The WHO 2022 classification of thyroid tumors introduced the category of low-risk neoplasms including NIFTP. A thyroid nodule fulfills criteria for NIFTP (Noninvasive Follicular Thyroid Neoplasm with Papillary-like nuclear features) if it has:

• A Papillary growth pattern with PNFs, encapsulated, no lymph node metastasis — reclassified from papillary thyroid carcinoma, encapsulated follicular variant
• B Follicular growth pattern (no papillary architecture), encapsulated or clearly demarcated, papillary-like nuclear features (PNFs), no vascular/capsular invasion, no psammoma bodies, and Ki-67 <1% ✓
• C Follicular growth pattern with high-grade nuclear features, complete fibrous encapsulation, and TERT promoter mutation
• D Mixed papillary-follicular architecture with central fibrosis and psammoma bodies, encapsulated without invasion

Explanation

NIFTP was introduced to reclassify encapsulated follicular-variant PTC without invasion as a non-malignant neoplasm with extremely low recurrence risk (<1%). Diagnostic criteria (Nikiforov 2016/WHO 2022) require: (1) follicular growth pattern — no papillary architecture, no psammoma bodies; (2) clear demarcation or fibrous encapsulation; (3) presence of nuclear features of PTC (PNFs — nuclear enlargement/elongation, nuclear clearing/pale chromatin, nuclear pseudoinclusions, nuclear membrane irregularities, grooves); (4) no capsular invasion; (5) no vascular invasion; (6) <3 mitoses/HPF, Ki-67 <3%; (7) no solid/trabecular/insular areas (>30% would reclassify). If any true papillary structures exist, psammoma bodies are present, or invasion is identified, the diagnosis reverts to encapsulated follicular-variant PTC with appropriate management implications.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.