For example, imatinib mesylate, a tyrosine kinase inhibitor with activity against PDGFRα, has been associated with a high response rate in patients with chronic eosinophilic leukemia [2], in which an FIP1L11-PDGFRα fusion leads to aberrant activation of PDGFRα in eosinophils and other hematopoietic precursors [3]. Here, PDGFRA is linked to Chronic Eosinophilic Leukemia, Not Otherwise Specified.