8558 Background: Patients with relapsed or refractory diffuse large B-cell lymphoma (DLBCL) are salvaged with high dose chemotherapy followed by autologous stem cell rescue. Ibritumomab tiuxetan is an anti-CD20 antibody conjugated to the radionuclide 90yttrium. 90Y ibritumomab tiuxetan has demonstrated clinical efficacy in DLBCL with a favorable toxicity profile relative to transplant. Methods: This phase II trial investigated the overall response rate (ORR), event free survival (EFS), overall survival (OS) and toxicity of treatment with ibritumomab followed by rituximab in patients with relapsed or refractory DLBCL, not candidates for transplant. Patients were treated with an initial dose of rituximab (250 mg/m2) followed one week later by ibritumomab (0.4 mCi90Y/kg or 0.3 mCi90Y/kg based on plateles) followed by 4 weekly doses of rituximab (375mg/m2). All non-progressing patients received maintenance rituximab (375 mg/m2) weekly for 4 doses every 6 months for 4 cycles. Results: 25 patients were enrolled. Median age was 79 (range 45-95). 12 of 25 (48%) had stage 3 or 4 disease. 13 (52%) had 2 or more prior regimens. At 12 weeks 5 patients (21%) had a complete response (CR), 3 (13%) a partial response, 2 (8%) stable disease and 14 (58%) progressed for an ORR of 32% (8/25). At best response 7 patients obtained a CR. Median EFS was 2.5 months. Median OS was 8.1 months. No patient who obtained CR later relapsed, with follow up of 18.3-100.1 months. Deaths unrelated to treatment occurred in remission in 5 patients. 2 patients remain free of disease at 67.4 and 100.1 months. 11 (65%) patients had grade 3 or 4 thrombocytopenia, but no significant bleeding was observed. 9 (36%) patients had grade 3 non-hematologic toxicity. Grade 1 and 2 fatigue occurred in 41%. Patients who progressed through a rituximab containing regimen were at high risk of early progression. Conclusions: The ORR of ibritumomab as salvage therapy for DLBCL compares favorably to other regimens with acceptable toxicity. Those patients with disease refractory to rituximab are not likely to benefit. For a subset of patients not candidates for salvage with autologous transplant, this treatment can produce a durable remission. Clinical trial information: NCT00110149.