Somatic gain-of-function (GOF) variants in STAT5B drive leukemias and lymphomas, and variants in the Src homology 2 (SH2) domain were reported in three patients with nonclonal eosinophilia, atopic dermatitis, diarrhea, and urticaria (2, 3, 4, 5). Here, STAT5B is linked to Increased total eosinophil count.