Rate of malignancy for thyroid nodules with AUS/FLUS cytopathology in a tertiary care center – a retrospective cohort study

Abstract

Background Thyroid nodules are stratified through fine-needle aspiration (FNA) and are often categorized using The Bethesda System for Reporting Thyroid Cytopathology, which estimates the risk of malignancy for six cytopathological categories. The atypia of undetermined significance (AUS) and follicular lesion of undetermined significance (FLUS) categories have varying malignancy rates reported in the literature which can range from 6 to 72.9%. Due to this heterogeneity, we assessed the malignancy rate and effectiveness of repeat FNA (rFNA) for AUS/FLUS thyroid cytopathology at our institution. Methods Electronic health records of patients with AUS/FLUS thyroid cytopathology on FNA at our center since the implementation of the Bethesda System on May 1, 2014–December 31, 2019 were retrospectively reviewed. Patient demographics, treatment pathway, and pathology results were collected. The treatment pathway of the nodules, the rFNA results, and the malignant histopathology results were reported. Malignancy rates were calculated as an upper and lower limit estimate. Results This study described 182 AUS/FLUS thyroid nodules from 177 patients. In total, 24 thyroid nodules were deemed malignant upon histopathology, yielding a final malignancy rate of 13.2–25.3%. All of the malignancies were variants of papillary thyroid carcinoma. The malignancy rate of the nodules which underwent resection without rFNA (21.5%) was lower than the malignancy rate of the nodules which underwent resection after rFNA (43.8%). 45.5% of the rFNA results were re-classified into more definitive categories. Conclusion The malignancy rate of AUS/FLUS thyroid cytopathology at our center is in line with the risk of malignancy stated by the 2017 Bethesda System. However, our malignancy rate is lower than some other Canadian centers and approximately half of our rFNAs were re-classified, highlighting the importance of establishing center-specific malignancy and rFNA re-classification rates to guide treatment decisions.

Performance of Afirma genomic sequencing classifier and histopathological outcome in Bethesda category III thyroid nodules: Initial versus repeat fine‐needle aspiration

“…Several studies have demonstrated the importance of repeat FNA in thyroid nodules with an initial AUS diagnosis. Repeat FNA establishes a definitive diagnosis (TBSRTC category II or VI) in up to 50% of nodules with an initial diagnosis of AUS, reducing unnecessary surgical intervention in benign nodules and providing useful pre‐operative information for malignant nodules 10,11,15,16 . However, a notable portion of nodules remained as AUS after repeat aspiration.…”

“…Studies of TBSRTC category III thyroid nodules reported that repeating FNA resulted in a definitive diagnostic entity in 45%-50% of the cases, in which nearly 45% were recategorized into benign category. 10,11 A case series from one institution suggested repeat FNA cytology can help optimize molecular testing for a subset of cytologically indeterminate thyroid nodules. 12 Accordingly, performing Afirma GEC only on nodules with repeat Bethesda III/IV cytology would reduce the rate of surgery for benign nodules.…”

“…These findings indicate that the pretest probability of malignancy (thus the performance characteristics of Afirma GSC) is similar whether (1) an endocrinologist/surgeon's assessment of concerning clinical/sonographic features is used to refine the selection of a nodule for potential molecular testing based on the initial AUS diagnosis or (2) repeat diagnosis of AUS is used to refine the selection of a nodule for potential molecular testing.Several studies have demonstrated the importance of repeat FNA in thyroid nodules with an initial AUS diagnosis. Repeat FNA establishes a definitive diagnosis (TBSRTC category II or VI) in up to 50% of nodules with an initial diagnosis of AUS, reducing unnecessary surgical intervention in benign nodules and providing useful pre-operative information for malignant nodules 10,11,15,16. However, a notable portion of nodules remained as AUS after repeat aspiration.…”

Optimization of the Management of Category III Thyroid Nodules Using Repeat FNA and TIRADS

“…It is one of the probable causes of discrepancies between reported results in that respect. Some studies showed a similar frequency of cancers in patients treated surgically after or without rFNA [ 21 , 22 , 23 ]; others indicated an increased rate of malignancy after rFNA, non-significantly [ 8 , 24 , 25 , 26 , 27 , 28 , 29 ] or significantly [ 20 , 30 , 31 , 32 , 33 ] and there are reports that suggested slightly lower malignancy rates in patients undergoing surgery after rFNA in comparison to those treated directly after the diagnosis of category III [ 34 , 35 ].…”

Patient Compliance With Surveillance of Thyroid Nodules Classified as Atypia of Undetermined Significance

“…9 While patients who have a benign repeat FNA likely have a very low ROM, they still require further monitoring unless their ultrasound is very low suspicion, and surveillance of even those nodules is still an option. 2,9,16 Once a nodule has had 2 benign FNA results, ultrasound surveillance is no longer indicated. Therefore, unless a patient had a very low suspicion ultrasound, at least 2 surveillance points were indicated in our cohort based on these guidelines.…”