STAT3 and STAT5 are aberrantly tyrosine‐phosphorylated in cancer cells and are crucial effectors of different tyrosine kinase oncogenes (TKO) such as FLT3‐ITD in acute myeloid leukaemia (AML) and BCR‐ABL in CML.25, 26. Here, STAT5B is linked to acute myeloid leukemia.