Chronic eosinophilic leukemia (CEL) is a disease in which too many eosinophils (a type of white blood cell) are found in the bone marrow, blood, and other tissues. CEL may stay the same for many years, or it may progress quickly to acute leukemia. It is generally caused by overactivation of the oncogene PDGFRA through a chromosome translocation event. Though a highly rare disease, CEL is extremely manageable with the use of Gleevec, which suppresses the oncogenic effects of PDGFRA.