Interferon-α Therapy in Polycythemia Vera and Essential Thrombocythemia

Essential thrombocythemia (ET) and polycythemia vera (PV) are chronic clonal myeloid disorders that originate from the multipotential hematopoietic stem cell. They are characterized, respectively, by excessive thrombocytosis and erythrocytosis, a high incidence of thrombohemorrhagic events, vasomotor symptoms, and an inherent tendency to undergo leukemic transformation. Current standard therapies to control the excess accumulation of myeloid cells and to provide symptomatic relief carry either a persistent risk of thrombosis, as in the case of phlebotomy, or, in the case of hydroxyurea, the potential for inducing leukemia. None alter the natural history of these diseases. Interferon-alpha has been shown to have potent antiproliferative effects on the hematopoietic stem cells and bone marrow fibroblasts and, as a result, has received much attention as a therapeutic agent for chronic myeloproliferative disorders. The ability of interferon-alpha to induce hematologic and cytogenetic remission in chronic phase chronic granulocytic leukemia has further increased interest in this agent. Interferon-alpha has shown therapeutic activity in PV and ET, as demonstrated in multiple small studies and single-arm trials reviewed in this article. Reported beneficial effects include the ability to control excessive erythrocytosis and thrombocytosis and such disease-related features as vasomotor symptoms, pruritus, and splenomegaly. Recent reports of cytogenetic remission and reversal of bone marrow fibrosis after interferon therapy are of interest. Advantages over current therapeutic standards include lack of known leukemogenic and teratogenic effects and the potential to alter the underlying course of disease. Nevertheless, none of the information available allows definite therapeutic recommendations for the use of interferon-alpha in PV or ET. The available data support the need for randomized controlled trials comparing interferon-alpha with standard therapy.