A clinical and scientific overview of tositumomab and iodine I 131 tositumomab.

The majority of patients with non-Hodgkin's lymphoma (NHL) who respond to conventional chemotherapy will relapse and eventually become refractory to chemotherapy. Each subsequent remission is typically of similar or shorter duration than the last. Recent developments in radioimmunotherapy using monoclonal antibodies to specifically target malignant B cells have yielded promising results in relapsed and refractory NHL patients. The radiolabeled anti-CD20 antibody tositumomab and iodine 131 tositumomab (Bexxar; Corixa Corp, South San Francisco, CA and GlaxoSmithKline, Philadelphia, PA) has been shown to be safe and effective in the treatment of patients with relapsed low-grade (indolent) NHL. Objective responses were achieved in 57% to 71% of patients in phase I to phase III trials, and remission durations were significantly longer in the phase III trial compared with the last remission induced by chemotherapy. In addition, tositumomab and iodine I 131 tositumomab was shown to be effective in the subset analysis of patients with transformed low-grade NHL, which is particularly resistant to conventional therapies. The incidence of transient, nonhematologic adverse events was low and mainly mild to moderate in severity. Hematologic toxicity is the major dose-limiting toxicity associated with radioimmunotherapy; however, patient-specific dosimetry maintained hematologic toxicity within predictable, transient, and manageable limits in the phase II and phase III trials of tositumomab and iodine I 131 tositumomab. Although approximately 10% of patients treated with tositumomab and iodine I 131 tositumomab developed human-antimouse antibodies, treatment with tositumomab does not preclude the administration of subsequent chimeric antibody therapies. In conclusion, these studies show that tositumomab and iodine I 131 tositumomab treatment is safe and induces high response rates and durable remissions in heavily pretreated patients with low-grade or transformed low-grade NHL.