A 70-year-old woman presents with a rapidly enlarging, fixed anterior neck mass that developed over six weeks, accompanied by hoarseness, dysphagia, and stridor. Fine needle aspiration shows highly pleomorphic spindle and multinucleated giant cells with numerous atypical mitoses. Immunohistochemistry is negative for thyroglobulin and calcitonin. The most likely diagnosis is:

• A Anaplastic (undifferentiated) thyroid carcinoma ✓
• B Primary thyroid lymphoma
• C Medullary thyroid carcinoma
• D Poorly differentiated (insular) thyroid carcinoma

Explanation

Anaplastic carcinoma occurs in the elderly, grows over weeks, invades local structures causing hoarseness and dysphagia, and shows undifferentiated spindle, giant, and epithelioid cells. It arises from dedifferentiation of pre-existing papillary or follicular carcinoma and carries TP53 mutations. Negative calcitonin excludes medullary carcinoma, and negativity for thyroglobulin plus the extreme pleomorphism excludes poorly differentiated carcinoma, which retains some follicular differentiation.

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.