Impact of noninvasive follicular thyroid neoplasm with papillary-like nuclear features on fine-needle aspiration diagnoses of thyroid nodules

In 2016, the entity of noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) was proposed. This study investigated the impact of NIFTP nomenclature on fine-needle aspiration (FNA) evaluation of thyroid nodules and clinical management, as well as the molecular profile of NIFTP. The study included 23 out of 275 cases diagnosed as follicular variant papillary thyroid carcinoma from 2005 to 2015 that were reclassified as NIFTP, as well as 14 cases with an original diagnosis of NIFTP from 2016 to 2019. Information on demographic characteristics, FNA diagnoses, and follow-up was collected. Before 2016, 43.5% of NIFTP surgical cases were diagnosed as malignant or suspicious for malignancy by presurgical FNA, 80% of which received total thyroidectomy. Since 2016, only 15.4% of NIFTP cases were diagnosed as malignant or suspicious for malignancy and treated with total thyroidectomy. The overall total thyroidectomy rate decreased from 56.5% to 21.4% for NIFTP cases. RAS mutations (KRAS^Q61R and NRAS^Q61R) were present in 57.1% of NIFTP cases, with no BRAF mutations identified. Our study demonstrates a significant impact of NIFTP nomenclature on FNA diagnosis of thyroid nodules with reduced diagnoses as malignant or suspicious for malignancy, thus avoiding overdiagnosis and overtreatment of NIFTP patients. The molecular study indicates that RAS mutations play an important role in NIFTP tumorigenesis.