Interferon alfa-2b in the treatment of chronic granulocytic leukemia.

Studies of the effect of interferon on the growth of colonies of myeloid leukemic blast cells, myeloma colony-forming cells, and normal hemopoietic precursor cells have demonstrated that interferon shows no specificity in inhibiting the growth of these cells in culture (ie, growth of the malignant and normal precursor cells is equally inhibited). However, interferon markedly reduces the self-renewal capacity of acute myeloid leukemic blast cells and myeloma cells. This observation suggested that interferon's ability to prolong rather than induce remissions should be tested. We have studied the ability of interferon alfa-2b (Intron A) to prolong remissions induced by busulfan (Myleran) in patients with chronic granulocytic leukemia (CGL). The leukocyte doubling time and remission duration among patients receiving no therapy was compared with the values observed during interferon alfa-2b maintenance therapy. Nine patients have begun the study; five have completed 3 months of interferon alfa-2b therapy. In four (80%) of the five patients, there has been a significant slowing of the leukocyte doubling time and prolongation of the remission duration. A larger study, with longer follow-up, will be required to determine whether interferon alfa-2b therapy will slow progression of CGL to the blast phase and prolong survival.