Chronic eosinophilic leukemia (CEL) is a subtype of myeloproliferative neoplasms characterized by an increased number of eosinophils with blastoid cell proliferation or chromosomal abnormality involving platelet‐derived growth factor receptor alpha (PDFGRA; MIM #173490), platelet‐derived growth factor receptor beta (PDGFRB; MIM #173410), or fibroblast growth factor receptor1 (MIM #136350) (Apperley et al., 2002; Cools et al., 2003; Gotlib, 2017). The gene discussed is PDGFRB; the disease is Chronic Eosinophilic Leukemia, Not Otherwise Specified.