Predictive factors of non-invasive follicular thyroid neoplasm with papillary-like nuclear features: A single-center study

Objective: Distinguishing preoperative criteria and postoperative histological features of non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) from those of other thyroid tumors with follicular architecture and papillary nuclear features (non-NIFTP) is crucial to prevent overtreatment. In this study, we aim to identify the predictive factors of NIFTP. Material and Methods: We conducted a retrospective study in which we collected cases of thyroid tumors with follicular architecture and papillary nuclear features diagnosed between 2012 and 2022. Clinicopathological characteristics, therapeutic modalities, and follow-up were compared between NIFTP and non-NIFTP tumors. Results: Forty cases of NIFTP and 44 cases of non-NIFTP were identified. NIFTP accounted for 8.83% of all PTCs and 33.6% of all thyroid tumors with follicular architecture and papillary nuclear features. NIFTP was associated with younger age (p=0.005), isoechoic nodules on ultrasound (US) (p=0.004), regular contours (p=0.028), absence of microcalcifications (p=0.005), and predominance in European Thyroid Imaging Reporting and Data System 2 and 3 scores (p<0.001). They predominantly exhibited a nuclear score of 2 (p<0.001), focal nuclear abnormalities (p=0.015), and a thin capsule (p=0.004). No case of NIFTP showed distant or lymph node metastases. Multivariate analysis identified a nuclear score of 2, focal nuclear abnormalities, and a thin tumor capsule as independently associated with NIFTP. Conclusion: Our findings demonstrated the indolent nature of NIFTP and the utility of cervical US in raising preoperative suspicion for this entity. Because findings regarding the Bethesda classification were not available in our study, a prospective multicenter study with a larger sample size and a longer follow-up period is warranted to address this limitation.