First-Line Radio-Immunotherapy of Newly Diagnosed, Advanced Follicular Non-Hodgkin Lymphoma with ¹³¹I-Rituximab: The INITIAL Study,

Radio-immunotherapy (RIT) with ¹³¹I-rituximab has demonstrated efficacy in relapsed and refractory non-Hodgkin lymphoma (NHL). ¹³¹I-tositumomab has been shown to be an effective first-line agent in follicular NHL with durable response. We aimed to evaluate the efficacy and safety of first-line ¹³¹I-rituximab RIT and the duration of response in previously untreated patients with follicular NHL, given that this radiolabeled chimeric antibody treatment can be repeated upon relapse.

Fifty consecutive patients with newly diagnosed, symptomatic, advanced follicular NHL received a prescribed therapy activity of ¹³¹I-rituximab predicated upon a fixed, whole-body radiation dose of 0.75 Gy. All patients were treated as outpatients. All patients received a standard four-week course of rituximab at a dose of 375 mg/m² in conjunction with the radionuclide therapy, and subsequent rituximab maintenance at 3-monthly intervals for one year. Response was determined by ¹⁸F-FDG PET/CT scans at baseline, and at 3 and 12 months post-treatment.

Overall response rate (ORR) at 3 months was 98%, with complete response (CR) seen in 38 patients (76%) and partial response (PR) in 11 patients (22%). Four patients (36%) assessed as having PR at 3 months converted to CR in the year following treatment, so that 84% of patients were in CR at one year. During median follow-up of 33 months (range 12–61 months) only one patient (2.6%) among those who had achieved CR has relapsed, while progressive disease has been seen in seven patients (64%) of those with PR at first post-treatment assessment. Only three of the seven patients with PD have so far required further treatment; one with local radiotherapy and two who have received combination chemotherapy. Median progression-free survival (PFS) has not yet been reached. Toxicity was limited to hematological Grade 4 neutropenia in 5 patients (10%) and thrombocytopenia in 5 patients (10%). One patient received a single platelet transfusion. There were no episodes of bleeding or infection. Three patients have died; one from transformed, aggressive NHL (the only non-responder) and the other two from non-hematological malignancies not apparent at study entry.

First-line ¹³¹I-rituximab RIT of advanced follicular NHL is effective and safe. Early response rates are similar to those observed with combination chemotherapy and rituximab regimens. Durable CR is present in 82% of patients over a median follow-up of 33 months and median PFS has not yet been reached. Of those with documented PR at 3 months, approximately one-third subsequently converted to CR, while the remaining two-thirds developed PD.

Off Label Use: radiolabelled rituximab.