[Therapy of thrombocytosis in myeloproliferative syndromes using recombinant interferon-alpha-2a].

In a prospective open study 16 consecutive patients with a myeloproliferative syndrome and thrombocytosis were treated with interferon (IFN) alpha-2a. 4 patients had polycythemia vera, 4 essential thrombocythemia, 3 myeloid metaplasia and 5 chronic granulocytic leukemia. Platelet counts decreased in all treated patients within 2 to 12 weeks from a median value of 1010 x 10(9)/l to 350 x 10(9)/l. No primary or secondary resistance was observed. The initial dose of IFN was 9 m U per day. After correction of the thrombocytosis, it was progressively reduced to a minimum dose of 3 m U per week. Despite the good platelet response to IFN, leukocytosis persisted in 3 patients and polycythemia in a further 3. Side effects and poor compliance required discontinuation of therapy in 6 patients. Special attention is focused on the follow-up in 6 patients who have been treated for more than 15 months.