The use of ibritumomab tiuxetan radioimmunotherapy for patients with relapsed B-cell non-Hodgkin's lymphoma

Rituximab (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.