According to WHO classification system, HES can be classified as molecularly characterized eosinophilic disorders, such as platelet-derived growth factor receptor (PDGFR)-rearranged myeloid neoplasm, eosinophilia associated with phenotypically abnormal and/or clonal T lymphocytes, and chronic eosinophilic leukemia (CEL) [2]. Here, PDGFRB is linked to Chronic Eosinophilic Leukemia, Not Otherwise Specified.