STAT3 and acute myeloid leukemia: The anti-tumor activity of MM-206 was confirmed in vivo by reducing blast count and improving survival in AML-engrafted mice.99 OPB-31121 is a small molecule inhibitor of STAT3 and STAT5 phosphorylation, which has demonstrated activity in advanced solid tumors.100 Treatment of various leukemic cell lines with this compound resulted in significant growth inhibition, including FLT3-ITD-positive AML cells.101 Importantly, OPB-31121 was able to overcome FLT3 receptor ligand-induced STAT3 phosphorylation, and may help to prevent the emergence of resistance in patients receiving FLT3-ITD TKI.