Hypereosinophilic syndrome: approach to treatment in the era of precision medicine.

Hypereosinophilic syndromes (HESs) are a heterogeneous group of rare disorders characterized by peripheral eosinophilia and eosinophilic end organ complications. Conventional therapies, including glucocorticoids and cytotoxic and immunomodulatory agents, have variable efficacy and significant toxicity. Although the recent development of agents that target eosinophils, including tyrosine kinase inhibitors and monoclonal antibodies, provides the possibility of more effective, less toxic approaches to treatment of HES, there are little available data to guide their use in these conditions. In the following review, the controversies regarding the definition and classification of HES will be discussed, and a pragmatic approach to treatment based on clinically defined HES variants will be presented. An illustrative case will be used to highlight the complexities of treatment selection in HES patients.