MEIS1 and acute myeloid leukemia: Notably, none of these samples harbored activating mutations in FLT3. We found that AML samples expressing high levels of both HOXA9 and MEIS1 exhibited increased expression of SYK and pSYK, and were more sensitive to the SYK inhibitors PRT062607 and R406 compared with samples with weak MEIS1 expression (Figures 7H–7I).