M. Mao1, T. Joyal2, O. Picado1, D. Kerr2, J. Lew1, J. Farra1 1University Of Miami Leonard M. Miller School Of Medicine,Division Of Endocrine Surgery, DeWitt Daughtry Family Department Of Surgery,Miami, FL, USA 2University Of Miami Leonard M. Miller School Of Medicine,Department Of Pathology,Miami, FL, USA
Introduction: The reclassification of a proportion of follicular variant papillary thyroid carcinoma (FVPTC) to noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) may have significant implications for patients and physicians. NIFTP may change overall malignancy rates and minimize extent of surgical treatment. This study reviews overall malignancy rate, FNA cytopathology, and treatment of a surgical cohort of patients with a diagnosis of FVPTC reclassified as NIFTP.
Methods: A retrospective review of 847 patients who underwent thyroidectomy at a single institution from January 2010 to April 2016 was performed. Overall rate of thyroid malignancy was determined, and further subdivided into those with papillary thyroid cancer (PTC) and its follicular variant. The subgroup with FVPTC (n=181) was re-reviewed by an endocrine pathologist for reclassification to NIFTP. Thirty-five patients were excluded from the analysis due to inability to retrieve the pathology slides (n=22) or the lesion being too small to assess infiltrative pattern (n=13). Further review of patients reclassified as NIFTP was performed for preoperative FNA cytopathology, extent of thyroidectomy, central neck dissection (CND), and postoperative radioactive iodine (RAI) treatment.
Results: Of 847 patients who underwent thyroidectomy, 495 patients had a thyroid cancer, yielding a 58% malignancy rate. The majority were PTC (n= 454, 92%). FVPTC was identified in 181 patients, of which 146 patients underwent pathology re-review for NIFTP. There were 32 cases (22%) reclassified as NIFTP, reducing the overall malignancy rate to 55%. Within the NIFTP cohort, pre-operative FNA cytopathology revealed the following: 3% Bethesda I, 31% Bethesda II, 35% Bethesda III, 19% Bethesda IV, 9% Bethesda V, and 3% Bethesda VI. Overall, 66% of the NIFTP cohort had Bethesda classifications III-VI. Among NIFTP patients, 16 underwent total thyroidectomy and 16 underwent thyroid lobectomy, of which 12 had completion thyroidectomies (75%). Twenty patients (63%) underwent CND, and 9 underwent postoperative RAI treatment (28%).
Conclusion: A significant proportion of FVPTC patients were reclassified as NIFTP. The implementation of this classification may decrease overall institutional thyroid malignancy rates. The majority of reclassified NIFTP cases were from Bethesda III-VI categories, which suggests a need to reassess the predicted malignancy rates within the Bethesda System for Reporting Thyroid Cytopathology (BSRTC) categories. When a NIFTP is found on final pathology, surgeons should regard this diagnosis as an indolent tumor requiring no further surgical or medical treatment as these patients have been shown to derive no long term benefit from completion thyroidectomy or RAI.