EP45 – Cytopathology Findings in NIFTP vs. Non-NIFTP Follicular Variant Papillary Thyroid Cancer

      Eckhoff, Austin1; Griffith, Christopher2; Schmitt, Alessandra2; Chen, Amy3 1 Medical Student Class of 2018, Emory University School of Medicine, Atlanta, Georgia, USA 2 Department of Pathology and Laboratory Medicine, Emory University, Atlanta, Georgia, USA 3 Department of Otolaryngology – Head and Neck Surgery, Emory University, Atlanta, Georgia, USA   Background/Purpose: A recent international, multidisciplinary study published in JAMA Oncology suggested the reclassification of a subset of encapsulated follicular variant of papillary thyroid carcinoma (EFVPTC) as a separate pathologic diagnosis.1 These noninvasive follicular thyroid neoplasms with papillary-like nuclear features (NIFTP) have highly indolent behavior and are genetically distinct from infiltrative tumors.1,2 NIFTP rarely recur or metastasize, obviating the need for aggressive treatment potentially decreasing healthcare costs and morbidity.1 Objectives: To evaluate if thyroid fine-needle aspiration (FNA) cytopathology findings are predictive of NIFTP versus PTC on surgical pathology. Methods: Pathology slides of patients with a diagnosis of follicular variant PTC were reexamined to evaluate for NIFTP vs non-NIFTP follicular variant PTC. Cytology from this patient cohort were classified via the The Bethesda System for Reporting Thyroid Cytopathology.3 Chi-squared test and Mann-Whitney U test were used to correlate cytology to surgical pathology. Results: The study cohort consisted of 54 patients. Overall, there were 16 (29.6%) NIFTP and 38 (70.3%) non-NIFTP follicular variant PTC. A total of 45 patients (83.3%) had prior FNA. Patients with non-NIFTP follicular variant PTC had a statistically significant higher cytopathology category than patients with NIFTP (U= 106.5 P=0.036 two-tailed). Discussion & Conclusion: Patients with NIFTP had FNA cytology findings that were associated with lower cytology grade than patients with non-NIFTP follicular variant PTC. This suggests that cytology could be an important pre-operative diagnostic tool but that further analysis with large sample sizes needs to take place to better preoperatively characterize NIFTP tumors.   References:
    1. Nikiforov YE, Seethala RR, Tallini G, et al. Nomenclature Revision for Encapsulated Follicular Variant of Papillary Thyroid Carcinoma. JAMA Oncology. 2016;2(8):1023. doi:10.1001/jamaoncol.2016.0386.
    2. Daniels, G. H. Follicular Variant of Papillary Thyroid Carcinoma: Hybrid or Mixture?. Thyroid. 2016; 26(7): 872-874. doi:10.1089/thy.2016.0244.
    3. Cibas ES, Ali SZ. The Bethesda System for Reporting Thyroid Cytopathology. American Journal of Clinical Pathology. 2009;132(5):658–665. doi:10.1309/ajcpphlwmi3jv4la.


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