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JPTM > Ahead-of Print

doi: https://doi.org/10.4132/jptm.2018.04.03    [Epub ahead of print]
Cytologic Diagnosis of Noninvasive Follicular Thyroid Neoplasm with Papillary-like Nuclear Features and Its Impact on the Risk of Malignancy in the Bethesda System for Reporting Thyroid Cytopathology: An Institutional Experience
Milim Kim1,2, Joung Eun Kim3, Hyun Jeong Kim1, Yul Ri Chung1,2, Yoonjin Kwak2, So Yeon Park1,2
1Department of Pathology, Seoul National University Bundang Hospital, Seongnam, Korea
2Department of Pathology, Seoul National University College of Medicine, Seoul, Korea
3Seoul National University College of Medicine, Seoul, Korea
Corresponding Author: So Yeon Park ,Tel: +82-31-787-7712, Fax: +82-31-787-4012, Email: sypmd@snu.ac.kr
Received: March 14, 2018;  Accepted: April 3, 2018.  Published online: April 3, 2018.

This study was performed to analyze cytologic diagnosis of noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) and its impact on the risk of malignancy (ROM) in the Bethesda System for Reporting Thyroid Cytopathology (TBSRTC).
5549 cases of thyroid fine-needle aspiration cytology (FNAC) diagnosed between 2012 and 2014 were included in this study. Diagnostic categories based on TBSRTC were compared with final surgical diagnoses, and the ROM in each category was calculated both including and excluding NIFTP from the malignant lesions.
Of the 5549 thyroid FNAC cases, 1891 cases underwent surgical resection. In final diagnosis, 1700 cases were revealed as papillary thyroid carcinoma (PTC), and 25 cases were reclassified as NIFTP. The cytologic diagnoses of NIFTP were non-diagnostic in one, benign in five, atypia of undetermined significance (AUS) in 14, follicular neoplasm in two, and suspicious for malignancy in three cases. Collectively, NIFTP/encapsulated follicular variant of PTC (EFVPTC) were more frequently classified as benign, AUS, or follicular neoplasm and less frequently categorized as malignant compared to conventional PTCs. Exclusion of NIFTP from malignant diagnoses resulted in a slight decrease in malignancy rates in non-diagnostic, benign, AUS, follicular neoplasm, and suspicious for malignancy categories without any statistical significance.
The decrease in the ROM was not significant when excluding NIFTP from malignant lesions. In thyroid FNACs, NIFTP/EFVPTCs were mostly classified into indeterminate categories. Therefore, it might be feasible to separate NIFTP/EFVPTC from conventional PTC on FNAC to guide conservative clinical management for patients with NIFTP/EFVPTC.
Key Words: Thyroid, Fine-needle aspiration cytology, Encapsulated follicular variant of papillary thyroid carcinoma, Noninvasive follicular thyroid neoplasm with papillary-like nuclear features, Risk of Malignancy, Bethesda system