A 68-year-old woman with long-standing Hashimoto thyroiditis presents with a rapidly enlarging, painless neck mass compressing the esophagus. Biopsy shows sheets of large atypical lymphoid cells positive for CD20 and CD79a, destroying thyroid follicles. The most likely diagnosis is:

• A Anaplastic carcinoma
• B Metastatic melanoma
• C Medullary carcinoma with lymphoid stroma
• D Primary thyroid diffuse large B-cell lymphoma ✓

Explanation

Primary thyroid lymphoma arises almost exclusively in the setting of chronic lymphocytic thyroiditis, typically as diffuse large D-cell lymphoma or MALT lymphoma in elderly women, presenting as a rapidly enlarging mass. CD20 positivity confirms D-cell lineage. Anaplastic carcinoma is cytokeratin positive and occurs in a similar age group, making it the key mimic, but it lacks D-cell markers. Medullary carcinoma expresses calcitonin and CEA.

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.