Follow-Up Results of a Phase II Study of Ibritumomab Tiuxetan Radioimmunotherapy in Patients with Relapsed or Refractory Low-Grade,Follicular,or Transformed B-Cell Non-Hodgkin's Lymphoma and Mild Thrombocytopenia

This report presents updated time-to-event variables from a multicenter phase II trial of reduced-dose ⁹⁰Y ibritumomab tiuxetan in patients with relapsed or refractory low-grade, follicular, or transformed B-cell non-Hodgkin's lymphoma (NHL) and mild thrombocytopenia (platelet counts of 100 to 149 × 10⁹ platelets/L). Patients received a single course of ibritumomab tiuxetan radioimmunotherapy, with ⁹⁰Y ibritumomab tiuxetan administered at 0.3 mCi/kg (compared to a standard dose of 0.4 mCi/kg). In 30 patients, the overall response rate was 83%, with complete responses (confirmed [CR] and unconfirmed [CRu]) of 47%. Median follow-up time is currently 36.5 months (range: 7.5–54.9 months). Median duration of response was 11.5 months (range: 1.0–53.9 months), median time to progression was 9.4 months(range: 1.7–54.8+ months), and median time to next lymphoma therapy was 14.6 months (range: 2.3–54.9+ months). Median overall survival time has not yet been reached. Long-term responses, defined as time to progression of 12 months or greater, have been seen in 14 of 30 patients (47%) overall, and 12 of 14 CR/CRu patients (86%). Toxicities were primarily hematologic and reversible. No additional long-term adverse events have been observed in the follow-up period, and treatment did not preclude subsequent lymphoma therapies.