A 62-year-old woman with a 15-year history of Hashimoto thyroiditis presents with rapid thyroid enlargement. Biopsy shows sheets of large atypical lymphoid cells positive for CD20. What is the most likely diagnosis and its strongest risk factor?

• A Papillary carcinoma; childhood irradiation
• B Anaplastic carcinoma; iodine deficiency
• C Medullary carcinoma; RET germline mutation
• D Primary thyroid DLBCL; chronic autoimmune thyroiditis ✓

Explanation

Primary thyroid lymphoma is typically diffuse large D-cell lymphoma (CD20 positive) and almost always arises on a background of Hashimoto thyroiditis, reflecting chronic antigenic stimulation of mucosa-associated lymphoid tissue acquired in the gland. CD20 positivity excludes all epithelial thyroid malignancies listed. Childhood radiation predisposes to papillary carcinoma, not lymphoma, making option A the tempting but incorrect pairing.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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