BACKGROUND.
Recombinant interferon-␣-2b (rIFN-␣-2b) has shown therapeutic potential in patients with chronic myelogenous leukemia and other myeloproliferative disorders (MPDs), including the ability to suppress the abnormal hematopoietic clone and to reverse myelofibrosis. This study was conducted to evaluate further the efficacy and safety of rIFN-␣-2b in a large group of patients with polycythemia vera, essential thrombocythemia, or agnogenic myeloid metaplasia and to determine maintenance of response after treatment discontinuation.
METHODS.
Induction therapy began with subcutaneous rIFN-␣-2b at 5.0 ϫ 10 6 IU/day until a complete or partial response was achieved. Treatment continued at 2.5 ϫ 10 6 IU/day until spleen size and hematologic parameters stabilized.
RESULTS.
Fifty-four patients were studied (median follow-up, 7.3 years); at last follow-up 27 patients still were participating (median follow-up, 3.8 years). Twenty-four of 24 patients with thrombocythemia (100%) and 14 of 14 patients with hyperleukocytosis (100%) responded to induction therapy, whereas 26 of 39 patients (67%) experienced Ͼ 10% decrease in splenomegaly. Thirty-nine of 54 patients (72%) maintained response for a median of 39 weeks after withdrawal of rIFN-␣-2b; repeat courses in previously responding patients produced similar results. The survival rate at 8 years was 60%. rIFN-␣-2b generally was well tolerated, but toxicity caused treatment withdrawal in 7 patients (13%).
CONCLUSIONS. rIFN-␣-2b can produce regression of splenomegaly and control of leukocyte and platelet counts in patients with MPD. These responses are sustained for prolonged periods in some patients after therapy discontinuation. In patients with recurrent disease, disease control can be attained again with reinitiation of rIFN-␣-2b. Therefore this therapy should be an important treatment consideration for patients with MPD.