An Update on the Risk of Lymph Node Metastasis for the Follicular Variant of Papillary Thyroid Carcinoma with the New Diagnostic Paradigm.

Previous data has shown that the risk of nodal metastases is significantly greater for classical papillary thyroid carcinoma (PTC) as compared to the follicular variant (FVPTC). Given a recent change in diagnostic paradigm and definition of the noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) we intended to investigate if there remains a significant difference in nodal involvement between classical PTC and FVPTC. A 6-year retrospective review of all cases with FVPTC in the diagnostic line from the University of Utah/ARUP Laboratories was conducted. Two pathologists reviewed the remaining cases using the recently described histologic criteria of NIFTP to determine the total number the FVPTCs fitting the new classification paradigm. Histologic and clinical follow-up was tracked for all patients to determine the rate of nodal disease for all groups. 127 cases were identified using the above listed criteria. Forty-seven cases (37%) were classified as NIFTPs. None of the 47 patients had nodal disease either at the time of surgery or on follow-up. Twenty-eight cases met the current criteria for FVPTC (21%); of these 7/28 (25%) had evidence of nodal disease. By comparison, 17/45 (38%) of patients with mixed classical and FVPTC had nodal disease. Overall, there was no statistically significant difference in the risk of nodal metastasis between the pure FVPTC and mixed classical/FVPTC groups (p = 0.43). Our data indicates that implementing new definition for FVPTC will narrow the gap in the risk of nodal metastases between the classical PTC and FVPTC histologic subtypes.