• T E Witzig.
• Division of Internal Medicine and Hematology, Mayo Clinic and Mayo Foundation, Rochester, MN 55905, USA.
• Semin. Oncol. 2000 Dec 1; 27 (6 Suppl 12): 74-8.

AbstractRituximab (Rituxan; Genentech, Inc, South San Francisco, CA and IDEC Pharmaceutical Corporation, San Diego, CA) is a monoclonal antibody that targets the CD20 antigen present in most B-cell non-Hodgkin's lymphomas. Previous studies have shown overall response rates (ORR) of approximately 50% in relapsed patients. Ibritumomab is the murine parent anti-CD20 antibody that is linked through a MX-DTPA chelator to yttrium 90 (90Y) to form the radioimmunoconjugate 90Y-ibritumomab tiuxetan (Zevalin; IDEC Pharmaceuticals, San Diego, CA). A phase I study of 90Y-ibritumomab tiuxetan determined that 0.4 mCi/kg was the maximum tolerated dose, and responses were reported in 67% of all patients and in 82% of patients with low-grade non-Hodgkin's lymphoma. A separate trial randomized eligible patients to either rituximab or 90Y-ibritumomab tiuxetan. An interim analysis of the first 90 patients showed an ORR of 80% with 90Y-ibritumomab tiuxetan versus 44% with rituximab (P < .05). A subsequent trial for patients with rituximab-refractory disease showed a 46% ORR. These studies show that 90Y-ibritumomab tiuxetan is an active agent in relapsed non-Hodgkin's lymphoma and appears to have a higher ORR compared with unconjugated rituximab.

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