Chronic eosinophilic leukemia/hypereosinophilic syndrome.

Although HES and CEL are indeed rare clinical entities, interest in these disorders has been reborn due to a renaissance in uncovering the biologic basis of previously idiopathic cases. Unmasking the molecular basis for such cases has, in turn, led to the development of semimolecular classification schemes for categorizing patients based on recurrent genetic alterations, usually related to constitutively activated tyrosine kinases. In turn, increasing sophistication in unmasking the molecular underpinnings of eosinophilia in patients heretofore classified as idiopathic HES now permits the rationale use biologically targeted therapies such as imatinib mesylate and recombinant anti-IL-5 antibody. The WHO convenes in 2007 to review prior diagnostic criteria for both HES and CEL. It will be of interest to see how the new genetic information becomes integrated with traditional histopathologic criteria in establishing a practical road map for clinicians who treat these diseases.