Hyperleukocytosis, is generally defined as circulating white blood cell count (WBC) count exceeding 50 to100 × 109/L and mostly occurs in acute leukemias. High WBC count is a clear adverse prognostic factor for overall survival in both pediatric and adult ALL and its presence is associated with adverse survival outcome in AML as well. Furthermore hyperleukocytosis was associated with increased early mortality in a large group of pediatric and adult AML patients. The reason probably reside in the occurrence of blast cell aggregates and WBC thrombi in the capillary beds of the lung, brain, and heart (demonstrated at autopsy) resulting in clinically observed signs and symptoms. Novotny et al. (
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