For example, we know very well that only some AML patients withFLT3-internal tandem duplication (FLT3-ITD) mutations respond to kinase inhibitors, only some with del(5q) myelodysplastic syndromes (MDSs) respond to lenalidomide, and only some with isocitrate dehydrogenase 2 (IDH2) mutations respond to IDH2 inhibitors. This evidence concerns the gene IDH2 and acute myeloid leukemia.