M. S. Sussman1, M. B. Mulder1, O. Picado1, J. I. Lew1, J. C. Farra1 1University Of Miami,DeWitt Daughtry Department Of Surgery: Division Of Endocrine Surgery,Miami, FL, USA
Introduction: The reclassification of noninvasive encapsulated follicular variant papillary thyroid carcinoma (FVPTC) to noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) has been shown to decrease the reported risk of malignancy (ROM) for all categories within the Bethesda System for Reporting Thyroid Cytology (BSRTC), with the greatest impact seen in atypia /follicular lesion of undetermined significance (AUS/FLUS) or Bethesda III thyroid nodules. There are currently no clinical factors to help predict malignancy vs. NIFTP in indeterminate thyroid nodules. This study evaluates the utility of gene expression classifier (GEC) testing and surgeon performed ultrasound (SUS) features as predictive factors for NIFTP in patients with thyroid nodules.
Methods: A retrospective review of prospectively collected data of 847 patients who underwent thyroidectomy at a single institution from 2010 to 2016 was performed. Pathology slides with a diagnosis of FVPTC (n=146) were re-reviewed by endocrine pathologists for reclassification to NIFTP. Risk of malignancy (ROM) overall and within each BSRTC classification was determined before and after the reclassification of NIFTP. GEC testing and SUS characteristics were compared in FVPTC vs. NIFTP patients to evaluate for predictive value with significance defined as P<0.05.
Results: Of 146 patients who underwent thyroidectomy for FVPTC, 22% were reclassified as NIFTP (n=32). Of the NIFTP group, 35% (n=11) had AUS/FLUS thyroid nodules. GEC testing was performed in 25 patients, of which 22 had a suspicious result. Suspicious GEC results between FVPTC (12%) and NIFTP (12%) pathologies were identical. On multivariate regression, SUS characteristics of echogenicity and microcalcifications were independent predictors of NIFTP vs. FVPTC. Isoechogenicity was predictive of NIFTP, whereas hypoechogenicity was predictive of FVPTC (OR 3 95% CI 1.3 – 7, p<0.05). Additionally, microcalcifications was predictive of FVPTC compared to NIFTP (OR 4 95% CI .9-18, p<0.05).
Conclusion: A significant proportion of AUS/FLUS thyroid nodules are NIFTP on final pathology. Although GEC testing has limited utility, SUS features such as isoechogenicity and the absence of microcalcifications may favor a diagnosis of NIFTP in such thyroid nodules. This may help guide and determine extent of thyroidectomy in these select cases.