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.

Malignancy risk for solitary and multiple nodules in Hürthle cell-predominant thyroid fine-needle aspirations: A multi-institutional study

BACKGROUND

Hürthle cell metaplasia is common in hyperplastic nodules, particularly within the setting of lymphocytic thyroiditis (LT). The Bethesda System for Reporting Thyroid Cytopathology indicates that it is acceptable to classify Hürthle cell-predominant fine-needle aspiration (HC FNA) specimens as atypia of undetermined significance (AUS) rather than suspicious for a Hürthle cell neoplasm (HUR) within the setting of multiple nodules or known LT. The goal of the current study was to address whether this approach is justified.

METHODS

HC FNA specimens were identified and correlated with ultrasound and surgical pathology reports if available. Multinodularity was determined based on findings on macroscopic examination if imaging results were unavailable.

RESULTS

A total of 698 HC FNA specimens were identified, including 576 resected nodules, 455 of which (79%) were benign. The overall risk of malignancy for HUR was 27%, whereas the risk of malignancy for AUS was 10%. The mean size of the benign nodules was 2.1 cm on surgical resection specimens, with multiple nodules noted in 293 cases (64%) and histologic LT noted in 116 cases (25%). The mean size of the malignant nodules was 2.8 cm, with multiple nodules and histologic LT noted in 74 cases (61%) and 22 cases (18%), respectively. The malignancy rate did not differ between solitary or multiple nodules (P = .52) or in the presence or absence of LT (P = .12). However, size did significantly differ between malignant and benign nodules (P < 0.01).

CONCLUSIONS

The malignancy rate did not differ significantly in the presence of multiple nodules or LT, although the latter demonstrated a statistical trend. A diagnosis of AUS over HUR based solely on the presence of multinodularity is not warranted.

Qualifiers of atypia in the cytologic diagnosis of thyroid nodules are associated with different Afirma gene expression classifier results and clinical outcomes

BACKGROUND

Thyroid nodules with atypia of undetermined significance (AUS) on fine‐needle aspiration (FNA) have a low risk of malignancy that appears to vary based on specific features described in the AUS diagnosis. The Afirma gene expression classifier (GEC) is a molecular test designed to improve preoperative risk stratification of thyroid nodules, but its performance for different patterns of AUS has not been defined. The objective of this study was to assess GEC results and clinical outcomes in AUS nodules with architectural atypia (AUS‐A), cytologic atypia (AUS‐C) or both (AUS‐C/A).

METHODS

This was a retrospective review of all thyroid nodules with AUS cytopathology that underwent GEC testing at the authors' institution over a period of >4 years.

RESULTS

In 227 nodules that had AUS cytology results and Afirma GEC testing, the rate of benign GEC results was higher in AUS‐A nodules (70 of 107; 65%) than in AUS‐C/A nodules (25 of 65; 38%; P = .0008), and AUS‐C nodules exhibited an intermediate rate of benign results (27 of 55 nodules; 59%). The risk of cancer among patients who had GEC‐suspicious nodules, 86% of whom underwent resection, was 19% (6 of 25) for AUS‐A nodules compared with 57% (21 of 37) for AUS‐C/A nodules (P = .003) and 45% (10 of 22) for AUS‐C nodules (P = .07). In nodules that had an indeterminate repeat cytology result, no difference was observed in the rate of benign GEC results or in the malignancy rate compared with nodules that had a single cytology result.

CONCLUSIONS

The performance characteristics of Afirma GEC testing vary, depending on qualifiers of cytologic atypia. Recognition of these differences may enable clinicians to provide improved counseling and treatment recommendations to patients. Cancer Cytopathol 2017;125:313–322. © 2017 American Cancer Society.

Thyroid nodules with atypia of undetermined significance cytology and Afirma gene expression classifier (GEC) testing are analyzed based on the presence of architectural, cytologic, or both cytologic and architectural atypia. Nodules with architectural atypia are the most likely to have a benign GEC result and least likely to be malignant, suggesting that clinicians should be aware of these cytologic qualifiers when advising patients regarding GEC testing and the risk of malignancy.

Institution-specific risk of papillary thyroid carcinoma in atypia/follicular lesion of undetermined significance

BACKGROUND

The Bethesda System for Reporting Thyroid Cytopathology (BSRTC) is used in surgical decision-making according to malignancy risk in each category. Malignancy risk in atypia/follicular lesion of undetermined significance (AUS/FLUS) is estimated in BSRTC to be 5% to 15%, but institutional data have varied widely.

METHODS

We conducted a post-BSRTC 4-year retrospective analysis of index thyroid nodule cytology and histopathology in an academic head and neck endocrine surgery setting.

RESULTS

Of 2939 thyroid cytology reports from 1944 patients, the most advanced BSRTC category was AUS/FLUS in 233 patients (12.0%) of which 187 went to thyroidectomy. In AUS/FLUS, the upper and lower boundary estimates of the malignancy rate were 46% and 37%, accordingly. The malignancy rate did not vary significantly by cytopathologist or cytopathologic features.

CONCLUSION

Malignancy rates in AUS/FLUS vary by institution from 6% to 46%. Given the subjective nature of thyroid cytopathology and interpretation of the BSRTC categories, guidelines should encourage the use of institution-specific data on malignancy risk in treatment decisions. © 2015 Wiley Periodicals, Inc. Head Neck 38: E1210-E1215, 2016.

Follicular lesion of undetermined significance in thyroid FNA revisited

Controversy exists regarding the validity of follicular lesion of undetermined significance (FLUS), an indeterminate diagnostic category of The Bethesda System for Reporting Thyroid Cytopathology (BSRTC). According to BSRTC, FLUS carries a 5-15% risk of cancer. This study was designed to determine if cytomorphology could stratify FLUS into subgroups with different risks of malignancy. Reports of 127 consecutive FNAs reported as FLUS with subsequent tissue diagnoses were evaluated for the presence of various cytologic features and the results were correlated with histological diagnoses. FLUS cases with focal nuclear atypia (nuclear overlap/crowding, nuclear grooves/membrane irregularities, nuclear enlargement, and/or nuclear pseudoinclusions) were more frequently malignant on excision whereas those with architectural atypia (microfollicles) were more often benign on excision (P < 0.05). The presence of any one or more of these nuclear features increased the risk of carcinoma in subsequent thyroid resection. Papillary carcinomas predominated in excised FLUS cases with focal nuclear atypia whereas most FLUS with architectural atypia were adenomas or hyperplastic nodules on histological evaluation. BSRTC recommends that thyroid aspirates containing follicular cell nuclear and/or architectural atypia insufficient for a diagnosis of suspicious for follicular neoplasm, suspicious for malignancy or malignant be classified as FLUS. Our findings indicate that FLUS cases with focal nuclear atypia carry a risk for malignancy that is substantially higher than that assigned to FLUS and are best classified as suspicious. FLUS cases lacking these atypical nuclear features have a risk for malignancy that approximates the risk BSRTC has assigned to FLUS.