Chronic myeloproliferative disorders (CMPD) are classified according to the WHO classification of 2001 as polycythemia vera (PV), chronic idiopathic myelofibrosis (CIMF), essential thrombocythemia (ET), CMPD/unclassifiable (CMPD-U), chronic neutrophilic leukemia, and chronic eosinophilic leukemia (CEL)/hypereosinophilic syndrome, all to be delineated as different from another member of the group, BCR/ABL-positive chronic myeloid leukemia (CML). This article addresses specifically the rare hypereosinophilic syndrome.
Hypereosinophilic syndromes (HES) and systemic mastocytosis (SMCD) are a group of disorders with clinical symptoms from local and remote effects of excessive proliferation of eosinophils, a type of a blood cell and mast cells, respectively. Interferon alpha (IFN-alpha), alone or in combination with other medications, can be a useful, and at times life-saving, treatment for patients with HES. Receptors for IFN-alpha are present on eosinophils, and clinical benefits are due to its effect on eosinophil growth, movement, activation, and survival. These effects are likely mediated through multiple pathways, not all of which are known or understood. A number of case reports showed that IFN-alpha has been life-saving for patients with intractable HES that were resistant to prednisone, hydroxyurea, and other agents used for myeloproliferative syndromes. There are reports of its combined use with hydroxyurea and prednisone. There are also reports of the use of peg-interferon.
Unfortunately, HES is rare and prospective trials are not reasonable to expect. I did find that the PDQ from the National Cancer Institute recommended interferon for this disease.
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