Long-term follow-up of patients with hairy cell leukemia after cladribine treatment.

Hairy cell leukemia is a chronic B-cell disorder that follows an indolent, but progressive course. Cladribine (2-chlorodeoxyadenosine) induces complete remissions in the majority of patients after a single course. We report the long-term outcomes, including response rates and their duration; time-to-treatment failure (TTF) rates; retreatment results; toxicities; and survival rates of patients treated at Scripps Clinic (La Jolla, CA). A total of 358 patients with hairy cell leukemia were treated with cladribine at 0.087 or 0.1 mg/kg body weight per day by continuous intravenous infusion for 7 days. The expected number of second neoplasms was based on the National Cancer Institute's Surveillance Epidemiology and End Results data. Of 349 evaluable patients, 319 (91%) achieved an initial complete response and 22 (7%) a partial response with an overall median duration of response follow-up of 52 months. Ninety patients (26%) had relapsed at a median of 29 months. The TTF rate for all 341 responders was 19% at 48 months, 16% for complete responders, and 54% for partial responders. Of 53 evaluable patients treated with second courses of cladribine at first relapse, 33 (62%) achieved complete responses and 14 (26%) partial responses. Twenty-seven patients (8%) developed second neoplasms (only 1 hematopoietic) with an observed-to-expected ratio of 1.88 (95% confidence interval, 1.24 to 2.74). The overall survival rate was 96% at 48 months. Single courses of cladribine induced long-lasting complete responses in the vast majority of patients. Relapse rates for complete responders were low. Patients who relapse can be successfully retreated with cladribine. Cladribine has high efficacy and a favorable acute and long-term toxicity profile when administered to patients with hairy cell leukemia.