Activating mutations in the fms-like tyrosine kinase 3 (FLT3) (2) are present in 25%–30% of patients with AML, approximately 10% of patients with myelodysplastic syndrome (MDS) (3), and 5–6% of patients with acute lymphoblastic leukemia (ALL). The gene discussed is FLT3; the disease is acute lymphoblastic leukemia.