Y90 ibritumomab tiuxetan with maintenance rituximab as initial therapy for high tumor burden follicular lymphoma: A Wisconsin Oncology Network study.

Abstract

e18503 Background: Yttrium90 ibritumomab tiuxetan (Y90IT) radio-immunotherapy has proved to be an effective therapy in relapsed follicular lymphoma (FL). The Wisconsin Oncology Network conducted a clinical trial in which Y90IT followed by maintenance rituximab (MR) was evaluated as initial therapy for high tumor burden FL. Methods: Eligible patients had histologically confirmed follicular lymphoma and met GELF criteria for high tumor burden. All patients received a single dose of Y90IT. At 6 months, patients without PD received 4 weekly doses of rituximab 375 mg/m² followed by MR consisting of a single dose every 3 months for a planned duration of 5 years. Results: Sixteen eligible patients were enrolled from 1/05-11/07. The protocol was closed in 5/08 secondary to slow accrual (planned N = 36). Baseline characteristics include median age of 55 years (37-75) and FLIPI distribution of 19% low, 44% int, and 37% high. The major toxicities from Y90IT were expected myelosuppression with 88% and 31% experiencing grade 3 and 4 heme toxicity, respectively. Median nadir was 752/mm³ for ANC, 46k/ mm³ for platelets, and 11.5 g/dL for hemoglobin. Median duration of grade 3 and grade 4 toxicities was 2.5 weeks (1-7) and 1 week (1-2), respectively. One patient developed MDS/AML and has since expired. Response to Y90IT induction therapy included 7 CR/CRu, 4 PR, 3 SD, and 2 PD. All 4 PR patients converted to CR/CRu during MR therapy. We identified 6 patients with early PD (range 4-16 months) and 10 patients with prolonged remissions (range 37-71+ months). All patients with baseline masses over 9 cm experienced early PD, while 7/9 patients with masses less than 9 cm are experiencing prolonged remissions ranging from 39+ to 71+ months. With a median follow up of 48 months, the 3 year PFS and OS were 63% and 94% respectively. Conclusions: The ORR to Y90IT was 69% in previously untreated, high tumor burden FL patients, which is lower than what is observed with contemporary rituximab-chemotherapy combinations. FL patients with large nodal masses (> 9cm) should be considered for alternative therapies while patients with intermediate size masses (3-9 cm) have the potential for durable responses.