A 70-year-old woman presents with a rapidly enlarging neck mass over 3 weeks, associated with stridor and dysphagia. Imaging shows a large infiltrative thyroid mass invading the trachea. Biopsy reveals highly pleomorphic spindle cells, giant cells, and numerous mitoses. Which immunohistochemical marker profile best supports the diagnosis over thyroid lymphoma?

• A Cytokeratin positive, TTF-1 positive, CD45 negative ✓
• B CD20 positive, CD3 positive, cytokeratin negative
• C Calcitonin positive, CEA positive, thyroglobulin negative
• D S100 positive, HMB-45 positive, thyroglobulin negative

Explanation

The vignette describes anaplastic thyroid carcinoma. It arises from follicular epithelium and expresses cytokeratin and TTF-1, distinguishing it from lymphoma (CD45 positive, cytokeratin negative). Option B describes lymphoma. Option C is medullary thyroid carcinoma. Option D is melanoma. Anaplastic carcinoma is cytokeratin positive, though it can show variable TTF-1 expression.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.