Real World Long-term Follow-up Experience with Yttrium-90 ibritumomab tiuxetan in Previously Untreated Patients with Low-Grade Follicular Lymphoma and Marginal Zone Lymphoma

Introduction: Yttrium-90 ibritumomab tiuxetan [(90)Y-IT] is a CD20-targeted radio-immuno conjugate. Clinical trials of (90)Y-IT as a first-line stand-alone treatment in follicular lymphoma (FL) and/or marginal zone lymphoma (MZL) showed high efficacy. However, long-term survival outcomes and toxicities are not well-defined. Methods: We report a retrospective single-institution, multi-center study of (90)Y-IT in previously untreated low grade (LG)-FL and MZL at Mayo Clinic Cancer Center between January 2000 and October 2019. We selected patients with LG-FL and MZL who received standard-dose (90)Y-IT as a single agent in the first line setting. Results: The cohort (n = 51) consists of previously untreated LG-FL (n = 41) or MZL (n = 10). Median follow-up was 5.3 years (95% CI; 4.2, 6.2). Overall response rate (ORR) was 100% with complete response rate (CR) of 94%. Continuous CR was observed in 59% patients who had more than 2 years of follow-up. Long-term CR (>7 years) was seen in 25% of patients. Median progression free survival (mPFS) for the whole cohort was not reached (NR) (95% CI; 4.9, NR). Bulky disease was associated with shorter median PFS of 3.5 years (CI 95%; 0.8, 4.9) compared to non-bulky disease NR (CI 95%; 5.8, NR), P = .02. The incidence of grade 3 or higher thrombocytopenia, neutropenia and anemia were 47%, 37%, and 4% respectively. No therapy-related myelodysplasia or acute myeloid leukemia were observed. Conclusion: Long real-life follow-up showed that single-agent (90)Y-IT is highly efficacious with durable long-term survival in previously untreated LG-FL and MZL without significant risk for secondary malignancies.