Evolution to eosinophilic leukemia with a t(5:11) translocation in a patient with idiopathic hypereosinophilic syndrome

The idiopathic hypereosinophilic syndrome (HES) comprises a diverse group of diseases that may ultimately lead to multiorgan dysfunction and death. We present a case of a man who was followed for over 9 years with HES that underwent malignant transformation to acute leukemia with eosinophilic features. The patient's clinical acceleration was accompanied by the development of a malignant clone that was identified with banding techniques as 46,XY,t(5:11)(p15;q13). Electron microscopy reaffirmed findings reported in earlier cases of eosinophilic leukemia. At no time during his illness were cytotoxic drugs administered. In addition to delineating the natural evolution and cytostructural details of the case, we emphasize the role of cytogenetics in the predicting of malignant variants of the hypereosinophilic syndrome and in identifying eosinophilic leukemia.