The influence of the reclassification of NIFTP as an uncertain tumour on risk of malignancy for the diagnostic categories according to the Bethesda system for reporting thyroid cytopathology.

ABSTRACT

INTRODUCTION: The noninvasive encapsulated, follicular variant of papillary thyroid carcinoma was reclassified as noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP). The exclusion of NIFTP from the group of malignant tumours decreases the risk of malignancy (RoM) as defined by the Bethesda System for Reporting Thyroid Cytopathology (TBSRTC). The aim of the present study was to evaluate the RoM for each category in TBSRTC with and without exclusion of NIFTP from the tally of malignancies. MATERIAL AND METHODS: The present study included 998 thyroid nodules cases. All patients underwent diagnostic tests, including fine-needle aspiration cytology, and received surgical treatment. Slides for all resection specimens with a diagnosis of cancer were reviewed to identify NIFTP. The RoM for each of the categories in TBSRTC with and without exclusion of NIFTP from the malignant tumours was evaluated. RESULTS: The RoM decreased with the exclusion of NIFTP from malignant categorisation with the following values for the different TBSRTC categories non-diagnostic (ND) 0%; benign 0%; atypia/follicular lesion of undetermined significance (AUS/FLUS) 1.6%; follicular neoplasm/suspicious for follicular neoplasm (FN/SFN) 0.7%; suspicious for malignancy (SUS) 6.9%; and malignant 2.5%. The difference of 2.5% in the malignant category was statistically significant (p = 0.0253). CONCLUSIONS: The RoM for specific TBSRTC categories needs to be defined for each treatment centre because it is important for the selection of the appropriate surgical treatment for thyroid tumours.