Abstract

Recent progress in understanding indolent thyroid tumors has prompted the reclassification of a subset of non-invasive encapsulated follicular variant of papillary thyroid carcinoma (NI-EFVPTC). Given its indolent clinical course, this entity is now reclassified in 2016 as “non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP)” and is no longer considered a carcinoma. The definition of NIFTP has undergone several refinements, particularly with the 2018 update, which introduced more stringent requirements, requiring complete absence of well-formed papillae to reduce diagnostic errors. In the 2022 classification of the World Health Organization (WHO), the threshold of < 1% papillae was reconsidered and accepted again based on recent evidence, further reinforcing the position of NIFTP within the low-risk neoplasm category. Key histopathological features-such as nuclear characteristics and complete histologic examination of the capsule to exclude invasive growth-remain essential for diagnosis. However, preoperative cytologic diagnosis continues to be limited due to the lack of specific features. This review summarizes evidence from recent studies and updates the cytologic and histopathologic diagnostic criteria of NIFTP across different periods, while also presenting changes related to the risk of malignancy within the Bethesda System for Reporting Thyroid Cytopathology (TBSRTC).