Is the Specificity of Benign Cytology Affected by Changing the Nomenclature of Encapsulated Follicular Variant of Papillary Thyroid Carcinoma

Introduction: It has been recently proposed to rename the “encapsulated follicular variant of papillary thyroid carcinoma” (FVPTC) as “NonInvasive Follicular Thyroid neoplasm with papillary-like nuclear features” (NIFT). This nomenclature addresses the fact that most of these tumors behave in an indolent manner. FVPTC without suspicious sonographic features are at particularly low risk for developing regional or distant metastasis, and recurrences. We evaluated what percentage of our “false negative” (FN) fine needle aspiration biopsy (FNAB) interpretations are due to indolent FVPTC. Because thyroid cancer recurrence can occur years after the original surgery, we used the sonographic pattern as a surrogate indicator of indolent FVPTC. Materials and Methods: We reviewed the records of all thyroid FNABs with subsequent histopathology (HP) between October-2008 and May-2014 at our institution under an IRB protocol. Thyroid FNABs were classified according to the Bethesda System. Only the most recent FNAB result was considered for nodules sampled multiple times. Samples with benign FNAB and malignant HP were considered FN results. The sonographic pattern of FN nodules was assessed following the classification proposed in the provisional revised ATA guidelines for the management of thyroid nodules. Results: HP confirmation was available in 1103 of 2829 nodules biopsied. Out of 239 resected nodules with benign FNAB, 23 were “malignant” (9.6% of FN rate) (Figure 1). FVPTC was diagnosed in 12 (52%) of them. (Figure 2) Low-suspicion sonographic pattern was observed in 9 (82%) of the 11 FVPTC with available US images. (Figure 3) Conclusions: Most FN results in benign thyroid cytopathology are due to FVPTC; most of these lesions show a low-suspicion sonographic pattern, associated with an indolent behavior, for which a NIFT diagnosis would probably be more appropriate. Using the new nomenclature, and treating these nodules as “benign”, would improve our benign FNABs specificity from 90% to at least 94% on resected nodules.