Papillary thyroid carcinoma expressing CD20

We identified a case of lymphadenopathy of metastatic papillary thyroid carcinoma (PTC) with CD20 expression, which was also expressed by the primary tumor. CD20 expression was identified using immunohistochemistry (IHC) in metastatic PTC biopsy samples from a 58‐year‐old woman. CD20 expression was initially determined using a CD20‐recognizing L26 clone. To validate this phenomenon, we performed IHC with another antibody that recognizes the N‐terminus of CD20 and fluorescent double staining using anti‐TTF‐1 and anti‐CD20 antibodies. Taken together, we concluded metastatic PTC expressed CD20. We also examined 21 additional PTC cases and found four more cases that were CD20 positive. Therefore, five of the 22 (23%) cases were positive for CD20. In the positive cases, four cases were classical papillary thyroid carcinoma and one case was a follicular variant of papillary thyroid carcinoma. CD20 is an important target for molecularly targeted therapy for a subset of B‐cell lymphomas. Complement‐dependent and antibody‐dependent cellular cytotoxicities are important effector mechanisms of anti‐CD20 therapy. Here, for the first time, we report PTC with expression of CD20. Our findings provide a rationale for treating CD20‐positive PTC patients with anti‐CD20 therapy.