Non-invasive follicular neoplasm with papillary-like nuclear features: a challenging and infrequent entity in Argentina

Abstract

Purpose: Non-invasive encapsulated follicular variant of papillary thyroid cancer was reclassi ed as noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP). These neoplasms have an extremely low malignant potential. The aim of this study was 1) to assess the prevalence of NIFTP in patients with papillary thyroid carcinoma, 2) to evaluate their outcomes and 3) to determine their molecular pro le. Methods: Multicenter, descriptive, retrospective study. Patients with papillary thyroid cancer diagnosed from January 2006 to December 2016 from 11 referral centers were included. Diagnosis of NIFTP was based on criteria described by Nikiforov et al. in 2018. At least two pathologists agreed on the diagnosis. Two thousand six hundred and seventy-seven papillary thyroid cancer patients were included; 456 (17%) of them were follicular variant papillary thyroid cancer, and 30 (1.12%) ful lled diagnostic criteria for NIFTP.Results: Each of the 30 included patients underwent a total thyroidectomy, and 50% were treated with radioiodine (median dose 100 mCi). After a median follow up of 37 months, 84% of patients had an excellent response, 3% had an indeterminate response and data was missing in the remaining 13%. No metastatic lymph nodes, distant metastases or recurrences were found. RAS mutations were detected in 4 patients (13%). Conclusion:The prevalence of NIFTP in our series is amongst the lowest reported. Excellent outcomes of patients underscore their low malignant potential. Molecular ndings differ from other series, probably related to environmental or ethnic features of our population and the meticulous criteria for diagnosing NIFTP.