Pegylated interferon for the treatment of high risk essential thrombocythemia: results of a phase II study

Abstract

BACKGROUND AND OBJECTIVES: Patients with high-risk essential thrombocythemia require cytoreductive therapy in order to normalize the elevated platelet counts. We evaluated the efficacy and toxicity of pegylated interferon in high-risk essential thrombocythemia in a phase II trial. DESIGN AND METHODS: Thirty-six patients with high-risk essential thrombocythemia (median age 54 years; range, 24-72 years) were studied. The dose of pegylated interferon was initially 50 mg per week and could be escalated up to 150 mg per week. RESULTS: During the first three months platelet counts decreased significantly from a median baseline count of 895x10(9)/L (range: 383-1779) to a median count of 485x10(9)/L (range: 211-1283; p<=0.001). A complete response was defined as platelet counts < 450x10(9)/L. The complete response rate was 39%, 47%, 58% and 67% at 3, 6, 9 and 12 months of treatment, respectively. There were 25%, 11%, 8% and 0% poor responders, defined as patients with platelet counts > 600x10(9)/L, at 3, 6, 9 and 12 months of treatment, respectively. After a median time of 23 months (range 3-39 months) 23 of 36 patients (64%) are still receiving pegylated interferon. In ten patients (28%) treatment was stopped due to grade 1 to 2 toxicity, classified according to the WHO standard toxicity scale. One patient, who responded partially to pegylated interferon (platelet count 542x10(9)/L), had a cerebral stroke after 23 months of treatment. INTERPRETATION AND CONCLUSIONS: In high-risk essential thrombocythemia sustained treatment with pegylated interferon is effective and safe in reducing platelet counts with a toxicity comparable to that of conventional interferon.