Yttrium 90-ibritumomab tiuxetan plus rituximab maintenance as initial therapy for patients with high-tumor-burden follicular lymphoma: a Wisconsin Oncology Network study.

Introduction: Yttrium 90-ibritumomab tiuxetan (90Y-IT) radioimmunotherapy has proved to be effective in relapsed follicular lymphoma (FL). We conducted a clinical trial in which 90Y-IT followed by maintenance rituximab (MR) was evaluated as initial therapy for high-tumor-burden FL.

Methods: Eligible patients had histologically confirmed FL and met the GELF (Groupe d'Etude des Lymphomes Folliculaires) criteria for high tumor burden. All patients received a single dose of 90Y-IT. Patients with platelet counts of 150,000/mm³ or higher received 0.4 mCi/kg, and patients with platelet counts between 100,000/mm³ and 149,000/mm³ received 0.3 mCi/kg. At 6 months, patients without progressive disease (PD) received rituximab weekly for 4 weeks at a dose of 375 mg/m² (consolidation therapy), followed by MR consisting of the same dose every 3 months for a planned 5 years.

Results: From January 2005 through November 2007, a total of 16 patients were enrolled. The median age was 52 years (range, 37-75). The major toxicity from 90Y-IT was myelosuppression, with 88% and 31% of the patients experiencing grade 3 and grade 4 hematologic toxicity, respectively. The responses to 90Y-IT induction therapy were as follows: 7 patients with complete response/unconfirmed complete response (CR/Cru), 4 with partial response (PR), 3 with stable disease (SD), and 2 with progressive disease (PD). We identified 6 patients with early PD (range, 4-16 months) and 10 patients with prolonged remission (range, 37-101+ months). Compared with the patients who had prolonged remission, the patients who had early PD tended to have larger baseline nodal masses. The median progression-free survival (PFS) has not been reached after a median follow-up period of 48 months. The 3-year PFS and overall survival (OS) rates were 56% (95% CI, 37%-87%) and 93% (95% CI, 80%-100%), respectively.

Conclusion: The overall response rate (ORR) to 90Y-IT was 69% in patients who had previously untreated, high-tumor-burden FL, which is lower than what is observed with contemporary rituximab/chemotherapy combinations. MR after 90Y-IT did convert all PRs to CRs. Alternative therapies should be considered for patients who have FL with large nodal masses (>9 cm), whereas very durable responses are possible in patients who have intermediate-size masses (>9 cm).