Obinutuzumab‐induced acute thrombocytopenia: Report of two cases and review of literature

Summary Obinutuzumab (GA101) is a humanized anti‐CD20 monoclonal antibody used in the treatment of B‐cell malignancies. Under rare occasions, obinutuzumab may induce acute and severe thrombocytopenia. However, little is known about this side effect, referred to as “obinutuzumab‐induced acute thrombocytopenia” (OIAT). Here, we report 2 cases of OIAT and review the literature to inform the management and outcome of this rare but life‐threatening complication. The first case is a 74 year‐ old woman who was treated with obinutuzumab‐Cyclophosphamide, Vincristine, Prednisone (CVP) for a previously untreated follicular lymphoma. This patient experienced an acute thrombocytopenia with a drop in her platelet count from 376 G/L to 3 G/L the day after treatment. The second case is a 44 year‐ old woman who was treated with obinutuzumab as a pre‐treatment dose (day‐8) before glofitamab infusion as a 4th line therapy for mantle cell lymphoma. This patient experienced an acute thrombocytopenia with a drop in her platelet count from 76 G/L (due to splenomegaly and bone marrow involvement) to 3 G/L the day after treatment. OIAT is a rare but life‐threatening complication. Physicians should be aware of this adverse event to optimally detect and treat this complication.