A 45-year-old woman has a thyroid mass. Biopsy shows follicular patterned cells with capsular invasion but NO vascular invasion on extensive sampling. IHC shows loss of PTEN and RAS mutation. This is classified as:
- A Minimally invasive follicular carcinoma (capsular invasion only) ✓
- B Follicular adenoma — no malignant features
- C Widely invasive follicular carcinoma
- D Follicular variant of papillary thyroid carcinoma
Correct answer: A. Minimally invasive follicular carcinoma (capsular invasion only)
Explanation
The distinction between follicular adenoma and carcinoma depends entirely on the presence of capsular and/or vascular invasion — NOT cytological atypia. Minimally invasive follicular carcinoma shows capsular invasion (penetration through the entire capsule) without vascular invasion and carries an excellent prognosis (~near 100% 10-year survival with lobectomy). Widely invasive FTC shows extensive vascular invasion and has a worse prognosis with hematogenous metastasis. RAS mutations are common in follicular neoplasms; BRAF V600E is characteristic of PTC.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.