Efficacy of Yttrium-90 Iburitumomab Tiuxetan for Early Relapsed/Refractory Indolent B-Cell Lymphoma: A Single Institute Retrospective Analysis in the Rituximab Era
Authors: Nakata Keiichi , Fuji Shigeo , Nakata Ryo , Tsutsumi Kazuhito , Kida Shuhei , Koike Midori , Tada Yuma , Masaie Hiroaki , Yoshida Hitoshi , Ishikawa Jun 
Published: October 2019

Abstract
Introduction: Indolent B-cell lymphoma is a type of non-Hodgkin's lymphoma that grows slowly and is not a curative disease. Yttrium-90 (90Y) iburitumomab tiuxetan is used in patients with relapsed/refractory indolent B-cell lymphoma, data is still limited in the rituximab era. In addition, previous studies did not assess the impact of early progression of disease within 2 years (POD24) which was reported to be associated with a poor prognosis in follicular lymphoma (Casulo et al, J Clin Oncol 2015) on the efficacy of 90Y iburitumomab tiuxetan. Thus, here we assessed the efficacy of 90Y iburitumomab tiuxetan in relapsed/refractory indolent B-cell lymphoma, and analyzed the impact of POD24 in this setting.
Methods: We retrospectively analyzed the clinical outcomes of 51 patients with a relapsed/refractory indolent B-cell lymphoma who received 90Y iburitumomab tiuxetan at our institute from February 2009 to January 2018. POD24 was defined as progression within 24 months from the beginning of induction chemotherapy. Survival outcomes including overall survival (OS) and progression-free survival (PFS) were analyzed by Kaplan-Meier analysis and Cox proportional hazard models.
Results: The median age was 64 years (range 37-88 years) at the time of receiving 90Y iburitumomab tiuxetan, and 29 (56.9%) were male. Disease subtypes were as follows: follicular lymphoma (n=44, 86.3%), mantle cell (n=4, 7.8%), marginal zone (n=2, 3.9%), and MALT lymphoma (n=1, 2.0%). The median number of previous regimens was 2 (range 1-9) and included rituximab-based therapy in all patients. Disease status at the time of receiving 90Y iburitumomab tiuxetan were as follows: complete remission (CR n=3, 5.9%), partial remission (PR n=13, 25.5%), stable disease (SD n=3, 5.9%), progression disease (PD n=32, 62.7%). The median follow-up time was 3.7 years (range 0.3-8.8 years) and overall response rate (ORR) was 94.1% (CR 56.9%, PR 37.3%). The ORR in patients with POD 24 was 95.0% (CR 60.0%, PR 35.0%), compared to 93.5% (CR 54.8%, PR 38.7%) with non-POD24. The 3-year OS and PFS rates for all patients receiving 90Y iburitumomab tiuxetan were 83.6% and 41.0%, respectively. POD24 was a significant prognostic factor for PFS in univariate analysis (1.2 years in patients with POD24 vs. 3.3 years in patients with non-POD24, (P=0.02) (Figure1). In multivariate analysis, POD24 was an independent prognostic marker of PFS (hazard ratio (HR) 0.43, 95% confidence interval (CI) 0.22-0.87, P=0.02).
Conclusion: 90Y iburitumomab tiuxetan was highly effective in patients with relapsed/refractory indolent B-cell lymphoma patients. However, in patients with POD24, duration of response was short. Thus, another treatment strategy including hematopoietic stem cell transplantation should be considered.

Disclosures
No relevant conflicts of interest to declare.