In humans, CEL also requires the overexpression of IL-5 through a single nucleotide polymorphism of IL5RA. The same holds true for systemic mastocytosis (SM), in which the constitutive activation of c-KIT alone is insufficient to induce the neoplastic phenotype and requires the stimulation of stem cell factor (SCF) as well [30]. This evidence concerns the gene KITLG and Chronic Eosinophilic Leukemia, Not Otherwise Specified.