Three years' continuous low-dose interferon-alpha treatment of hairy-cell leukaemia: evaluation of response and maintenance dose.

Thirty-six HCL patients were treated with 2 x 10(6) U/m2 IFN-alpha-2b three times weekly for 24 months, followed by 12 months of treatment with one of three doses ranging from 0.5 x 10(6) U to 2 x 10(6) U/m2. For most patients the response continued to improve during the whole treatment period, and there were no cases of disease progression during treatment. Patients with disease of short duration before IFN treatment and/or non-splenectomized patients seemed to respond more slowly than others, but there were no differences between patients treated with the different IFN doses. Toxicity was usually WHO grade 1 or 2. The continued improvement in a large number of patients even with very small IFN doses might indicate that only a small number of true complete responses are reached after 24 months of treatment, thus explaining the reported high relapse rate after early discontinuation of treatment. It therefore seems worthwhile--also from a cost/benefit point of view--to test long-term or continuous IFN-alpha treatment at other centres.