A 40-year-old woman undergoes total thyroidectomy for a 3 cm thyroid nodule. Histology shows well-formed follicles lined by cells with ground-glass ('Orphan Annie eye') nuclei, nuclear grooves, and intranuclear pseudoinclusions — but the entire tumor is encapsulated with NO capsular or vascular invasion. According to the current WHO classification (2022), this tumor is classified as:
- A Follicular thyroid carcinoma, minimally invasive
- B Non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) ✓
- C Classical papillary thyroid carcinoma
- D Follicular adenoma with papillary nuclear changes
Explanation
NIFTP (Non-invasive follicular thyroid neoplasm with papillary-like nuclear features) was introduced in 2016 and retained in WHO 2022 to reclassify a subset of encapsulated follicular-patterned thyroid neoplasms with PTC nuclear features (ground-glass nuclei, grooves, pseudoinclusions) but NO capsular or vascular invasion and NO papillary architecture exceeding 1%. These were previously called encapsulated follicular variant of PTC but have a near-zero risk of metastasis. The reclassification to NIFTP (from 'carcinoma' to 'neoplasm') has significant clinical impact: lobectomy alone may suffice, and no RAI ablation is needed. Absence of invasion is the critical distinguishing criterion from invasive encapsulated follicular variant PTC.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.