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Indian J Pathol Microbiol. 2019 Oct-Dec;62(4):544-548. doi: 10.4103/IJPM.IJPM_319_19.

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

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Department of Pathology, Medanta-The Medicity Hospital, Gurgaon, India.
Department of Head and Neck Oncology, Medanta-The Medicity Hospital, Gurgaon, India.



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.

Settings and Design:

Retrospective analytic study.

Methods and Materials:

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.

Statistical Analysis Used:

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.


Atypia of undetermined significance; fine-needle aspiration; risk of malignancy; subcategory; thyroid cytopathology


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