Endocrine Abstracts

Introduction: ‘Atypia of undetermined significance/follicular lesion of undetermined significance’ (AUS/FLUS) is a heterogeneous diagnostic thyroid fine needle aspiration biopsy (FNAB) category. AUS/FLUS is comprised of cases that cannot be definitively diagnosed as benign, suspicious for/consistent with neoplasm, suspicious for malignancy or malignant. The recommended management strategy for these cases is to perform a repeat FNAB after an appropriate time course. Although the estimated risk of malignancy for AUS/FLUS is reported 5–15%, there is growing evidence in the literature that suggest higher incidence of malignancy for this category The purpose of this study is to estimate the malignancy risk of repeated AUS/FLUS diagnosis of thyroid fine needle aspiration biopsies.

Methods: We report retrospective analyses of 56 cases with repeated AUS/FLUS diagnosis among 5396 thyroid FNABs. The demographic data and histologic follow-up were evaluated in the study. Histological outcome was categorised as benign, malignant or well-differentiated tumors of uncertain malignant potential (WDT-UMP).

Results: Initial AUS/FLUS diagnosis was 5.2% of our FNAB series. Among these 63 (22%) of were diagnosed again as AUS/FLUS on repeated FNAB. Seven patients were lost during follow-up. Among 56 cases with a repeated diagnosis of AUS/FLUS, histologic follow-up revealed 28 (50%) benign outcome, 23 (41%) malignant outcome and 5 (9%) WDT-UMP outcome. The mean age was similar in both malignant and benign groups.

Discussion: The malignancy risk of AUS/FLUS category in thyroid FNABs was higher than anticipated in Bethesda System. The malignancy risk was reported up to 43% even with single biopsy in some studies. In current study the risk was 41% in repeated AUS/FLUS diagnosis. The reported malignancy rate of follicular neoplasm or suspicious for a follicular neoplasm (FN/SFN) was 15–30%, for whom surgery is recommended management. Therefore, the management strategy of AUS/FLUS should also be revised as the malignancy rate was same or even higher than FN/SFN.