Phase II Study of Yttrium-90-Ibritumomab Tiuxetan as Part of Reduced-Intensity Conditioning (with Melphalan, Fludarabine ± Thiotepa) for Allogeneic Transplantation in Relapsed or Refractory Aggressive B Cell Lymphoma: A GELTAMO Trial

•Y-90 ibritumomab tiuxetan was used as a part of a reduced-intensity conditioning regimen phase II multicenter trial•Conditioning regimen with radioimmunotherapy is safe and well tolerated•The addition of radioimmunotherapy results in a long-term progression-free survival of 44%•No significant toxicities related to Y-90 ibritumomab tiuxetan have been reported•Our 46-month median follow-up is the longest reported in a radioimmunotherapy allogeneic stem cell transplantation trial

We designed a phase II clinical trial including Y-90 ibritumomab-tiuxetan as part of a reduced-intensity conditioning (RIC) allogeneic stem cell transplantation (AlloSCT) in high-risk non-Hodgkin lymphoma (Clinical Trials Identifier: NCT00644371). Eligible patients had high-risk relapsed/refractory aggressive lymphoma. The conditioning regimen consisted of rituximab 250 mg (days −21 and −14), Y-90 ibritumomab IV (.4 m Ci/kg, day −14), fludarabine 30 mg/m2 i.v. (days −3 and −2) plus melphalan 70 mg/m2 i.v. (days −3 and −2) or 1 dose of melphalan and thiotepa 5 mg/kg (day −8). Donors were related. Eighteen patients were evaluable. At the time of transplantation, responses were complete remission (CR) (n = 7, 39%), partial remission (n = 6, 33%) or refractory disease (n = 4, 28%). Y-90-ibritumomab infusions were well tolerated, with no adverse reactions. Nonrelapse mortality at 1 year was 28%. Median follow-up was 46 (range, 39 to 55) months. Estimated 1-year progression-free survival (PFS) was 50%, and 4-year overall survival (OS) and PFS were both 44.4%. CR at the moment of AlloSCT had significant impact on PFS (71% versus 27%, P = .046) and OS (71% versus 27%, P = .047). Our results show that Y-90-ibritumomab-tiuxetan as a component of RIC for AlloSCT is feasible in patients with high-risk B cell lymphoma. Development of phase III clinical trials is needed to clarify the contribution of radioimmunotherapy to RIC AlloSCT.