Phase 1 study of radiosensitization using bortezomib in patients with relapsed non-Hodgkin lymphoma receiving radioimmunotherapy with131I-tositumomab

Radioimmunotherapy (RIT) is effective treatment for indolent non-Hodgkin lymphomas (NHLs), but response durations are usually limited, especially in aggressive NHL. We hypothesized that administration of bortezomib as a radiosensitizer with RIT would be tolerable and improve efficacy in NHL. This phase 1 dose-escalation study evaluated escalating doses of bortezomib combined with 131I-tositumomab in patients with relapsed/refractory NHL. Twenty-five patients were treated. Treatment was well tolerated, with primarily hematologic toxicity. The maximum tolerated dose (MTD) was determined to be 0.9 mg/m2 bortezomib, in combination with a standard dose of 75 cGy 131I-tositumomab. Sixteen patients responded (64%), including 44% complete responses (CRs), with 82% CR in patients with follicular lymphoma (FL). At a median follow-up of 7 months, median progression-free survival was 7 months, and seven of 11 patients with FL remained in remission at a median of 22 months. In conclusion, bortezomib can be safely administered in combination with 131I-tositumomab with promising response rates.