Hairy cell leukemia is an indolent B-cell neoplasm, strongly expressing CD20.  Despite initial very high response rates following cladribine, many patients ultimately relapse.  Having relapsed after prior treatment with cladribine, 24 HCL patients (21 male, 3 female) with a median age of 53.5 years were treated with rituximab at 375 mg/m3 intravenously weekly for 4 weeks.  Of the patients, 3 (13%) achieved full remissions and 3 (13%), partial responses.  Thus, 6 (25%) of 24 patients achieved a response following rituximab.  At a median follow-up of 14.6 months, 2 responders have relapsed; median time to relapse was not yet reached.  The only grade III or IV toxicities demonstrated were culture-negative febrile neutropenia, transient and reversible disseminated intravascular coagulation related to rituximab administration, and a diverticular abscess, each in single patients.  Of 18 responders, 9 patients subsequently  received other treatments; 5 patients were retreated with cladribine, 3 underwent splenectomy, and 1 received pentostatin.  Follow-up data are available on 7 of these 9 patients; all 7 patients achieved improvements in hematologic parameters.  Rituximab, administered at this dose and schedule, has only modest single-agent activity in cladribine-failed HCL patients when compared with other agents active in this disease. (Blood. 2003; 102:000-000) (American Society of Hematology)