The myeloproliferative neoplasm, myelofibrosis, is a morbid and frequently fatal illness encompassing primary myelofibrosis, and end-stage essential thrombocythemia and polycythemia. Bevacizumab (15 mg/kg intravenous (i.v.) every 21 days) was tested in a phase II international trial conducted by the Myeloproliferative Disorders Research Consortium. Thirteen patients were enrolled in the first stage of this 2-stage trial. Among the 11 patients who received therapy, only 3 received more than 4 cycles of therapy; none of the patients achieved an objective response. Furthermore, significant toxicity, not directly related to the vascular or gastrointestinal events typically associated with the anti-VEGF monoclonal antibody preparation in other disease states, was observed. Lack of objective responses coupled with toxicity led to the decision to terminate the study early. If future studies incorporate bevacizumab in combination therapy for myelofibrosis, more modest doses should be considered.
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