Bexxar®: Novel Radioimmunotherapy for the Treatment of Low-Grade and Transformed Low-Grade Non-Hodgkin's Lymphoma

Purpose. Immunotherapy using monoclonal antibodies to specifically target B cells has provided new hope to many patients with indolent lymphomas, particularly those with chemotherapy-refractory disease. Lymphomas are extremely sensitive to radiation, and significant progress has been made over the last decade in the development of radioimmunotherapy with anti-CD20 antibodies. Materials and Methods. Herein we review clinical experience with tositumomab and iodine I 131 tositumomab (Bexxar®; Corixa Corporation; South San Francisco, CA; and GlaxoSmithKline; Philadelphia, PA) in patients with non-Hodgkin's lymphoma. Results. Therapy with Bexxar has demonstrated high response rates and long durations of response compared with unconjugated anti-CD20 antibodies in patients with relapsed low-grade and transformed low-grade non-Hodgkin's lymphomas. Iodine-131 (I-131) has a long history of clinical experience, an excellent safety record, and favorable nuclear and pharmacologic properties. Importantly, the gamma emissions of iodine-131 facilitate accurate dosimetry to calculate the appropriate patient-specific therapeutic activity to deliver a predetermined total-body dose of radiation, thereby minimizing hematologic toxicity. In clinical trials of Bexxar, objective response rates ranged from 54%-71% in heavily pretreated patients. In the pivotal trial, the number of patients with a longer duration of response after treatment with Bexxar was significantly greater than the number of patients with a longer duration of response after their last qualifying chemotherapy regimen. In 76 newly diagnosed patients, the objective response rate was 97%, and 63% of patients achieved complete responses. Conclusion. These data suggest that Bexxar will become an important new option in the treatment of indolent lymphoma.