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.