Eosinophilic myeloid disorders: new classification and novel therapeutic strategies

The aim of this brief review is to evaluate recent developments in the classification and treatment of eosinophilic myeloid disorders in the context of reactive, lymphocyte-variant, and idiopathic eosinophilias.

The revised 2008 WHO classification recognizes both molecularly defined ('myeloid and lymphoid neoplasms with eosinophilia and abnormalities of PDGFRA, PDGFRB, or FGFR1') and undefined (chronic eosinophilic leukemia, not otherwise specified) eosinophilic myeloid disorders. An increasingly sophisticated understanding of the molecular underpinnings of eosinophilia has translated into rational use of biologically targeted therapies such as imatinib mesylate. Conventional cytotoxics and interferon-alpha still have an established role in treating these diseases. Although studied in idiopathic hypereosinophilic syndrome, the therapeutic niche of anti-interleukin-5 (mepolizumab) and anti-CD52 (alemtuzumab) antibody therapy in eosinophilic myeloid diseases has yet to be established.

Molecular/genetic analysis is now mandatory for the diagnosis, classification, and treatment of eosinophilic myeloid disorders. The finding of rearranged, constitutively activated PDGFRA/B identifies patients who are eminently treatable with tyrosine kinase inhibitors.