Efficacy of anti-CD20 monoclonal antibodies (Mabthera) in patients with progressed hairy cell leukemia.

Background and Objectives: Recently, a chimeric monoclonal antibody (MoAb) directed against the CD20 antigen (rituximab) has been successfully introduced in the treatment of several CD20-positive B-cell neoplasias and particularly of follicular lymphomas. Based on these premises we evaluated the efficacy and the toxicity of chimeric anti-CD20 monoclonal antibody (MoAb) in relapsed/progressed hairy cell leukemia (HCL).
Design and Methods: Ten patients with relapsed/progressed HCL entered the study. Eight patients were males and two females with a median age of 55 years (range 41-78) and all of them had been previously treated with 2-chlorodeoxyadenosine and/or deoxycoformycin and a-interferon. Two out of 10 patients were anemic (Hb < 10 g/dL), 4 thrombocytopenic (Plt < 100 x 10(9)/L), 3 had fewer than 1.0 x 10(9)/L neutrophils and 3 had circulating hairy cells (HC). All patients received 375 mg/m2 i.v. of anti-CD20 MoAb once a week for 4 doses.
Results: All patients were evaluable for response, one patient showing a complete remission and 4 a partial response. Adverse reactions, such as fever, chills, bone pain, hypotension and thrombocytopenia, were transient and mild (grade 1-2) and occurred only during the first course of treatment. One month after the last infusion, patients who had had anemia, neutropenia or thrombocytopenia, recovered normal peripheral blood values. Circulating HC also disappeared within one month. Immunostained bone marrow biopsies were checked 1, 3 and 6 months after the end of therapy and in 5 out of 10 patients a >50% reduction of bone marrow HC infiltration was recorded.
Interpretation and Conclusions: On the basis of these preliminary results observed in 10 patients with progressed HCL, it appears that treatment with anti-CD20 MoAb is safe and effective in at least 50% of patients, particularly in those with a less evident bone marrow infiltration (50%) and in those previously splenectomized.