Recent studies on hematological malignancies have reported that the overexpression or downregulation of S100A8 and S100A9 is associated with acute myeloid leukemia (AML), chronic lymphoid leukemia (CLL), and myeloproliferative diseases (12–14) However, the function of S100A8 and S100A9 in chronic eosinophilic leukemia is not fully understood. This evidence concerns the gene S100A9 and Chronic Eosinophilic Leukemia, Not Otherwise Specified.