Spectrum of Risk of Malignancy in Subcategories of ‘Atypia of Undetermined Significance’

Abstract

Objective: To determine if focal ‘nuclear atypia’ or ‘microfollicular architecture’ portends a higher risk of malignancy than other subcategories of atypia of undetermined significance (AUS) in thyroid fine-needle aspirations (FNAs). Study Design: The frequencies of The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) categories were calculated from 3,956 thyroid FNAs interpreted over a 26-month period at The Johns Hopkins Hospital after adoption of TBSRTC. TBSRTC criteria were applied strictly. The risk of malignancy, specifically for AUS subcategories, was analyzed by cyto-histo correlation. Results: Of the 133 cases diagnosed as AUS, 32% were found to have stageable carcinoma (not incidental microcarcinoma) on resection. When the subset of AUS with ‘nuclear atypia’ (AUS-N) was separated from other AUS cases, 48% (30/62) of them had stageable carcinoma on resection; of the AUS subset with ‘microfollicular architecture’ (AUS-F), 27% (8/30) were malignant on resection. The ‘suspicious for papillary thyroid carcinoma’ (SPTC) group maintained a higher risk of malignancy versus AUS-N (relative risk, RR 1.57; 95% CI 1.23–1.81). Conclusion: The subcategory of ‘nuclear atypia’ within AUS indicates a higher risk of malignancy than other subcategories of AUS but has a lower risk of malignancy than SPTC does. Thus, it is an important distinction with potential clinical implications.

Analiza znaczenia klinicznego niejednoznacznych wyników biopsji tarczycy ze szczególnym uwzględnieniem kategorii ZPBN na podstawie 5 lat stosowania nowej klasyfikacji rozpoznań cytologicznych

“…As a consequence of the above-mentioned factors the risk of malignancy in FLUS nodules as assessed on the basis of postoperative histopathological examination ranges from 4% up to as much as 50% [12,[22][23][24][25][26][27][28][30][31][32][33][34][35][36][37][38][39][40][41], so it exceeds by several times the values suggested by NCI recommendations. Many authors indicate that the final malignancy results were observed several times more frequently in AUS than in FLUS [7][8][9][10][11][12][13][14]. In our material, in 1 of 3 cases of FLUS with features of nuclear atypia a papillary cancer was found in postoperative examination.…”

“…A particularly controversial problem is the degree of nuclear atypia (polymorphism) that allows the categorisation of aspirate as FLUS and not SM. Some authors even distinguish the separate category for smears with abnormalities in cellular nuclei, such as the presence of occasional nuclear grooves, an abnormal chromatin pattern, or nuclear overlapping and crowding [7][8][9][10][11]22].…”

“…Those smears showed characteristics between SM and ND categories and in consequence were classified in the analysis as SM-low diagnostic. Because of the aforementioned factors the FLUS diagnosis constitutes, according to various authors, between 1% up to nearly 20% of all results [9,19,[24][25][26][27][28][29][30][31][32][33][34].…”

“…Another assumption was that FLUS diagnosis would not be a direct indication for surgical treatment, in contrast to other ISC categories (SFN and SM). However, numerous reports indicate that FLUS may be related to higher than assumed risk of malignancy [7][8][9][10][11][12][13][14]. It is also unclear whether implementation of the new FLUS category does not significantly affect the malignancy risk related to other ISC categories (SFN and SM).…”

Malignancy Rates in Bethesda Category AUS/FLUS: Single Center Experience

“…However, the published reports after the widespread use of BRSTC informed highly variable risk of malignancy ranging between 6 %-96,7% in this group (3)(4)(5)(6)(7)(8). The malignancy rate in AUS/FLUS category of our center was 45,8% and is placed centrally in previosly reported wide risk spectrum (3)(4)(5)(6)(7)(8).…”