This study is an ongoing study of the efficacy and toxicity of interferon alfa-2a in patients with hairy cell leukemia. Patients responding and tolerating this therapy are being continued on interferon at a dose of 3 million units administered subcutaneously 3 times per week. So far the therapeutic activity of interferon in this disease has been confirmed. Of 53 patients evaluable for response (out of a total of 56 entered), there were 3 complete responders, 24 partial responders, 24 minor responders, and only 2 nonresponders. Minor responses in this disease are clinically meaningful responses in that peripheral blood counts have returned to essentially normal levels, but minor responders continued to have a significant marrow hairy cell infiltrate. Of the 51 responding patients, 34 continue to receive interferon at the standard dose of 3 million units given three times per week. Three patients are continuing on interferon but require more than the standard dose of interferon to maintain their response. The six were removed from study because of progressive disease while continuing to receive interferon, and eight were removed from interferon for a variety of reasons including myocardial infarction, squamous cell carcinoma of the lung, the late development of a sensory neuropathy, depression, erythrocytosis, noncompliance, impaired cognition, and flare of a rheumatic syndrome. By far and away the most common reason for removal of patients from the study has been disease progression while they continue to receive interferon. The development of interferon resistance in these patients has been correlated with the development of anti-interferon antibodies and this latter finding is the subject of a new ongoing study at the BRMP.
