While most prior studies of G-CSF have focused on the activation of STAT3 or STAT5 in leukemia cell lines, Tanaka et al. [28] demonstrated that G-CSF activates both STAT3 and STAT5 in humanized mice, suggesting the critical role of STAT3 and STAT5 for normal granulocytic differentiation from hematopoietic stem cells. This evidence concerns the gene STAT5B and leukemia.