Incidence of noninvasive follicular thyroid neoplasm with papillary-like nuclear features and change in risk of malignancy for “The Bethesda System for Reporting Thyroid Cytology”

Introduction: The second edition of The Bethesda System for Reporting Thyroid Cytopathology has incorporated the recent change in nomenclature, noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP), with an anticipated change in the risk of malignancy (ROM). We examined our institutional experience in the incidence of NIFTP and the change in the ROM in The Bethesda System for Reporting Thyroid Cytopathology. Materials and methods: A computerized search was performed from January 2013 to August 2017 for all thyroid fine needle aspirations (FNAs), the corresponding surgical resection specimens, and clinical follow-up data. All thyroid specimens reported as follicular variant of papillary thyroid carcinoma were reviewed and reclassified, and all NIFTP diagnoses from April 2016 to August 2017 were identified. The ROM for each category was calculated before and after the change and analyzed for significance. Results: A total of 4500 thyroid FNA cases were collected. Of these, 479 cases had surgical resection specimens available and 36 cases had been diagnosed as NIFTP. Of these, 22 had been previously diagnosed as FVPT. Of 27 cases of NIFTP, 14 and 13 were atypia of undetermined significance/follicular lesion of undetermined significance and follicular neoplasm/suspicious for follicular neoplasm, respectively. A reduction in the ROM was observed in these 2 categories (P = 0.03 and P = 0.04, respectively). Conclusions: In our institution, NIFTP has accounted for 13% of all malignant thyroid neoplasms since the change in nomenclature. Although the ROM was decreased in the affected categories, with absolute statistically significant decreases in ROM of 15% and 16.2% for category III and IV, respectively, the overall ROM change was marginal.