A 40-year-old woman undergoes thyroidectomy for a 2.5 cm follicular thyroid lesion. Histology shows an encapsulated follicular-patterned tumour with definitive capsular invasion (a few foci of tumour cells penetrating through the full capsule thickness) but no vascular invasion. According to the WHO 2022 endocrine tumour classification, what is the diagnosis?
- A Encapsulated follicular variant of papillary thyroid carcinoma (EFVPTC) — molecular signature would be RAS-mutant, not BRAF
- B Non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) — a low-risk neoplasm no longer classified as carcinoma
- C Widely invasive follicular thyroid carcinoma (WIFTC) — based on the detection of any invasion at all
- D Minimally invasive follicular thyroid carcinoma (MIFTC) — capsular invasion only without vascular invasion; carries excellent prognosis (>97% 10-year survival) after surgery alone ✓
Explanation
The WHO 2022 classification of follicular thyroid carcinoma (FTC) stratifies by degree of invasion. Minimally invasive FTC (MIFTC) = capsular invasion only (transcapsular tumour budding through the full capsule thickness), no angioinvasion. MIFTC carries an excellent prognosis with >97% 10-year survival and is adequately treated by surgical resection (thyroidectomy). Encapsulated angioinvasive FTC = vascular invasion (<4 vessels) and carries intermediate risk. Widely invasive FTC = gross invasion of surrounding thyroid/blood vessels. NIFTP is the non-invasive encapsulated follicular variant of PTC (no definitive capsular OR vascular invasion, nuclear features of PTC) — NOT carcinoma since 2016 WHO. EFVPTC requires PTC nuclear features, not present here.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.