Allogeneic hematopoietic cell transplantation (allo-HCT) can be curative for relapsed or refractory B-cell lymphomas (BCL), though outcomes are worse in aggressive disease and most patients will still experience relapse. Radioimmunotherapy (RIT) using 90Y-Ibritumomab tiuxetan can induce disease control across lymphoma subtypes in a dose-dependent fashion. We hypothesized that mega-doses of 90Y-Ibritumomab tiuxetan with reduced-intensity conditioning (RIC) could safely produce deeper remissions in aggressive BCL further maintained with the immunologic effect of allo-HCT. In this phase 2 study, CD20+ BCL patients received outpatient 90Y-Ibritumomab tiuxetan (1.5mCi/kg, maximum 120mCi), fludarabine, then 2Gy total body irradiation (TBI) prior to HLA-matched allo-HCT. Twenty patients were enrolled after a median of 4.5 prior lines of therapy including 14 with prior autologous transplant and 4 with prior anti-CD19 chimeric T-cellular therapy. A median 90Y activity of 113.6 mCi (range 71.2-129.2) was administered delivering a median of 552cGy to liver (range 499-2411cGy). The estimated 1 and 5-year PFS was 55% (95% CI, 31-73%) and 50% (95% CI, 27-69%) with a median PFS of 1.57 years. The estimated 1- and 5-year overall survival (OS) was 80% (95% CI, 54-92%) and 63% (95% CI, 38-81%) with a median OS of 6.45 years. Sixteen patients (80%) experienced grade ≥3 toxicities, although nonrelapse mortality was 10% at 1-year. No patients developed secondary AML/MDS. Mega-dose 90Y-Ibritumomab tiuxetan, fludarabine, and low-dose TBI followed by an HLA-matched allo-HCT was feasible, safe, and effective in treating aggressive BCL, exceeding the prespecified endpoint while producing nonhematologic toxicities comparable to standard RIC regimens. (Registered at ClinicalTrials.gov as NCT01434472).
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