Interferon alpha‐2b as treatment for Philadelphia‐negative chronic myeloproliferative disorders with excessive thrombocytosis

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Abstract
Summary. We treated 32 patients with Ph1‐negative chronic myeloproliferative disorders (CMD) with excessive thrombocytosis with Interferon α‐2b (IFN α‐2b): 26 had essential thrombocythaemia, ET (18 previously untreated, eight pretreated); one thrombocythaemia after treatment for Hodgkin's disease (HD); two thrombocythaemia associated with non‐Hodgkin's lymphoma (NHL); three stage II idiopathic myelofibrosis (IM). IFN was given at daily doses of 1−4 × 106 IU. Twenty‐seven patients (84%) responded, 17 (53%) achieved complete haematologic response after a median time of 12 weeks, and 10 (31%) partial haematologic response. Median platelet levels declined in complete haematologic response patients from 1190 to 335 × 109/I. Normalization of megakaryocyte (MK) levels was observed in 8/17 complete haematologic response patients treated for 9–12 months, with decreased bone marrow (BM) cellularity. Side effects requiring dose reduction or discontinuation of treatment occurred in 28% of cases with IFN doses of 2 or 4 × 106 IU. After 1 year of continuous IFN treatment, responses were maintained with conventional chemotherapy or low‐dose IFN. This study demonstrates that IFN has definite therapeutic activity in CMD with excessive thrombocytosis. This biological agent, either alone or in combination with other antineoplastic treatment, may represent a new therapeutic approach for these disorders.