A 60-year-old woman with long-standing Hashimoto thyroiditis presents with rapid thyroid enlargement. Biopsy shows sheets of large atypical lymphoid cells that are CD20 positive, CD3 negative, and CD5 negative. The most likely diagnosis is:

• A Reactive lymphoid hyperplasia of the thyroid
• B Anaplastic thyroid carcinoma
• C Medullary thyroid carcinoma with lymphoid reaction
• D Diffuse large B-cell lymphoma arising from MALT ✓

Explanation

Chronic autoimmune thyroiditis carries a markedly increased risk of primary thyroid non-Hodgkin lymphoma, usually diffuse large B-cell lymphoma arising from mucosa-associated lymphoid tissue. Sheets of large CD20 positive B cells confirm this. Anaplastic carcinoma is epithelial and cytokeratin positive, medullary carcinoma expresses calcitonin and chromogranin, and reactive hyperplasia preserves architecture with mixed populations rather than monomorphic sheets of atypical B cells.

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.