A 35-year-old woman has a 2 cm thyroid nodule. Fine needle aspiration cytology shows Bethesda category V (suspicious for malignancy) with nuclear clearing, grooves, and intranuclear pseudoinclusions. Molecular analysis reveals a BRAF V600E mutation. The final thyroidectomy specimen shows a 2.1 cm tumor with complete fibrous capsule, focal capsular penetration but NO vascular invasion. How should this be classified?

• A Classical papillary thyroid carcinoma — papillary architecture with nuclear features
• B Non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) — low-risk; not carcinoma
• C Papillary thyroid carcinoma, encapsulated follicular variant — now renamed NIFTP if non-invasive, but with capsular invasion is classified as invasive EFVPTC ✓
• D Minimally invasive follicular thyroid carcinoma — defined by capsular invasion without vascular invasion

Explanation

The 2017 reclassification of NIFTP from carcinoma to a low-risk neoplasm requires: follicular-patterned growth, encapsulated or well-circumscribed, NO invasion (capsular OR vascular), and PTC nuclear features. When capsular invasion IS present (even focal), the lesion is classified as invasive encapsulated follicular variant PTC (EFVPTC), not NIFTP. BRAF V600E mutation is more common in classical PTC with papillary architecture but can occur in follicular variant. NIFTP is specifically defined by complete absence of invasion; capsular penetration disqualifies NIFTP designation and the tumor is malignant (low to intermediate risk depending on extent of invasion).

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

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Written and medically reviewed by the StethoPrep medical team.