Japanese phase II study of 90Y‐ibritumomab tiuxetan in patients with relapsed or refractory indolent B‐cell lymphoma

There is no data about the efficacy and safety of radioimmunotherapy with 90Y‐ibritumomab tiuxetan in patients with relapsed or refractory indolent B‐cell lymphoma pretreated with rituximab‐containing chemotherapy. We focused on this in a Japanese phase II study. Radioimmunotherapy with 90Y‐ibritumomab tiuxetan (11.1 and 14.8 MBq) was evaluated in patients with 100–149 × 109 and >150 × 109 platelets/L, respectively. The primary endpoint was the overall response rate. Forty patients were treated with 90Y‐ibritumomab tiuxetan (18 with 11.1 MBq/kg and 22 with 14.8 MBq/kg). Thirty‐five patients (88%) had been pretreated with rituximab, including 27 (68%) pretreated with rituximab‐containing chemotherapy. The overall response rate was 83% (33/40; 95% confidence interval, 67–93%), and the complete response rate was 68% (27/40; 95% confidence interval, 51–81%). The overall response rates in patients pretreated with rituximab‐containing chemotherapy and rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone (R‐CHOP) were 83% (19/23) and 94% (17/18), respectively. The median progression‐free survival time of the 40 patients who received 90Y‐ibritumomab tiuxetan was 9.6 months. Toxicity was primarily hematological and mostly transient. No grade 4 non‐hematological toxicity was observed. In conclusion, radioimmunotherapy with 90Y‐ibritumomab tiuxetan is safe and highly effective in patients with relapsed or refractory indolent B‐cell lymphoma, including those pretreated with rituximab‐containing chemotherapy. (ClinicalTrials.gov number NCT00220285) (Cancer Sci 2009; 100: 158–164)