Role of Yttrium-90 Ibritumomab Tiuxetan (Zevalin®) in Inducing and Maintaining Complete Molecular Response in B Non Hodgkin’s Lymphoma Patients in Clinical Complete Remission after Chemotherapy Regimen.

Introduction: Radioimmunotherapy (RIT) is a new treatment for B non Hodgkin’s lymphoma (NHL) patients. ⁹⁰Y ibritumomab tiuxetan (Zevalin®) consists of a murine monoclonal antibody to CD20, conjugated to a metal chelator tiuxetan for retention of the beta emitter ⁹⁰Y. Thus Zevalin® delivers radiation to B-NHL, combining the tumor targeting attributes of a monoclonal antibody and the beta radiation of ⁹⁰Y. Zevalin® is approved for the treatment of follicular lymphoma (FL) refractory to or relapsed after rituximab, on the bases of clinical trials where it achieved a response rate as high as 83%. Several ongoing registrational trials are evaluating the efficacy of Zevalin® in other NHL, as diffuse large B cell (DLCL) and mantle cell lymphoma (MCL). We are here evaluating the effect of Zevalin® as consolidation therapy in NHL patients that achieved a complete clinical response (CCR) with chemotherapy.

Methods: In B cell NHL patients that achieved a CCR after 1st or multiple lines anthracyclines based chemotherapy +/− Rituximab, minimal residual disease was evaluated by PCR on bone marrow samples, for the following rearrangements: JH, Bcl-1, Bcl-2. Patients received Zevalin® 6-9 weeks post chemotherapy. Evaluation of molecular response was assessed after a follow up period at 12 weeks. The aim of the study was the role of Zevalin® in inducing a complete molecular response (CMR).

Results: 23 B-NHL patients (13 FL, 6 MCL, 4 DLCL; male:female 13:10, median age 63, range 42–73. See table) in a CCR after chemotherapy (documented by TC scan and/or PET-scan negative for abnormal lesions or glucose captation) have been enrolled. 10 patients had a pathological rearrangement before RIT, while 13 were already in a CMR condition. Zevalin® was completed in all 23 patients and the post infusion evaluation was performed after 12 weeks. In the follow-up period thrombocitopenia was commonly documented, but it was not associated to bleeding or need of platelet transfusion, but in one singular case. After 12 weeks from RIT a new molecular evaluation was performed on bone marrow samples. All the 23 patients have completed the 12 weeks follow-up: 8 of 10 (80%) patients positive before RIT achieved a CMR with Zevalin® administration. The 13 PCR negative patients maintained the CMR. The 21 PCR negative patients are now under follow-up to evaluate the molecular disease free survival after Zevalin® RIT.

Conclusion: Zevalin® is an efficient consolidation therapy in B cell NHL patients after chemotherapy. In this series of patients Zevalin® administration allowed to convert 8 of 10 CCR to CMR. In the remaining 13 patients Zevalin® maintained the CMR. Zevalin® addition to medication treatment is feasible and associated with manageable hematological toxicity.