Cytologic subclassification of atypia of undetermined significance may predict thyroid nodules more likely to be malignant at surgery

Exploring the atypia of undetermined significance: Malignant ratio, ThyroSeq v3 positive call rate, molecular-derived risk of malignancy, and risk of malignancy as possible quality metric tools in thyroid cytology

BACKGROUND

The atypia of undetermined significance (AUS) category is heterogeneous, leading to variations in its use. To prevent excessive usage, the AUS rate should be ≤10%. Although this recommendation aims to maintain diagnostic quality, it lacks supporting data. The AUS:Malignant (AUS:M) ratio has been proposed as a metric tool to evaluate AUS use. Furthermore, integrating ThyroSeq v3 (TSV3) positive call rate (PCR) and the molecular-derived risk of malignancy (MDROM) have been put forward as performance improvement tools. The authors reviewed their AUS:M ratios, TSV3 PCR, MDROM, and ROM.

METHODS

Thyroid aspirates evaluated in the laboratory (from August 2022 to September 2023) by seven cytopathologists (CPs) were identified. AUS:M ratio, MDROM, ROM, and TSV3 PCR results for the laboratory and each CP were recorded and analyzed.

RESULTS

A total of 2248 aspirates were identified (462 AUS and 80 malignant). The AUS:M ratio for the laboratory was 5.8 (CPs range, 2.8 to 7.3). The TSV3 PCR for the laboratory was 23% (CPs range, 11% to 41%). The MDROM for the laboratory was 19% (CPs range, 9% to 31%), whereas the ROM was 36% (CPs range, 29% to 50%). Linear regression analysis of AUS:M ratio versus TSV3 PCR and MDROM demonstrated a moderate positive correlation but a weak negative correlation to the ROM. Deviations from established targets were attributed to multiple factors.

CONCLUSION

The findings of this study underscore the importance of using a combination of metrics to evaluate diagnostic practices. By dissecting the practice patterns of each CP, the authors can measure different aspects of their performance and provide individualized feedback.

A Comprehensive Approach to the Thyroid Bethesda Category III (AUS) in the Transition Zone Between 2nd Edition and 3rd Edition of The Bethesda System for Reporting Thyroid Cytopathology: Subcategorization, Nuclear Scoring, and More

Significant interobserver variabilities exist for Bethesda category III: atypia of undetermined significance (AUS) of The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC). Thus, subcategorization of AUS including AUS "nuclear" and AUS "other" is proposed in the recent 3rd edition of TBSRTC. This study investigated the impact of the nuclear features/architectural features/nuclear score (NS) (3-tiered)/subcategories and subgroups on risk of malignancy (ROM) in thyroid fine-needle aspirations (FNA). 6940 FNAs were evaluated. 1224 (17.6%) cases diagnosed as AUS were reviewed, and 240 patients (initial FNAs of 260 nodules and 240 thyroidectomies) were included. Subcategories and subgroups were defined according to TBSRTC 2nd and 3rd editions. Histological diagnostic groups included nonneoplastic disease, benign neoplasm, low-risk neoplasm, and malignant neoplasm. Overall, ROM was 30.7%. ROM was significantly higher in FNAs with nuclear overlapping (35.5%), nuclear molding (56.9%), irregular contours (42.1%), nuclear grooves (74.1%), chromatin clearing (49.4%), and chromatin margination (57.7%), and these features were independent significant predictors for malignancy. FNAs with NS3 had significantly higher ROM (64.2%). Three-dimensional groups were significantly more frequent in malignant neoplasms (35.7%). ROM was significantly higher in AUS-nuclear subcategory (48.2%) and in AUS-nuclear and architectural subcategory (38.3%). The highest ROM was detected in AUS-nuclear1 subgroup (65.2%). ROM was significantly higher in the group including AUS-nuclear and AUS-nuclear and architectural subcategories, namely "high-risk group" than the group including other subcategories, namely "low-risk group" (42.0%vs 13.9%). In conclusion, subcategorization may not be the end point, and nuclear scoring and evaluation of architectural patterns according to strict criteria may provide data for remodeling of TBSRTC categories.

Thyroid fine-needle aspiration cytology: malignancy rate in the category of indeterminate significant atypia/indeterminate significant follicular lesion

BACKGROUND

Fine needle aspiration cytology (FNAC) is a standard preoperative diagnostic modality for thyroid nodules. The Bethesda Thyroid Cytopathology Reporting System (TBSRTC) defines the FNAC atypia group as atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS).

OBJECTIVES

Determine the risk of malignancy after surgical resection in patients with AUS/FLUS.

DESIGN

Retrospective.

SETTING

Pathology department of a tertiary care center.

PATIENTS AND METHODS

All thyroid FNACs between 2015 and 2023 that were diagnosed as AUS/FLUS in Turkey. Patient demographics, preoperative ultrasonographic features, and follow-up data were collected.

MAIN OUTCOME MEASURES

Relationship between AUS/FLUS diagnosis and final histopathological diagnosis.

SAMPLE SIZE

562.

RESULTS

In total, 562 thyroid nodules were diagnosed as AUS/FLUS, and 267 (47.5%) were surgically excised. A malignant histopathological diagnosis was given in 28 cases (10.4%). Malignancy risk sensitivity of AUS/FLUS diagnosis was 75.68% (95% CI=58.80-88.23%), specificity was 55.24% (95% CI=50.91-59.52%), positive predictive value was 10.49% (95% CI=8.71-12.58%), and negative predictive value was 97.04% (95% CI=94.86-98.31%). In the ultrasonographic data, having symptomatic nodules, nodule calcification, and irregular nodule borders were all statistically significant signs of cancer in a one-variable analysis (P<.01). The presence of a family history emerged as a statistically significant prognostic marker for malignancy (P=.012). Although not statistically significant, the malignancy rate for nodules with nuclear atypia was 11.9%, significantly higher than the rate of 8.3% for nodules with architectural atypia only (P=0.32).

CONCLUSIONS

The diagnosis of AUS/FLUS has a high rate of predicting the risk of malignancy and should continue to be offered. In addition to cytopathological features, ultrasound data and family history should be taken into consideration when evaluating the case.

LIMITATIONS

Retrospective design and no molecular studies.

Binary subclassification scheme (AUS-Nuclear versus AUS-Other) adequately risk-stratifies thyroid fine needle aspiration specimens classified as Atypia of Undetermined Significance

INTRODUCTION

The Bethesda System for Reporting Thyroid Cytopathology previously described 4 subclasses of atypia within the Atypia of Undetermined Significance (AUS) category: nuclear (AUS-Nuc), architectural (AUS-A), oncocytic (AUS-Onc), and atypia not otherwise specified (AUS-NOS). Accumulating evidence supports a binary AUS subclassification scheme based primarily on the presence of nuclear atypia only. The purpose of this study is to compare the risk stratification of binary versus 4-tier AUS subclassification systems among AUS nodules with molecular and/or histologic follow-up.

MATERIALS AND METHODS

Thyroid aspirates classified as AUS and tested using Afirma (Veracyte, Inc.) between 6/2013 and 7/2021 were included. For resected nodules, histological classification was considered as the final outcome. For unresected nodules, benign Afirma results were considered low-risk outcomes, similar to histologically benign nodules. Suspicious or nondiagnostic Afirma results were considered indeterminate outcomes. The prevalence of outcomes warranting surgery (noninvasive follicular thyroid neoplasm with papillary-like nuclear features [NIFTP] or cancer) was calculated for each AUS subclass.

RESULTS

A total of 559 AUS nodules with Afirma testing were identified. Excluding nodules with indeterminate molecular outcomes, NIFTP/cancer prevalence for AUS-Nuc was 21% (57/266), which was higher than that for AUS-A (6%, 11/188), AUS-Onc (8%, 4/53), and AUS-NOS (0%, 0/9). A binary AUS subclassification scheme based on nuclear atypia showed a significant difference in NIFTP/cancer prevalence (21% versus 6%, P < 0.0001).

CONCLUSIONS

Binary reporting of AUS subclasses based on nuclear atypia distinguishes cases with a higher risk of NIFTP/cancer. There is a low but non-negligible prevalence of NIFTP/cancer in cases without nuclear atypia.

Use of molecular testing results to analyze the overuse of atypia of undetermined significance in thyroid cytology

INTRODUCTION

The suggested atypia of undetermined significance (AUS) rate for thyroid fine-needle aspiration biopsies is 10% or less. Prompted by a high institutional AUS rate, we examined using molecular testing results (MTR) as a potential quality metric tool to reduce the AUS rate. We correlated MTR with AUS cytologic findings, surgical pathology follow-up, and individual pathologist AUS rates.

MATERIALS AND METHODS

Demographic data, cytologic diagnoses, MTR, and surgical pathology diagnoses were retrospectively obtained. MTR were classified as either positive or negative. AUS rates and MTR proportions were compared among pathologists. The cytomorphologic features of 143 AUS cases were assessed and correlated with MTR.

RESULTS

Between 2017 and 2022, 710 of 3247 thyroid fine-needle aspirations were classified as AUS, with a yearly average rate of 22% (range = 19%-26%). AUS cases included: 331 (47%) with architectural atypia; 204 (29%) with oncocytic (Hürthle cell) atypia; 99 (14%) with combined architectural and cytologic atypia; and 76 (10%) with isolated cytologic atypia. Most AUS cases with molecular testing had negative MTR (360/492, 73%). AUS with cytologic atypia had higher positive MTR risk (logarithm of odds ratio = 1.27, 95% credible interval [0.5-2.04], P = 0.001). The average positive MTR rate by pathologist was 21.5% (range 0%-35%); higher positive MTR rates had better correlation with subsequent neoplastic/malignant histologic diagnoses. The MTR sensitivity for malignant disease was 89% and the negative predictive value was 91%.

CONCLUSIONS

MTR analysis reveals the importance of cytologic atypia as a determinant of malignancy risk in AUS cases. Periodic analysis of MTR data alongside individual pathologist AUS rates can help refine diagnostic criteria and potentially reduce AUS overuse.

Malignancy Rates of Atypia of Undetermined Significance/Follicular Lesion of Undetermined Significance (AUS/FLUS) Cases: A Tertiary Center Study

Aim

To evaluate the malignancy rates of Atypia of undetermined significance /follicular lesion of undetermined significance (AUS/FLUS) cases in the light of clinical and sonographic features.

Material and Methods

The percentage of AUS/FLUS cases, second fine needle aspiration cytology (FNAC) results, cyto-histopathological correlations and risk of malignancy were analyzed.

Results

113 out of 1461 thyroid FNAC samples (7.7%) were diagnosed as AUS/FLUS and included in the study. Seventy three out of 113 cases (64.6 %) underwent repeat biopsies or surgery. From 45 cases repeat biopsies were taken and 28 had thyroidectomy or lobectomy. There was a significant relation between nodule size and underwent surgery or repeat FNAC (p=0.036). Malignancy rate was 24.6% for cases which had any managements. The malignancy rates were higher in AUS/FLUS cases with cytological atypia (28.8%). After surgery the most common malignancy was papillary thyroid carcinoma, followed by follicular carcinoma.

Conclusion

The risk of malignancy of AUS/FLUS cases is quite high because of the heterogeneity of the group. The sub-classification of this category according to cytological or/and architecture atypia may be more useful in predicting malignancy risk. Further larger studies with ancillary techniques including molecular analysis may be more useful in determining the malignancy risk and appropriate management of this heterogeneous category.

Combined molecular and histologic end points inform cancer risk estimates for thyroid nodules classified as atypia of undetermined significance

BACKGROUND

Thyroid nodules classified as atypia of uncertain significance (AUS) on fine-needle aspiration cytology are heterogeneous. Prior studies reported a higher risk of noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP)/cancer among AUS nodules that had cytologic (AUS-C) versus architectural (AUS-A) atypia; however, such studies were generally confined to resected cohorts, introducing bias into risk calculations. The authors hypothesized that combined histologic and molecular end points would permit clinically meaningful calculations of NIFTP/malignancy risk among AUS nodules.

METHODS

The study consisted of 279 thyroid nodules classified as AUS on initial fine-needle aspiration and tested by the Afirma Gene Expression Classifier (GEC) between June 2013 and October 2017. Results of GEC testing and histopathologic diagnoses were stratified by AUS classifiers. The AUS-A category was further subclassified as 1) hypocellular microfollicular or 2) cellular with mixed but predominantly microfollicular architecture. NIFTP/cancer risk was calculated for each subgroup, with the inclusion of unresected nodules that had benign GEC results as low-risk end points comparable to histologically benign nodules.

RESULTS

When only histologic end points were considered, there was no difference in NIFTP/cancer risk (25% vs 23%; P = .82). By using molecular and histologic end points, AUS cases with cytologic atypia trended toward higher NIFTP/cancer risk than AUS-A cases (14% vs 6%; P = .06). Furthermore, AUS-A cases showed a trend toward lower NIFTP/cancer risk for hypocellular microfollicular aspirates (3%) compared with cellular samples that had mixed/predominantly microfollicular architecture (13%; P = .18).

CONCLUSIONS

The inclusion of unresected benign GEC nodules in risk-of-malignancy calculations provides more accurate results, which may be helpful for informing patient management as well as quality improvement in the cytopathology laboratory.

A Large Thyroid Fine Needle Aspiration Biopsy Cohort with Long-Term Population-Based Follow-Up

Background: Prior studies evaluating thyroid fine needle aspiration biopsies (FNABs) have limited the calculation of risk of malignancy (ROM) to cytologic specimens with corresponding histologic specimens, and clinical follow-up for those patients who do not undergo immediate surgery has been largely disregarded. Moreover, there is marked variability in how researchers have approached thyroid FNAB statistical analyses. This study addresses the urgent need for information from a large cohort of patients with long-term clinical follow-up to more accurately determine the performance of thyroid FNAB and ROM for each diagnostic category. Methods: A retrospective review of the University of California, San Francisco (UCSF), pathology database for thyroid FNABs from January 1, 1997, to December 31, 2004, was performed. Diagnoses were coded using the 2017 The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC), and patients were matched to both the UCSF cancer registry and California Cancer Registry. Data were analyzed using the Kaplan-Meier method, and stratified by TBSRTC diagnostic category. Kaplan-Meier curves were used to estimate incidence rates of malignancy, stratified by FNAB category. Cox proportional hazards models were used to determine the instantaneous ROM. Results: Initial FNABs from 2207 patients were included. Median follow-up period after the first thyroid FNAB was 13.9 years (range: 10.5-18.4 years). During follow-up, there were 279 confirmed diagnoses of thyroid malignancy. Estimates derived from Kaplan-Meier curves demonstrated that the risk of having a thyroid malignancy was low for nondiagnostic and benign categories, intermediate for atypia of undetermined significance (AUS), follicular lesion of undetermined significance (FLUS), AUS/FLUS combined, and follicular neoplasm, and high for suspicious and malignant categories. A total of 52/1575 false-negative cases (3.2%) were identified. Excluding papillary microcarcinomas, the false-negative rate was 1.5% (23/1575). No patients with a false-negative diagnosis died of thyroid cancer during the follow-up period. Conclusions: Asymptomatic patients with low-risk clinical and radiologic features and initially benign or unsatisfactory biopsy are unlikely to develop thyroid malignancy and highly unlikely to die of thyroid cancer. FNAB is highly accurate in detecting malignancy. Additional studies evaluating similar large data sets after the adoption of TBSRTC and the integration of molecular testing are needed.

Cancer prevalence in the subcategories of the indeterminate class III (AUS/FLUS) of the Bethesda system for thyroid cytology: a meta-analysis

PURPOSE

The indeterminate cytologic report represents a major challenge in the field of thyroid nodule. The indeterminate class III of the Bethesda classification system (i.e., AUS/FLUS) includes a heterogeneous group of subcategories characterized by doubtful nuclear and/or architectural atypia. The study aim was to  conduct a systematic review and meta-analysis to evaluate the rate of malignancy in each subcategory of Bethesda III.

METHODS

PubMed, CENTRAL, and Scopus databases were searched until April 2020. Original articles reporting data on the subcategories of Bethesda III were included. The histological diagnosis was the reference standard to classify true/false negative and true/false positive cases.

RESULTS

The pooled cancer prevalence in each subcategory of Bethesda III was estimated using a random-effects model. Twenty-three papers with 4241 nodules were included. Overall, 1163 (27.4%) were malignant. The cancer rate observed in the subcategories ranged from 15%, in "Hürthle cell aspirates with low risk pattern", to 44%, in "Focal cytologic atypia".

CONCLUSIONS

The overall cancer rate found in the Bethesda III ranged more largely than that originally estimated (10-30%) and varied among any scenarios. These evidence-based data represent a reference for the clinical management of these patients.

Subclassification of the Bethesda Category III (AUS/FLUS): A study of thyroid FNA cytology based on ThinPrep slides from the National Cancer Center in China

BACKGROUND

The atypia of an undetermined significance/follicular lesion of undetermined significance (AUS/FLUS) category in the Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) is a heterogeneous category, which includes various cell patterns. The subclassification of AUS/FLUS was suggested in the 2017 TBSRTC. However, the risk of malignancy (ROM) associated with different subgroups remains unresolved. Herein, AUS/FLUS aspirates were subclassified, from which the ROM of each subgroup was determined.

METHODS

All cases undergoing fine-needle aspiration (FNA) from July 2013 to December 2018 were reviewed. Of 12,913 thyroid FNAs, 1053 (8.2%) were AUS/FLUS. The slides of 222 patients with AUS/FLUS with surgical follow-up were reviewed and subclassified according to the recommendations of the 2017 TBSRTC. There were 195 aspirates consistently diagnosed as AUS/FLUS and subclassified as cytologic atypia 1 (AUS-C1); cytologic atypia 2 (AUS-C2); architectural atypia (AUS-A); cytologic and architectural atypia (AUS-C&A); Hürthle cell aspirates (AUS-H); atypia, not otherwise specified (AUS-NOS); and atypical lymphoid cells, rule out lymphoma (AUS-L).

RESULTS

Malignancy was identified in 83.3% (185 of 222) of the AUS/FLUS nodules. The AUS-C1 group was the most common (62.1%), followed by the AUS-C&A (12.8%), AUS-C2 (10.8%), AUS-H (6.7%), AUS-NOS (5.6%), AUS-L (1.5%), and AUS-A (0.5%) groups. AUS-C1 had the highest ROM (92.6%) among the groups and varied significantly from that of the AUS-C&A (P = .171), AUS-C2 (P = .001), AUS-H (P = .001), and AUS-NOS (P < .001) groups.

CONCLUSIONS

As a heterogeneous category of TBSRTC, the ROM for AUS/FLUS varies greatly among medical centers. Subclassification of AUS/FLUS might be helpful in identifying nodules with a high ROM in this category and improving the management of such nodules.

Is Subdivision of Atypia of Undetermined Significance AUS/Follicular Lesion of Undetermined Significance Cases According to Detailed Nuclear Features Vital for Assessing the Risk of Malignancy?

Background:

It has been known that the “atypia of undetermined significance (AUS)/follicular lesion of undetermined significance (FLUS)” category is the most problematic category in Bethesda system due to its highly heterogeneous morphological features. Recently, it has been reported that aspirates including nuclear atypia in the AUS/FLUS category have a higher risk of malignancy.

Aims:

This study aimed to assess each nuclear property in aspirates with cytological atypia and also to determine the relationship with the risk of malignancy.

Material and Methods:

We reviewed 980 AUS/FLUS fine-needle aspirations (FNAs) performed between '2012 and 2019' at a single institution. We classified these aspirates into four groups: AUS-N (nuclear atypia), AUS-A (architectural atypia), AUS-H (Hurthle cell change), and AUS-O (other). Nuclear features were detailed sub-classified; size and shape (enlargement, elongation, and overlapping), membrane irregularities (irregular contours, grooves, pseudoinclusion), and chromatin characteristics (pale chromatin). The estimated risk of malignancy (ROM) was calculated for each subgroup.

Results:

Of 980 AUS/FLUS cases, follow-up histological outcome data were available for 209 cases. Among these cases, the estimated ROM was 27.8%. The ROM were 26.4%, 15.4%, and 22.5% for AUS-N, A, and H, respectively. The most common nuclear findings associated with ROM were nuclear groove (67.9%); irregular contours (76.9%) suspected pseudoinclusion (100%) and overlapping (56%) (P < 0,001). But nuclear findings such as nuclear enlargement, mild pleomorphism, or pale chromatin have a similar ROM as architectural atypia.

Conclusion:

Although it is known that the presence of cytological atypia in an AUS/FLUS nodule increases the estimated risk of malignancy, all nuclear properties are not equally effective in predicting malignancy risk. Emphasizing nuclear atypia details in reports of AUS case may be a more sensitive way to identify nodules with a high risk of malignancy.

What is Thy3a? A study of 336 Thy3a (AUS/FLUS) thyroid FNAs with histology compares UK RCPath with other reporting systems and shows how Thy3a subclassification can improve risk stratification and help address overuse of this category

INTRODUCTION

Thy3a (AUS/FLUS) is an indeterminate and heterogeneous category in thyroid cytology. Thy3a reporting rates vary widely, with many laboratories documenting overuse. Subclassification of Thy3a helps with risk stratification. We aimed to investigate whether subclassification can also help address Thy3a overuse. We compare the UK reporting system with other terminologies.

METHODS

An audit of thyroid fine needle aspirations (FNAs) reported at our institution between 2012 and 2017 was performed. Thy3a FNAs followed by histology were reviewed and subcategorised into four subgroups: Scanty Atypia (SA), Scanty Microfollicular (SMF), Favour Benign (FB) and Thyroiditis versus Neoplasm (TVN). Review and subclassification were blinded to histology outcomes. FNAs were correlated with histology and statistical analysis was performed.

RESULTS

Our Thy3a rate was high (24% of all thyroid FNAs). For 336 Thy3a FNAs with histology, the malignancy rates of the four subgroups were: SA 68%, SMF 20%, FB 4%, TVN 31%. There were significant associations between subgroup and malignancy risk, and between subgroup and tumour risk. On histology, SA had more malignancies than expected and FB had fewer. SA and SMF had more tumours than expected and FB had fewer. SMF and Thy3f FNAs were similar in terms of tumour and malignancy outcomes.

CONCLUSIONS

Subclassification of Thy3a FNAs into these four subgroups is recommended. This can improve risk stratification and help address overuse of Thy3a. We propose that some FB and SMF cases could be safely diverted to Thy2 and Thy3f respectively. We compare various reporting terminologies and question how indeterminate FNAs should be classified.

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.

Thyroid nodules with Hürthle cells: the malignancy risk in relation to the FNA outcome category

PURPOSE

The aim was to find whether the presence of Hürthle cells (HC) in a smear influences the categorization of FNA results or the risk of malignancy (RoM) of particular categories of cytological diagnosis.

METHODS

25,220 FNA performed in a single center in years 2005-2017 were analyzed. Almost all the examined patients were exposed to moderate iodine deficiency for most of their lives. The distribution of FNA outcome categories was compared between two groups: with or without HC (HC and non-HC). The RoM was evaluated on the basis of postoperative histopathological examination (3082 patients).

RESULTS

HC were found in 7.5% of diagnostic FNA. HC nodules were classified into categories II (78.2% vs. 91.9%, p < 0.0000) and VI (0.4% vs. 1.2%, p = 0.0017) less often than non-HC nodules, but more frequently to categories III (14.4% vs. 5.8%, p < 0.0000), IV (11.2% vs. 0.9%, p < 0.0000) and V (1.5% vs. 0.8%, p = 0.0013). There were no significant differences in RoM between HC and non-HC nodules. The RoM in HC and non-HC nodules of particular categories of the Bethesda system was as follows: II: 1.8% vs. 0.8%, III: 9.7% vs. 3.8% when only the last FNA was considered and 10.8% vs. 6.4% when the category III in any performed FNA was considered; IV: 12.7% vs. 10.9%; V: 41.7% vs. 58.2%; and VI: 100% vs. 96.9%.

CONCLUSIONS

HC nodules are classified into categories of equivocal cytological outcomes more often than nodules without HC. Nevertheless, the presence of HC in a smear does not significantly affect the RoM of FNA categories.

Semiquantitative assessment of cytomorphologic features can predict mutation status of thyroid nodules with indeterminate cytologic diagnosis

Molecular diagnostics increasingly direct the management of thyroid nodules with an indeterminate cytologic diagnosis. This study was undertaken to correlate cytomorphologic features with the molecular profiles in an effort to identify features predictive of molecular aberrations. One hundred eighty-nine thyroid nodules with an indeterminate thyroid cytology diagnosis (atypia of undetermined significance, suspicious for follicular lesion, and suspicious for malignancy) with an adequate sample submitted for targeted mutation detection by polymerase chain reaction or next-generation sequencing were assessed semiquantitatively for the following cytomorphologic parameters: cellularity, Hurthle cell changes, microfollicles, nuclear elongation, nuclear grooves, nuclear enlargement, nuclear atypia, extent of atypia, and colloid. Based on this evaluation, a cumulative cytomorphologic score (CCS) and a more simplified overall atypia score (OAS) were assigned to each case. Associations among mutational status and each of the aforementioned parameters, CCS, and OAS were determined. Of the 189 nodules with indeterminate cytology, 63 (33.3%) harbored at least 1 mutation. RAS and BRAF were the most common mutations, found in 34 (18.0%) and 13 (6.9%) cases, respectively. Both CCS and OAS were highly associated with the presence of all mutations (P < .0001) and with the presence of BRAF and RAS mutations in particular (all P < .01). Semiquantitative assessment of various cytomorphologic features in indeterminate thyroid cytology cases showed a strong association of higher OAS and CCS and incidence of BRAF and RAS mutations. Using a more objective approach to thyroid cytology can potentially decrease the overall number of indeterminate diagnoses, leading to fewer repeat procedures and unnecessary surgical procedures.

Differences in Thyroid Nodule Cytology and Malignancy Risk Between Children and Adults

Background: The Bethesda System for Reporting Thyroid Cytopathology (BSRTC) is used to interpret fine-needle aspiration (FNA) cytology of thyroid nodules in children and adults. Nodule management is guided by the implied malignancy risk of each cytological category, which has been derived from adult populations. Whether these implied risks are applicable to pediatric thyroid nodules remains uncertain. We compared malignancy rates between pediatric and adult thyroid nodules within each cytological category. Methods: We evaluated consecutive thyroid nodules ≥1 cm that underwent FNA at the Boston Children's Hospital and Brigham and Women's Hospital from 1998 to 2016. All cytology was interpreted by a single cytopathology group according to the BSRTC. Malignancy rates were compared between pediatric (<19 years) and adult (≥19 years) patients. Results: Four hundred thirty pediatric thyroid nodules and 13,415 adult nodules were analyzed. Pediatric nodules were more likely to be malignant than adult nodules (19% vs. 12%, p = 0.0002). Within cytological categories, malignancy rates were higher in pediatric nodules than in adult nodules that were cytologically nondiagnostic (11% vs. 4%, p = 0.03), atypia of undetermined significance (AUS; 44% vs. 22%, p = 0.004), or suspicious for follicular neoplasm (SFN; 71% vs. 28%, p = 0.001). There were no significant differences between children and adults in the types of thyroid cancers diagnosed in these cytological categories. Among cytologically benign nodules, the difference in malignancy rates was statistically significant but clinically minimal (0.7% vs. 1%, p = 0.001). Malignancy rates did not differ between children and adults among nodules with cytology suspicious for papillary carcinoma (73% vs. 68%, p = 0.67) or positive for malignancy (97% vs. 95%, p = 1). Among the subset of nodules that were resected, the malignancy rate was higher in children than in adults only in nodules that were SFN (71% vs. 36%, p = 0.007). Conclusions: Among thyroid nodules that are cytologically AUS, SFN, or nondiagnostic, malignancy rates are higher in children than in adults. These discrepancies likely represent true differences in malignancy risk between pediatric and adult patients, rather than differences in cytological interpretation. Our findings provide pediatric-specific data to inform the optimal management of thyroid nodules in children, which may differ from that of adult nodules with equivalent cytology.

An Insight into the Utility of Sub-Categorisation of Atypia of Undetermined Significance for Risk Stratification: A Retrospective Study on an Indian Cohort with Histopathological Correlation

BACKGROUND

Atypia of undetermined significance or follicular lesion of undetermined significance (AUS/FLUS) criterion in thyroid fine-needle aspirates (FNAs) has been a heterogeneous entity with much inter-observer variation. Sub-categorisation of AUS/FLUS has been observed to play an effective role in risk stratification. We aimed to validate AUS/FLUS sub-categorisation in correlation with the spectrum of malignancy.

STUDY DESIGN

Subjects included patients with AUS/FLUS diagnosed between January 2015 and December 2016. AUS/FLUS cases were sub-categorised into those exhibiting (1) architectural atypia, (2) cytological atypia, (3) architectural and cytological atypia, (4) AUS with Hürthle cells, and (5) AUS not otherwise specified (AUS-NOS). Each sub-category was correlated with their corresponding incidence of malignancy in surgical resections.

RESULT

The overall incidence of AUS/FLUS in our centre was 13% (132/1,018). On retrospective review of 117 patients with AUS/FLUS, smears with cytological atypia showed a higher incidence of malignancy (78.3%) than those with architectural atypia (75.3%). AUS/FLUS cases with both cytological and architectural atypia had a malignancy rate of 71.4%.

CONCLUSION

AUS/FLUS cases with cytological atypia had a higher risk of malignancy than those with architectural atypia. The sub-categorisation of AUS/FLUS is diagnostically important for the proper risk stratification of patients.

Clinical Parameter for Deciding the BRAFV600E Mutation Test in Atypia of Undetermined Significance/Follicular Lesion of Undetermined Significance Thyroid Nodules: US Features According to TIRADS

This study aimed to investigate the usefulness of a thyroid imaging reporting and data system (TIRADS) to select thyroid nodules with atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS) cytology for additional BRAF mutation testing. Three hundred three thyroid nodules were included. Statistical analysis was performed at both patient and nodule levels according to BRAF mutation positivity and clinical factors. Univariate and multivariate logistic regression analyses were performed to assess independent associations between BRAF mutation positivity and clinical factors. Of 303 AUS/FLUS nodules, 16 (5.3%) of 303 nodules had the BRAF mutation. The frequency of the BRAF mutation according to the TIRADS was 35.7% for category 5, 10.8% for category 4c, 2.5% for category 4b, 1.1% for category 4a, and 0% for category 3 nodules (P < 0.001). On multivariate analysis, BRAF mutation positivity was significantly associated with high suspicion on the TIRADS (odds ratio, 15.247; P < 0.001). In conclusion, the ultrasonography patterns of the TIRADS can be used as a clinical parameter for deciding the BRAF mutation test in thyroid nodules with AUS/FLUS cytology.

Cytomorphologic, Imaging, Molecular Findings, and Outcome in Thyroid Follicular Lesion of Undetermined Significance/Atypical Cell of Undetermined Significance (AUS/FLUS): A Mini-Review

OBJECTIVES

Since the introduction of the entity of "Atypical cell of undetermined significance /follicular lesion of undetermined significance" (AUS/FLUS) by The Bethesda System for Reporting Thyroid Cytology (TBSRTC) in 2007, there have been many published studies about the cytomorphologic criteria, subclassification, outcome, and management of patients with the diagnosis of AUS/FLUS. There have been many studies in different aspects of this indeterminate category, i.e., cytologic and molecular findings, ultrasonographic findings, and in some instances even core-needle biopsy to address a better and safer way of the management of patients with this fine-needle aspiration cytology diagnosis. The second edition of TBSRTC and the 2015 American Thyroid Association guidelines provide an update on the follow-up and management of AUS/FLUS. A multidisciplinary team consisting of pathologists, endocrinologists, surgeons, and radiologists should be involved in the diagnosis and management of AUS/FLUS, and all of them should be aware of the heterogeneity of this lesion for the prediction of the treatment and outcome.

STUDY DESIGN

In this review, we consider different research platforms (2008-2017) to find the best and key reports for the above-mentioned challenging aspects of AUS/FLUS.

CONCLUSION

AUS/FLUS is now a well-defined group of thyroid lesions, which can be most accurately diagnosed and managed with cytomorphology, molecular, and ancillary studies.

Prevalence and associated malignancy of Bethesda category III cytologies of thyroid nodules assigned to the "cytological atypia" or "architectural atypia" groups

OBJECTIVE

To ascertain the prevalence of Bethesda category III cytologies and their malignancy rate, and to analyze differences in the second cytology, malignancy rate, type of carcinoma, and TNM stage between the cytological atypia (CA) and architectural atypia (AA) groups.

PATIENTS AND METHOD

A retrospective study of 973 biopsies. Bethesda category III cytologies were classified as CA when nuclear atypia was seen but they were not diagnostic or suspicious of malignancy, and as AA when smears had few cells but had a predominantly microfollicular pattern and minimal or absent colloid. The cytological and pathological results were correlated.

RESULTS

There were 87 (8.9%) Bethesda category III cytologies (34 CC, 53 AA). Second cytologies were performed in 23 patients (16 with CA, 7 with AA), and a benign result was found in 68.7% of CA and 71.4% of the AA group. Sixty-four patients (23 CA, 41 AA) underwent surgery and 15 of these (23.4%) had a malignant disease: 39.1% CA vs 14.6% AA (P=.029). There was a false negative result in the CA group. The follicular variant of papillary thyroid carcinoma was the most common malignancy (60%). There were no differences in type of carcinoma or TNM stage between CA and AA patients.

CONCLUSIONS

The reported prevalence of Bethesda category III cytologies was as expected. The malignancy rate was significantly higher in the CA group, but there were no differences in the result of the second cytology, type of carcinoma found, or TNM stage. The division of Bethesda category III cytologies is useful to provide a better stratification of the risk of malignancy.

Subclassification of Bethesda Atypical and Follicular Neoplasm Categories According to Nuclear and Architectural Atypia Improves Discrimination of Thyroid Malignancy Risk

BACKGROUND

Although The Bethesda System for Reporting Thyroid Cytopathology has provided clinicians with a standardized classification scheme for the diagnosis of thyroid fine-needle aspiration cytology (FNAC) specimens, the indeterminate categories of Bethesda III (B3)-atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS)-and Bethesda IV (B4)-follicular neoplasm/suspicious for follicular neoplasm (FN/SFN)-continue to pose challenges with regards to ideal diagnostic and therapeutic management. Having previously demonstrated the presence of nuclear atypia as a high-risk subgroup in B3, the objective of this study was to evaluate the malignancy rates in the B4 subgroup with nuclear atypia.

METHODS

A retrospective review of all thyroid FNACs diagnosed as B4 (FN/SFN) between 2008 and 2015 was conducted at a tertiary referral center in Singapore. Data on patient demographics, sonographic features, and final histological diagnosis were collected. This was compared to data from a previous analysis on all nodules diagnosed as B3 (AUS/FLUS) over a similar period.

RESULTS

A total of 137/309 (44.3%) and 88/111 (79.3%) FNACs diagnosed as B3 and B4, respectively, underwent surgical excision yielding final histopathological diagnoses. The malignancy rate of B4 was 31/88 (35.2%) compared to B3, which was 37/137 (27.0%). Subclassification based on the presence of architectural versus nuclear atypia showed significantly higher malignancy rates in B4 nodules with nuclear atypia (21.8% vs. 57.6%; p < 0.01). These findings corroborate previous results within the B3 category (malignancy rate of 14.7% vs. 36.8%; p < 0.01). The only sonographic features predictive of malignancy were the presence of macrocalcifications in B4 compared to irregularity of margins in B3.

CONCLUSION

The presence of nuclear atypia identifies subgroups with significant differential malignancy risks within both the B3 and B4 categories. This supports the notion that subclassification is a useful risk stratification tool that can guide diagnostic and therapeutic management of indeterminate thyroid nodules with heterogenous risk profiles.

The impact of noninvasive follicular thyroid neoplasm with papillary-like nuclear features on the rate of malignancy for atypia of undetermined significance subcategories

BACKGROUND

The recent revision in terminology, with noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) replacing noninvasive follicular variant of papillary thyroid carcinoma, has reclassified the clinically indolent tumor as nonmalignant. The objective of this study was to evaluate the impact of this change on the rate of malignancy (ROM) for subcategories of an atypia of undetermined significance (AUS) diagnosis on fine-needle aspiration (FNA) cytology.

METHODS

Consecutive thyroid FNAs interpreted as AUS over a period of 4 years were retrospectively analyzed. The ROM for AUS subcategories, including atypia of undetermined significance with nuclear atypia (AUS-N), atypia of undetermined significance with a microfollicular pattern (AUS-F), atypia of undetermined significance with nuclear atypia and a microfollicular pattern (AUS-N/F), atypia of undetermined significance with Hürthle cells (AUS-H), and atypia of undetermined significance, not otherwise specified (AUS-NOS), were analyzed.

RESULTS

Of the 426 nodules interpreted as AUS, 244 were surgically excised. The incidence of NIFTP in each subcategory was as follows: 18% for AUS-N, 18% for AUS-F, 9% for AUS-N/F, 3% for AUS-H, and 0% for AUS-NOS. After the reclassification of NIFTP as nonmalignant, the ROM based on histologic follow-up significantly decreased from 43% to 26% for AUS-N (P < .001) and from 29% to 10% for AUS-F (P = .008). The ROM for AUS-N remained significantly higher than the ROM for AUS-F (P = .030).

CONCLUSIONS

A subset of resected AUS nodules can be reclassified as NIFTP, and that significantly decreases the ROM, especially for AUS-N and AUS-F. Nonetheless, AUS-N still harbors a substantially higher ROM than AUS-F. Cancer Cytopathol 2018;126:309-16. © 2018 American Cancer Society.

Malignancy rates for Bethesda III subcategories in thyroid fine needle aspiration biopsy (FNAB)

OBJECTIVES

Most thyroid diseases are nodular and have been investigated using ultrasound-guided fine needle aspiration biopsy (FNAB), the reports of which are standardized by the Bethesda System. Bethesda category III represents a heterogeneous group in terms of lesion characteristics and the malignancy rates reported in the literature. The objective of the present study was to evaluate the differences in the malignancy rates among Bethesda III subcategories.

METHODS

Data from 1,479 patients who had thyroid surgery were reviewed. In total, 1,093 patients (89.6% female, mean age 52.7 (13-89) years) were included, and 386 patients were excluded. FNAB results (based on Bethesda Class) and histopathological results (benign or malignant) for coincident areas were collected. Bethesda III patients were subcategorized according to cytopathological characteristics (FLUS: follicular lesion of undetermined significance, Bethesda IIIA; AUS: atypia of undetermined significance, Bethesda IIIB). Data were correlated to obtain the malignancy rates for each Bethesda category and the newly defined subcategory.

RESULTS

FNAB results for these patients were as follows: Bethesda I: 3.1%; Bethesda II: 18.6%; Bethesda III: 35.0%; Bethesda IV: 22.1%; Bethesda V: 4.1%; and Bethesda VI: 17.1%. The malignancy rates for Bethesda Class IIIB were significantly higher than those for Bethesda Class IIIA (p<0.001) and Bethesda Class IV (p<0.001). Bethesda Class IIIA showed significantly lower malignancy rates than Bethesda Class III overall (p<0.001) CONCLUSIONS: Improvements of the Bethesda System should consider this subcategorization to better reflect different malignancy rates, which may have a significant impact on the decision-making process.

Utility of a formatted pathologic reporting system in thyroid core needle biopsy: A validation study of 1998 consecutive cases

OBJECTIVE

Thyroid core needle biopsy (CNB) is increasingly being used as a tool for evaluating thyroid nodules; thus, standardization of its diagnostic terminology is called for. We aimed to analyse the pathologic reporting system of thyroid CNB based on the recently proposed protocol by the Korean Endocrine Pathology Thyroid Core Needle Biopsy Study Group and evaluate its usefulness.

DESIGN/METHODS

A total of 1998 consecutive cases of thyroid CNBs were reviewed and divided into six categories according to the protocol. Malignancy rate in each category and the diagnostic performance of thyroid CNB were calculated using 705 resected cases.

RESULTS

Thyroid CNB yielded 132 nondiagnostic (6.6%), 791 benign (39.6%), 328 indeterminate (16.4%), 227 follicular neoplasm (11.4%), 69 suspicious for malignancy (3.5%) and 451 malignant lesions (22.6%). In resected specimens, all of the cases designated as suspicious for malignancy and malignant categories in CNB were proven to be true malignant lesions. Lesions diagnosed with follicular neoplasm in CNB were identified as malignant lesions in 57.0%. Malignancy rate was significantly higher in indeterminate lesions with nuclear atypia compared to those with architectural atypia (80.0% vs 28.2%). When CNB diagnoses of indeterminate lesions or higher categories were considered positive, the sensitivity and positive predictive value for final malignant diagnoses were 99.2% and 81.3%, respectively.

CONCLUSIONS

CNB is an accurate method of evaluating thyroid nodules and can serve as an alternative to fine needle aspiration when it is used and reported according to standardized diagnostic categories.

Comparison of risk of malignancy in a subgroup with atypia of undetermined significance/follicular lesion of undetermined significance: A meta-analysis

BACKGROUND

As heterogeneous findings are included in the atypia of undetermined significance (AUS)/follicular lesion of undetermined significance (FLUS) category, differing risks of malignancy in subgroups have been reported in several articles.

METHODS

We performed a meta-analysis of full-text publications written in English found in the Embase and PubMed databases.

RESULTS

The 4-tiered subgroup proportion meta-analysis showed that the 95% confidence interval (95% CI) of the risk of malignancy in the cellular atypia group did not overlap with the other 3 subgroups and demonstrated a significant difference. Two-tiered analysis using the cytologic and architectural atypia groups showed that cytologic atypia group had a 2.64-fold increase in the risk of malignancy compared with the architectural atypia group.

CONCLUSION

The cytologic atypia had a significantly higher risk of malignancy than the architectural atypia group, and it should be considered as a separate category.

Malignancy rate in thyroid nodules categorized as atypia of undetermined significance or follicular lesion of undetermined significance - An institutional experience

Introduction:

Atypia of undetermined significance (AUS) or follicular lesion of undetermined significance (FLUS) of Bethesda system for reporting thyroid cytopathology has emerged as most controversial category due to its heterogeneity and inconsistent usage. Initially associated risk of malignancy was estimated to be about 5–15%, but eventually different results have been obtained across institutions due to variable follow-ups and interpretation. The present study was conducted to evaluate the rate of malignancy along with appropriate management in this category.

Materials and Methods:

The study included AUS/FLUS cases diagnosed over period of 4 years on thyroid fine needle aspiration cytology (FNAC). Detailed clinical history and radiological examination were recorded along with follow-ups and management of all cases. Histopathology was available for cases which underwent surgery due to high clinical suspicion, worrisome radiological features or two consecutive AUS/FLUS reports.

Results:

The incidence of AUS/FLUS was 6.4% with repeat FNAC done in 39.6%, immediate surgery in 49.2% and follow-up without intervention in 11.1% cases. The overall malignancy rate was 28.5% with most common malignancy being follicular variant of papillary carcinoma (FVPC). Malignancy rate was more in cases (24.1%) which morphologically showed atypical nuclear features in comparison to architectural atypia.

Conclusion:

AUS/FLUS is associated with higher risk of malignancy than previously anticipated. Surgical intervention may have greater implication than repeat FNAC in appropriate management of this category. Substratification of this category according to nuclear features and architecture may be more useful in predicting malignancy risk and reducing the variability in the group.