Because mTOR is hyperactived or upregulated when Pten is mutated or deteleted in human cancers [28], we treated LSCs from CML mice or human CML cell line K562 in vitro with rapamycin, a mTOR inhibitor, and found that rapamycin induced apoptosis of these cells, suggesting that a blockade of the mTOR pathway may help to inhibit LSCs and CML development. This evidence concerns the gene PTEN and chronic myelogenous leukemia, BCR-ABL1 positive.