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

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.