Hairy cell leukemia (HCL) is an indolent B-cell neoplasm that strongly expresses CD20. Despite initial very high response rates with cladribine(Drug information on 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(Drug information on 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.