Thyroid Bethesda Category AUS/FLUS in Our Microscopes: Three-Year-Experience and Cyto-Histological Correlation

The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) introduced a new category: Atypia of Undetermined Significance/Follicular Lesion of Undetermined Significance (AUS/FLUS) comprising of heterogenous lesions with a lesser degree of atypia. Its routine use is a bit controversial. The study cohort included AUS/FLUS thyroid cytopathological diagnoses signed out at Fimlab Laboratories from the period of 1 October 2013 to 31 December 2016. We analyzed all the AUS/FLUS cases, their cytology subclassification, and their cyto-histological correlation, when available. In total, there were 331 AUS/FLUS cases from 252 patients. The mean age was 59.8 years and there were 196 females and 56 males. Repeated AUS/FLUS was diagnosed in 75 (29.8%) cases. Out of 252 patients, 118 (46.8%) were operated on. Sixty-eight were operated on after the first AUS/FLUS diagnosis, 46 after 2 AUS/FLUS diagnoses, and 4 after 3 AUS/FLUS diagnoses. In total, there were 37 (14.7%) malignancies and 40 benign tumors. The risk of malignancy for AUS/FLUS (14.7%) is in agreement with the original TBSRTC risk of malignancy. The risk of neoplasia was 30.6% in our series.