[OA-10] The thyroid Bethesda AUS/FLUS category subgroup and the risk of malignancy in Thammasat University Hospital

Chutima Jiragawasan and Wanwisa Himakhun

Department of Pathology, Thammasat University Hospital, Pathumthani, Thailand

The atypia of undetermined significance / follicolar lesion of undetermined significance (AUS/FLUS) is one of the categories in the Bethesda System for Reporting Thyroid Cytopathology. The rate of reporting and risk of malignancy (ROM) varies among intuitions. The aim of this study was to determine the reporting rate and risk of malignancy for AUS/FLUS and subgroups in Thammasat University Hospital. A retrospective study collected the data of patients who underwent thyroid FNAs from January 2016 to December 2019. All slides were re-evaluated and subcategorised as cytological atypia, architectural atypia, cytological and architectural atypia, Hurthle cell aspirates and atypia of non-specific (NOS). The ROM was calcolated as the lower and upper limits. There were 258 out of 2,995 FNAs (8.6%) diagnosed as AUS/FLUS (mean age, 54.1 years). Of 81 (38.9%) patients had histological correlations. The ROM of the AUS/FLUS was 9.1% – 23.5%. The subgroups of cytological atypia and atypia, NOS risks, were 11.4% – 28.1% and 16.7% – 50%, respectively. No malignancy was present in the other subgroups. Features of pseudonuclear-inclusions had the highest ROM (33.3% – 42.9%). In conclusion, AUS/FLUS interpretation rate of less than 10% is in the practice agreement. The subclassification and histology correlation enhance diagnostic criteria and proper managements.

Keywords: AUS/FLUS; FNA; ROM; subclassification; thyroid