Noninvasive follicular thyroid neoplasm with papillary-like nuclear features reclassification and its impact on thyroid malignancy rate and treatment

BACKGROUND:The reclassification of noninvasive encapsulated follicular variant papillary thyroid carcinoma (FVPTC) to noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) may have significant implications by changing overall malignancy rates and minimizing the extent of surgical treatment. METHODS:A retrospective review of 847 patients who underwent thyroidectomy at a single institution from January 2010 to April 2016 was performed. The subgroup with FVPTC (n = 181) was re-reviewed by endocrine pathologists for reclassification to NIFTP. The overall rate of malignancy (ROM) and within each Bethesda classification was determined before and after the reclassification of NIFTP. The extent of thyroidectomy among others in patients reclassified as NIFTP was further reviewed. RESULTS:Of 847 patients who underwent thyroidectomy, there was an overall ROM of 58% (n = 495), the majority being papillary thyroid cancer (PTC) (n = 454, 92%). In 181 patients with FVPTC, 146 underwent pathology re-review. There were 32 cases (22%) reclassified as NIFTP, reducing the overall ROM to 55%. ROM decreased across Bethesda categories I to V by the following: 3% Bethesda I, 8% Bethesda II, 8% Bethesda III, 10% Bethesda IV, and 3% Bethesda V. Among NIFTP patients, 16 underwent total thyroidectomy and 16 underwent thyroid lobectomy, of which 12 had completion thyroidectomies (75%). Twenty patients (63%) underwent central neck dissection, and nine underwent postoperative radioactive iodine ablation treatment (28%). CONCLUSIONS:A significant proportion of patients with FVPTC reclassified as NIFTP may decrease the overall institutional thyroid ROM. On final pathology, NIFTP should be regarded as an indolent tumor requiring no further surgical treatment.