MTOR and acute lymphoblastic leukemia: The efficacy of mTOR inhibitor sirolimus (one of the so-called “rapalogs”) in abrogating leukemic cells expansion has been tested in vivo in pediatric Ph-like ALL xenografts, a recently described subtype of pediatric high-risk B-precursor ALL (B-ALL) which exhibits a gene expression signature similar to Ph+ ALL with a poor prognosis, even though the therapeutic potential of this approach remains preclinical [56].