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Phase II Study of Rituximab in the Treatment of Cladribine-Failed Patients With Hairy Cell Leukemia

Phase II Study of Rituximab in the Treatment of Cladribine-Failed Patients With Hairy Cell Leukemia

Hairy cell leukemia (HCL) is an indolent B-cell neoplasm that strongly expresses CD20. Despite initial very high response rates with cladribine (Leustatin), many patients ultimately relapse.

From January 2000 to February 2001, 16 patients (15 male, 1 female) with HCL, with a median age of 57 years (range: 38-81 years), having relapsed after prior treatment with cladribine, were treated with rituximab (Rituxan) at 375 mg/m² weekly × 4. All patients had received at least one prior course of cladribine (median: 44 months from last cladribine; range: 19-119 months), eight patients received two prior courses of cladribine, five patients received interferon, and two patients had undergone splenectomy.

A total of 15 patients are currently evaluable for response, with at least a 6-month follow-up. Three patients (20%) achieved complete remissions, defined as the absence of hairy cells in the peripheral blood and bone marrow with the following peripheral blood parameters: ³ 1.5 × 109 neutrophils/mL, hemoglobin concentration ³ 12 g/dL, and ³ 100,000 platelets/mL. One patient (7%) had minimal residual disease as evidenced by positive staining on DBA.44 and CD20 without morphologic evidence of HCL by light microscopy. One patient (7%) achieved a partial response, defined as at least 50% improvement in all cytopenias with at least a 50% reduction of hairy cells from the peripheral blood and bone marrow. Thus, 5 of 15 (33%) patients achieved a response. At a median follow-up of 12 months (range: 9-20 months), no responders had relapsed. Three patients (20%) achieved hematologic improvement without sufficient reduction in marrow HCL cells to qualify as a response; both lasted less than 3 months in duration.

The only grade 3/4 toxicities demonstrated were culture-negative febrile neutropenia, transient and reversible disseminated intravascular coagulation related to rituximab administration, and a diverticular abscess. Of 10 patients who failed to respond, 6 subsequently received other treatments: 3 were retreated with cladribine, 2 underwent splenectomy, and 1 received pentostatin (Nipent). All six patients treated after rituximab achieved hematologic improvements, although no bone marrow follow-up data are presently available.

CONCLUSION: Rituximab, administered at this dose and schedule, has only modest activity in cladribine-failed HCL patients when compared to other agents active in this disease.

Click here to read Dr. Bruce Cheson's commentary on this abstract.

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