We report updated time-to-event variables of a phase III randomized study comparing
yttrium 90-labeled ibritumomab with
rituximab standard
therapy in 143
rituximab-naive patients with relapsed or refractory low-grade, follicular, or transformed CD20+
non-Hodgkin's lymphoma (NHL). Most patients (79%) had
follicular lymphoma. Patients were randomized to receive a single intravenous (I.V.) dose of 90Y
ibritumomab tiuxetan 0.4 mCi/kg (n = 73) or
rituximab 375 mg/m2 I.V. weekly for 4 doses (n = 70). The
radioimmunotherapy group was pretreated with 2
rituximab doses (250 mg/m2) to improve biodistribution and one dose of
Indium 111-labeled
ibritumomab tiuxetan for imaging. The overall response rate was 80% versus 56% (P = 0.002) and complete response (CR)/CR unconfirmed (CRu) rates were 34% for 90Y
ibritumomab tiuxetan versus 20% for
rituximab. With a median follow-up of 44 months, the data are mature as all ongoing patients in both groups exceeded the median Kaplan-Meier estimated time to progression (
TTP), duration of response (DR), and time to next
therapy. Although this study was not powered to detect differences in time-to-event variables, the results from this randomized trial demonstrate trends toward longer median
TTP (15 vs. 10.2 months; P = 0.07), DR (16.7 vs. 11.2 months; P = 0.44) and time to next
therapy (21.1 vs. 13.8 months; P = 0.27) in follicular NHL patients treated with 90Y
ibritumomab tiuxetan compared with the
rituximab control arm. In patients achieving a CR/CRu, the median
TTP was 24.7 months for patients treated with 90Y
ibritumomab tiuxetan compared with 13.2 months for
rituximab-treated patients (P = 0.41), and ongoing responses of > 5 years have been observed. These results confirm that 90Y
ibritumomab tiuxetan produces high response rates and durable remissions in patients with previously treated low-grade, follicular, and transformed NHL.