Treatment paradigms in the management of myeloproliferative disorders.

Myeloproliferative disorders (MPDs) are chronic conditions that require long-term treatment. MPDs have been considered neoplastic disorders that have a propensity to transform to acute leukemia or myelodysplastic syndrome. One of the MPDs, chronic myeloid leukemia (CML), has the distinct cytogenetic abnormality of the Philadelphia chromosome. In CML, transformation to acute leukemia is a common occurrence, with the timeline measured in years rather than decades. With the other three disorders from this group, polycythemia vera (PV), essential thrombocythemia (ET), and idiopathic myelofibrosis (IMF), transformation to acute leukemia is less frequently seen and, although variable, can take a longer period of time. The choice of therapy used for MPDs may contribute to leukemic transformation; chlorambucil, busulfan, and radiophosphorus are all examples of therapy that have been shown to be leukemogenic. Several studies have suggested the potential leukemogenicity of hydroxyurea (HU), but this remains controversial because no randomized studies have been conducted. The two newest agents used for MPDs, interferon-alpha and anagrelide, have both been studied for efficacy, but their influence on the potential for leukemic transformation has not been well studied to date.