Granulocyte–macrophage colony-stimulating factor, which is produced primarily by tumor cells and enhances the metastatic ability of several tumors [41], induces de novo transferrin synthesis in neutrophils through the Jak/Stat5β pathway, while its neutralization curtailed neutrophil transferrin expression as well as cancer metastasis, indicating neutrophil-derived transferrin as an important regulator of metastatic tumor cell growth [42]. Here, STAT5B is linked to cancer.