A Phase II Study of ¹³¹I-rituximab for Patients With Relapsed or Refractory Marginal Zone Lymphoma

Background: Radioimmunotherapy (RIT) is a rare treatment option for relapsed or refractory B-cell non-Hodgkin's lymphoma (NHL). We investigated the safety and efficacy of I-131-rituximab in patients with relapsed or refractory marginal zone lymphomas.Methods: Patients with pathologically confirmed marginal zone lymphoma who relapsed or were resistant to prior therapy were enrolled. The patients received 250 mg/m(2) of unlabeled rituximab immediately before receiving a therapeutic I-131-rituximab dose. The primary endpoint was the objective response rate (ORR), and the secondary endpoints were toxicity assessment, progression-free survival (PFS), and overall survival (OS).Results: Ten patients (median age = 57.5 years; range = 32-71) were included. Owing to poor enrollment, only 10 of the initially intended 25 patients were included in the study, rendering it unfeasible to perform the primary endpoint analysis. Before RIT, patients received chemotherapy, with 40% (n = 4) receiving rituximab therapy. Median PFS and OS were 18.9 months (95% confidence interval [CI]: 0.0-38.9) and 100.0 months (95% CI: 39.8-160.1), respectively. The ORR was 90%, and the duration of response was 29.7 months (95% CI: 0.0-61.3). Considering a median follow-up of 78.5 months (95% CI: 42.7-114.3), 4 patients (40%) were diagnosed with secondary malignancy. Hematological toxicities were common treatment-related adverse events, and 60% and 50% of the patients experienced grade 3 to 4 thrombocytopenia and neutropenia, respectively.Conclusions: I-131-rituximab showed marked efficacy in patients with relapsed or refractory marginal zone lymphoma, with a considerable risk of secondary malignancies during long-term follow-up. Radioimmunotherapy is not a recommended treatment option for relapsed or refractory marginal zone lymphoma but may be considered when other treatment options are not feasible.