Phase II clinical study of cladribine in the treatment of hairy cell leukemia.

We conducted a phase II clinical study to evaluate the therapeutic efficacy of cladribine (2-chlorodeoxyadenosine [2-CdA]) in the treatment of Japanese patients with hairy cell leukemia (HCL). Seven patients with classic HCL and 3 with a prolymphocytic HCL variant were administered 2-CdA (0.09 mg/kg per day) by continuous intravenous infusion for 7 days. Seven patients responded to this therapy, with 5 patients achieving a complete response (CR). After a median follow-up of 792 days (range, 599-1253 days), there were no cases of clinical relapse, and the median duration of the response in the responders was 670+ days (range, 470+ to 1121+ days). The median duration of the CR in the CR patients was 953+ days (range, 480+ to 1121+ days). At treatment initiation, most patients had hematologic impairment as a manifestation of HCL. During the early stage after administration, further hematologic impairment occurred, but subsequent peripheral blood counts gradually recovered as 2-CdA treatment showed antitumor activity. Infections occurred at a high incidence at this time, but all cases could be controlled with appropriate treatment. 2-CdA was surmised to represent a useful therapeutic approach for Japanese patients with HCL.