A constitutively activated, mutated version of the class III receptor tyrosine kinase, FLT3 (Fms-Like Tyrosine kinase-3; STK-1, human Stem Cell Tyrosine Kinase-1; or FLK-2, Fetal Liver Kinase-2), is expressed in approximately 30% of AML patients and a subset of ALL patients [1]. The gene discussed is FLT3; the disease is acute lymphoblastic leukemia.