Mid-term observations on the efficacy of alpha-interferon in hairy cell leukemia and status of the interferon system of patients in remission.

We summarize our experience using alpha-interferon (IFN-alpha) in the treatment of 93 patients with hairy cell leukemia. Both partially purified interferon and recombinant IFN-alpha produced over 85% response rate. Equal efficacy at 12 months of treatment was found for both types of IFN-alpha. However, continuation of treatment up to 24 months with partially purified IFN-alpha resulted in an increased number of complete remissions. An increase in the number of bone marrow's hairy cells occurred in 70-80% of the patients in whom a treatment was discontinued. Only 20% of the patients required reinitiation of treatment, and in all, reinduction of remission was readily obtained. Toxicity to IFN-alpha in patients with hairy cell leukemia was minimal. IFN-alpha production by patients in remission was studied. Only those patients in complete remission showed adequate IFN-alpha production. The role of endogenous IFN-alpha in the induction and sustenance of remission in hairy cell leukemia is discussed.