Yttrium-90 Ibritumomab Tiuxetan Radioimmunotherapy in Richter Syndrome

BACKGROUND. ⁹⁰Y ibritumomab tiuxetan is a radioimmunotherapeutic construct that is reported to be an effective treatment for patients with lymphoma. The aim of the current analysis was to evaluate retrospectively the efficacy and safety of ⁹⁰Y ibritumomab tiuxetan in patients with Richter syndrome (RS). METHODS. Patients with histologically proven CD20-positive RS and < 25% lymphoma and/or chronic lymphocytic leukemia in the bone marrow were treated. Patients received an imaging dose of ¹¹¹In-labeled ibritumomab tiuxetan of 1.6 mg (5.0 mCi of ¹¹¹In) intravenously. One week later, they received 0.3 or 0.4 mCi/ kg of ⁹⁰Y ibritumomab tiuxetan. Rituximab, at a dose of 250 mg/m ² intravenously, was given immediately before ibritumomab tiuxetan on Days 1 and 8. RESULTS. Seven patients were treated. Their median age was 56 years (range, 44-70 years). The median time to transformation was 7.9 years (range, 0.7-28.4 years). The median number of previous therapies received was five (range, one to seven previous therapies). The median number of previous therapies received for RS was one (range, none to three previous therapies). Six patients were treated previously with hyperfractionated cyclophosphamide, vincristine, doxorubicin, and dexamethasone alternating with methotrexate and cytosine arabinoside. No patient responded to ⁹⁰Y ibritumomab tiuxetan therapy. All patients developed disease progression. The median time to disease progression was 41 days (range, 39-89 days). Side effects included hematologic toxicity. Grade 3-4 (according to the second version of the National Cancer Institute Common Toxicity Criteria) thrombocytopenia and neutropenia occurred in 5 patients (71%) and 2 patients (29%), respectively. There was one episode of septic shock in a patient with Grade 4 neutropenia. CONCLUSIONS. ⁹⁰Y ibritumomab tiuxetan had no significant antitumor activity and hematologic toxicity was severe in these heavily pretreated patients with RS.