90yttrium-ibritumomab-tiuxetan as first-line treatment for follicular lymphoma: 30 months of follow-up data from an international multicenter phase II clinical trial

Purpose: We report on a multicenter phase II trial of ⁹⁰yttrium- ibritumomab-tiuxetan (⁹⁰YIT) as first-line stand-alone therapy for patients with follicular lymphoma (FL). Patients and Methods: Fifty-nine patients with CD20⁺ FL grade 1 to 3a in stages II, III, or IV, age 50 years old or older requiring therapy were enrolled. They received ⁹⁰YIT according to standard procedure. If complete response (CR) or unconfirmed complete response (CRu) without evidence for minimal residua disease (MRD) 6 months after application of ⁹⁰YIT was achieved, patients were observed without further intervention. The same applied to patients with partial response (PR) or with stable disease (SD). Patients with CR but with persisting MRD were to receive a consolidation treatment with rituximab. Primary end point was the clinical and molecular response rate. Secondary end points were time to progression, safety, and tolerability. Results: Six months after treatment with ⁹⁰YIT, 56% of the patients showed a CR or CRu and 31% achieved a PR. After a median follow-up of 30.6 months, the progression-free survival (PFS) was 26 months. There was a trend for shorter PFS in patients with increased lactate dehydrogenase (LDH). Of the 26 patients who had CR 12 months after ⁹⁰YIT, only three had relapsed. Median time to next treatment has not been reached. The most common toxicities were transient thrombocytopenia and leukocytopenia. Nonhematologic toxicities never exceeded grade 2 according to Common Terminology Criteria for Adverse Events (CTCAE v2.0) Conclusion: ⁹⁰YIT is well tolerated and achieves high response rates. Patients with increased LDH tend to relapse earlier, and individuals in remission 1 year after ⁹⁰YIT appear to have longlasting responses