Purpose: A single treatment of (131)I-rituximab in patients with B cell non-Hodgkin lymphoma (NHL) showed a modest rate of response (29 %) in a relatively short duration (median 2.9 months). On the basis of this result, we investigated whether repeated treatment with (131)I-rituximab could improve the response.
Patients and methods: Thirty-one patients with relapsed or refractory B cell NHL received unlabeled rituximab (70 mg) immediately prior to the administration of a therapeutic dose of (131)I-rituximab. The tumor response was evaluated 1 month later by contrast-enhanced (18)F-fluorodeoxyglucose positron emission tomography/computed tomography. Radioimmunotherapy (RIT) was repeated at 4-week intervals.
Results: A total of 87 cycles of RIT were administered. Repeated RIT yielded twofold increases in response rate (68 %) and in median response duration (8.6 months). This protocol also induced a favorable response in patients with an aggressive histology compared to that induced by a single treatment (50 vs. 9 %, respectively, p = 0.063). The toxicities were principally hematologic with grade 4 thrombocytopenia occurring in 12 % and neutropenia occurring in 17 % of the 85 assessable cycles.
Conclusions: Compared to a single treatment, repeated RIT with (131)I-rituximab increased the response rate and duration for patients with relapsed or refractory B cell NHL, including those with an aggressive histology.