A Case of Cold Agglutinin Disease With Transformation to High-Grade Lymphoma During Sutimlimab Treatment

Cold agglutinin disease (CAD) is an autoimmune hemolytic anemia characterized by monoclonal immunoglobulin M-mediated cold agglutinins and monoclonal B-cell proliferation. Sutimlimab, a complement C1s inhibitor, alleviates hemolytic anemia in CAD by blocking the classical complement pathway. We report a case of a 67-year-old Japanese woman with CAD who experienced temporal improvement in anemia following sutimlimab treatment. ¹⁸F-fluorodeoxyglucose positron-emission tomography/computed tomography and bone marrow biopsy (BMB) revealed histological transformation into aggressive B-cell lymphoma. Subsequent chemotherapy with polatuzumab vedotin, rituximab, cyclophosphamide, doxorubicin, and prednisolone resulted in further improvement in anemia. This case highlights the importance of reassessing underlying conditions through BMB in cases where sutimlimab treatment is ineffective.