S0433 Iodine I 131 Tositumomab, Rituximab, and Combination Chemotherapy in Treating Older Patients With Stage II, Stage III, or Stage IV Non-Hodgkin's Lymphoma

OBJECTIVES: * Determine the 2-year progression-free survival of older patients with previously untreated bulky stage II or stage III or IV diffuse large B-cell non-Hodgkin's lymphoma treated with iodine I 131 tositumomab in combination with rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone. * Determine the response rate (partial response, complete unconfirmed response, and complete response) in patients treated with this regimen. * Determine the 2-year progression-free survival and response rate (partial response, complete unconfirmed response, and complete response) in B-cell lymphoma 2 (BCL-2) positive patients treated with this regimen. OUTLINE: This is a multicenter study. * Rituximab and chemotherapy: Patients receive R-CHOP comprising rituximab IV over 6 hours; cyclophosphamide IV over 15-45 minutes; doxorubicin IV over 5-20 minutes; and vincristine IV over 5-15 minutes on day 1 and oral prednisone on days 1-5. Treatment repeats every 21 days for up to 6 courses in the absence of disease progression or unacceptable toxicity. Patients then undergo a restaging evaluation. Patients without progressive disease receive CHOP chemotherapy comprising cyclophosphamide, doxorubicin, vincristine, and prednisone as outlined above. Treatment with CHOP chemotherapy repeats every 21 days for 2 courses. * Radiolabeled monoclonal antibody therapy: Approximately 4-8 weeks after completion of chemotherapy, patients receive tositumomab IV over 1 hour followed by a dosimetric dose of iodine I 131 tositumomab IV over 20 minutes. Patients then undergo gamma scans over a 1-week period in order to determine the correct treatment dose of iodine I 131 tositumomab. No more than 2 weeks after administration of the dosimetric dose, patients receive tositumomab IV over 1 hour followed by a treatment dose of iodine I 131 tositumomab IV over 20 minutes. After completion of study treatment, patients are followed periodically for up to 5 years. PROJECTED ACCRUAL: A total of 80 patients will be accrued for this study within 15 months.