The 2022 WHO Classification of Thyroid Tumors introduced the category of 'non-invasive follicular thyroid neoplasm with papillary-like nuclear features' (NIFTP). NIFTP was separated from invasive encapsulated follicular variant of papillary thyroid carcinoma (PTC). The DEFINING criterion for classifying a lesion as NIFTP rather than encapsulated follicular variant PTC is:

• A Complete fibrous encapsulation without capsular or vascular invasion, follicular growth pattern, and papillary-type nuclei with less than 1% papillary architecture ✓
• B Complete encapsulation with absence of BRAF V600E mutation and TERT promoter mutation
• C Complete encapsulation with papillary architecture comprising >30% of the tumour
• D Complete encapsulation with RAS mutation and absence of lymph node metastases

Explanation

NIFTP (originally described by Nikiforov et al., 2016 and incorporated into WHO 2022) requires all of the following criteria: (1) Encapsulated or well-circumscribed tumour; (2) Follicular growth pattern (NO papillary architecture OR papillary architecture comprising <1% of tumour volume); (3) Papillary-type nuclear features (nuclear enlargement, pallor, grooves, pseudo-inclusions) meeting nuclear score ≥2/3; (4) NO capsular invasion; (5) NO vascular invasion; (6) NO tumour necrosis; (7) NO high mitotic activity (≥3/10 HPF). Molecular exclusion criteria: BRAF V600E mutation or TERT promoter mutation excludes NIFTP diagnosis (as these indicate higher malignant potential). NIFTP has essentially zero risk of metastasis and is treated with lobectomy without radioiodine, reclassifying it from 'carcinoma' to 'neoplasm with low malignant potential'.

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

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Written and medically reviewed by the StethoPrep medical team.