PTEN and leukemia: When the negative mTOR regulator, PTEN, was deleted in murine hematopoietic stem cells (HSCs), PTEN-mutant bone marrow showed rapid depletion of normal HSCs followed by an increased presence of leukemia initiating stem cells (LSCs or CSCs in leukemia) which subsequently resulted in leukemogenesis (Yilmaz et al., 2006; Zhang et al., 2006; Guo et al., 2008; Lee et al., 2010).