Long term outcome of patients with hairy cell leukemia treated with pentostatin.

Background: With the introduction of new drugs such as interferon-alpha (IFN) and purine analogs, the management of hairy cell leukemia (HCL) patients has changed. However, pentostatin has been found to produce higher complete remission rates than IFN. The current study was undertaken to investigate response and long term follow-up in HCL patients treated with pentostatin.

Methods: Between March 1989 and October 1996, 49 patients with HCL and 1 patient with a HCL variant were treated with pentostatin. Eighteen patients had received no prior therapy, 31 patients had received prior treatment with IFN, and 1 patient had received prior treatment with 2'-chlorodeoxyadenosine (2'CdA) and IFN. All patients except 1 were treated with a dose of 4 mg/m2 every 2 weeks. The median number of cycles was 12.

Results: The overall response rate was 96% (48 of 50 patients); 22 patients (44%) achieved a complete response, 18 patients (36%) achieved a good partial response (defined as residual bone marrow infiltration < 5%), 8 patients (16%) achieved a partial response, and 2 patients died. For a median follow-up of 33 months off therapy, there were 5 recurrences between 12-66 months; 3 of these patients were treated further with and responded to 2'CdA and 2 died of disease progression at 12 and 40 months, respectively. In addition, 3 patients died of unrelated causes (1 of very early infection, 1 of toxic death and another of cardiac arrest) comprising an overall death rate of 14% (7 of 50 patients). The overall survival rate was 86% for a median follow-up of 38 months (range, 8-105 months). Major side effects were febrile episodes, herpes zoster, nausea/emesis, and pancytopenia.

Conclusions: This analysis confirms both the high remission rate and durable responses that may be achieved with pentostatin treatment in HCL patients. Although pentostatin is active, the risk of cytopenia and immunosuppression must be evaluated carefully.