Durability of responses to interferon alfa-2b in advanced hairy cell leukemia.

Previous studies have demonstrated that significant hematologic improvement occurs in the majority of patients with hairy cell leukemia (HCL) treated with partially purified or recombinant interferon (IFN). Fifty-three patients received IFN alfa-2b for at least 3 months in a dose of 2 X 10(6) U/m2 subcutaneously thrice weekly. Of the 49 patients evaluable for response (at least 6 months of IFN therapy), there were ten complete responses and 29 partial responses for a total response rate of 80%. The peripheral blood counts and bone marrow continued to improve over the course of a full year of therapy. IFN was well tolerated, with no patients discontinuing therapy because of toxicity. Transient myelosuppression occurred in most patients during the first 1 to 2 months of therapy, occasionally precipitating a transfusion requirement. After IFN treatment was discontinued, there was a marked decrease in normal marrow elements and a relative increase in marrow hairy cells. This was associated with a transient increase in normal elements in the peripheral blood. Only one of 24 patients followed after receiving IFN for a median of 8.5 months (range, 3 to 16 months) has required further therapy. We conclude that low-dose IFN alfa-2b is highly effective in advanced HCL; responding patients should be treated for at least 1 year. The decision to initiate a second course of IFN therapy should be based primarily on peripheral blood counts and the clinical status of the patient rather than on the bone marrow.