A phase 2 study of yttrium-90 ibritumomab tiuxetan (Zevalin) in patients with chronic lymphocytic leukemia

BACKGROUND: Radioimmunotherapy (RIT) with radio-labeled monoclonal antibodies to CD20 produce a high response rate in patients with relapsed lymphoma. Use of this modality in patients with chronic lymphocytic leukemia (CLL) has been hampered by the extensive marrow involvement seen in patients with CLL, which would produce a high risk for marrow aplasia after treatment with RIT. Patients with lymphoma and marrow involvement have been treated with RIT if involved marrow was less than 25% of the total marrow. Thus, we adapted this approach as consolidation therapy in patients with CLL responding to chemoimmunotherapy. METHODS: Fourteen patients with relapsed CLL either in partial remission or in complete remission but with disease documented by flow cytometry were treated with 90Y ibritumomab tiuxetan. RESULTS: One patient responded and achieved a complete remission but with residual disease detected by flow cytometry. Of note was that grade 3 or 4 hematologic toxicity was seen in 12 of the 13 (92%) evaluable patients, with grade 3 or 4 thrombocytopenia noted in 11 (85%) of the patients. In addition, myelosuppression was prolonged with a median duration of grade 3 or 4 thrombocytopenia of 37 days. Five patients had persistent thrombocytopenia 3 months post-therapy. CONCLUSIONS: Even in patients with CLL and limited marrow involvement, the use of RIT results in unacceptable hematologic toxicity.