Institution-specific risk of papillary thyroid carcinoma in atypia/follicular lesion of undetermined significance.

BACKGROUND The Bethesda System for Reporting Thyroid Cytopathology (BSRTC) is used in surgical decision-making according to malignancy risk in each category. Malignancy risk in atypia/follicular lesion of undetermined significance (AUS/FLUS) is estimated in BSRTC to be 5% to 15%, but institutional data have varied widely. METHODS We conducted a post-BSRTC 4-year retrospective analysis of index thyroid nodule cytology and histopathology in an academic head and neck endocrine surgery setting. RESULTS Of 2939 thyroid cytology reports from 1944 patients, the most advanced BSRTC category was AUS/FLUS in 233 patients (12.0%) of which 187 went to thyroidectomy. In AUS/FLUS, the upper and lower boundary estimates of the malignancy rate were 46% and 37%, accordingly. The malignancy rate did not vary significantly by cytopathologist or cytopathologic features. CONCLUSION Malignancy rates in AUS/FLUS vary by institution from 6% to 46%. Given the subjective nature of thyroid cytopathology and interpretation of the BSRTC categories, guidelines should encourage the use of institution-specific data on malignancy risk in treatment decisions. © 2015 Wiley Periodicals, Inc. Head Neck 38: E1210-E1215, 2016.