Phase 2 Study of Iodine-131 Tositumomab Plus Chemotherapy in Patients With Previously Untreated Mantle-Cell Lymphoma

Mantle-cell lymphoma (MCL) is sensitive to radiotherapy, and the CD20 antigen is relatively highly expressed in MCL. Therefore, radioimmunotherapy using radiolabeled anti-CD20 monoclonal antibodies has the potential to treat MCL. The objective of this study was to investigate the efficacy, pharmacokinetics, and safety of tositumomab (TST) and iodine-131 tositumomab (I-131 TST) followed by 6 cycles of cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) in patients with previously untreated MCL (ClinicalTrials.govNCT00022945).

In this phase 2 open-label study, patients received dosimetric (day 0: 450 mg TST, then 35 mg I-131 TST [5 mCi]) and therapeutic (between days 7 and 14: 450 mg TST, then an individualized dose of I-131 TST [65-75 cGy]) TST/I-131 TST, with CHOP treatment commencing approximately 13 weeks after the therapeutic dose. The primary end point was the MCL response rate to treatment; secondary end points included confirmed complete response rate and total body residence time.

Twenty-six patients were enrolled, and 25 were included in the intent-to-treat population. The overall unconfirmed response rate was 84%, and the confirmed complete response rate was 44%. The median progression free-survival was 27.6 months. The median total body residence time was 94.5 hours. No new or unexpected safety signals were identified.

Patients with previously untreated MCL who received radioimmunotherapy with TST/I-131 TST followed by CHOP had a high response rate and a long duration of response, indicating that radioimmunotherapy is a therapeutic option in this patient population.