Fmk treatment induces significant apoptosis in FLT3-ITD– but not BCR-ABL–expressing primary human leukemia cells. Inhibition of RSK2 by treatment with fmk does not affect cell viability nor induce apoptosis (left, A and B, respectively) in primary BCR-ABL–positive leukemia cells from 2 CML patients, and primary FLT3-ITD-negative leukemia cells from 2 AML patients (right, A and B, respectively), whereas fmk treatment results in decreased cell viability and increased apoptosis in primary FLT3-ITD–positive leukemia cells from 2 AML patients. Apoptotic population was determined as the percentage of annexin V–positive cells of total treated cells. (C) Clinical information for the leukemia patients. P value was determined by 2-tailed Student t test. ns indicates not significant.* P < .05; **P < .01.