131I tositumomab

I-131 tositumomab is a radiolabelled murine anti-CD20 monoclonal antibody that binds specifically to the CD20 antigen on normal and malignant B lymphocytes. It has antitumour activity as a result of emission of beta particles, and activation of antibody-dependent cellular and complement-mediated cytotoxicity. I-131 tositumomab monotherapy consistently produced objective response rates of greater than or equal to 60% in patients with relapsed or refractory, low grade or transformed low grade non-Hodgkin's lymphoma (NHL) in clinical trials. 62% of patients responded to retreatment in 1 small trial. In 2 studies, objective and complete response rates were higher and overall durations of response were significantly longer in patients treated with I-131 tositumomab compared with their last chemotherapy regimen. High dose I-131 tositumomab combined with autologous stem cell transplant produced an objective response rate of 86% in relapsed or refractory patients. I-131 tositumomab alone or in combination with fludarabine achieved an objective response rate of 100% in 2 preliminary reports in patients with previously untreated NHL. The dose-limiting toxicity of I-131 tositumomab is reversible myelosuppression. with approximate to 18% of patients requiring haematological support in combined trial data. Other nonhaematological toxicities occur in approximate to 20 to 40% of patients and include mild to moderate flu-like symptoms.