Phase II study of yttrium-90-ibritumomab tiuxetan in patients with relapsed or refractory mantle cell lymphoma

Purpose: This phase II trial evaluated the safety and efficacy of yttrium-90 (⁹⁰Y)-ibritumomab tiuxetan in patients with relapsed or refractory mantle cell lymphoma (MCL). Patients and Methods: Patients with relapsed or refractory MCL were eligible for the study if they had adequate major organ function and performance status. Those with CNS disease, pleural effusion, circulating lymphoma cells ≥ 5,000/μL, or history of stem-cell transplant were ineligible. Patients with a platelet count ≥ 150,000/μL received a dose of 0.4 mCi/kg of ⁹⁰Y-ibritumomab tiuxetan, whereas those with a platelet count less than 150,000/μL received a dose of 0.3 mCi/kg. Results: Thirty-four patients with a median age of 68 years (range, 52 to 79 years) received the therapeutic dose. The patients had received a median of three prior treatment regimens (range, one to six treatment regimens), including those that contained rituximab (n = 32) and bortezomib (n =7). Of the 32 patients with measurable disease, 10 (31%) achieved complete or partial remission. After a median follow-up of 22 months (range, 2 to 72+ months), an intent-to-treat analysis revealed a median event-free survival (EFS) duration of 6 months and an overall survival duration of 21 months. The median EFS for those who achieved partial or complete remission was 28 months, while it was 3 months for those whose disease did not respond (P < .0001); it was 9 months for patients whose tumor measured less than 5 cm in the largest diameter before treatment and 3 months for those whose tumor measured ≥ 5 cm (P = .015). Conclusion: The single-agent activity of ⁹⁰Y-ibritumomab tiuxetan and its favorable safety profile warrant its further development for the treatment of MCL.