Risk of malignancy in Thyroid "Atypia of undetermined significance/Follicular lesion of undetermined significance" and its subcategories - A 5-year experience.

Abstract

Atypia of undetermined significance/Follicular lesion of undetermined significance [AUS/FLUS] is a heterogeneous category with a wide range of risk of malignancy [ROM] reported in the literature. The Bethesda system for reporting thyroid cytopathology [TBSRTC], 2017 has recommended subcategorization of AUS/FLUS. To evaluate the ROM in thyroid nodules categorized as AUS/FLUS, as well as separate ROM for each of the five subcategories. Retrospective analytic study. A retrospective audit was conducted for all thyroid fine-needle aspiration cytology (FNAC) from January 2013 to December 2017. Slides for cases with follow-up histopathology were reviewed, classified into the five recommended subcategories, and differential ROM was calculated. z test for comparison of proportions was done to evaluate the difference in ROM among different subcategories of AUS/FLUS. The P value of less than 0.05 was taken as statistically significant. Total number of thyroid FNACs reported was 1,630, of which 122 were AUS/FLUS (7.5%). Histopathology was available in 49 cases, out of which 18 were malignant (ROM = 36.7%). The risk of malignancy (ROM) for nodules with architectural and cytologic atypia was higher (43.8%) than ROM for nodules with only architectural atypia (16.7%). The sub-classification of AUS/FLUS into subcategories as recommended by TBSRTC, 2017 may better stratify the malignancy risk and guide future management guidelines.