A tale of two antibodies: obinutuzumab versus rituximab.

While rituximab has dramatically improved outcomes for patients with CD20+ malignancies for two decades, responses are not universal and resistance can develop. Obinutuzumab was developed to potentiate activity and overcome resistance. Pre-clinical data suggests obinutuzumab is superior to rituximab at effecting B cell depletion; however recent phase III clinical trial results have been mixed. The decision of which antibody to employ will probably be further complicated by the approval of a subcutaneous preparation of rituximab and several anti-CD20 biosimilars. Clinicians are now challenged with deciding whether to switch to obinutuzumab in approved settings, accepting the potential for increased toxicity and probable increased cost. The benefit conferred by obinutuzumab over rituximab may be context-specific and vary based on histological subtype and immune integrity. This comprehensive review will explore the preclinical differences, investigate the proposed pathogenesis of rituximab resistance, compare the employed dosing strategies and interrogate available clinical results to help inform practice.