There are several blood disorders associated with abnormally high numbers of a rare white blood cell type called eosinophils. Normal eosinophils are believed to help the body fight against parasitic infections, or cancer, or can cause allergic reactions.
Chronic eosinophil leukemias (CEL) are conditions where higher than normal numbers of eosinophils exist, but they aren’t needed by the body. Many of these CELs are associated with particular mutations in growth factor receptors such as PDGFRA, PDGFRB or FGFR1.
Chronic eosinophil leukemia, not otherwise specified (CEL-NOS) is different in that too many eosinophils are found in the bone marrow, blood, and other tissues but known mutations are not identified. It is possible that CEL may stay the same for many years. Alternatively, it could progress to an acute leukemia.