxic nodules responsible for hyperthyroidism or compressive nodules warranting treatment. The diagnosis and treatment of thyroid nodules requires close collaboration between endocrinologists, nuclear medicine physicians and surgeons, but also involves other specialists. Therefore, this consensus statement was established jointly by 3 societies: the French Society of Endocrinology (SFE), French Association of Endocrine Surgery (AFCE) and French Society of Nuclear Medicine (SFMN); the various working groups included experts from other specialties (pathologists, radiologists, pediatricians, biologists, etc.). This section deals with the technique and interpretation of thyroid fine-needle aspiration biopsy (FNAB), a reference test for the analysis of thyroid nodules.

Comparative BRAF V600E immunohistochemical expression in differentiated thyroid tumors with papillary features

Differentiated thyroid tumors (DTC) are the most common indolent tumors associated with a good prognosis compared with other tumors. Its incidence during the last few decades has increased. DTC includes papillary carcinoma and follicular carcinoma. The BRAF is the most prevalent genetic mutation in thyroid carcinoma, occurring in more than 50% of papillary thyroid cancers (PTCs). The study aimed to evaluate BRAF expression in differentiated thyroid tumors with papillary-like nuclear features. Formalin-fixed paraffin-embedded blocks (FFPE) were collected from archival samples of patients in private histopathology labs in Al-Najaf city from 55 cases, which included 27 papillary thyroid carcinoma (PTC) cases, 10 cases of NIFTP, 13 FVPTC cases, 2 papillary microcarcinoma cases, and 3 NIFTP coexist with papillary microcarcinoma cases. All samples were stained using the immunohistochemistry method in the Middle Euphrates unit for cancer research at the University of Kufa/Faculty of Medicine. 15/55 (27.3%) of cases increased BRAF expression. The BRAF expression was statistically significant with tumor type (p=0.008). The higher expression was associated with 13 (48.15%) of PTC cases. However, the BRAF expression did not correlate with gender (p=0.2), tumor size (p=0.07), and tumor focality (p=0.09). BRAF V600E has prognostic value as it correlates with tumor progression.

Noninvasive Follicular Thyroid Neoplasm with Papillary-like Nuclear Features (NIFTP): Tumour Entity with a Short History. A Review on Challenges in Our Microscopes, Molecular and Ultrasonographic Profile

Since Noninvasive Follicular Thyroid Neoplasm with Papillary-like Nuclear Features (NIFTP) was introduced as a new thyroid tumour entity, many studies, and meta-analyses on diagnosing NIFTP have been published. NIFTP-revised histopathological criteria emerged in 2018. NIFTP is defined as a histological entity and its diagnosis requires a careful histological examination. Its molecular profile is similar to follicular-like tumours. Ultrasound features are unable to differentiate NIFTP. NIFTP is not a cytological diagnosis, but it influences the risk of malignancy in several categories of The Bethesda System for Reporting Thyroid Cytopathology terminology.

The dilemma of 18F-FDG PET/CT thyroid incidentaloma: what we should expect from FNA. A systematic review and meta-analysis

PURPOSE

¹⁸F-FDG thyroid incidentaloma (TI) occurs in ~2% of PET/CT examinations with a cancer prevalence of up to 35-40%. Guidelines recommend fine-needle aspiration cytology (FNA) if a focal ¹⁸F-FDG TI corresponds to a sonographic nodule >1 cm. The aim of this systematic review and meta-analysis was to provide evidence-based data on the diagnostic distribution of ¹⁸F-FDG TIs in the six Bethesda systems for reporting thyroid cytopathology (BETHESDA) subcategories.

METHODS

Original studies reporting ¹⁸F-FDG TIs and cytologically classified according to BETHESDA were included. Six separate meta-analyses were performed to obtain the pooled prevalence (95% confidence interval, 95% CI) of ¹⁸F-FDG TIs in the six BETHESDA subcategories.

RESULTS

Fifteen studies were finally included. Nine studies were from Asian/Eastern and six from Western countries. FNA data according to BETHESDA was available in 2304 cases. The pooled prevalence of ¹⁸F-FDG TIs according to BETHESDA was BETHESDA I 10% (6-14), BETHESDA II 45% (37-53), BETHESDA III 8% (3-13), BETHESDA IV 8% (5-12), BETHESDA V 6% (4-9), BETHESDA VI 19% (13-25). A significantly different prevalence was found in the BETHESDA IV between Asian/Eastern (2%) and Western (19%) studies.

CONCLUSION

Two-thirds of focal ¹⁸F-FDG TIs undergoing FNA have either malignant (BETHESDA VI) or benign (BETHESDA II) cytology while a minority will have indeterminate (BETHESDA III or IV) FNA results. Significant differences between Asian/Eastern and Western studies are also present in the prevalence of indeterminate FNA results.

Significance of RAS Mutations in Thyroid Benign Nodules and Non-Medullary Thyroid Cancer

Simple Summary

Only about 4% of thyroid nodules are carcinomas and require surgery. Fine-needle aspiration cytology is the most accurate tool to distinguish benign from malignant thyroid nodules, however it yields an indeterminate result in about 30% of the cases, posing diagnostic and prognostic dilemmas. Testing for genetic mutations, including those of RAS, has been proposed for indeterminate cytology to solve these dilemmas and support the clinician decision making process. A passionate debate is ongoing on the biological and clinical significance of RAS mutations, calling into question the utility of RAS as tumor marker. Recently, the description of a new entity of non-invasive follicular thyroid neoplasm and the accurate review of more recent analyses demonstrate that RAS mutations have limited utility in both the diagnostic and prognostic setting of thyroid nodular disease.

Abstract

Thyroid nodules are detected in up to 60% of people by ultrasound examination. Most of them are benign nodules requiring only follow up, while about 4% are carcinomas and require surgery. Malignant nodules can be diagnosed by the fine-needle aspiration cytology (FNAC), which however yields an indeterminate result in about 30% of the cases. Testing for RAS mutations has been proposed to refine indeterminate cytology. However, the new entity of non-invasive follicular thyroid neoplasm, considered as having a benign evolution and frequently carrying RAS mutations, is expected to lower the specificity of this mutation. The aggressive behavior of thyroid cancer with RAS mutations, initially reported, has been overturned by the recent finding of the cooperative role of TERT mutations. Although some animal models support the carcinogenic role of RAS mutations in the thyroid, evidence that adenomas harboring these mutations evolve in carcinomas is lacking. Their poor specificity and sensitivity make the clinical impact of RAS mutations on the management of thyroid nodules with indeterminate cytology unsatisfactory. Evidence suggests that RAS mutation-positive benign nodules demand a conservative treatment. To have a clinical impact, RAS mutations in thyroid malignancies need not to be considered alone but rather together with other genetic abnormalities in a more general context.

Impact of Molecular Testing on the Management of Indeterminate Thyroid Nodules Among Western and Asian Countries: a Systematic Review and Meta-analysis

Molecular testing has a potential to improve the management of patients with indeterminate thyroid nodules considered for surgery. This study examined the influence of molecular tests on the treatment of indeterminate nodules, particularly the differences between Western and Asian countries. Electronic databases including PubMed and Web of Science were searched for relevant articles from 2010 to March 2019. We computed meta-analysis of proportion and their 95% confidence intervals (CIs) utilizing the random-effect model. We used independent samples t test to compare the resection rate (RR), rate of malignancy (ROM), rate of preoperative molecular testing (RMT), and rate of positive test (RP) between subgroups. We included a total of 34 studies with 7976 indeterminate nodules. The multigene panel testing methods were exclusively used in the USA. Compared with the non-molecular era, molecular testing was associated with a significantly increased ROM (47.9% versus 32.1%; p = 0.001). The ROM of indeterminate nodules in Asian institutes was significantly higher than that in Western countries (75.3% versus 36.6%; p < 0.001, respectively). Institutes employing single-gene tests achieved a higher ROM (59.8% versus 37.9%; p = 0.013). Molecular testing is a promising method to tailor the clinical management for indeterminate thyroid FNA. Certain differences in routine thyroid cytopathology practice among the West and the East are still present. The combination of molecular testing and active surveillance enhances the accuracy of case selection for surgery in Asian countries.

Outcome and diagnostic reproducibility of the thyroid cytology "indeterminate categories" SIAPEC/SIE 2014 in a consecutive series of 302 cases

PURPOSE

The clinical impact of the SIAPEC/SIE 2014 classification for thyroid cytology has been addressed in few studies that evaluated the malignancy rate and the relative prevalence of each category. No study analyzed its intra-observer and inter-observer reproducibility, so far.

METHODS

We retrospectively collected all "indeterminate" lesions diagnosed before (2011-2014) and after (2015-2018) the application of the SIAPEC/SIE 2014 classification at our Institution. Their relative malignancy risks were calculated based on available histological diagnoses. Cytological and clinical features of TIR3A were compared with the surgical outcome. Finally, a large set of samples was re-evaluated in blind of the original cytological and histological diagnoses by two pathologists, independently.

RESULTS

The prevalence of "indeterminate" diagnoses increased in years 2015-2018 (302/1482, 21% with 14% of TIR3A and 7% TIR3B categories) compared to years 2011-2014 (261/1680, 16%). Surgery was performed in 27% TIR3A and in 97% TIR3B cases. Malignancy rates were 40% for TIR3B and 17% for TIR3A, but were greatly influenced by the adoption of the WHO 2017 re-classification of encapsulated follicular-patterned lesions (decreasing to 28% and 6%, respectively). No criteria except for tumor size were associated to malignancy in TIR3A category. Intra-observer agreement of the experienced pathologist was 122/141 (86%), whereas inter-observer agreement between the expert and in-training pathologist was 95/141 (67%).

CONCLUSIONS

In this real-life experience, the sub-classification of TIR3A and TIR3B slightly increased the overall prevalence of "indeterminate" diagnoses. Malignancy rates were higher than estimated for both TIR3A and TIR3B categories. Agreement among observers highly depended on pathologist's training.

Thyroid Papillary Microtumor: Validation of the (Updated) Porto Proposal Assessing Sex Hormone Receptor Expression and Mutational BRAF Gene Status

Given the high incidence and excellent prognosis of many papillary thyroid microcarcinomas, the Porto proposal uses the designation papillary microtumor (PMT) for papillary microcarcinomas (PMCs) without risk factors to minimize overtreatment and patients' stress. To validate Porto proposal criteria, we examined a series of 190 PMC series, also studying sex hormone receptors and BRAF mutation. Our updated Porto proposal (uPp) reclassifies as PMT incidental PMCs found at thyroidectomy lacking the following criteria: (a) detected under the age of 19 years; (b) with multiple tumors measuring >1 cm adding up all diameters; and (c) with aggressive morphologic features (extrathyroidal extension, angioinvasion, tall, and/or hobnail cells). PMCs not fulfilling uPp criteria were considered "true" PMCs. A total of 102 PMCs were subclassified as PMT, 88 as PMC, with no age or sex differences between subgroups. Total thyroidectomy and iodine-131 therapy were significantly more common in PMC. After a median follow-up of 9.6 years, lymph node metastases, distant metastases, and mortality were only found in the PMC subgroup. No subgroup differences were found in calcifications or desmoplasia. Expression of estrogen receptor-α and estrogen receptor-β, progesterone receptor, and androgen receptor was higher in PMC than in nontumorous thyroid tissue. BRAF mutations were detected in 44.7% of PMC, with no differences between subgroups. In surgical specimens, the uPp is a safe pathology tool to identify those PMC with extremely low malignant potential. This terminology could reduce psychological stress associated with cancer diagnosis, avoid overtreatment, and be incorporated into daily pathologic practice.

The Japanese reporting system for thyroid aspiration cytology 2019 (JRSTAC2019)

We introduce the Japanese reporting system for thyroid aspiration cytology 2019 (JRSTAC2019) proposed by the Japan Association of Endocrine Surgery and the Japanese Society of Thyroid Pathology. Pathological classification and recommended clinical management for thyroid nodules in Japan are different from those described in the World Health Organization classification or the Bethesda System for Reporting Thyroid Cytopathology (TBSRTC). Therefore, it was necessary to develop a reporting system adapted for Japan. JRSTAC2019 is a modified version of TBSRTC. Currently, JRSTAC2019 is widely used in Japan, although the details of the system have not been introduced in English. JRSTAC2019 comprises seven categories: (I) unsatisfactory, (II) cyst fluid, (III) benign, (IV) undetermined significance, (V) follicular neoplasm (FN), (VI) suspicious for malignancy (SFM), and (VII) malignant. "Cyst fluid" nodules are classified as an independent category, and "recommended management" is in the same category as "benign" nodules. Surgical resection for FN nodules is decided upon by considering several parameters, and the decision is made without performing gene analysis. Non-invasive follicular thyroid neoplasm with papillary-like nuclear features tends to be more often diagnosed as papillary carcinoma. The risk of malignancy of SFM in Japan is higher than that in Western countries, and resection rates of SFM and malignant tumors are lower owing to active surveillance for low-risk papillary microcarcinoma. We recommend that each country should develop its reporting system, suitable for its medical and social needs. However, it should be easily compatible with TBSRTC for the ease of academic data sharing.

Atypia of undetermined significance/follicular lesion of undetermined significance: Asian vs. non-Asian practice, and the Singapore experience

The Bethesda System for Reporting Thyroid Cytopathology has paved the way for comparisons of the practice of thyroid cytology in many different regions. However, there have been comparatively few studies documenting differences between Asian and non-Asian practice. Here, we aim to compare a few key parameters between the two regions, focusing on the indeterminate category of atypia of undetermined significance (AUS)/follicular lesion of undetermined significance (FLUS). We compared its incidence, resection rates (RRs), risk of malignancy (ROM), rate of repeat fine needle aspiration (rFNA), ROMs of cytomorphologic subcategories of nuclear atypia (AUS-N) vs. architectural atypia (AUS-A), and, finally, the incidence of papillary thyroid carcinoma (PTC) vs. follicular neoplasms (FNs) in resected AUS/FLUS cases in Asian and non-Asian regions. Where possible, these metrics were compared with the Singapore experience from a tertiary referral institution. While the incidence of AUS/FLUS was similar in both regions, we found geographical differences in the RRs and ROMs, which may reflect a higher collective threshold for surgery in Asian countries. However, both cohorts showed higher ROMs in the AUS-N subcategory as compared to the AUS-A subcategory, supporting the subclassification of the AUS/FLUS based on the presence of nuclear atypia. We also observed a higher incidence of AUS-N coupled with a higher incidence of PTC in resected AUS/FLUS nodules in Asian cohorts, while AUS-A and follicular-patterned neoplasms featured more prominently in the non-Asian cohorts. These incidences may account for the starkly different molecular approaches that we noted-in Asian (chiefly Korean and Chinese) centers, BRAF mutational analysis was favored, while gene panels and gene expression classifiers were more frequently applied in non-Asian centers (chiefly in the United States of America). Overall, the data from Singapore appears more closely aligned to non-Asian trends, despite its geographical location in Southeast Asia and its predominantly Asian population. We conclude that there is significant heterogeneity in the outcomes of the AUS/FLUS categories between and within regions, which is only partially explained by regional variations, and may also reflect different regional diagnostic and management practices. This highlights the importance of understanding the local context in the interpretation of indeterminate Bethesda categories, rather than adopting a "one-size fits all" approach.

Practice Paradigms Before and After Introduction of the Diagnosis-Noninvasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features (NIFTP): an Institutional Experience

The recently adopted terminology of "Noninvasive follicular thyroid neoplasm with papillary-like nuclear features" (NIFTP) reflects the indolent behavior of these tumors. In contrast to conventional papillary thyroid carcinomas, NIFTP can be managed conservatively. The purpose of this study was to investigate changes in surgical and pathologic practice patterns at our institution since the introduction of the NIFTP diagnosis in 2016. A retrospective analysis of all thyroid specimens received in our laboratory between January 2015 and April 2017 was performed. The final cohort consisted of 1508 thyroidectomy specimens from 1508 patients (1153 (76.5%) women and 355 (23.5%) men), of which 1011 (67%) were total thyroidectomies and 497 (33%) were partial thyroidectomies. There were 558 (69.2%) total thyroidectomies and 248 (30.8%) partial thyroidectomies performed prior to introduction of the NIFTP diagnosis and 453 (64.5%) and 249 (35.5%) total and partial thyroidectomies, respectively, after the change in nomenclature. Within a year following the initial use of this diagnosis, 67 NIFTP cases were identified (9.5% of all thyroidectomies), whereas compared with the year preceding it, malignant diagnoses decreased from 54.5 (439) to 44.6% (313), and the benign category remained unchanged from 44.5 (367) to 45.9% (322). For the entirely submitted 67 NIFTP cases, the mean number of blocks submitted was 14.7 (0.98 blocks/g); for malignant lesions 17.7 (0.92 blocks/g); and for benign lesions 16.6 (0.75 blocks/g). The results of our study suggest that NIFTP are encountered in almost 10% of thyroidectomies at our institution with expected shifts in cytology and surgical pathology diagnoses as a result of the change in nomenclature. During this time period, significant shifts towards less aggressive surgical management were not observed. All 67 NIFTP nodules were submitted entirely with no significant difference in the number of cassettes submitted for NIFTP nodules as compared with follicular variant papillary thyroid carcinoma (PTC), classic variant PTC, or follicular adenoma.

Noninvasive follicular thyroid neoplasm with papillary-like nuclear features: a problematic entity

Noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) is a borderline thyroid tumour formerly known as noninvasive encapsulated follicular variant of papillary thyroid carcinoma. The prevalence of NIFTP is estimated at 4.4-9.1% of all papillary thyroid carcinomas worldwide; however, the rate of occurrence of NIFTP is eight times lower in Asian countries than in Western Europe and America. At the molecular level, NIFTP is characterised by the lack of BRAF V600E and BRAF V600E-like mutations or other high-risk mutations (TERT, TP53), and a high rate of RAS mutations, which is similar to other follicular-pattern thyroid tumours. The diagnosis of NIFTP can only be made after histological examination of the entire tumour removed during surgery, and is based on strictly defined inclusion and exclusion criteria. Although the diagnosis is postoperative, the combination of certain findings of preoperative tests including ultrasonography, cytology, and molecular testing may raise suspicion of NIFTP. These tumours can be effectively treated by lobectomy, although total thyroidectomy remains an option for some patients. Radioactive iodine and thyroid stimulating hormone suppression therapy are not required. NIFTP has an extremely good prognosis, even when treated conservatively with lobectomy alone. Nevertheless, it cannot be considered as a benign lesion. The risk of adverse outcomes, including lymph node and distant metastases, is low but not negligible.

Noninvasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features: From Echography to Genetic Profile

In thyroid pathology, the great variety of types and the wide range of aggressiveness of thyroid cancers complicate both diagnosis and management. In 2016, a subset of noninvasive encapsulated follicular variant of papillary thyroid carcinoma was reclassified as noninvasive follicular thyroid tumor with papillary-like nuclear features (NIFTP) to reduce overtreatment of this low-risk tumor that follows a benign course after surgery. Starting from a paradigmatic clinical case, in this short review, we will summarize the ultrasonography, cytological, histological and molecular features of this new entity. In the preoperative settings, the recognition of some peculiar elements may only suggest the possibility of a NIFTP, thus favoring a less aggressive surgical approach. However, the diagnosis of NIFTP can only be made after complete resection of the lesion by detecting well-defined inclusion and exclusion histopathological criteria. Since NIFTP is not 'malignant,' surgery may be considered curative with no further treatment or surveillance needed. NIFTP-related issues, including nodule size, multifocality, oncocytic changes, heterogeneous incidence across different geographical areas and its occurrence in the pediatric age, will be discussed.

Noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) is rare, benign lesion using modified stringent diagnostic criteria: Reclassification and outcome study

BACKGROUND

Rigid diagnostic criteria for NIFTP have been recently proposed. The frequency of NIFTP using the new criteria is unknown, and whether abortive papillae are associated with BRAF^V600E mutation has not been studied. The aim of this study is to identify NIFTP by a retrospective review of Follicular Variant of Papillary Thyroid Carcinoma (FVPTC), and to study its incidence as well as the association between immunohistochemical BRAF^V600E expression and abortive papillae in NIFTP.

DESIGN

Thyroid tumors diagnosed as FVPTC or NIFTP over a period of 18 years (2000-2017) were identified using the laboratory information system. The final pathology reports were reviewed and potential NIFTP were retrieved. The archived slides for these cases were independently reviewed by 2 pathologists. BRAF^V600E (clone: VE1) immunostain was performed on representative tumor blocks. Clinical information including follow-up data was obtained from the electronic medical records.

RESULTS

Among the 1918 cases with the diagnosis of papillary thyroid carcinoma (PTC), 589 (30.7%) of FVPTC and 136 cases of potential NIFTP were identified. After the review of the archived pathology slides, 29 lesions were morphologically reclassified as NIFTP. Four (13.7%) of these were positive for BRAF^V600E; no association was found between the presence of abortive papillae and BRAF^V600Eexpression (p=0.3). Exclusion of the 4 cases with BRAF^V600Eexpression resulted in 25 lesions of final NIFTP, representing 4.2% of the FVPTC and 1.3% of the PTC. The mean age of the NIFTP patients was 50 years, 87.5% were females. The mean size of the lesions was 1.4 cm (0.1-4.0 cm). Intranuclear pseudoinclusions were not identified, and abortive papillae were identified in 60% of NIFTP. The average follow-up was 70 (28-166) months. There were no adverse events (recurrence or metastasis) in the NIFTP group.

CONCLUSION

When strictly defined, NIFTP comprises 1.3% of cases perviously classified as PTC. In morphological NIFTP, no correlation is found between the presence of abortive papillae and the BRAF^V600E expression. Intranuclear pseudo-inclusions are not observed in NIFTP. Modification of current morphological criteria to include BRAF^V600E immunohistochemistry test may stratify NIFTP with benign outcome.

Computerized Cytological Features for Papillary Thyroid Cancer Diagnosis-Preliminary Report

Fine needle aspiration cytology (FNAC) is the final diagnosis of thyroid nodules before surgery. It is important to further improve the indeterminate FNAC diagnosis results using computerized cytological features. This retrospective cross-sectional study included 240 cases, of whom 110 had histologic diagnosis of papillary thyroid cancers (PTC), 100 had nodular/adenomatous goiters/hyperplasia (benign goiters), 10 had follicular/Hurthle cell carcinomas, and 20 had follicular adenomas. Morphological and chromatic features of FNAC were quantified and analyzed. The result showed that six quantified cytological features were found significantly different between patients with a histologic diagnosis of PTC and patients with histologic diagnosis of benign goiters in multivariate analysis. These cytological features were used to estimate the malignancy risk in nodules with indeterminate FNAC results. The Area Under the Receiver Operating Characteristics (AUROC) of the diagnostic accuracy with a benign or malignant nature was 81.3% (p < 0.001), 78.7% (p = 0.014), and 56.8% (p = 0.52) for nodules with FNAC results of atypia, which is suspicious for malignancy and follicular neoplasm, respectively. In conclusion, quantification of cytological features could be used to develop a computer-aided tool for diagnosing PTC in thyroid nodules with indeterminate FNAC results.

The Role of Molecular Testing for the Indeterminate Thyroid FNA

Thyroid nodules are common in the adult population where a majority are benign and only 4.0% to 6.5% are malignant. Fine needle aspiration (FNA) is a key method used in the early stages to evaluate and triage patients with thyroid nodules. While a definitive cytological diagnosis is provided in more than 70–75% of all thyroid FNA cases, the group of indeterminate lesions offers a challenge in terms of interpretation and clinical management. Molecular testing platforms have been developed, are recognized as an option by the 2015 American Thyroid Association Guidelines, and are frequently used in conjunction with FNA as an integral part of the cytologic evaluation. In this review, the utility of molecular testing options for nodules assigned to the group of indeterminate thyroid FNAs is described.