Background and objective: In the 1980s alpha-interferon (alpha-IFN) dramatically improved the management of hairy cell leukemia (HCL), producing normalization of hematologic parameters including the disappearance of circulating hairy cells in the majority of treated patients, within 6 months. The quality and durability of the response depended on the duration of alpha-IFN treatment; progression of the disease consistently followed discontinuation of alpha-IFN. In this report, we examine the characteristics of long-term responders from our series of 44 HCL patients treated with alpha-IFN.
Methods: We report follow-up data on 44 HCL patients who underwent alpha-IFN as first-line treatment between 1985 and 1990. The alpha-IFN dose was 3 x 10(6) U daily for 12-15 months, with 20 patients continuing to receive the same dose three times a week as maintenance treatment for an additional 6-12 months. Of the 44 patients, 8 achieved a CR, 28 a PR and 8 a MR, with an overall response rate of 82%. Thirty-eight (86%) of these patients showed disease progression and were retreated with alpha-IFN (2 pts), 2-chlorodeoxyadenosine (35 pts), or pentostatin (1 pt). So far, all 38 patients are alive and in good unmaintained second response, except for two patients who developed a second neoplasm.
Results: Six of the 8 first complete responders are alive and have not required further treatment after completing alpha-IFN. These long responders most often (5/6) presented a hairy cell index (HCI) < 0.50 at diagnosis; all 6 registered a significant reduction in bone marrow infiltration (HCI < 0.10) after induction therapy and underwent alpha-IFN maintenance treatment. These three parameters turned out to be statistically significant when the long-term responders were compared with the failure patients subset (p = 0.003 for HCI at diagnosis; p = 0.001 for HCI at the end of the induction phase; p = 0.003 for the maintenance phase). The median progression-free survival of these 6 long-term responders was 75 months (range, 62 to 78).
Interpretation and conclusions: Overall, alpha-IFN represents an excellent palliative treatment for most HCL patients. A small subset of these patients could become long-term responders following first-line alpha-IFN therapy alone.